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
①
③
②
+2
L30
Unconfined aquifer
Clay
Aquifer boundaryBorehole
(muddy sandstone)Upper cretaceous age +2
Middle-upper
(metamorphic sandstone)Cambrian age Є2-3
①
Middle confined aquifer
Deep confined aquifer
Groundwater flowLeakage
Aquitard (clay layer)
③
②
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 Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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
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Geological ResearchJournal of
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Geology Advances in
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
①
③
②
+2
L30
Unconfined aquifer
Clay
Aquifer boundaryBorehole
(muddy sandstone)Upper cretaceous age +2
Middle-upper
(metamorphic sandstone)Cambrian age Є2-3
①
Middle confined aquifer
Deep confined aquifer
Groundwater flowLeakage
Aquitard (clay layer)
③
②
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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GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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OceanographyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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MineralogyInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
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
①
③
②
+2
L30
Unconfined aquifer
Clay
Aquifer boundaryBorehole
(muddy sandstone)Upper cretaceous age +2
Middle-upper
(metamorphic sandstone)Cambrian age Є2-3
①
Middle confined aquifer
Deep confined aquifer
Groundwater flowLeakage
Aquitard (clay layer)
③
②
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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Mining
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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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Advances in
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MineralogyInternational Journal of
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Geological ResearchJournal of
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Geology Advances in
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
①
③
②
+2
L30
Unconfined aquifer
Clay
Aquifer boundaryBorehole
(muddy sandstone)Upper cretaceous age +2
Middle-upper
(metamorphic sandstone)Cambrian age Є2-3
①
Middle confined aquifer
Deep confined aquifer
Groundwater flowLeakage
Aquitard (clay layer)
③
②
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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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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International Journal of
OceanographyInternational Journal of
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Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
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MineralogyInternational Journal of
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Geological ResearchJournal of
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Geology Advances in
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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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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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
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Journal ofPetroleum Engineering
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Advances in
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MineralogyInternational Journal of
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Geological ResearchJournal of
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Geology Advances in
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
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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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
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MineralogyInternational Journal of
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MeteorologyAdvances in
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Geological ResearchJournal of
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Geology Advances in
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
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
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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International Journal of
OceanographyInternational Journal of
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Journal of Computational Environmental SciencesHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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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Geological ResearchJournal of
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Geology Advances in
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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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
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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International Journal of
OceanographyInternational Journal of
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
GeochemistryHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Atmospheric SciencesInternational Journal of
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MineralogyInternational Journal of
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Geological ResearchJournal of
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Geology Advances in
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
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Mining
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
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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
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MineralogyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
MeteorologyAdvances in
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
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Geology Advances in
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
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
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geological ResearchJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Geology Advances in
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
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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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
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
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
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
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
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
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
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