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Research Article Hydrochemistry and Isotope Hydrology for Groundwater Sustainability of the Coastal Multilayered Aquifer System (Zhanjiang, China) Pengpeng Zhou, 1 Ming Li, 2 and Yaodong Lu 3 1 Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Science, No. 19 Beitucheng West Road, Chaoyang District, Beijing 100029, China 2 Appraisal Center for Environment and Engineering, Ministry of Environmental Protection, No. 28 Anwaibeiyuan Road, Chaoyang District, Beijing 100012, China 3 e First Hydrogeological Team, Guangdong Geological Bureau, Kangning Road, Chikan District, Zhanjiang 524049, China Correspondence should be addressed to Pengpeng Zhou; [email protected] Received 18 May 2017; Accepted 13 September 2017; Published 19 October 2017 Academic Editor: Tobias P. Fischer Copyright © 2017 Pengpeng Zhou et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Groundwater sustainability has become a critical issue for Zhanjiang (China) because of serious groundwater level drawdown induced by overexploitation of its coastal multilayered aquifer system. It is necessary to understand the origins, material sources, hydrochemical processes, and dynamics of the coastal groundwater in Zhanjiang to support its sustainable management. To this end, an integrated analysis of hydrochemical and isotopic data of 95 groundwater samples was conducted. Hydrochemical analysis shows that coastal groundwater is fresh; however, relatively high levels of Cl , Mg 2+ , and total dissolved solid (TDS) imply slight seawater mixing with coastal unconfined groundwater. Stable isotopes ( 18 O and 2 H) values reveal the recharge sources of groundwater in the multilayered aquifer system. e unconfined groundwater originates from local modern precipitation; the confined groundwater in mainland originates from modern precipitation in northwestern mountain area, and the confined groundwater in Donghai and Leizhou is sourced from rainfall recharge during an older period with a colder climate. Ionic relations demonstrate that silicate weathering, carbonate dissolutions, and cation exchange are the primary processes controlling the groundwater chemical composition. Declining trends of groundwater level and increasing trends of TDS of the confined groundwater in islands reveal the landward extending tendency of the freshwater-seawater mixing zone. 1. Introduction Increases of both population and water demand in coastal areas have made groundwater an important water resource for coastal regions; however, coastal groundwater is vulner- able to overexploitation and contamination [1, 2]. erefore, sustainable management of coastal groundwater has become a critical issue [3]. Understanding the hydrochemical charac- teristics of coastal groundwater could provide guidance for sustainable groundwater management [4–6]. e characteristics of groundwater chemistry are primar- ily influenced by recharge water chemistry, water-rock inter- actions, solute transport, and chemical processes occurring along the flow paths [6–10]. By analyzing the hydrochemical and isotopic data together with considering the hydrogeo- logical conditions, the origins, chemical compositions, and dominating hydrochemical processes (e.g., water-rock inter- actions, evaporation, and mixing between different water) of groundwater in aquifers can be assessed comprehensively [11– 14]. In hydrogeological studies about the coastal groundwater management, analysis of the hydrochemistry and hydrogen- oxygen isotopes data has been used widely to determine the hydrogeological conditions, such as groundwater recharge sources, recharge rates, and flow patterns [15–20]. e appli- cation of chemistry and hydrogen-oxygen isotopes can be used also to identify processes of groundwater salinization induced by seawater intrusion [21–25]. In addition, many Hindawi Geofluids Volume 2017, Article ID 7080346, 19 pages https://doi.org/10.1155/2017/7080346
Transcript
Page 1: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Research ArticleHydrochemistry and Isotope Hydrology for GroundwaterSustainability of the Coastal Multilayered Aquifer System(Zhanjiang China)

Pengpeng Zhou1 Ming Li2 and Yaodong Lu3

1Key Laboratory of Shale Gas and Geoengineering Institute of Geology and Geophysics Chinese Academy of ScienceNo 19 Beitucheng West Road Chaoyang District Beijing 100029 China2Appraisal Center for Environment and Engineering Ministry of Environmental Protection No 28 Anwaibeiyuan RoadChaoyang District Beijing 100012 China3The First Hydrogeological Team Guangdong Geological Bureau Kangning Road Chikan District Zhanjiang 524049 China

Correspondence should be addressed to Pengpeng Zhou zhoupengpengmailiggcasaccn

Received 18 May 2017 Accepted 13 September 2017 Published 19 October 2017

Academic Editor Tobias P Fischer

Copyright copy 2017 Pengpeng Zhou et alThis is an open access article distributed under the Creative CommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Groundwater sustainability has become a critical issue for Zhanjiang (China) because of serious groundwater level drawdowninduced by overexploitation of its coastal multilayered aquifer system It is necessary to understand the origins material sourceshydrochemical processes and dynamics of the coastal groundwater in Zhanjiang to support its sustainable management Tothis end an integrated analysis of hydrochemical and isotopic data of 95 groundwater samples was conducted Hydrochemicalanalysis shows that coastal groundwater is fresh however relatively high levels of Clminus Mg2+ and total dissolved solid (TDS) implyslight seawater mixing with coastal unconfined groundwater Stable isotopes (12057518O and 1205752H) values reveal the recharge sourcesof groundwater in the multilayered aquifer system The unconfined groundwater originates from local modern precipitationthe confined groundwater in mainland originates from modern precipitation in northwestern mountain area and the confinedgroundwater in Donghai and Leizhou is sourced from rainfall recharge during an older period with a colder climate Ionicrelations demonstrate that silicate weathering carbonate dissolutions and cation exchange are the primary processes controllingthe groundwater chemical composition Declining trends of groundwater level and increasing trends of TDS of the confinedgroundwater in islands reveal the landward extending tendency of the freshwater-seawater mixing zone

1 Introduction

Increases of both population and water demand in coastalareas have made groundwater an important water resourcefor coastal regions however coastal groundwater is vulner-able to overexploitation and contamination [1 2] Thereforesustainable management of coastal groundwater has becomea critical issue [3] Understanding the hydrochemical charac-teristics of coastal groundwater could provide guidance forsustainable groundwater management [4ndash6]

The characteristics of groundwater chemistry are primar-ily influenced by recharge water chemistry water-rock inter-actions solute transport and chemical processes occurringalong the flow paths [6ndash10] By analyzing the hydrochemical

and isotopic data together with considering the hydrogeo-logical conditions the origins chemical compositions anddominating hydrochemical processes (eg water-rock inter-actions evaporation and mixing between different water) ofgroundwater in aquifers can be assessed comprehensively [11ndash14]

In hydrogeological studies about the coastal groundwatermanagement analysis of the hydrochemistry and hydrogen-oxygen isotopes data has been used widely to determine thehydrogeological conditions such as groundwater rechargesources recharge rates and flow patterns [15ndash20] The appli-cation of chemistry and hydrogen-oxygen isotopes can beused also to identify processes of groundwater salinizationinduced by seawater intrusion [21ndash25] In addition many

HindawiGeofluidsVolume 2017 Article ID 7080346 19 pageshttpsdoiorg10115520177080346

2 Geofluids

other isotopes (eg radium carbon chlorine boron andstrontium) have been used as tracers for characterizing thehydrogeological conditions and hydrochemical processes incoastal aquifers specifically identifying submarine ground-water discharge and describing seawater intrusion [10 13 2627]

This study focused on the coastal multilayered aquifersystem (including three layers of aquifer and two layers ofaquitard) of Zhanjiang which is located in the southwestof Guangdong Province China (Figure 1) The groundwaterin the middle and deep confined aquifers (Figure 2) hasbeen the sole source of drinking water for the populationof the city of Zhanjiang since the 1960s According to thewater resources bulletin of Zhanjiang groundwater pumpingamount has been about 22times 108m3a for the resident popula-tion and local industry in recent years Because of this intenseexploitation of groundwater the confined groundwater levelhas dropped to about 20m below sea level since the 1990s [2829] (Figures 3(b) and 3(c)) Recent investigations have shownthat the groundwater in this multilayered aquifer systemremains fresh but parts of the unconfined groundwater inisland areas (eg Donghai and Naozhou) and small parts ofthe confined groundwater in Naozhou island have sufferedseawater intrusion [30ndash33] It is a concern that the confinedgroundwater in Zhanjiang city will be risky in suffering fromseawater intrusion in the future Therefore it is necessaryand urgent to conduct a research to identify the originsmineralization processes andhydrochemical dynamics of thecoastal groundwater to assess the risk of seawater intrusion

The main objective of this study is to identify theorigins material sources and hydrochemical processes ofthe groundwater in the coastal multilayered aquifer systemof Zhanjiang through integrated analysis of hydrochemicaland isotopic data In addition the risk of seawater intrusioninto the confined groundwater is assessed by analysis ofthe dynamic data of groundwater level and hydrochemistryThe results will contribute to generate scientific informationfor the local coastal hydrogeology and be supportive forthe sustainable management of the groundwater in thismultilayered aquifer system

2 Study Area and Its Hydrogeology Condition

Zhanjiang city with a land area of 1491 km2 is located insouthwestern Guangdong China (Figure 1) The topographyis high in the northwest and low in the south The averageannual precipitation and evaporation are 1347 and 1774mmrespectively [29 32]

The geology of the study area mainly consists of conti-nental and marine sediments of upper Tertiary-Quaternaryage overlying a basement of muddy sandstone of Cretaceousage (K

2) According to earlier geological investigation [29

35 36] the sedimentary formations are characterized by fivestratigraphic units which include Holocene stratum (sandand clay) Beihai Group of middle Pleistocene age (Q

2b

sand with gravel in the lower portion and clayey sand in theupper portion) Zhanjiang Group of lower Pleistocene age(Q1z coarse sand with gravel and scattered lenses of clay)

Xiayang Group of Pliocene age (N2x medium to coarse sand

with gravel and thin layers or scattered lenses of clay) andWeizhou Group of Miocene age (N

1w silty sand and fine

sand with clay) These geological formations are intercalatedwith basalt and pyroclastic rock The sediments mentionedabove constitute themultilayered aquifer system that includesthree aquifers (the unconfined aquifer the middle confinedaquifer and the deep confined aquifer) separated by claylayers (aquitards) (Figure 2)

The unconfined aquifer is about 30-m thick and is com-posed of deposits of Holocene age Beihai Group of middlePleistocene age and upper portion of Zhanjiang Group oflower Pleistocene age This aquifer overlies a thick layer ofclay that extends laterally under the seabed The hydraulicconductivity (119870) of this unconfined aquifer is 5ndash25mdBecause exploitation of the unconfined groundwater is scat-tered and intermittent the groundwater flow field remains anapproximately natural flow regime with the water table abovethe mean sea level (Figure 3(a)) The groundwater whichis recharged mainly by rainfall infiltration and dischargedthrough evaporation and runoff to the ocean flows radiallyfrom the watershed to the ocean (Figures 2 and 3(a))

The middle confined aquifer is composed of ZhanjiangGroup deposits of lower Pleistocene age (Q

1z) with thickness

of about 120m and hydraulic conductivity (119870) of 20ndash60mdInduced by overexploitation the groundwater level of thisconfined aquifer has dropped to minus24 to 16m (Figure 3(b))The deep confined aquifer is composed of Xiayang Groupdeposits of Pliocene age (N

2x) with 119870 of 20ndash50md The

groundwater level of the deep confined aquifer has droppedto minus22 to minus4m (Figure 3(c)) These two confined aquifers arerecharged mainly via lateral runoff and they are dischargedby pumping

3 Sampling and Analysis Method

To investigate the hydrochemistry of the groundwater inthe multilayered aquifer system of Zhanjiang 3 times ofgroundwater sampling activities were conducted fromMarch2009 to March 2011 As shown in Figure 1 and Table 1 a totalof 95 groundwater samples were collected from public supplywells These comprised 22 samples from the unconfinedaquifer (depth lt 30m sample numbers starting with Q)35 samples from the middle confined aquifer (50 lt depthlt 140m sample numbers starting with Z) and 38 samplesfrom the deep confined aquifer (depth gt 200m samplenumbers starting with S) All samples were filtered throughmembranes (045-120583m pore size) and stored in high-densitypolyethylene bottles which were pretreated using deionizedwater and rinsed using sampledwaterThen the sampleswerepreserved and acidified with HNO

3for cation analysis All

bottles were sealed with wax to ensure a watertight sealThe total dissolved solid (TDS) temperature and pH

were measured in situ using a portable multiparameterwater analyzer (Hach Sension156) The concentration ofHCO3

minus was also determined in the field via titration onthe day of sampling The major cations (K+ Ca2+ Na+ andMg2+) were analyzed by Inductively Coupled Plasma MassSpectrometry (ICP-MS pHPerkin-Elmer Sciex Elan DRC-e)at the Institute of Geology andGeophysics Chinese Academy

Geofluids 3

Zhanjiang city

Donghai island

A

B

Hydrogeology cross-section

Sampling site of theunconfined groundwater

Beijing

China seaSouth

China

10000

Guangdong

0 4(km) Naozhou

Study area

Sampling site of the middleconfined groundwaterSampling site of the deepconfined groundwaterSamples of the unconfined groundwater(observed by Zhang et al [34])

