ORI GIN AL PA PER

Sources, Distribution and Behavior of Major and TraceElements in a Complex Karst Lake System

Jelena Dautovic • Zeljka Fiket • Jadranka Baresic • Marijan Ahel •

Nevenka Mikac

Received: 17 May 2013 / Accepted: 28 August 2013 / Published online: 8 September 2013� Springer Science+Business Media Dordrecht 2013

Abstract Sources and distribution of major and trace elements were investigated in the

Plitvice Lakes, a pristine cascade hydrological system of sixteen karst lakes situated in a

sparsely populated area of the central Croatia. Water and surface sediment samples from

17 locations, including springs, tributaries and lakes, were analyzed for the content of 22

elements by high-resolution inductively coupled mass spectrometry. Principal component

analysis of the collected data set showed that different springs and tributaries displayed

distinct multielemental compositions, reflecting primarily the differences in their corre-

sponding geological backgrounds. It was shown that the springs situated in the Upper and

Middle Jurassic dolomite bedrock represented the main source of several trace elements,

including some toxic metals (Cd, Zn, Ni and Tl), to the Plitvice Lakes system. The

concentrations of most of the trace elements (Mn, Fe, Al, Cd, Zn, Cu, Ni, Pb, Co, Cr and

Tl) showed decreasing spatial trends in the downstream direction, from sources to the

lakes. Such a distribution was interpreted to be a consequence of an efficient removal of the

dissolved elements in the lentic parts of the system, mainly by co-precipitation with

authigenic calcite and Mn oxides. Nevertheless, most of the elements in the lake sediments

were highly correlated with Al, which indicated their prevalent association with terrigenic

material. It was shown that the multicascade system of the Plitvice Lakes had an enhanced

autopurification efficiency regarding the elimination of most of the trace metals from the

aqueous phase.

Electronic supplementary material The online version of this article (doi:10.1007/s10498-013-9204-9)contains supplementary material, which is available to authorized users.

J. Dautovic � Z. Fiket � M. Ahel � N. Mikac (&)Division for Marine and Environmental Research, Ruder Boskovic Institute, Bijenicka 54,Zagreb, Croatiae-mail: mikac@irb.hr

J. BaresicDivision of Experimental Physics, Ruder Boskovic Institute, Bijenicka 54, Zagreb, Croatia

123

Aquat Geochem (2014) 20:19–38DOI 10.1007/s10498-013-9204-9

Keywords Major elements � Trace metals � Water � Sediment � Plitvice

Lakes � Autopurification

1 Introduction

Release of toxic metals by human activities is a global problem (Pacyna and Pacyna 2001)

that threatens terrestrial and aquatic environment and represents a particular challenge

regarding the protection of pristine areas. Metal inputs in pristine areas, like mountain

lakes and national parks, derive mainly from the natural sources and depend primarily on

the local geology and weathering rates (Zaharescu et al. 2009). Such pristine aquatic

systems are characterized by comparatively low concentrations of individual contaminants

(Camarero et al. 2009) but as such, they are highly vulnerable to additional anthropogenic

inputs and represent ideal systems to study relative importance of various sources of metals

into the lakes (Bindler et al. 2009; Thevenon et al. 2011). In order to distinguish anthro-

pogenic from natural sources, complex approaches including multielemental analysis and

the application of multivariate statistical analyses are required (De Bartolomeo et al. 2004;

Zaharescu et al. 2009).

The Plitvice Lakes (central Croatia) are a pristine cascade hydrological system of

sixteen karst lakes separated by tufa barriers. Since 1979, this exceptional natural phe-

nomenon is included in the UNESCO World Natural and Cultural Heritage List. Most of

the studies in this unique ecosystem were devoted to the processes, which are responsible

for the precipitation of calcium carbonate and the formation of the tufa barriers (Srdoc

et al. 1986; Horvatincic et al. 2008; Baresic et al. 2011). However, only few reports dealt

with the anthropogenic influence on the Plitvice Lakes, including both eutrophication and

input of various contaminants (Srdoc et al. 1992; Horvatincic et al. 2006; Mikac et al.

2011). The study by Horvatincic et al. (2006) was able to indicate an increasing trend of

eutrophication in the lakes, however, similar trends for metals and organic contaminants

could not be confirmed (Horvatincic et al. 2006). More recently, a detailed study of dated

sediment cores (Mikac et al. 2011) from the two biggest lakes (Prosce and Kozjak) clearly

demonstrated increasing trends of typical anthropogenic contaminants such as Pb, poly-

cyclic aromatic hydrocarbons and linear alkylbenzene sulfonates, in the last five decades.

In this work, we present for the first time the results of a comprehensive investigation of

trace elements in the Plitvice Lakes, based on a simultaneous analysis of water and surface

sediment samples for 22 major and trace elements. The applied approach included a

systematic analysis of all major springs, tributaries and most of the lakes of the complex

Plitvice Lakes system. The main aim of this work was to elucidate the sources of trace

element inputs into the lakes using principal component analysis (PCA) and to identify

main processes which govern their distribution in the complex lake system.

2 Materials and Methods

2.1 Study Area

The Plitvice Lakes (Fig. 1) are a complex cascade system of 16 lakes, which is usually

divided into two major parts: Upper Lakes (locations 9–14) and Lower Lakes (locations

15–16). The most significant compartments of the system are the two largest lakes, lake

20 Aquat Geochem (2014) 20:19–38

123

Prosce (0.68 km2) and lake Kozjak (0.82 km2) (Babinka 2008). A more detailed

description of the individual lakes is given in Table S1 (Supplementary information).

Majority of the water enters the Plitvice Lakes system in the Upper Lakes from the springs

Bijela Rijeka (location 1) and Crna Rijeka (location 2), which join to form Matica River

(location 4), a tributary to the lake Prosce with an average discharge of 2.14 m3s-1 from

which 75 % is coming from the spring Crna Rijeka (Biondic et al. 2010). The small stream

Susanj (locations 5 and 6), which periodically flows into the lake Prosce, has a very small

average discharge of only 0.05 m3s-1. The largest lake, the lake Kozjak, receives on

average an additional 24 % of water from the immediate catchment, mostly from the

Rjecica creek (location 7) (Biondic et al. 2010). The spring Plitvica (location 3), with its

tributary Sartuk (location 8), has an average discharge of 0.58 m3s-1. It joins the system

only in the Lower Lakes region and thus has a relatively small effect on overall hydrology

and geochemistry of the system (Biondic et al. 2010).

The Plitvice Lakes drainage area is characterized by several geological karst units,

mainly carbonates and dolomites (Velic and Vlahovic 2009). Upper Triassic bedded

dolomites predominate in the area of the Upper and Lower Lakes and the streams Rjecica

and Sartuk. The spring Crna Rijeka and most of its course are situated in Lower Jurassic

dolomites with intercalations of limestone. The spring Bijela Rijeka and small stream

Susanj are situated in the area of Upper Jurassic bedded limestone with intercalations of

dolomite and massive and crystalline dolomite, whereas part of their flow passes through

the Middle Jurassic bedded limestone with intercalations of dolomite. Upper Cretaceous

very thick bedded and massive rudistid limestone forms the bottom and the flanks of the

north-eastern part of the Kozjak Lake and part of the Korana River.

The key process responsible for the formation of the Plitvice Lakes system is the

precipitation of calcium carbonate (Baresic et al. 2011). Calcite does not precipitate in

Fig. 1 Map of the Plitvice Lakes system with indicated sampling locations for water and sediment

Aquat Geochem (2014) 20:19–38 21

123

springs due to the non-favorable physico-chemical conditions (pH = 7.3–7.9, high level of

dissolved CO2 and consequently low calcite saturation index ISAT & 1). Tributaries are

characterized by the conditions which are favorable for calcite precipitation

(pH = 8.0–8.8, ISAT = 2–18), however, the precipitation does not take place (Baresic

et al. 2011), presumably due to the intensive water movement or enhanced content of

dissolved organic matter (Srazmek et al. 2007). The lakes and the Korana River are

oversaturated with respect to calcite (ISAT = 4–10) and are characterized with intensive

calcite precipitation in the form of tufa barriers and lake sediment, especially during the

warm, summer periods (Baresic et al. 2011). As a consequence, the percentage of calcite in

the Plitvice Lakes sediment is very high (70–95 %) while the content of other minerals

such as dolomite and quartz is rather low (Horvatincic et al. 2006).

Since the Plitvice Lakes are situated in a pristine area, the major anthropogenic pressure

on the system represents tourist activities (1 million visitors per year, Biondic et al. 2010).