Samples of the confined groundwater(observed by Zhang et al [34])

36 14

20

26

451

7

18

21

2328

3034

41

38

Haikou

(a)

(b)

S1

S2

S3

S4S5S6

S7

S8

S9

S10

S12

S11

Z1Z2

Z4

Z5

Z6Z7

Z9

Z8

Z10

Z11

Q6Q3

Q1

Q2

Q5

Q7

Q4

Q9Z13

Z14

Z12

S14

S13

Z3

A B

Hong Kong

0 100 200

China seaSouth

Guangdong Province

3

614

20

22

26

45

1

7

18

21

2328

30

34

41

38Naozhou

(d)

Leiz

hou

8

22

(km)

(km)

N

N

N

(c)

Q1

Z1

S1

1

20

Figure 1 Location map of Zhanjiang (Line A-B illustrates the location of the hydrogeological cross-section displayed in Figure 2)

4 Geofluids

BA

South Chinasea

0 5

L30Sk10Sk7L19S19L16L12

L34-1S60

Precipitation infiltration

Withdrawals

(km)

52

0

minus100

minus200

minus300

minus400

(m)

1Q

10653G8844G4760G

8608 G

Holocene (sandy clay)Holocene (sand)

Beihai group of middle

(sand with gravel)Pleistocene age 12<

Zhanjiang group of lower

(coarse sand with gravel)Pleistocene age 11T

Xiayang group of

(medium to coarse sand with gravel)Pleistocene age 2R

(silty-fine sand)

Weizhou group ofMiocene age 1Q

Є2-3

+2

2R

11z

12<

14

+2

L30

Unconfined aquifer

Clay

Aquifer boundaryBorehole

(muddy sandstone)Upper cretaceous age +2

Middle-upper

(metamorphic sandstone)Cambrian age Є2-3

Middle confined aquifer

Deep confined aquifer

Groundwater flowLeakage

Aquitard (clay layer)

Figure 2 Hydrogeological cross-section (Line A-B in Figure 1) of the study area

of Sciences (IGGCAS) The anions (Clminus SO4

2minus and NO3

minus)were measured by Ion Chromatography System (DionexICS-1500) at IGGCAS Dissolved silica (SiO

2) was analyzed

by spectrophotometry using themolybdate bluemethodThecharge balance (119864 = (sum119898

119888minus sum119898

119886)(sum119898

119888+ sum119898

119886) times 100

where119898119888is the milligram equivalent of the cations and119898

119886is

the milligram equivalent of the anions) varied from minus497to 495 (within plusmn5) with an average of minus184 (withinplusmn5) This balance number can indicate the accuracy of thedata

The analyses of stable oxygen (18O) hydrogen (2H) andsulfur (34S) isotopes were conducted using mass spectrome-ters (Finigan MAT 253 for 18O-2H and Delta S for 34S) at theStable Isotope Laboratory IGGCASThe isotope ratios (12057518O1205752H and 12057534S) were given in the usual 120575-units calculatedwithrespect to standard sample 120575sample = ((119877sample119877standard) minus1) times 1000(permil) in which 119877sample and 119877standard represent theratio of heavy to light isotopes of the sample and standard

respectively The results of the stable isotope are shown inTable 2

In this study first according to the groundwater chemicaland isotopic data (Tables 1 and 2) statistical analyses (includ-ing general statistics and Pearson correlation analysis) andPiper diagramwere used to illustrate the general hydrochem-ical characteristics (eg groundwater composition domi-nating ions and groundwater type) (Table 3 and Figure 4)and to assess the correlation between the hydrochemicalcompositions (Table 4) in the groundwater of this multilay-ered aquifer system Second isotope analyses Gibbs plotsand bivariate analyses of the compositions were conductedto determine the origins controlling physicalchemical pro-cesses and material sources of the groundwater Third basedon the understanding of the groundwater origins and the con-trolling processes the groundwater dynamics were analyzedto assess the risk of seawater intrusion into this coastal aquifersystem

Geofluids 5

Groundwater levelminus8

0 4 8

Naozhou

N

Leiz

hou Donghai island

Zhanjiang city

J20

J23

J9

J18

6050 40

30

20

10

6 42

2

1

10862

(km)

Depression cone of theconfined groundwaterObservation well of theunconfined aquifer

J9

(a)Groundwater levelminus8

N

L38-1(B)

L40-1(B)

L39-1(B)

L8-1(B)1612

8 4

0

minus4

minus12

minus12minus

16

minus20

minus8

0 4 8(km)

Observation well of themiddle confined aquifer

L8-1

Depression cone of theconfined groundwater

(b)Groundwater levelminus8

N

L24-3L25-3

minus22

minus18minus14

minus6 minus10

0 4 8(km)

Observation well of thedeep confined aquifer

L24-3

Depression cone of theconfined groundwater

(c)

Figure 3 Groundwater level contour maps for the multilayered aquifer system (a) the unconfined aquifer (b) the middle confined aquiferand (c) the deep confined aquifer

4 Results

41 Groundwater Hydrochemistry Understanding the char-acteristics of groundwater chemistry is the base to identify thegroundwater origins and the hydrochemical processes occur-ring in the aquiferThe hydrochemical data of groundwater inthemultilayered aquifer system of Zhanjiang are presented inTable 1 and the statistical results of those data are presentedin Table 3 As shown the TDS of the unconfined groundwatervaries from 149mgL to 82339mgL with a mean value of36028mgL that of themiddle confined groundwater rangesfrom 6431mgL to 25294mgL with an average value of12447mgL and that of the deep confined groundwaterchanges from 9952mgL to 32598mgL with a mean valueof 15801mgL These low values of TDS indicate that thegroundwater in this aquifer system is mainly fresh (TDS lt1000mgL) According to the hydrogeological conditions ofthis aquifer system it can be concluded that the approx-imately natural flow regime of the water table above themean sea level (Figure 3(a)) is the primary reason why mostof the unconfined groundwater has not become salinizedFurthermore the confined aquiferrsquos roof with extremely lowpermeability prevents seawater intrusion into the confinedgroundwater The pH value of the unconfined groundwatervaries from 4 to 825 with an average value of 604 that ofthe middle confined groundwater changes from 415 to 734with an average value of 625 and that of the deep confinedgroundwater ranges from 534 to 781 with an average valueof 672 Therefore the groundwater is generally acidity Theaverage concentrations of major cations in the unconfinedand the middle confined groundwater follow the order of

Na+ gt Ca2+ gt K+ gt Mg2+ and those of the major anionsfollow the order of HCO

3

minus gt Clminus gt SO4

2minus gt NO3

minus

(Table 3) The average concentrations of major cations in thedeep confined groundwater follow the order of Na+ gt K+ gtCa2+ gtMg2+ and those of the major anions follow the orderof HCO

3

minus gt SO4

2minus gt Clminus gt NO3

minus (Table 3)The relations between the major ions and TDS are useful

for interpreting the major hydrogeochemical evolution pro-cesses occurring in the aquifer and for deducing the materialsources of the ions in the groundwater [37ndash39] In thisstudy correlation coefficients were calculated to representthe relations between TDS and the major ions (Na+ K+Ca2+ Mg2+ HCO

3

minus NO3

minus Clminus and SO4

2minus) As shownin Table 4 the correlations between TDS and the majorions are not strong (correlation coefficients lt 0900) whichindicates no single ion can take dominant role in groundwatermineralization This result also implies that the dissolutionof various minerals together constitutes the groundwatercomposition

42 Groundwater Types Piper diagram can help to under-stand the groundwater type and the potential hydrochemicalprocesses controlling groundwater chemistry [40] Accord-ing to the concentrations of major ions shown in Table 1the Piper plot was made (Figure 4) As shown the uncon-fined and middle confined groundwater show a relativelylarge range in the rhombus area (areas I and II) Theunconfined groundwater is characterized by HCO

3-CasdotNa

HCO3sdotCl-CasdotNa ClsdotSO

4-NasdotCa and Cl-NasdotCasdotMg hydro-

chemical types With comprehensive consideration of the

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

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Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

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OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MineralogyInternational Journal of

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MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 2: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

2 Geofluids

other isotopes (eg radium carbon chlorine boron andstrontium) have been used as tracers for characterizing thehydrogeological conditions and hydrochemical processes incoastal aquifers specifically identifying submarine ground-water discharge and describing seawater intrusion [10 13 2627]

This study focused on the coastal multilayered aquifersystem (including three layers of aquifer and two layers ofaquitard) of Zhanjiang which is located in the southwestof Guangdong Province China (Figure 1) The groundwaterin the middle and deep confined aquifers (Figure 2) hasbeen the sole source of drinking water for the populationof the city of Zhanjiang since the 1960s According to thewater resources bulletin of Zhanjiang groundwater pumpingamount has been about 22times 108m3a for the resident popula-tion and local industry in recent years Because of this intenseexploitation of groundwater the confined groundwater levelhas dropped to about 20m below sea level since the 1990s [2829] (Figures 3(b) and 3(c)) Recent investigations have shownthat the groundwater in this multilayered aquifer systemremains fresh but parts of the unconfined groundwater inisland areas (eg Donghai and Naozhou) and small parts ofthe confined groundwater in Naozhou island have sufferedseawater intrusion [30ndash33] It is a concern that the confinedgroundwater in Zhanjiang city will be risky in suffering fromseawater intrusion in the future Therefore it is necessaryand urgent to conduct a research to identify the originsmineralization processes andhydrochemical dynamics of thecoastal groundwater to assess the risk of seawater intrusion

The main objective of this study is to identify theorigins material sources and hydrochemical processes ofthe groundwater in the coastal multilayered aquifer systemof Zhanjiang through integrated analysis of hydrochemicaland isotopic data In addition the risk of seawater intrusioninto the confined groundwater is assessed by analysis ofthe dynamic data of groundwater level and hydrochemistryThe results will contribute to generate scientific informationfor the local coastal hydrogeology and be supportive forthe sustainable management of the groundwater in thismultilayered aquifer system

2 Study Area and Its Hydrogeology Condition

Zhanjiang city with a land area of 1491 km2 is located insouthwestern Guangdong China (Figure 1) The topographyis high in the northwest and low in the south The averageannual precipitation and evaporation are 1347 and 1774mmrespectively [29 32]

The geology of the study area mainly consists of conti-nental and marine sediments of upper Tertiary-Quaternaryage overlying a basement of muddy sandstone of Cretaceousage (K

2) According to earlier geological investigation [29

35 36] the sedimentary formations are characterized by fivestratigraphic units which include Holocene stratum (sandand clay) Beihai Group of middle Pleistocene age (Q

2b

sand with gravel in the lower portion and clayey sand in theupper portion) Zhanjiang Group of lower Pleistocene age(Q1z coarse sand with gravel and scattered lenses of clay)

Xiayang Group of Pliocene age (N2x medium to coarse sand

with gravel and thin layers or scattered lenses of clay) andWeizhou Group of Miocene age (N

1w silty sand and fine

sand with clay) These geological formations are intercalatedwith basalt and pyroclastic rock The sediments mentionedabove constitute themultilayered aquifer system that includesthree aquifers (the unconfined aquifer the middle confinedaquifer and the deep confined aquifer) separated by claylayers (aquitards) (Figure 2)

The unconfined aquifer is about 30-m thick and is com-posed of deposits of Holocene age Beihai Group of middlePleistocene age and upper portion of Zhanjiang Group oflower Pleistocene age This aquifer overlies a thick layer ofclay that extends laterally under the seabed The hydraulicconductivity (119870) of this unconfined aquifer is 5ndash25mdBecause exploitation of the unconfined groundwater is scat-tered and intermittent the groundwater flow field remains anapproximately natural flow regime with the water table abovethe mean sea level (Figure 3(a)) The groundwater whichis recharged mainly by rainfall infiltration and dischargedthrough evaporation and runoff to the ocean flows radiallyfrom the watershed to the ocean (Figures 2 and 3(a))

The middle confined aquifer is composed of ZhanjiangGroup deposits of lower Pleistocene age (Q

1z) with thickness

of about 120m and hydraulic conductivity (119870) of 20ndash60mdInduced by overexploitation the groundwater level of thisconfined aquifer has dropped to minus24 to 16m (Figure 3(b))The deep confined aquifer is composed of Xiayang Groupdeposits of Pliocene age (N

2x) with 119870 of 20ndash50md The

groundwater level of the deep confined aquifer has droppedto minus22 to minus4m (Figure 3(c)) These two confined aquifers arerecharged mainly via lateral runoff and they are dischargedby pumping

3 Sampling and Analysis Method

To investigate the hydrochemistry of the groundwater inthe multilayered aquifer system of Zhanjiang 3 times ofgroundwater sampling activities were conducted fromMarch2009 to March 2011 As shown in Figure 1 and Table 1 a totalof 95 groundwater samples were collected from public supplywells These comprised 22 samples from the unconfinedaquifer (depth lt 30m sample numbers starting with Q)35 samples from the middle confined aquifer (50 lt depthlt 140m sample numbers starting with Z) and 38 samplesfrom the deep confined aquifer (depth gt 200m samplenumbers starting with S) All samples were filtered throughmembranes (045-120583m pore size) and stored in high-densitypolyethylene bottles which were pretreated using deionizedwater and rinsed using sampledwaterThen the sampleswerepreserved and acidified with HNO

3for cation analysis All

bottles were sealed with wax to ensure a watertight sealThe total dissolved solid (TDS) temperature and pH

were measured in situ using a portable multiparameterwater analyzer (Hach Sension156) The concentration ofHCO3

minus was also determined in the field via titration onthe day of sampling The major cations (K+ Ca2+ Na+ andMg2+) were analyzed by Inductively Coupled Plasma MassSpectrometry (ICP-MS pHPerkin-Elmer Sciex Elan DRC-e)at the Institute of Geology andGeophysics Chinese Academy

Geofluids 3

Zhanjiang city

Donghai island

A

B

Hydrogeology cross-section

Sampling site of theunconfined groundwater

Beijing

China seaSouth

China

10000

Guangdong

0 4(km) Naozhou

Study area

Sampling site of the middleconfined groundwaterSampling site of the deepconfined groundwaterSamples of the unconfined groundwater(observed by Zhang et al [34])

Samples of the confined groundwater(observed by Zhang et al [34])

36 14

20

26

451

7

18

21

2328

3034

41

38

Haikou

(a)

(b)

S1

S2

S3

S4S5S6

S7

S8

S9

S10

S12

S11

Z1Z2

Z4

Z5

Z6Z7

Z9

Z8

Z10

Z11

Q6Q3

Q1

Q2

Q5

Q7

Q4

Q9Z13

Z14

Z12

S14

S13

Z3

A B

Hong Kong

0 100 200

China seaSouth

Guangdong Province

3

614

20

22

26

45

1

7

18

21

2328

30

34

41

38Naozhou

(d)

Leiz

hou

8

22

(km)

(km)

N

N

N

(c)

Q1

Z1

S1

1

20

Figure 1 Location map of Zhanjiang (Line A-B illustrates the location of the hydrogeological cross-section displayed in Figure 2)

4 Geofluids

BA

South Chinasea

0 5

L30Sk10Sk7L19S19L16L12

L34-1S60

Precipitation infiltration

Withdrawals

(km)

52

0

minus100

minus200

minus300

minus400

(m)

1Q

10653G8844G4760G

8608 G

Holocene (sandy clay)Holocene (sand)

Beihai group of middle

(sand with gravel)Pleistocene age 12<

Zhanjiang group of lower

(coarse sand with gravel)Pleistocene age 11T

Xiayang group of

(medium to coarse sand with gravel)Pleistocene age 2R

(silty-fine sand)

Weizhou group ofMiocene age 1Q

Є2-3

+2

2R

11z

12<

14

+2

L30

Unconfined aquifer

Clay

Aquifer boundaryBorehole

(muddy sandstone)Upper cretaceous age +2

Middle-upper

(metamorphic sandstone)Cambrian age Є2-3

Middle confined aquifer

Deep confined aquifer

Groundwater flowLeakage

Aquitard (clay layer)

Figure 2 Hydrogeological cross-section (Line A-B in Figure 1) of the study area

of Sciences (IGGCAS) The anions (Clminus SO4

2minus and NO3

minus)were measured by Ion Chromatography System (DionexICS-1500) at IGGCAS Dissolved silica (SiO

2) was analyzed

by spectrophotometry using themolybdate bluemethodThecharge balance (119864 = (sum119898

119888minus sum119898

119886)(sum119898

119888+ sum119898

119886) times 100

where119898119888is the milligram equivalent of the cations and119898

119886is

the milligram equivalent of the anions) varied from minus497to 495 (within plusmn5) with an average of minus184 (withinplusmn5) This balance number can indicate the accuracy of thedata

The analyses of stable oxygen (18O) hydrogen (2H) andsulfur (34S) isotopes were conducted using mass spectrome-ters (Finigan MAT 253 for 18O-2H and Delta S for 34S) at theStable Isotope Laboratory IGGCASThe isotope ratios (12057518O1205752H and 12057534S) were given in the usual 120575-units calculatedwithrespect to standard sample 120575sample = ((119877sample119877standard) minus1) times 1000(permil) in which 119877sample and 119877standard represent theratio of heavy to light isotopes of the sample and standard

respectively The results of the stable isotope are shown inTable 2

In this study first according to the groundwater chemicaland isotopic data (Tables 1 and 2) statistical analyses (includ-ing general statistics and Pearson correlation analysis) andPiper diagramwere used to illustrate the general hydrochem-ical characteristics (eg groundwater composition domi-nating ions and groundwater type) (Table 3 and Figure 4)and to assess the correlation between the hydrochemicalcompositions (Table 4) in the groundwater of this multilay-ered aquifer system Second isotope analyses Gibbs plotsand bivariate analyses of the compositions were conductedto determine the origins controlling physicalchemical pro-cesses and material sources of the groundwater Third basedon the understanding of the groundwater origins and the con-trolling processes the groundwater dynamics were analyzedto assess the risk of seawater intrusion into this coastal aquifersystem

Geofluids 5

Groundwater levelminus8

0 4 8

Naozhou

N

Leiz

hou Donghai island

Zhanjiang city

J20

J23

J9

J18

6050 40

30

20

10

6 42

2

1

10862

(km)

Depression cone of theconfined groundwaterObservation well of theunconfined aquifer

J9

(a)Groundwater levelminus8

N

L38-1(B)

L40-1(B)

L39-1(B)

L8-1(B)1612

8 4

0

minus4

minus12

minus12minus

16

minus20

minus8

0 4 8(km)

Observation well of themiddle confined aquifer

L8-1

Depression cone of theconfined groundwater

(b)Groundwater levelminus8

N

L24-3L25-3

minus22

minus18minus14

minus6 minus10

0 4 8(km)

Observation well of thedeep confined aquifer

L24-3

Depression cone of theconfined groundwater

(c)

Figure 3 Groundwater level contour maps for the multilayered aquifer system (a) the unconfined aquifer (b) the middle confined aquiferand (c) the deep confined aquifer

4 Results

41 Groundwater Hydrochemistry Understanding the char-acteristics of groundwater chemistry is the base to identify thegroundwater origins and the hydrochemical processes occur-ring in the aquiferThe hydrochemical data of groundwater inthemultilayered aquifer system of Zhanjiang are presented inTable 1 and the statistical results of those data are presentedin Table 3 As shown the TDS of the unconfined groundwatervaries from 149mgL to 82339mgL with a mean value of36028mgL that of themiddle confined groundwater rangesfrom 6431mgL to 25294mgL with an average value of12447mgL and that of the deep confined groundwaterchanges from 9952mgL to 32598mgL with a mean valueof 15801mgL These low values of TDS indicate that thegroundwater in this aquifer system is mainly fresh (TDS lt1000mgL) According to the hydrogeological conditions ofthis aquifer system it can be concluded that the approx-imately natural flow regime of the water table above themean sea level (Figure 3(a)) is the primary reason why mostof the unconfined groundwater has not become salinizedFurthermore the confined aquiferrsquos roof with extremely lowpermeability prevents seawater intrusion into the confinedgroundwater The pH value of the unconfined groundwatervaries from 4 to 825 with an average value of 604 that ofthe middle confined groundwater changes from 415 to 734with an average value of 625 and that of the deep confinedgroundwater ranges from 534 to 781 with an average valueof 672 Therefore the groundwater is generally acidity Theaverage concentrations of major cations in the unconfinedand the middle confined groundwater follow the order of

Na+ gt Ca2+ gt K+ gt Mg2+ and those of the major anionsfollow the order of HCO

3

minus gt Clminus gt SO4

2minus gt NO3

minus

(Table 3) The average concentrations of major cations in thedeep confined groundwater follow the order of Na+ gt K+ gtCa2+ gtMg2+ and those of the major anions follow the orderof HCO

3

minus gt SO4

2minus gt Clminus gt NO3

minus (Table 3)The relations between the major ions and TDS are useful

for interpreting the major hydrogeochemical evolution pro-cesses occurring in the aquifer and for deducing the materialsources of the ions in the groundwater [37ndash39] In thisstudy correlation coefficients were calculated to representthe relations between TDS and the major ions (Na+ K+Ca2+ Mg2+ HCO

3

minus NO3

minus Clminus and SO4

2minus) As shownin Table 4 the correlations between TDS and the majorions are not strong (correlation coefficients lt 0900) whichindicates no single ion can take dominant role in groundwatermineralization This result also implies that the dissolutionof various minerals together constitutes the groundwatercomposition

42 Groundwater Types Piper diagram can help to under-stand the groundwater type and the potential hydrochemicalprocesses controlling groundwater chemistry [40] Accord-ing to the concentrations of major ions shown in Table 1the Piper plot was made (Figure 4) As shown the uncon-fined and middle confined groundwater show a relativelylarge range in the rhombus area (areas I and II) Theunconfined groundwater is characterized by HCO

3-CasdotNa

HCO3sdotCl-CasdotNa ClsdotSO

4-NasdotCa and Cl-NasdotCasdotMg hydro-

chemical types With comprehensive consideration of the

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Page 3: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 3

Zhanjiang city

Donghai island

A

B

Hydrogeology cross-section

Sampling site of theunconfined groundwater

Beijing

China seaSouth

China

10000

Guangdong

0 4(km) Naozhou

Study area

Sampling site of the middleconfined groundwaterSampling site of the deepconfined groundwaterSamples of the unconfined groundwater(observed by Zhang et al [34])

Samples of the confined groundwater(observed by Zhang et al [34])

36 14

20

26

451

7

18

21

2328

3034

41

38

Haikou

(a)

(b)

S1

S2

S3

S4S5S6

S7

S8

S9

S10

S12

S11

Z1Z2

Z4

Z5

Z6Z7

Z9

Z8

Z10

Z11

Q6Q3

Q1

Q2

Q5

Q7

Q4

Q9Z13

Z14

Z12

S14

S13

Z3

A B

Hong Kong

0 100 200

China seaSouth

Guangdong Province

3

614

20

22

26

45

1

7

18

21

2328

30

34

41

38Naozhou

(d)

Leiz

hou

8

22

(km)

(km)

N

N

N

(c)

Q1

Z1

S1

1

20

Figure 1 Location map of Zhanjiang (Line A-B illustrates the location of the hydrogeological cross-section displayed in Figure 2)

4 Geofluids

BA

South Chinasea

0 5

L30Sk10Sk7L19S19L16L12

L34-1S60

Precipitation infiltration

Withdrawals

(km)

52

0

minus100

minus200

minus300

minus400

(m)

1Q

10653G8844G4760G

8608 G

Holocene (sandy clay)Holocene (sand)

Beihai group of middle

(sand with gravel)Pleistocene age 12<

Zhanjiang group of lower

(coarse sand with gravel)Pleistocene age 11T

Xiayang group of

(medium to coarse sand with gravel)Pleistocene age 2R

(silty-fine sand)

Weizhou group ofMiocene age 1Q

Є2-3

+2

2R

11z

12<

14

+2

L30

Unconfined aquifer

Clay

Aquifer boundaryBorehole

(muddy sandstone)Upper cretaceous age +2

Middle-upper

(metamorphic sandstone)Cambrian age Є2-3

Middle confined aquifer

Deep confined aquifer

Groundwater flowLeakage

Aquitard (clay layer)

Figure 2 Hydrogeological cross-section (Line A-B in Figure 1) of the study area

of Sciences (IGGCAS) The anions (Clminus SO4

2minus and NO3

minus)were measured by Ion Chromatography System (DionexICS-1500) at IGGCAS Dissolved silica (SiO

2) was analyzed

by spectrophotometry using themolybdate bluemethodThecharge balance (119864 = (sum119898

119888minus sum119898

119886)(sum119898

119888+ sum119898

119886) times 100

where119898119888is the milligram equivalent of the cations and119898

119886is

the milligram equivalent of the anions) varied from minus497to 495 (within plusmn5) with an average of minus184 (withinplusmn5) This balance number can indicate the accuracy of thedata

The analyses of stable oxygen (18O) hydrogen (2H) andsulfur (34S) isotopes were conducted using mass spectrome-ters (Finigan MAT 253 for 18O-2H and Delta S for 34S) at theStable Isotope Laboratory IGGCASThe isotope ratios (12057518O1205752H and 12057534S) were given in the usual 120575-units calculatedwithrespect to standard sample 120575sample = ((119877sample119877standard) minus1) times 1000(permil) in which 119877sample and 119877standard represent theratio of heavy to light isotopes of the sample and standard

respectively The results of the stable isotope are shown inTable 2

In this study first according to the groundwater chemicaland isotopic data (Tables 1 and 2) statistical analyses (includ-ing general statistics and Pearson correlation analysis) andPiper diagramwere used to illustrate the general hydrochem-ical characteristics (eg groundwater composition domi-nating ions and groundwater type) (Table 3 and Figure 4)and to assess the correlation between the hydrochemicalcompositions (Table 4) in the groundwater of this multilay-ered aquifer system Second isotope analyses Gibbs plotsand bivariate analyses of the compositions were conductedto determine the origins controlling physicalchemical pro-cesses and material sources of the groundwater Third basedon the understanding of the groundwater origins and the con-trolling processes the groundwater dynamics were analyzedto assess the risk of seawater intrusion into this coastal aquifersystem