The most exposed lake is the Lake Kozjak with tree hotels located near its shore.

2.2 Sampling

Sediment and water samples comprised all parts of the hydrological system of the Plitvice

Lakes (Fig. 1), including major springs (locations 1, 2, 3), tributaries (locations 4, 5, 6, 7,

8) and 7 lakes (locations 9, 10, 11, 12, 13, 15, 16) and the Korana River (location 17). The

sampling campaigns for water samples were performed in May, June and September 2004,

September and December 2006 and April 2007. Surface sediments were collected in May

2004. Water samples were collected manually from the shore in acid-cleaned plastic

bottles, filtered through 0.45 lm filters and acidified with 1 % supra pure nitric acid. A

care was taken to avoid contamination of water samples during sampling and all manip-

ulations in the laboratory. Sediments were collected manually from the shore into the

plastic bags and stored at -20 �C till further processing within 1 week. Before analysis,

the bulk sediments were dried at the room temperature under the laminar flow, sieved

through the 2-mm sieve and milled to obtain fine powder for further analysis.

2.3 Analyses of Major and Trace Elements

Before instrumental analysis, sediment subsamples (0.1 g) were digested with 10 mL of nitric

acid in the microwave oven (Multiwave 3000, Anton Paar, Graz, Austria). Upon digestion, the

samples were diluted with Milli-Q water to achieve concentration levels, optimal for ICP-MS

measurements. To the adequately diluted sediment digest or to the water sample In (1 lg L-1)

was added as an internal standard. Multielemental analysis of the prepared samples was

performed by high-resolution inductively coupled plasma mass spectrometry (HR ICP-

MS) using an Element 2 instrument (Thermo Finnigan, Bremen, Germany). The measure-

ments of the selected isotopes were performed at three different resolutions: low resolution

(7Li, 95Mo, 111Cd, 205Tl, 208Pb, 238U), medium resolution (23Na, 25Mg, 27Al, 42Ca, 51V, 52Cr,55Mn, 56Fe, 59Co, 60Ni, 63Cu, 66Zn, 86Sr, 138Ba) and high resolution (39K, 75As). External

calibration in the range of 0.1–10 lgL-1 was used for the quantification. Standards were

prepared by appropriate dilution of a multielemental reference standard (Analytika, Czech

Republic) containing Al, As, Ba, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Pb, Sr, Tl, V and Zn in

which single element standard solutions of U (Aldrich, Milwaukee, WI, USA) was added. For

major elements determination, a multielemental reference standard (Fluka, Germany) con-

taining Na, K, Ca and Mg was used. Quality control of analytical procedure was performed by

simultaneous analysis of the blank and certified reference materials (CRM) for natural river

22 Aquat Geochem (2014) 20:19–38

123

water (SLRS-4, NRC, Canada) and sediment (marine sediment MESS-3, NRC Canada and

stream sediment NCS DC 73307, Beijing, China) with each group of samples. Regular

measurements of the field blanks for water samples as well as the good results for the low-

level trace elements CRM proved that the used protocol was good enough to avoid con-

tamination. Detection limits for the measured elements varied from 0.001 to 0.1 lgL-1 for

water and from 0.005 to 5 mg kg-1 for sediment, depending on the element, with a precision

(measurements of replicates) better than 5 %. More details on the analytical methods are

given elsewhere (Fiket et al. 2007; Cukrov et al. 2008).

2.4 Statistical Analysis

The data were treated statistically using SigmaPlot 11.0 and Statistica 7 software for

Windows. Analysis of variance on ranks and subsequent pairwise comparison by Dunn’s

method was applied to test the differences between the levels of measured elements at

different sampling sites, with level of significance set at P \ 0.05. Chemometric charac-

terization of the investigated water and sediment samples was made by PCA.

3 Results and Discussion

3.1 Levels of Major and Trace Elements in Water and Sediments

Average concentrations of elements determined in water and sediment samples, collected

from springs, tributaries and lakes, are presented in Tables 1 and 2, respectively. For

comparison, some literature data on the average levels of metals and metalloids in natural

waters and aquatic sediments, as well as the existing environmental quality standards and

guidelines are also provided in the tables.