Geofluids 5

Groundwater levelminus8

0 4 8

Naozhou

N

Leiz

hou Donghai island

Zhanjiang city

J20

J23

J9

J18

6050 40

30

20

10

6 42

2

1

10862

(km)

Depression cone of theconfined groundwaterObservation well of theunconfined aquifer

J9

(a)Groundwater levelminus8

N

L38-1(B)

L40-1(B)

L39-1(B)

L8-1(B)1612

8 4

0

minus4

minus12

minus12minus

16

minus20

minus8

0 4 8(km)

Observation well of themiddle confined aquifer

L8-1

Depression cone of theconfined groundwater

(b)Groundwater levelminus8

N

L24-3L25-3

minus22

minus18minus14

minus6 minus10

0 4 8(km)

Observation well of thedeep confined aquifer

L24-3

Depression cone of theconfined groundwater

(c)

Figure 3 Groundwater level contour maps for the multilayered aquifer system (a) the unconfined aquifer (b) the middle confined aquiferand (c) the deep confined aquifer

4 Results

41 Groundwater Hydrochemistry Understanding the char-acteristics of groundwater chemistry is the base to identify thegroundwater origins and the hydrochemical processes occur-ring in the aquiferThe hydrochemical data of groundwater inthemultilayered aquifer system of Zhanjiang are presented inTable 1 and the statistical results of those data are presentedin Table 3 As shown the TDS of the unconfined groundwatervaries from 149mgL to 82339mgL with a mean value of36028mgL that of themiddle confined groundwater rangesfrom 6431mgL to 25294mgL with an average value of12447mgL and that of the deep confined groundwaterchanges from 9952mgL to 32598mgL with a mean valueof 15801mgL These low values of TDS indicate that thegroundwater in this aquifer system is mainly fresh (TDS lt1000mgL) According to the hydrogeological conditions ofthis aquifer system it can be concluded that the approx-imately natural flow regime of the water table above themean sea level (Figure 3(a)) is the primary reason why mostof the unconfined groundwater has not become salinizedFurthermore the confined aquiferrsquos roof with extremely lowpermeability prevents seawater intrusion into the confinedgroundwater The pH value of the unconfined groundwatervaries from 4 to 825 with an average value of 604 that ofthe middle confined groundwater changes from 415 to 734with an average value of 625 and that of the deep confinedgroundwater ranges from 534 to 781 with an average valueof 672 Therefore the groundwater is generally acidity Theaverage concentrations of major cations in the unconfinedand the middle confined groundwater follow the order of

Na+ gt Ca2+ gt K+ gt Mg2+ and those of the major anionsfollow the order of HCO

3

minus gt Clminus gt SO4

2minus gt NO3

minus

(Table 3) The average concentrations of major cations in thedeep confined groundwater follow the order of Na+ gt K+ gtCa2+ gtMg2+ and those of the major anions follow the orderof HCO

3

minus gt SO4

2minus gt Clminus gt NO3

minus (Table 3)The relations between the major ions and TDS are useful

for interpreting the major hydrogeochemical evolution pro-cesses occurring in the aquifer and for deducing the materialsources of the ions in the groundwater [37ndash39] In thisstudy correlation coefficients were calculated to representthe relations between TDS and the major ions (Na+ K+Ca2+ Mg2+ HCO

3

minus NO3

minus Clminus and SO4

2minus) As shownin Table 4 the correlations between TDS and the majorions are not strong (correlation coefficients lt 0900) whichindicates no single ion can take dominant role in groundwatermineralization This result also implies that the dissolutionof various minerals together constitutes the groundwatercomposition

42 Groundwater Types Piper diagram can help to under-stand the groundwater type and the potential hydrochemicalprocesses controlling groundwater chemistry [40] Accord-ing to the concentrations of major ions shown in Table 1the Piper plot was made (Figure 4) As shown the uncon-fined and middle confined groundwater show a relativelylarge range in the rhombus area (areas I and II) Theunconfined groundwater is characterized by HCO

3-CasdotNa

HCO3sdotCl-CasdotNa ClsdotSO

4-NasdotCa and Cl-NasdotCasdotMg hydro-

chemical types With comprehensive consideration of the

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Mining

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Journal of

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International Journal of

OceanographyInternational Journal of

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Atmospheric SciencesInternational Journal of

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MineralogyInternational Journal of

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Page 4: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

4 Geofluids

BA

South Chinasea

0 5

L30Sk10Sk7L19S19L16L12

L34-1S60

Precipitation infiltration

Withdrawals

(km)

52

0

minus100

minus200

minus300

minus400

(m)

1Q

10653G8844G4760G

8608 G

Holocene (sandy clay)Holocene (sand)

Beihai group of middle

(sand with gravel)Pleistocene age 12<

Zhanjiang group of lower

(coarse sand with gravel)Pleistocene age 11T

Xiayang group of

(medium to coarse sand with gravel)Pleistocene age 2R

(silty-fine sand)

Weizhou group ofMiocene age 1Q

Є2-3

+2

2R

11z

12<

14

+2

L30

Unconfined aquifer

Clay

Aquifer boundaryBorehole

(muddy sandstone)Upper cretaceous age +2

Middle-upper

(metamorphic sandstone)Cambrian age Є2-3

Middle confined aquifer

Deep confined aquifer

Groundwater flowLeakage

Aquitard (clay layer)

Figure 2 Hydrogeological cross-section (Line A-B in Figure 1) of the study area

of Sciences (IGGCAS) The anions (Clminus SO4

2minus and NO3

minus)were measured by Ion Chromatography System (DionexICS-1500) at IGGCAS Dissolved silica (SiO

2) was analyzed

by spectrophotometry using themolybdate bluemethodThecharge balance (119864 = (sum119898

119888minus sum119898

119886)(sum119898

119888+ sum119898

119886) times 100

where119898119888is the milligram equivalent of the cations and119898

119886is

the milligram equivalent of the anions) varied from minus497to 495 (within plusmn5) with an average of minus184 (withinplusmn5) This balance number can indicate the accuracy of thedata

The analyses of stable oxygen (18O) hydrogen (2H) andsulfur (34S) isotopes were conducted using mass spectrome-ters (Finigan MAT 253 for 18O-2H and Delta S for 34S) at theStable Isotope Laboratory IGGCASThe isotope ratios (12057518O1205752H and 12057534S) were given in the usual 120575-units calculatedwithrespect to standard sample 120575sample = ((119877sample119877standard) minus1) times 1000(permil) in which 119877sample and 119877standard represent theratio of heavy to light isotopes of the sample and standard

respectively The results of the stable isotope are shown inTable 2

In this study first according to the groundwater chemicaland isotopic data (Tables 1 and 2) statistical analyses (includ-ing general statistics and Pearson correlation analysis) andPiper diagramwere used to illustrate the general hydrochem-ical characteristics (eg groundwater composition domi-nating ions and groundwater type) (Table 3 and Figure 4)and to assess the correlation between the hydrochemicalcompositions (Table 4) in the groundwater of this multilay-ered aquifer system Second isotope analyses Gibbs plotsand bivariate analyses of the compositions were conductedto determine the origins controlling physicalchemical pro-cesses and material sources of the groundwater Third basedon the understanding of the groundwater origins and the con-trolling processes the groundwater dynamics were analyzedto assess the risk of seawater intrusion into this coastal aquifersystem

Geofluids 5

Groundwater levelminus8

0 4 8

Naozhou

N

Leiz

hou Donghai island

Zhanjiang city

J20

J23

J9

J18

6050 40

30

20

10

6 42

2

1

10862

(km)

Depression cone of theconfined groundwaterObservation well of theunconfined aquifer

J9

(a)Groundwater levelminus8

N

L38-1(B)

L40-1(B)

L39-1(B)

L8-1(B)1612

8 4

0

minus4

minus12

minus12minus

16

minus20

minus8

0 4 8(km)

Observation well of themiddle confined aquifer

L8-1

Depression cone of theconfined groundwater

(b)Groundwater levelminus8

N

L24-3L25-3

minus22

minus18minus14

minus6 minus10

0 4 8(km)

Observation well of thedeep confined aquifer

L24-3

Depression cone of theconfined groundwater

(c)

Figure 3 Groundwater level contour maps for the multilayered aquifer system (a) the unconfined aquifer (b) the middle confined aquiferand (c) the deep confined aquifer

4 Results

41 Groundwater Hydrochemistry Understanding the char-acteristics of groundwater chemistry is the base to identify thegroundwater origins and the hydrochemical processes occur-ring in the aquiferThe hydrochemical data of groundwater inthemultilayered aquifer system of Zhanjiang are presented inTable 1 and the statistical results of those data are presentedin Table 3 As shown the TDS of the unconfined groundwatervaries from 149mgL to 82339mgL with a mean value of36028mgL that of themiddle confined groundwater rangesfrom 6431mgL to 25294mgL with an average value of12447mgL and that of the deep confined groundwaterchanges from 9952mgL to 32598mgL with a mean valueof 15801mgL These low values of TDS indicate that thegroundwater in this aquifer system is mainly fresh (TDS lt1000mgL) According to the hydrogeological conditions ofthis aquifer system it can be concluded that the approx-imately natural flow regime of the water table above themean sea level (Figure 3(a)) is the primary reason why mostof the unconfined groundwater has not become salinizedFurthermore the confined aquiferrsquos roof with extremely lowpermeability prevents seawater intrusion into the confinedgroundwater The pH value of the unconfined groundwatervaries from 4 to 825 with an average value of 604 that ofthe middle confined groundwater changes from 415 to 734with an average value of 625 and that of the deep confinedgroundwater ranges from 534 to 781 with an average valueof 672 Therefore the groundwater is generally acidity Theaverage concentrations of major cations in the unconfinedand the middle confined groundwater follow the order of

Na+ gt Ca2+ gt K+ gt Mg2+ and those of the major anionsfollow the order of HCO

3

minus gt Clminus gt SO4

2minus gt NO3

minus

(Table 3) The average concentrations of major cations in thedeep confined groundwater follow the order of Na+ gt K+ gtCa2+ gtMg2+ and those of the major anions follow the orderof HCO

3

minus gt SO4

2minus gt Clminus gt NO3

minus (Table 3)The relations between the major ions and TDS are useful

for interpreting the major hydrogeochemical evolution pro-cesses occurring in the aquifer and for deducing the materialsources of the ions in the groundwater [37ndash39] In thisstudy correlation coefficients were calculated to representthe relations between TDS and the major ions (Na+ K+Ca2+ Mg2+ HCO

3

minus NO3

minus Clminus and SO4

2minus) As shownin Table 4 the correlations between TDS and the majorions are not strong (correlation coefficients lt 0900) whichindicates no single ion can take dominant role in groundwatermineralization This result also implies that the dissolutionof various minerals together constitutes the groundwatercomposition

42 Groundwater Types Piper diagram can help to under-stand the groundwater type and the potential hydrochemicalprocesses controlling groundwater chemistry [40] Accord-ing to the concentrations of major ions shown in Table 1the Piper plot was made (Figure 4) As shown the uncon-fined and middle confined groundwater show a relativelylarge range in the rhombus area (areas I and II) Theunconfined groundwater is characterized by HCO

3-CasdotNa

HCO3sdotCl-CasdotNa ClsdotSO

4-NasdotCa and Cl-NasdotCasdotMg hydro-

chemical types With comprehensive consideration of the

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geology Advances in

Page 5: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 5

Groundwater levelminus8

0 4 8

Naozhou

N

Leiz

hou Donghai island

Zhanjiang city

J20

J23

J9

J18

6050 40

30

20

10

6 42

2

1

10862

(km)

Depression cone of theconfined groundwaterObservation well of theunconfined aquifer

J9

(a)Groundwater levelminus8

N

L38-1(B)

L40-1(B)

L39-1(B)

L8-1(B)1612

8 4

0

minus4

minus12

minus12minus

16

minus20

minus8

0 4 8(km)

Observation well of themiddle confined aquifer

L8-1

Depression cone of theconfined groundwater

(b)Groundwater levelminus8

N

L24-3L25-3

minus22

minus18minus14

minus6 minus10

0 4 8(km)

Observation well of thedeep confined aquifer

L24-3

Depression cone of theconfined groundwater

(c)

Figure 3 Groundwater level contour maps for the multilayered aquifer system (a) the unconfined aquifer (b) the middle confined aquiferand (c) the deep confined aquifer