Generally, the levels of all measured elements in water from the Plitvice Lakes system

were rather low (Table 1). For most of the trace elements, the average concentrations in the

Plitvice Lakes system were at least 10 times lower than the world river average (Gaillardet

et al. 2003). These concentrations are very similar to the concentrations found in uncon-

taminated deep waters of the lake Baikal (Suturin et al. 2003), which suggested a pristine

nature of the Plitvice Lakes. Among elements which typically derive from anthropogenic

sources (Pb, Cd, Ni, Cu, Zn), only the concentrations of Cd and Pb were enhanced in some

springs and tributaries, which suggested possible additional inputs of these two elements to

the Plitvice Lakes. With respect to European regulation on environmental quality standards

(EQS) in the field of water policy (EPCEU 2008), the maximal concentrations of Pb and Ni

were one order of magnitude lower than their corresponding EQS values, while for Cd the

maximum concentration was two times lower than its EQS value.

The average concentrations of trace elements (e.g., As, Cr, Ni, Cu, Pb) in the Plitvice

Lakes sediments (Table 2) were also relatively low and of the same order of magnitude as

the average concentrations of these elements in the pre-industrial sediments from the

remote Alpine and Arctic lakes (average from 275 lakes; Camarero et al. 2009). Only for

Cd, the average values in all parts of the lake system were higher than Cd concentration in

the contemporary sediments from the remote lakes (Camarero et al. 2009). Comparison of

the trace element concentrations in the Plitvice Lakes sediments with the average values

for limestone and shale (Table 2) shows that, for most of the elements, the concentrations

in springs and tributaries are higher than in limestones, but about two times lower than in

the average shale, which is in accordance with the prevalent carbonate background of the

Aquat Geochem (2014) 20:19–38 23

123

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5.0

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18

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Cd

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20

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Cr

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40

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Cu

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±0

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70

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±0

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±0

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03

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±0

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50

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62

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a0

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90

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70

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.71

24 Aquat Geochem (2014) 20:19–38

123

Ta

ble

1co

nti

nued

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once

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for

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b0

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±0

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±0

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±0

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Aquat Geochem (2014) 20:19–38 25

123

Ta

ble

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ton

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(Eu

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/PE

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13

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±7

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54

8

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1±

0.9

23

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±0

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0.6

6±

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70

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1.4

5±

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3–

–

Mn

b0

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±0

.255

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±0

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±0

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ce

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2±

3.0

35

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±0

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2±

0.9

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4±

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12

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01

2/6

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9/3

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Baa

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±1

4.9

76

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2.2

24

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8.3

34

.74

1.5

±2

3.6

––

Cd

1.4

4±

0.7

41

.83

±1

.34

1.1

3±

0.8

00

.40

1.3

6±

0.8

90

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0.1

30

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/4.9

8

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b7

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1±

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31

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21

9

Crb

24

.4±

11

.53

4.5

±3

.21

1.3

±1

0.0

12

.01

9.6

±1

3.2

11

90

43

.4/1

11

Cu

10

.5±

4.4

12

.6±

2.4

6.8

2±

4.3

55

.14

8.9

9±

4.4

84

45

28

/20

31

.6/1

49

Lib

12

.38

±7

.94

18

.92

±2

.30

3.4

3±

2.2

85

.42

9.0

7±

7.7

1–

–

Mo

0.7

9±

0.5

80

.94

±0

.31

0.3

4±

0.3

90

.28

0.5

8±

0.4

80

.41

.3

Nib

27

.8±

13

.82

5.5

±7

.79

.44

±5

.43

9.3

17

.4±

11

.71

56

82

2.7

/48.6

Pb

23

.8±

21

.33

9.0

±2

7.2

18

.4±

8.0

18

.62

4.3

±1

7.5

52

29

9/4

43

5.8

/128

Sr

57

.6±

6.1

61

.9±

15

.25

5.3

±1

0.1

62

.55

7.3

±1

0.1

––

Tlb

0.4

1±

0.2

50

.53

±0

.17

0.1

9±

0.0

70

.18

0.3

2±

0.2

00

.05

0.6

8

U1

.44

±0

.76

1.7

5±

0.2

01

.32

±1

.80

0.3

81

.45

±1

.32

––

Vb

36

.3±

24

.65

0.1

±2

.01

2.4

±1

2.2

14

.62

6.6

±2

1.3

20

13

0

26 Aquat Geochem (2014) 20:19–38

123

Ta

ble

2co

nti

nued

Ele

men

tC

once

ntr

atio

n(g

kg

-1

for

maj

or;

mg

kg

-1

for

trac

eel

emen

ts)

S(s

pri

ng

s)X

±S

TD

T(t

ribu

tari

es)

X±

ST

DL

(lak

es)

X±

ST

DR

(riv

er)

All

sam

ple

sX

±S

TD

Lim

esto

nec

Sh

alec

Rem

ote

lak

es(E

uro

pe)

dT

EC

/PE

Ce

Zn

b5

1.8

±1

8.0

68

.5±

15

.13

1.6

±1

6.9

21

.44

44

.8±

22

.12

39

51

30

/81

12

1/4

59

aT

her

eis

ast

atis

tica

lly

signifi

cant

dif

fere

nce

(P\

0.0

5)

bet

wee

ng

rou

ps

San

dT

for

this

elem

ent

bT

her

eis

ast

atis

tica

lly

sign

ifica

nt

dif

fere

nce

(P\

0.0

5)

bet

wee

ng

rou

ps

Tan

dL

for

this

elem

ent

cA

ver

age

conce

ntr

atio

ns

of

elem

ents

inli

mes

tone

and

shal

e;dat

afr

om

Wed

epohl

20

04

dA

ver

age

val

ues

from

275

alpin

ean

dar

ctic

lake

sedim

ents

(conte

mpora

ry/p

re-i

ndust

rial

conce

ntr

atio

ns)

;dat

afr

om

Cam

arer

oet

al.

20

09

eT

EC

Th

resh

old

effe

ctco

nce

ntr

atio

n;

PE

CP

robab

leef

fect

con

cen

trat

ion

(dat

afr

om

Mac

Do

nal

det

al.

20

00)

Aquat Geochem (2014) 20:19–38 27

123

area. Only for Cd and Pb, the concentrations in tributaries are 10 times (Cd) and two times

(Pb) higher than in the average shale, respectively. Comparison of the determined element

concentrations with sediment quality guidelines for freshwater sediments (MacDonald

et al. 2000) shows that the concentrations of As, Cr, Cu and Zn were lower than threshold

effect concentration (TEC) in all sediments from the Plitvice Lakes system. For Pb, Ni and

Cd in springs and tributaries, and for Cd even in lakes, the concentrations exceeded TEC,

however, all measured values for these elements were still lower than the probable effect

concentration (PEC).

3.2 Spatial Distributions of Major and Trace Elements

Spatial distributions of elements in water and sediments of the Plitvice Lakes system were

rather variable, depending on the sources and geochemical reactivity of individual con-

stituents. The data presented in Tables 1 and 2 clearly emphasized some significant dif-

ferences between various parts of the complex hydrological system of the Plitvice Lakes

for both major and trace elements. More detailed spatial distributions of elements in water

and sediment, for elements which showed significant differences between springs, tribu-

taries and lakes are shown in Figs. 2 and 3, while the distributions of other elements are

shown in supplementary Figure S1. The sampling locations presented in the figures were

grouped into four different location types (springs, tributaries, lakes and the outflow river)

and within each group the locations were ordered in the downstream direction. The data for

the tributary Matica are shown immediately before the data for lakes in order to facilitate

visualization of the changes in metal concentrations along the main water stream in the

Plitvice Lakes system. Presented box-plots for water summarize the data from all sampling

campaigns, including different years and seasons. For most of the elements, variability of

the observed concentrations on individual locations was rather small (10–30 %), indicating

relatively constant element levels during the studied period with no statistically significant

seasonal variations. Higher variations (40–60 %) were observed for oxide-forming metals

(Al, Fe, Mn), for which dissolved concentrations strongly depend on physico-chemical

conditions in water. However, the highest variabilities (50–90 %) were observed for metals

which usually derive from anthropogenic sources (Pb, Zn).

The major element Ca, which plays the key role in the geochemistry of the Plitvice

Lakes (Baresic et al. 2011), shows a statistically significant decrease in the dissolved

phase in the following order: springs [ tributaries [ lakes [ river (Table 1, Fig. 2), due

to the intensive calcite precipitation. In contrast, the maximum concentrations of Mg

were observed in tributaries followed by a significant decrease in the lakes. Concen-

trations of other major elements (K and Na) showed a rather conservative behavior (Fig.

S1). The distributions of trace elements in different parts of the system strongly varied.