4 Results

41 Groundwater Hydrochemistry Understanding the char-acteristics of groundwater chemistry is the base to identify thegroundwater origins and the hydrochemical processes occur-ring in the aquiferThe hydrochemical data of groundwater inthemultilayered aquifer system of Zhanjiang are presented inTable 1 and the statistical results of those data are presentedin Table 3 As shown the TDS of the unconfined groundwatervaries from 149mgL to 82339mgL with a mean value of36028mgL that of themiddle confined groundwater rangesfrom 6431mgL to 25294mgL with an average value of12447mgL and that of the deep confined groundwaterchanges from 9952mgL to 32598mgL with a mean valueof 15801mgL These low values of TDS indicate that thegroundwater in this aquifer system is mainly fresh (TDS lt1000mgL) According to the hydrogeological conditions ofthis aquifer system it can be concluded that the approx-imately natural flow regime of the water table above themean sea level (Figure 3(a)) is the primary reason why mostof the unconfined groundwater has not become salinizedFurthermore the confined aquiferrsquos roof with extremely lowpermeability prevents seawater intrusion into the confinedgroundwater The pH value of the unconfined groundwatervaries from 4 to 825 with an average value of 604 that ofthe middle confined groundwater changes from 415 to 734with an average value of 625 and that of the deep confinedgroundwater ranges from 534 to 781 with an average valueof 672 Therefore the groundwater is generally acidity Theaverage concentrations of major cations in the unconfinedand the middle confined groundwater follow the order of

Na+ gt Ca2+ gt K+ gt Mg2+ and those of the major anionsfollow the order of HCO

3

minus gt Clminus gt SO4

2minus gt NO3

minus

(Table 3) The average concentrations of major cations in thedeep confined groundwater follow the order of Na+ gt K+ gtCa2+ gtMg2+ and those of the major anions follow the orderof HCO

3

minus gt SO4

2minus gt Clminus gt NO3

minus (Table 3)The relations between the major ions and TDS are useful

for interpreting the major hydrogeochemical evolution pro-cesses occurring in the aquifer and for deducing the materialsources of the ions in the groundwater [37ndash39] In thisstudy correlation coefficients were calculated to representthe relations between TDS and the major ions (Na+ K+Ca2+ Mg2+ HCO

3

minus NO3

minus Clminus and SO4

2minus) As shownin Table 4 the correlations between TDS and the majorions are not strong (correlation coefficients lt 0900) whichindicates no single ion can take dominant role in groundwatermineralization This result also implies that the dissolutionof various minerals together constitutes the groundwatercomposition

42 Groundwater Types Piper diagram can help to under-stand the groundwater type and the potential hydrochemicalprocesses controlling groundwater chemistry [40] Accord-ing to the concentrations of major ions shown in Table 1the Piper plot was made (Figure 4) As shown the uncon-fined and middle confined groundwater show a relativelylarge range in the rhombus area (areas I and II) Theunconfined groundwater is characterized by HCO

3-CasdotNa

HCO3sdotCl-CasdotNa ClsdotSO

4-NasdotCa and Cl-NasdotCasdotMg hydro-

chemical types With comprehensive consideration of the

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

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Mining

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Page 6: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

6 Geofluids

Table1Hydrochem

icaldataof

grou

ndwater

inthem

ultilayered

aquifersystem

ofZh

anjiang

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Q1

Uncon

fined

aquifer

Mar

2009

1786

691

3124

645

1342

4977

3564

451293

21632

53

23Q2

154

7067

1774

4563

598

18335

5826

100

1049

53223

506

26Q3

1291

571

5138

659

17116

1921

1426

05

2565

22245

755

23Q4

7737

2375

4658

1466

20686

1117

716047

951392

78393

814

22Q5

5258

62712

1368

14584

3229

2973

40892

28376

703

25Q6

10515

1564

1018

14168

32444

15456

8559

325

1091

71027

727

22Q7

1836

842

2826

1440

166777

301105

2077

408

23Q1

Uncon

fined

aquifer

Mar

2010

1389

632

2993

719

939

5016

3449

125

1293

20204

523

Q2

4166

2165

10521

1493

539

19366

11652

55875

56374

487

27Q3

2778

182617

1306

5254

3424

3093

3096

520006

643

26Q4

7042

1955

3778

2263

19557

8816

2613

75837

45344

825

22Q5

2554

481

4613

1434

11826

2825

3684

4093

426451

715

22Q6

7639

2375

9339

12075

1313

818675

17238

80393

82339

672

22Q7

1537

813

2082

177

291

7488

21117

16434

425

Q8

942

881

1006

339

6933

844

1934

596

2149

552

23Q1

Uncon

fined

aquifer

Mar

2011

1321

743203

809

5339

4688

351343

2134

436

22Q2

4351

2282

10567

1754

534

20394

609

120

1526

5936

465

25Q3

2884

445

2127

1373

5425

2712

4452

325

911

20886

626

23Q4

3357

851

654

2322

14237

1048

3002

21181

20016

715

25Q5

2982

162

162

1353

11009

1774

4559

181546

1878

689

23Q6

7429

2104

7899

1584

16268

1374

11599

50383

5792

170

121

Q7

1661

771969

182

2889

7027

1010

16604

41

26Z1

Middlec

onfin

edaquifer

Mar

2009

743

332

1143

1004

6102

1223

24

01

2369

11388

67

28Z2

347

1275

618

598

1223

831

31462

6431

54

27Z3

724

361

397

728

4613

262

1306

4183

1098

8649

30Z4

447

451

2002

801

2233

2793

2613

2909

13688

61

27Z5

109

632

1142

643

8036

1049

475

03

4335

13867

678

28Z6

457

481

814

462

545

1308

3609

2757

13244

536

27Z7

649

481

794

462

5856

61

711

153508

11047

64

28Z8

248

391

535

366

744

787

2377

2442

7646

555

26Z9

794

601

887

145

6846

525

24

01

2931

9749

734

27Z10

844

722

1262

936

4467

2882

1902

2368

14474

625

28Z11

743

271

2063

609

9379

698

1202

2716

12072

719

295

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

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Geology Advances in

Page 7: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 7

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

Z1

Middlec

onfin

edaquifer

Mar

2010

992

361

1367

901

564

2605

596

1328

12548

669

26Z2

248

151

696

253

586

858

1282

21652

6853

565

28Z3

397

241

798

861

4746

429

596

4328

11046

659

29Z4

347

332

1871

678

3804

2257

01

253

1245

415

27Z5

1191

542

1339

673

7737

951547

3834

1437

68

29Z6

497

42

865

462

586

1383

3424

2801

11925

555

27Z7

942

512

751

432

6156

669

1306

03

3973

12462

66

25Z8

297

241

616

448

732

943

1902

01

2475

746

559

27Z9

844

571

914

163

6712

432

711

03

4019

11079

695

26Z10

992

722

1481

105224

3169

1191

01

2223

14677

652

27Z11

743

241

2039

675

9342

599

1202

2688

11944

705

30Z12

913

811

623

59

5822

102

221

2684

138

667

29Z13

846

672

644

421

5337

899

1806

3089

149

634

28Z14

58

404

988

274

3561

1074

1694

2942

150

644

28Z1

Middlec

onfin

edaquifer

Mar

2011

832

443

1091

1014

6114

1836

701

1802

12648

67

26Z2

343

148

891

293

1312

937

151791

734

438

24Z4

489

356

2182

816

1629

3588

2224

01

3721

14536

578

275

Z597

883

1164

737

8677

1049

1407

4638

15588

666

29Z6

424

593

824

568

752

1436

3818

01

3964

1514

6562

25Z7

2248

385

626

474

922

787

1287

4385

15507

68

26Z8

244

474

763

454

812

1312

2459

267

8965

552

25Z9

782

564

958

188

6779

351

701

14813

11908

683

27Z10

221007

2412

427

3527

7264

2109

5109

25294

637

25Z11

441

207

1843

553

6779

876

471

5411

13602

694

30S1

Deepconfi

ned

aquifer

Mar

2009

297

211

1082

1199

4912

525

711

03

269

10069

651

32S2

347

301

932

1234

5504

174

1306

2591

1010

364

32S3

447

451

1951

1076

9226

351

711

3295

1317

7699

32S4

1033

42

467

809

6547

436

24

02

4616

11782

684

325

S5297

241

696

1017

4928

262

526

140

95

1318

2656

30S6

645

361

866

981

67351

831

4594

127

674

30S7

3621

39

2525

1467

6956

3754

511

398

92391

63

33S8

992

451

1471

704

908

436

124

3439

12622

715

31S9

2281

993

4418

4549

2470

72882

1191

2626

32346

614

31S10

2287

541

124

1097

13247

61

1203

3103

1596

873

31S11

497

36

117

1015

6401

262

1071

05

5493

13568

67

325

S12

497

33

7110

5358

089

1306

5026

12401

648

32

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geology Advances in

Page 8: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

8 Geofluids

Table1Con

tinued

Samplen

umber

Aquifer

Samplingtim

eCa2+

Mg2+

Na+

K+HCO3

minusClminus

SO4

2minus

NO3

minusSiO2

TDS

pH119879

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(mgL)

(∘ C)

S1

Deepconfi

ned

aquifer

Mar

2010

297

211

1089

1356

544

599

831

01

2716

11074

664

31S2

297

211

739

134

5233

344

596

2617

9952

642

32S3

595

33

2004

1044

9049

691

831

02

3005

13304

697

32S4

491

566

1061

976

6993

436

1297

08

4344

13283

674

33S5

248

27

779

1016

5547

085

355

13357

10384

67

30S6

397

42

903

991

6219

344

951

03

538

13276

67

31S7

1009

662

5447

695

17659

1882

1426

01

2489

22626

781

33S8

942

452

147

819

9489

344

24

01

3571

12646

714

30S9

1687

1322

4688

4781

2495

72765

1662

2524

32598

612

325

S10

1255

872

1587

473

9782

173

831

03

4876

17026

672

31S11

1237

271

397

1232

6712

347

711

02

5293

13309

687

315

S12

595

361

974

997

6759

429

831

5169

13454

675

31S13

648

565

2606

87

6136

1986

1837

3223

214

668

30S14

753

519

2317

141278

3254

688

4728

195

723

31S1

Deepconfi

ned

aquifer

Mar

2011

293

208

104

168

515

525

1407

3444

12082

658

32S2

244

356

737

1225

5325

351

837

03

2968

10204

642

32S3

978

326

1971

1028

9897

702

821

02

4666

1610

8712

325

S4489

474

1065

948

8134

436

115

5413

13454

668

33S5

343

622

823

479

509

1751

2326

01

404

1635

534

31S6

486

385

925

1228

637

262

937

6003

14022

673

31S7

5335

741

1271

737

1477

92889

1287

112312

2315

476

633

S81424

503

978

1035

9897

351

586

446

7615036

699

31S9

1467

1363

4612

485

2213

3215

701

3222

2814

46

35S10

1417

83

1775

1008

11672

1049

2224

02

3683

19666

703

31S11

343

326

1231

1154

6511

351

701

075

6005

14208

668

32S12

635

533

929

994

6545

1574

235

02

3192

12366

662

32

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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EarthquakesJournal of

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Mining

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OceanographyInternational Journal of

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Page 9: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 9

Table 2 Isotope data of groundwater in the multilayered aquifersystem of Zhanjiang

Samplenumber Aquifer Sampling

time18O 2H 12057534S(permil) (permil) (permil)

Q1

Unconfinedaquifer Mar 2010

minus693 minus437Q2 minus556 minus384Q3 minus705 minus458Q4 minus693 minus465Q5 minus592 minus398Q6 minus649 minus415Q7 minus59 minus388Q8 minus693 minus454 652Z2

Middleconfinedaquifer

Mar 2010

minus642 minus44Z4 minus74 minus484Z6 minus67 minus457Z7 minus694 minus448Z8 minus691 minus468Z9 minus658 minus436Z11 minus7 minus461Z12 minus671 minus516Z13 minus742 minus519 1238Z14 minus705 minus529 1328S2

Deepconfinedaquifer

Mar 2010

minus716 minus501S3 minus734 minus496S6 minus745 minus501S7 minus701 minus465S13 minus709 minus538S14 minus69 minus546 1726

complicated hydrochemical types and relatively high levelsof Clminus Mg2+ and TDS (ie samples Q2 Q4 and Q6Figure 1 and Tables 1 and 3) of the unconfined groundwaterit can be concluded that slight seawater mixing occurs inthe unconfined groundwater near the coastline but thatseawater intrusion is still in the initial phase [32] Themiddle confined groundwater is characterized by HCO

3-

CasdotMgsdotNa ClsdotHCO3-NasdotCa and ClsdotSO

4-NasdotCasdotMg hydro-

chemical types The low TDS values and complicated hydro-chemical types of this confined groundwater suggest thatwater-rock interactions (eg mineral dissolution or cationexchange) might occur in the middle confined aquifer

Figure 4 also shows that the deep confined groundwatersamples which are distributed mainly in the bottom-leftcorner of rhombus area (II) are mainly represented byHCO3-NasdotCa(Mg) hydrochemical type indicating that deep

confined groundwater naturally evolveswithout any intensivehydrogeochemical process or anthropogenic impact

43 12057518O and 1205752HCompositions Thestable oxygen (18O) andhydrogen (2H) isotopes of groundwater samples are relatedto the recharge sources flow paths and residence times ofgroundwater The method of isotope analysis has been usedwidely in many hydrogeological studies [4 5 41 42] The