For most of the dissolved trace elements, the differences between the concentrations in

springs and tributaries were not statistically significant (Al, Ba, Cd, Cr, Li, Ni, Pb, Sr, Tl,

V, Zn). However, some elements, of which many are redox sensitive, (As, Co, Cu, Fe,

Mn, Mo and U) were significantly enhanced in tributaries (Table 1, Figs. 2, 3; Suppl. Fig

S1). Concentrations of dissolved trace elements in lakes water were consistently lower

than in tributaries for all elements, except for Na and Sr. Moreover, dissolved element

concentrations in the outflow of the lakes (Korana River) were very similar to their

concentrations in the Lower Lakes.

Similarly as in the dissolved phase, the concentrations of all measured elements in the

lake and outflow river sediments appeared to be lower than in the springs and tributaries.

(Table 2, Figs. 2, 3; Suppl. Fig S1). For most of the trace elements, this decrease was

28 Aquat Geochem (2014) 20:19–38

123

Fig. 2 Distributions of elements influenced by dolomite weathering (Ca, Mg, V, Sr, Cd, Tl, Ni and Zn) inwaters and sediments from the Plitvice Lakes system. Results for water are presented as box-plots whoseboundaries indicate minimal and maximal values and the line within the box marks the median value

Aquat Geochem (2014) 20:19–38 29

123

Fig. 3 Distributions of elements illustrating terrigenic (Fe, Al, Mn, Co, As and Cr) and anthropogenic (Cu,Pb) influences in waters and sediments from the Plitvice Lakes system. Results for water are presented asbox-plots whose boundaries indicate minimal and maximal values and the line within the box marks themedian value

30 Aquat Geochem (2014) 20:19–38

123

particularly sharp between the major tributary Matica River and the Lake Prosce. The

concentrations of trace elements remain generally low in all downstream lakes and show a

slight decrease in the downstream direction.

3.3 Identification of Element Sources by Principal Component Analysis

In order to identify the main sources of individual elements and to investigate the factors

controlling their distribution between different compartments of the Plitvice Lakes system,

the collected data were analyzed using PCA.

The results of PCA, showing correlation between concentrations of elements in water

and principal components 1 and 2 (PC1 and PC2), are presented in Fig. 4a. The first two

principal components explained 59 % of the total variability, with PC1 and PC2

accounting for 35 and 24 % of the total variance, respectively. On the negative side of the

first component, elements Mg, Cd, Zn, Tl, Ni, Mo, V, Cu and Mn are grouped together

(encircled on the figure), whereas on the positive side of PC1, the greatest effect ([0.7) was

obtained for Sr. PC1 was assumed to reflect the geological background and includes those

elements which are enhanced in springs and tributaries situated in the dolomite bedrock. It

is known from the literature (Srazmek et al. 2007) that waters derived from dolomites are

characterized by a high concentration of Mg and a high molar Mg/Ca ratio ([0.7).

Moreover, since dolomites and high-Mg calcites are low in Sr as compared with the low-

Mg calcites (Veizer and Demovic 1974), such water type usually contains lower con-

centration of Sr. All these characteristics can be found in the spring Bijela Rijeka (location

1) and the tributaries Susanj (locations 5 and 6), Rjecica (location 7) and Sartuk (location

8) (Fig. 2). Two of these tributaries (Bijela Rijeka and Susanj) also showed enhanced

concentrations of several trace metals, including Cd, Zn, Tl and Ni (Fig. 2), which, most

probably, reflects their common geological background. Mn, U and Mo were also corre-

lated with PC1, but for these elements, the highest concentrations were observed in the

Rjecica creek and the mouth of the stream Susanj (Fig. 3 and Fig. S1). Both locations are

characterized by high levels of organic debris and periodic events of anoxia at the sedi-

ment/water interface (Baresic 2009). Under such conditions, redox sensitive elements Mn,

Li Mo

Cd Tl

Pb

U

V

Cr

Ni

Co

Cu

Zn

As

Al

Ba

Fe

Mn

Sr

Na K

Mg

Ca

-1,0 -0,5 0,0 0,5 1,0

Factor 1 : 35,17%

-1,0

-0,5

0,0

0,5

1,0

Fac

tor 2

: 24

,22%

91011

1213

1615

7

1

2

4

17

8

3

5

146

-10 -8 -6 -4 -2 0 2 4 6 8

Factor 1: 35,17%

-10

-8

-6

-4

-2

0

2

4

6

8

Fac

tor

2: 2

4,22

%

(a) (b)

Fig. 4 Principal component analysis of elements in water of the Plitvice Lakes system: a correlationsbetween elements in the projection of principal components 1 and 2; b biplot of sites projected to principalcomponents 1 and 2

Aquat Geochem (2014) 20:19–38 31

123

U and Mo efficiently precipitate from the water column, but can be remobilized from

sediment upon changes of redox conditions (Tribovillard et al. 2006).