I

II

34

2minus+Fminus

-A2+

2+

+-A 2+

2+

+

+++

3

2minus+(3

minus

34 2minus

Fminus

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 4 Piper plots of chemical compositions of the coastalgroundwater of Zhanjiang

Deep confined groundwater

minus60

minus50

minus40

minus30

minus8 minus7 minus6 minus5 minus4

Unconfined groundwaterMiddle confined groundwater

I

II

LMWL (Hong Kong)LMWL (Haikou)GMWL

2(

(₀ )

18 (₀)

Figure 5 Stable isotope compositions of groundwater in themultilayered aquifers of Zhanjiang

analysis results of 12057518O and 1205752H are shown in Table 2 andFigure 5 According to the monthly rainwater data obtainedfrom the GNIP (Global Network of Isotopes in Precipitation)of the IAEA (International Atomic Energy Agency) the localmeteoric water lines (LMWLs) of Hong Kong and Haikouweather stations were calculated as 1205752H = 82812057518O + 1278and 1205752H = 75012057518O + 618 respectively Then these twoLMWLs were used as the LMWL of Zhanjiang As shown inFigure 5 and Table 2 the isotopic compositions of 1205752H and

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

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Geology Advances in

Page 10: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

10 Geofluids

Table 3 Statistical results of groundwater chemistry data of the multilayered aquifer system of Zhanjiang

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus SiO2

TDS pH 119879 (Na +K)Cl(mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (mgL) (∘C)

Unconfinedaquifer

Minimum 942 18 654 14 534 844 1426 05 383 149 4 21 038Maximum 10515 7067 10567 1466 32444 20394 17238 120 2565 82339 825 27 444Average 3727 1455 4336 2518 10691 7677 6261 4136 1121 36028 604 2359 158

Middleconfinedaquifer

Minimum 244 12 397 145 545 262 12 01 109 6431 415 24 057Maximum 2248 1007 2412 1014 9379 7264 3818 15 5411 25294 734 30 628Average 740 459 1130 563 4724 1486 1462 164 3052 12447 625 2731 222

Deepconfinedaquifer

Minimum 244 208 397 473 509 085 115 01 989 9952 534 30 091Maximum 5335 1363 5447 4781 24957 3754 511 11 6005 32598 781 35 2503Average 978 493 1604 1214 9033 915 1013 121 3828 15801 672 3167 695

Table 4 Correlation matrix between TDS and the major ions

Ca2+ Mg2+ Na+ K+ HCO3

minus Clminus SO4

2minus NO3

minus TDSUnconfined aquifer (119899 = 22)

Ca2+ 1Mg2+ 0188 1Na+ 0635 0185 1K+ 0601 0406 0314 1HCO

3

minus 0734 minus0141 0196 0351 1Clminus 0561 0693 0801 0481 minus0036 1SO4

2minus 0595 0346 0580 0758 0222 0649 1NO3

minus 0451 0670 0503 0566 minus0126 0798 0473 1TDS 0814 0570 0766 0774 0356 0881 0788 0760 1

Middle confined aquifer (119899 = 35)Ca2+ 1Mg2+ 0554 1Na+ 0204 0085 1K+ 0098 0096 0368 1HCO

3

minus 0550 0193 0237 0204 1Clminus 0348 0391 0648 0294 minus0239 1SO4

2minus minus0173 0262 minus0111 minus0049 minus0707 0305 1NO3

minus minus0012 minus0194 minus0081 minus0312 minus0339 0152 minus0022 1TDS 0715 0704 0518 0290 0272 0632 0217 minus0119 1

Deep confined aquifer (119899 = 38)Ca2+ 1Mg2+ 0431 1Na+ 0300 0727 1K+ 0181 0388 0468 1HCO

3

minus 0503 0826 0845 0584 1Clminus 0713 0661 0656 0381 0564 1SO4

2minus 0392 0146 0272 0162 0003 0630 1NO3

minus 0795 0267 minus0018 minus0143 0365 0464 0143 1TDS 0606 0844 0849 0569 0851 0835 0425 0463 1

12057518O of the unconfined groundwater vary from minus3840permil tominus4650permil (average minus4207permil) and from minus556permil to minus705permil(average minus640permil) respectively The isotopic compositionsof 1205752H and 12057518O of the middle confined groundwater varyfrom minus4360permil to minus5290permil (average minus4758permil) and from

minus642permil to minus742permil (average minus691permil) respectively Theisotopic compositions of 1205752H and 12057518O of the deep confinedgroundwater vary from minus4650permil to minus5462permil (averageminus5079permil) and from minus690permil to minus745permil (average minus716permil)respectively

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geology Advances in

Page 11: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 11

5 Discussions

51 Origin of the Groundwater For the unconfined ground-water as shown in Figure 5 all samples (except Q2 Figure 1)plot along the global meteoric water line (GMWL) [43]and LMWL indicating that the unconfined groundwater ismainly of meteoric origin In comparison with the othergroundwater samples sample Q2 is relatively enriched instable isotopes it deviates slightly from the LMWL (part I inFigure 5) and it is characterized by comparatively high levelsof TDS (56374mgL) and a low water table (255m) Thismight imply that this sample is influenced either by relativelyintense evaporation or by slight mixing with seawater in thearea near the coastline

For themiddle and deep confined groundwater as shownin Figure 5 the distribution of the confined groundwatersamples presents a pattern the deeper the aquifer depth is themore depleted the isotopic data are This pattern may implythat the hydraulic connection between this two confinedaquifers is relatively weak The samples collected in themainland area (ie Zhanjiang city area) are mainly locatedalong the GMWL and LMWL indicating that the confinedgroundwater in the mainland area is of meteoric originHowever the relativelymore depleted isotopic data comparedto those of the unconfined groundwater implies thatmeteoricrecharge to the confined groundwater is sourced from themountain area of the north and northwest area where theprecipitationrsquos isotopic data are more depleted Meanwhilethe confined groundwater flow fields (Figures 3(b) and 3(c))certify the occurrence of recharge from the northern andnorthwestern areas In addition the confined groundwatersamples collected in the southern and southwestern areas(samples Z13 Z14 and S14 in Donghai and samples Z12and S13 in Leizhou Figure 1) are characterized by moredepleted isotopic data than samples of the mainland areaThese samples deviate significantly from the LMWL and theyare distributed to the bottom-left of the LMWL (part II inFigure 5)This indicates that the confined groundwater of theDonghai and Leizhou areas is sourced from rainfall rechargeduring an older period with a colder climate From the sulfurisotopes (12057534S) of the groundwater in Donghai (Table 2)it can be concluded that the 12057534S values in groundwaterbecome more enriched with increasing depth This trend ofenrichment of 12057534S values in the confined fresh groundwaterof Donghai also demonstrates that the confined ground-water of island is palaeowater According to the rechargepattern of the confined groundwater in the southern andsouthwestern areas (Figures 3(b) and 3(c)) we consider thatthe palaeowater stored in the confined aquifers of Donghaiand Leizhou will flow toward Zhanjiang through lateral flowbecause of the intensive groundwater pumping of recentyears

In conclusion the unconfined groundwater is rechargedby local modern precipitation However the confinedaquifers are recharged by precipitation in northern andnorthwestern mountain areas and by palaeowater sourcedoriginally from rainfall infiltration during an older time witha colder climate

52 Controlling Processes and Material Sources of Groundwa-ter Chemistry To quantitatively study the controlling pro-cesses and material sources of the groundwater in ZhanjiangGibbs plots and bivariate analyses of the ionic relations werediscussed in this section

521 The Dominating Hydrochemical Process Gibbs plots(ie a TDS versus Na(Na + Ca) graph and a TDS versusCl(Cl+HCO

3) graph) can be used to determine the primary

hydrochemical processes (eg atmospheric precipitationrock weathering and evaporation) controlling groundwa-ter chemistry [44] According to the hydrochemical data(Table 1) Gibbs plots weremade as Figure 6Those plots indi-cate that rock weathering is themajormechanism controllingthe groundwater chemistry of themultilayered aquifer systemof Zhanjiang This conclusion is coincident with the resultsdeduced from the analysis of groundwater hydrochemistryand groundwater types

522 Dissolution Material and Dissolution Process To iden-tify the dominant mineral in the rock weathering processin this aquifer system molar ratio bivariate plots of Na-normalizedCaMg andHCO

3weremade [45 46] As shown

in Figure 7 the groundwater of the multilayered aquifer sys-tem ismainly influenced by silicate weathering and carbonatedissolution especially for the confined groundwater

The milligram equivalent ratio of (Na+ + K+)C1minus can bean indicator of the sources of cations and of the occurrence ofsilicate weathering where a ratio greater than 1 implies Na+released from silicate weathering and a ratio of 1 indicateshalite dissolution [47] As shown in Table 3 the (Na+ +K+)C1minus ratio values of the unconfined groundwater varyfrom 038 to 444 with an average value of 158 thosevalues of middle confined groundwater range from 057to 628 with an average value of 222 those values ofdeep confined groundwater change from 091 to 2503 withaverage value of 695 These averages (Na+ + K+)C1minus ratiogt 1 indicate the derivation of Na+ and K+ from silicateweathering Moreover the increase of the (Na+ + K+)Clminusratio with groundwater depth reveals that the silicate weath-ering in the confined aquifer is more remarkable than inthe unconfined aquifer Furthermore the relatively higherconcentration of SiO

2(Table 3) in confined groundwater

verifies evident silicate weathering in confined aquifers Thescatter plot of C1minus versus Na+ + K+ (Figure 8(a)) showsthat the unconfined groundwater samples are distributedalong the 1 1 line (or on either side of this line) whichimplies that ions (Na+ and K+) are mainly resultant fromthe silicate weathering and halite dissolution Converselymost samples of the confined groundwater fall below the1 1 line indicating that silicate weathering is the primaryhydrochemical process in the confined aquifers In additionas shown in Figure 8(a) the excess of (Na+ + K+) over C1minusalso implies that cation exchange may occur in the confinedaquifers

The plot of (HCO3

minus + SO4

2minus) versus (Ca2+ + Mg2+)(Figure 8(b)) shows that most samples of fresh unconfinedgroundwater fall along the 1 1 line and that some samples

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Mining

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OceanographyInternational Journal of

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Page 12: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

12 Geofluids

1

10

100

1000

10000

100000

0 02 04 06 08 1

TDS

(mg

L)

Na(Na + Ca)

Rock weathering dominance

Precipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

1

10

100

1000

10000

100000

0 02 04 06 08 1TD

S (m

gL)

Rock weathering dominancePrecipitation

dominance

Evaporat

ion

dominance

Deep confined groundwaterMiddle confined groundwaterUnconfined groundwater

Cl(F + (3)

Evaporat

ion

dominance

gPrecipitation

dominance

Evaporat

ion

dominance

Precipitation

dominance

Figure 6 Gibbs plots of the major ions in the coastal groundwater of Zhanjiang

001

01

1

10

100

001 01 1 10 100CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

3minus

Na

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

001

01

1

10

001 01 1 10 100

Mg

Na

CaNa

Silicateweathering

Carbonatedissolution

Evaporitedissolution

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

Figure 7 Bivariate plots of molar ratio (a) Na-normalized Ca versus Na-normalized HCO3 (b) Na-normalized Ca versus Na-normalized

Mg

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MineralogyInternational Journal of

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MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

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ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Geological ResearchJournal of

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Geology Advances in

Page 13: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 13

0

2

4

6

8

0 2 4 6 8 10

Fminus

(meq

L)

+ + ++ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(a)

0

2

4

6

8

0 2 4 6 8 10

342minus+(

3minus

(meq

L)

2+ + -A2+ (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(b)

0

1

2

3

4

5

0 2 4 6 8 10

3minus

(meq

L)

Fminus + 342minus (meqL)

1 1 line

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

(c)

Figure 8 Bivariate plots of ionic relation (a) Clminus versus Na+ + K+ (b) SO4

2minus + HCO3

minus versus Ca2+ +Mg2+ (c) HCO3

minus versus (Clminus + SO4

2minus)

fall below the 1 1 line which indicates that the combineddissolutions of carbonate and silicate are the main sourcesof Ca2+ and Mg2+ in the unconfined groundwater [48]Most samples of the confined groundwater fall above the 1 1line which demonstrates that silicate weathering is the mainsource of Ca2+ andMg2+ in the confined groundwater [9 49ndash51] The deficiency of Ca2+ + Mg2+ (Figure 8(b)) and the

excess of Na+ (Figure 8(a)) indicate the occurrence of cationexchange in the confined aquifers

The plot of HCO3

minus versus (Clminus + SO4

2minus) (Figure 8(c))shows that the groundwater samples of the unconfinedand middle confined aquifers are distributed on both sidesof the 1 1 line which implies that carbonate and evap-orite dissolutions are also the main material sources of

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Atmospheric SciencesInternational Journal of

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OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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MineralogyInternational Journal of

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Geological ResearchJournal of

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Geology Advances in

Page 14: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

14 Geofluids

the chemical compositions of the unconfined and middleconfined groundwater The groundwater samples of the deepconfined aquifer mainly plot above the 1 1 line indicatingthat carbonate dissolution is another material source ofthe chemical composition of the deep confined linebreakgroundwater

In conclusion silicate weathering is the dominant processinfluencing the material source of ions (Na+ K+ Ca2+ andMg2+) in the coastal aquifer system of Zhanjiang Carbonateand evaporite dissolutions also contribute to the ground-water compositions With the dissolution by carbonic acid(H2CO3) the general reaction of silicate weathering is

(Na+K+Ca2+Mg2+) silicates +H2CO3

997888rarr H4SiO4+HCO

3

minus +Na+ + K+ + Ca2+ +Mg2+

+ Clay

(1)

See [9]

523 Ion Exchange Asdescribed in Section 522most of theconfined groundwater samples show an excess of Na+ overCl+ and a deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minuswhichmay indicate the contribution of cation exchange to thegroundwater composition [39 52] The chloroalkaline index(CAI) of the groundwater samples can be an indicator of thetype and the intensity of the ion exchange reactions betweenthe groundwater and the aquifer matrix [53] The CAI iscalculated using the following formulae CAI = [Clminusminus(Na++K+)]Clminus Positive and negative values of the CAI indicatereverse cation exchange (2Na+ + Caclay rarr Ca2+ + 2Naclay)and cation exchange (Ca2+ + 2Naclay rarr 2Na+ + Caclay)respectively As shown in Figure 9 the CAI values of theconfined groundwater especially that of the deep confinedgroundwater aremainly negative supporting the assumptionof the occurrence of cation exchange in the confined aquifersMeanwhile the absolute value of the CAI can reflect theintensity of the cation exchange reactions Figure 9 shows thatthe absolute CAI values of the deep confined groundwater aregreater than the values of the middle confined groundwaterwhich means that the cation exchange reaction in the deepconfined aquifer is more intense than in the middle confinedaquifer

In addition to further investigate the occurrence of cationexchange in the confined aquifers a bivariate plot of (Ca2++ Mg2+ minus HCO

3

minus minus SO4

2minus) versus (Na+minus Clminus) can be used[54] If cation exchange is an important process controllingthe groundwater chemistry the groundwater samples will fallin the lower-right quadrant of this diagram and along a linewith a slope of minus1 According to the chemistry data plot of(Ca2+ +Mg2+minusHCO

3

minusminusSO4

2minus) versus (Na+minusClminus) wasmade(Figure 10) Figure 10 shows that most of the deep confinedgroundwater samples showed an excess of Na+ over Clminus anda deficiency of Ca2+ + Mg2+ over HCO

3

minus + SO4

2minus and thatthey mainly lie along the line with a slope of minus1 Thus it canbe concluded that cation exchange occurs in the confinedaquifer

minus25

minus20

minus15

minus10

minus5

0

5

0 200 400 600 800 1000

Chlo

roal

kalin

e ind

ex (C

AI)

TDS (mgL)

Unconfined groundwaterMiddle confined groundwaterDeep confined groundwater

Figure 9 Plot of the chloroalkaline index (CAI) versus TDS of thegroundwater in the multilayered aquifers of Zhanjiang

minus4

minus2

0

2

minus2 0 2 4

Middle confined groundwaterDeep confined groundwater

+ minus Fminus (meqL)

2

++-

A2+minus3

42minusminus(

3minus

(meq

L)

1 minus1 line

Figure 10 Plot of (Ca2+ + Mg2+ minus HCO3

minus minus SO4

2minus) versus (Na+minusClminus)

524 Anthropogenic Input In an area with considerabledemand for groundwater anthropogenic activity is alwaysan important factor regarding groundwater quality Theconcentrations of NO

3

minus can reflect the influence of anthro-pogenic activity on groundwater chemistry In this studythe NO

3

minus concentrations in the samples of the unconfined

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 15: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 15

0

100

200

300

400

0

3

6

9

12

15

Prec

ipita

tion

(mm

)

Gro

undw

ater

leve

l (m

)

Year

PrecipitationJ18J9

J20J23

2008 2009 2010 2011

(a)

minus16

minus12

minus8

minus4

0

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L40-1(B)L39-1(B)

L38-1(B)L8-1(B)

(b)

minus8

minus7

minus6

minus5

minus4

Gro

undw

ater

leve

l (m

)

Year2008 2009 2010 2011

L25-3L24-3

(c)

Figure 11 Observed groundwater level dynamics in the multilayered aquifers during 2008ndash2011 (a) Groundwater level dynamics of theunconfined aquifer (b) Groundwater level dynamics of the middle confined aquifer (c) Groundwater level dynamics of the deep confinedaquifer

groundwater range from 05 to 1200mgL with an averagevalue of 4136mgL exceeding the quality standard forgroundwater in China This implies that the unconfinedgroundwater has been influenced by anthropogenic activitiesThe NO

3

minus concentrations in the samples of the middle anddeep confined groundwater are lt15mgL which meet thegroundwater quality standard This indicates that anthro-pogenic influence on the confined groundwater is minor

53 Salinity Indications of the Seawater Intrusion Risk Asintroduced in Section 2 the confined groundwater level hasdropped to about 20m below the mean sea level since the1990s [28 29] Although the confined aquifers have notexperienced seawater intrusion it is of concern that theconfined groundwater will be at risk from seawater intrusionbecause of continuous groundwater demand low confinedgroundwater level and landward recharge flow pattern Inthis section based on the analysis of the flow regimegroundwater level dynamics and salinity dynamics of the

confined aquifers the seawater intrusion risk for confinedaquifer is discussed

First as shown in Figures 3(b) and 3(c) the confinedgroundwater level has dropped to approximately 20m belowthe mean sea level Two groundwater depression cones haveformed in the confined aquifers and the confined aquifersare partially recharged by lateral groundwater runoff fromthe south (ie the direction of the ocean) This rechargecharacteristic of confined aquifers constitutes a potential riskof seawater intrusion

Second the long-term monthly monitoring data in bore-holes (Figure 3) of the multilayered aquifers are analyzed toassess the dynamics of the groundwater level of ZhanjiangPlots of observed groundwater levels of the unconfinedaquifer middle confined aquifer and deep confined aquiferare shown in Figure 11 The groundwater level dynamics canbe concluded as follows (i) the unconfined groundwater levelis in a relatively steady state with fluctuations induced by rain-fall dynamics (Figure 11(a)) and (ii) the confined groundwater

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 16: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

16 Geofluids

100

200

300

400

500

600TD

S (m

gL)

TimeMar 2009 Mar 2010 Mar 2011

Q2 Q5Q3 Average TDS

(a)

100

140

180

220

260

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

Z10Average TDSZ11

Z5

(b)

120

140

160

180

200

TDS

(mg

L)

TimeMar 2009 Mar 2010 Mar 2011

S10Average TDS

S6

(c)

Figure 12 Salinity dynamics in the multilayered aquifers during 2009ndash2011 (a) TDS dynamics of the unconfined aquifer (b) TDS dynamicsof the middle confined aquifer (c) TDS dynamics of the deep confined aquifer

levels fluctuate with declining trends (Figures 11(b) and11(c))The declining trends of the confined groundwater levelare obvious even for the groundwater in recharge-runoffareas such as Donghai island (boreholes L38-1(B) and L40-1(B)) and Nanshan island (L39-1(B)) The declining trendsof the confined groundwater levels reveal that groundwaterexploitation in Zhanjiang city is excessive and unsustainableMeanwhile from the 12057518O-1205752H isotopic analysis result ofthe recharge sources of the confined groundwater it hasbeen established that the confined groundwater in Donghaiis palaeowater which is unrenewable in short time Thismeans that the unsustainable groundwater exploitation isconsuming the groundwater storage resources in the confinedaquifersTherefore this unsustainable groundwater exploita-tion will increase the risk of seawater intrusion

Third the TDS values during 2009ndash2011 were com-pared to analyze the salinity dynamics Figure 12 showsthe salinity dynamics in some of the monitoring boreholesof the three aquifers For the unconfined groundwater

the average TDS value presents a slightly decreasing trend(Figure 12(a)) However for the middle confined aquiferthe average TDS value shows a slightly increasing trend(from 11327 to 14053mgL) while the trend of increaseof the groundwater in Donghai (borehole Z10 increasingfrom 14474 to 25294mgL) is comparatively obvious (Fig-ure 12(b)) Similarly the average TDS value of the deepconfined groundwater also shows a slightly increasing trend(from 15152 to 16233mgL) while the trend of increase ofthe groundwater in Donghai (borehole S10 increasing from15968 to 19666mgL) is relatively notable (Figure 12(c))

According to the increasing trends of TDS values inthe confined groundwater (especially the groundwater inDonghai island) it can be deduced that the freshwater-seawater mixing zones in the coastal confined aquifers havebegun extending landward as the inland groundwater levelsdecline From the groundwater flow fields (Figure 3) it canbe seen that Naozhou island which is located in the offshorearea of Donghai island will be the first to suffer from seawater

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 17: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 17

Table 5 Groundwater chemistry data of Naozhou island observedby Zhang et al [34]

Sample number Aquifer Sampling time TDS(mgL)

1

Unconfined aquifer Mar 2011

24087 323618 444721 801323 614428 597330 536334 739238 536541 30933

Confined aquifer Mar 2011

2576 178114 1393 (salted)20 5229 (salted)22 10280 (salted)26 4711 (salted)45 2935

intrusion To address the possibility of seawater intrusion inNaozhou island we referred to the hydrochemistry data ofNaozhou island investigated by Zhang et al [34] in March2011 (Table 5) These hydrochemical data showed that theconfined groundwater in the southern and eastern coastalarea (eg samples 26 22 20 and 14 in Figure 1(d)) hasbeen saline with TDS value of 139ndash1028 gLThis means thatfreshwater-seawater mixing zones in the confined aquifersof Naozhou island have extended landward This landwardextension constitutes the reason for the increase in TDS of theconfined groundwater in Donghai island Thus the confinedgroundwater in Donghai island and Zhanjiang city will berisky in suffering from saltwater intrusion if the currentunsustainable groundwater exploitation is not optimized

6 Conclusions

Based on the analysis of the hydrochemistry and isotope ofgroundwater this study revealed the recharge sources hydro-chemical processes and seawater intrusion risk of the coastalgroundwater in the multilayered aquifer system of Zhan-jiang China The stable isotope values of unconfined andconfined groundwater indicate that the recharge sources ofgroundwater in those aquifers are different The unconfinedgroundwater is recharged from local modern precipitationthe confined groundwater in the city area (mainland area)is sourced from modern rainfall from the mountain area inthe northwest of Zhanjiang and the confined groundwaterin Donghai island and Leizhou areas is recharged frompalaeowater originated from precipitation during an oldertimeunder a colder climateNatural hydrochemical processessuch as silicateweathering carbonate dissolutions and cationexchange reaction are the dominant processes controlling thematerial sources of ions in groundwater of this multilayered

aquifer system However anthropogenic activities also haveaffected the quality of the unconfined groundwater leading tohigher concentrations of nitrate In addition increase trendof TDS in the confined groundwater reveals the occurrenceof seawater intrusion induced by groundwater exploitationThe confined groundwater exploitation is unsustainable andis consuming the palaeowater storage

Conflicts of Interest

The authors declare that they have no conflicts of interest

Acknowledgments

This research was supported by the National Natural ScienceFoundation of China (Grant no 41502255) The authorsthank the laboratory technicians of Institute of Geologyand Geophysics for their great help in testing groundwatersamples

References

[1] P M Barlow and E G Reichard ldquoSaltwater intrusion in coastalregions of North Americardquo Hydrogeology Journal vol 18 no 1pp 247ndash260 2010

[2] N R Green and K T B MacQuarrie ldquoAn evaluation of therelative importance of the effects of climate change and ground-water extraction on seawater intrusion in coastal aquifers inAtlantic Canadardquo Hydrogeology Journal vol 22 no 3 pp 609ndash623 2014

[3] A Singh ldquoManaging the environmental problem of seawaterintrusion in coastal aquifers through simulation-optimizationmodelingrdquo Ecological Indicators vol 48 pp 498ndash504 2015

[4] P Wu C Tang L Zhu C Liu X Cha and X Tao ldquoHydro-geochemical characteristics of surface water and groundwaterin the karst basin southwest ChinardquoHydrological Processes vol23 no 14 pp 2012ndash2022 2009

[5] D M Han X F Song M J Currell J L Yang and GQ Xiao ldquoChemical and isotopic constraints on evolution ofgroundwater salinization in the coastal plain aquifer of LaizhouBay Chinardquo Journal of Hydrology vol 508 pp 12ndash27 2014

[6] M E Zabala M Manzano and L Vives ldquoThe origin ofgroundwater composition in the Pampeano Aquifer underlyingthe Del Azul Creek basin Argentinardquo Science of the TotalEnvironment vol 518-519 pp 168ndash188 2015

[7] L Andre M Franceschi P Pouchan and O Atteia ldquoUsinggeochemical data and modelling to enhance the understandingof groundwater flow in a regional deep aquifer Aquitaine Basinsouth-west of Francerdquo Journal of Hydrology vol 305 no 1-4 pp40ndash62 2005

[8] F J Alcala and E Custodio ldquoUsing the ClBr ratio as a tracer toidentify the origin of salinity in aquifers in Spain and PortugalrdquoJournal of Hydrology vol 359 no 1-2 pp 189ndash207 2008

[9] K Rina P S Datta C K Singh and S Mukherjee ldquoCharacter-ization and evaluation of processes governing the groundwaterquality in parts of the Sabarmati basin Gujarat using hydro-chemistry integrated with GISrdquo Hydrological Processes vol 26no 10 pp 1538ndash1551 2012

[10] S Santoni FHuneau EGarel et al ldquoStrontium isotopes as trac-ers of water-rocks interactions mixing processes and residence

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 18: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

18 Geofluids

time indicator of groundwater within the granite-carbonatecoastal aquifer of Bonifacio (Corsica France)rdquo Science of theTotal Environment vol 573 pp 233ndash246 2016

[11] C D Frost and R N Toner ldquoStrontium isotopic identificationof water-rock interaction and ground water mixingrdquo Ground-water vol 42 no 3 pp 418ndash432 2004

[12] N O Joslashrgensen M S Andersen and P Engesgaard ldquoInvesti-gation of a dynamic seawater intrusion event using strontiumisotopes (87Sr86Sr)rdquo Journal of Hydrology vol 348 no 3-4 pp257ndash269 2008

[13] M Khaska C Le Gal La Salle J Lancelot et al ldquoOrigin ofgroundwater salinity (current seawater vs saline deep water) ina coastal karst aquifer based on Sr andCl isotopes Case study ofthe La Clape massif (southern France)rdquo Applied Geochemistryvol 37 pp 212ndash227 2013

[14] P Negrel R Millot S Roy C Guerrot and H Pauwels ldquoLeadisotopes in groundwater as an indicator of water-rock inter-action (Masheshwaram catchment Andhra Pradesh India)rdquoChemical Geology vol 274 no 3-4 pp 136ndash148 2010

[15] K Aji C Tang X Song et al ldquoCharacteristics of chemistry andstable isotopes in groundwater of Chaobai and Yongding Riverbasin North China Plainrdquo Hydrological Processes vol 22 no 1pp 63ndash72 2008

[16] P W Swarzenski and J A Izbicki ldquoCoastal groundwaterdynamics off Santa Barbara California Combining geochem-ical tracers electromagnetic seepmeters and electrical resistiv-ityrdquo Estuarine Coastal and Shelf Science vol 83 no 1 pp 77ndash892009

[17] N Ettayfi L Bouchaou J L Michelot et al ldquoGeochemicaland isotopic (oxygen hydrogen carbon strontium) constraintsfor the origin salinity and residence time of groundwaterfrom a carbonate aquifer in the Western Anti-Atlas MountainsMoroccordquo Journal of Hydrology vol 438-439 pp 97ndash111 2012

[18] S M Yidana and E Koffie ldquoThe groundwater recharge regimeof some slightly metamorphosed neoproterozoic sedimentaryrocks An application of natural environmental tracersrdquoHydro-logical Processes vol 28 no 7 pp 3104ndash3117 2014

[19] S Lamontagne A R Taylor D Herpich and G J HancockldquoSubmarine groundwater discharge from the South AustralianLimestone Coast region estimated using radium and salinityrdquoJournal of Environmental Radioactivity vol 140 pp 30ndash41 2015

[20] J J Tamborski J K Cochran and H J Bokuniewicz ldquoAppli-cation of 224Ra and 222Rn for evaluating seawater residencetimes in a tidal subterranean estuaryrdquo Marine Chemistry vol189 pp 32ndash45 2017

[21] A Zghibi L Zouhri J Tarhouni and L Kouzana ldquoGround-water mineralisation processes in Mediterranean semi-aridsystems (Cap-Bon North east of Tunisia) Hydrogeological andgeochemical approachesrdquoHydrological Processes vol 27 no 22pp 3227ndash3239 2013

[22] V Re E Sacchi J Mas-Pla A Mencio and N El AmranildquoIdentifying the effects of human pressure on groundwaterquality to support water management strategies in coastalregions A multi-tracer and statistical approach (Bou-Aregregion Morocco)rdquo Science of the Total Environment vol 500-501 pp 211ndash223 2014

[23] D Han V E A Post and X Song ldquoGroundwater salinizationprocesses and reversibility of seawater intrusion in coastalcarbonate aquifersrdquo Journal of Hydrology vol 531 pp 1067ndash1080 2015

[24] M A Eissa J M Thomas G Pohll O Shouakar-Stash RL Hershey and M Dawoud ldquoGroundwater recharge and

salinization in the arid coastal plain aquifer of the Wadi Watirdelta Sinai Egyptrdquo Applied Geochemistry vol 71 pp 48ndash622016

[25] S Lee M Currell and D I Cendon ldquoMarine water frommid-Holocene sea level highstand trapped in a coastal aquiferEvidence from groundwater isotopes and environmental sig-nificancerdquo Science of the Total Environment vol 544 pp 995ndash1007 2016

[26] L Cary E Petelet-Giraud G Bertrand et al ldquoOrigins and pro-cesses of groundwater salinization in the urban coastal aquifersof Recife (Pernambuco Brazil) a multi-isotope approachrdquoScience of the Total Environment vol 530-531 pp 411ndash429 2015

[27] S Santoni F Huneau E Garel et al ldquoResidence time miner-alization processes and groundwater origin within a carbonatecoastal aquifer with a thick unsaturated zonerdquo Journal ofHydrology vol 540 pp 50ndash63 2016

[28] Z Xun Y Xia L Juan Y Jinmei and D Wenyu ldquoEvolution ofthe groundwater environment under a long-term exploitationin the coastal area near Zhanjiang Chinardquo EnvironmentalGeology vol 51 no 5 pp 847ndash856 2007

[29] First Hydrogeological Team and Guangdong Geological Bu-reau ldquoReport of regional hydrogeologic investigation of Dong-hai islandrdquo (Chinese) 2009 (in Chinese)

[30] Z H Su ldquoThe layout of the monitoring system of groundwaterin Zhanjiang to prevent seawater invasionrdquo Geotechnical Inves-tigation Surveying vol 2 pp 17ndash21 2005 in chinese

[31] Q Luo and Z H Su ldquoThe characteristic analysis and theprevention and control methods from the sea water invasionin Naozhou islandrdquo Journal of Geological Hazards and Environ-ment Preservation vol 18 no 2 pp 28ndash32 2007 (Chinese)

[32] W Zhang X Chen H Tan Y Zhang and J Cao ldquoGeochemicaland isotopic data for restricting seawater intrusion and ground-water circulation in a series of typical volcanic islands in theSouth China SeardquoMarine Pollution Bulletin vol 93 no 1-2 pp153ndash162 2015

[33] Y Teng J Su JWang et al ldquoSoilmicrobial community responseto seawater intrusion into coastal aquifer of Donghai IslandSouth Chinardquo Environmental Earth Sciences vol 72 no 9 pp3329ndash3338 2014

[34] W Zhang H Tan X Chen J Cao G Zhang and H ZhouldquoGeochemical evolution and formation mechanism of ground-water in Naozhou island Guangdong provincerdquo Journal ofChina Hydrology vol 32 no 3 pp 51ndash59 2012 in chinese

[35] P Zhou G Li Y Lu and M Li ldquoNumerical modeling ofthe effects of beach slope on water-table fluctuation in theunconfined aquifer of Donghai Island Chinardquo HydrogeologyJournal vol 22 no 2 pp 383ndash396 2014

[36] X Zhou M Chen and C Liang ldquoOptimal schemes of ground-water exploitation for prevention of seawater intrusion in theLeizhou Peninsula in southern Chinardquo Environmental Geologyvol 43 no 8 pp 978ndash985 2003

[37] S K Kumar V Rammohan J D Sahayam and M Jee-vanandam ldquoAssessment of groundwater quality and hydrogeo-chemistry of Manimuktha River basin Tamil Nadu IndiardquoEnvironmental Modeling ampAssessment vol 159 no 1-4 pp 341ndash351 2009

[38] T Huang and Z Pang ldquoChanges in groundwater induced bywater diversion in the Lower Tarim River Xinjiang UygurNW China Evidence from environmental isotopes and waterchemistryrdquo Journal of Hydrology vol 387 no 3-4 pp 188ndash2012010

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 19: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Geofluids 19

[39] P Zhou Z Wang J Zhang Z Yang and X Li ldquoStudy onthe hydrochemical characteristics of groundwater along theTaklimakan Desert Highwayrdquo Environmental Earth Sciencesvol 75 no 20 article no 1378 2016

[40] A M Piper ldquoA graphic procedure in the geochemical interpre-tation of water-analysesrdquo Eos Transactions American Geophys-ical Union vol 25 no 6 pp 914ndash928 1944

[41] Z Kattan ldquoEnvironmental isotope study of the major karstsprings in damascus limestone aquifer systems Case of theFigeh and Barada springsrdquo Journal of Hydrology vol 193 no1-4 pp 161ndash182 1997

[42] M Barbieri T Boschetti M Petitta and M Tallini ldquoStableisotope (2H 18Oand 87Sr 86Sr) andhydrochemistrymonitoringfor groundwater hydrodynamics analysis in a karst aquifer(Gran Sasso Central Italy)rdquo Applied Geochemistry vol 20 no11 pp 2063ndash2081 2005

[43] H Craig ldquoIsotopic variations in meteoric watersrdquo Science vol133 no 3465 pp 1702-1703 1961

[44] R J Gibbs ldquoMechanisms controlling world water chemistryrdquoScience vol 170 no 3962 pp 1088ndash1090 1970

[45] J Gaillardet B Dupre P Louvat and C J Allegre ldquoGlobalsilicate weathering and CO

2consumption rates deduced from

the chemistry of large riversrdquo Chemical Geology vol 159 no1ndash4 pp 3ndash30 1999

[46] J Xiao ZD Jin JWang and F Zhang ldquoHydrochemical charac-teristics controlling factors and solute sources of groundwaterwithin the Tarim River Basin in the extreme arid region NWTibetan Plateaurdquo Quaternary International vol 380-381 pp237ndash246 2015

[47] A Mukherjee and A E Fryar ldquoDeeper groundwater chemistryand geochemical modeling of the arsenic affected westernBengal basinWest Bengal IndiardquoAppliedGeochemistry vol 23no 4 pp 863ndash894 2008

[48] E Lakshmanan R Kannan and M Senthil Kumar ldquoMajor ionchemistry and identification of hydrogeochemical processes ofground water in a part of Kancheepuram district Tamil NaduIndiardquo Environmental Geosciences vol 10 no 4 pp 157ndash1662003

[49] P S Datta S K Bhattacharya and S K Tyagi ldquo18O studieson recharge of phreatic aquifers and groundwater flow-paths ofmixing in the Delhi areardquo Journal of Hydrology vol 176 no 1-4pp 25ndash36 1996

[50] N Rajmohan and L Elango ldquoIdentification and evolution ofhydrogeochemical processes in the groundwater environmentin an area of the Palar and Cheyyar River Basins SouthernIndiardquo Environmental Geology vol 46 no 1 pp 47ndash61 2004

[51] I Matiatos A Alexopoulos and A Godelitsas ldquoMultivari-ate statistical analysis of the hydrogeochemical and isotopiccomposition of the groundwater resources in northeasternPeloponnesus (Greece)rdquo Science of the Total Environment vol476-477 pp 577ndash590 2014

[52] H El Mejri A Ben Moussa and K Zouari ldquoThe use of hydro-chemical and environmental isotopic tracers to understand thefunctioning of the aquifer system in the BouHafna andHaffouzregions Central TunisiardquoQuaternary International vol 338 pp88ndash98 2014

[53] H Khairy and M R Janardhana ldquoHydrogeochemical featuresof groundwater of semi-confined coastal aquifer in Amol-Ghaemshahr plain Mazandaran Province Northern IranrdquoEnvironmentalModeling ampAssessment vol 185 no 11 pp 9237ndash9264 2013

[54] R S Fisher and W F Mullican III ldquoHydrochemical evolutionof sodium-sulfate and sodium-chloride groundwater beneaththe Northern Chihuahuan Desert Trans-Pecos Texas USArdquoHydrogeology Journal vol 5 no 2 pp 4ndash16 1997

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in

Page 20: Hydrochemistry and Isotope Hydrology for Groundwater ...downloads.hindawi.com/journals/geofluids/2017/7080346.pdf · Hydrochemistry and Isotope Hydrology for Groundwater Sustainability

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ClimatologyJournal of

EcologyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

EarthquakesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Mining

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 201

International Journal of

OceanographyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofPetroleum Engineering

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

Atmospheric SciencesInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MineralogyInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MeteorologyAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Paleontology JournalHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geological ResearchJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Geology Advances in


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