The strongest contributions for PC2 were obtained for Al, Co and Fe (\-0.7). These

three elements were particularly enhanced in the dissolved phase in the stream Sartuk

(Fig. 3). This observation could be explained by a distinct water chemistry of this

watercourse, including enhanced pH (pH = 8.4) and comparatively high concentration of

dissolved organic matter (DOC = 2–3 mg L-1) (Baresic et al. 2011). High levels of

dissolved organic matter can stabilize Al/Fe colloids in the solution (Pokrovsky et al. 2005)

and enhance concentration of associated trace elements in water.

PC3 explained additional 11 % of the total variance, with Ca (0.8) and Pb (0.67)

showing the strongest contribution. Apparent correlation between these two elements

comes from the fact that both of them showed a significant decrease from springs to the

lakes (Figs. 2, 3). However, the reasons for such similar distributions are completely

different for the two elements: while permanently high Ca concentration in springs reflects

the weathering of carbonates, enhanced Pb levels derive from seasonally dependent

anthropogenic contamination in springs, where concentrations of Pb in July were 10 times

higher than in other sampling periods.

To help locate the main sources of trace elements, the plots of the principal component

scores for the studied locations are displayed in the planes of PC1 and PC2 (Fig. 4b). It can

be seen that all lakes (locations 9–16; encircled on the figure) have very similar metals

compositions. According to literature (Lalor and Zhang 2001), greater scores should be

interpreted as indications of anomalously high and strongly localized metal sources. Thus,

large scores on PC1 for locations 5, 6 and 1 (tributary Susanj and spring Bijela Rijeka)

indicate that these locations are important sources of several trace elements (Cd, Zn, Ni,

Tl). These watercourses are weathering the Upper and Middle Jurassic dolomites (Velic

and Vlahovic 2009), which seemed to be naturally enriched with Cd, Zn and, to a lesser

extent, with Ni and Tl. Anomalous enrichment of Jurassic limestone with Cd was dem-

onstrated in Swiss and French Jura Mountains (Quezada-Hinojosa et al. 2009), while

dolomites showed high enrichment of Zn (Martinez et al. 2007). A high score on PC2 for

location 8 (tributary Sartuk) is associated with enhanced levels of Al, Fe and Co in that

stream as explained earlier above (Fig. 3).

Results of PCA analysis of the sediment data are presented in Fig. 5a,b. PC1, explaining

already 71 % of the variance, showed an excellent correlation (\-0.9) with Al, Fe, Li, Tl,

V, Cr, Ni, Zn, As and Ba and a good correlation (\-0.7) with Na, K, Mo, Co, Cu, Mn

(encircled on the figure). Al is a major constituent of alumosilicates, particularly clay

minerals, and in most cases its concentration in sediments is not altered anthropogenically.

Consequently, the content of this element can be used as an indicator of the abundance of

clay minerals (Covelli and Fontolan 1997). Since clays are widely accepted as the excellent

indicators of the terrigenic input in the aquatic sediments, it was concluded that PC1 reflects

terrigenic component of sediments in the Plitvice Lakes system. Very good correlation of

most of the trace elements with PC1 indicates that they are primarily of terrigenic origin.

PC2, which explained additional 10 % of the variance, was negatively correlated with

Sr (\-0.8), reflecting association of Sr with the carbonate sediment fraction. This com-

ponent showed also a moderate correlation (0.5) with Pb, which was separated from other

trace elements and was not correlated with Al. This supported the assumption on the

distinct anthropogenic origin of Pb. High levels of Pb in spring waters in the peak of the

tourist season and elevated concentrations in the sediments of the spring Plitvica and

Rjecica creek (situated in the proximity of the main road crossing the area of the National

Park) suggested that Pb pollution was connected with the long-term use of tetraalkyllead as

32 Aquat Geochem (2014) 20:19–38

123

additive in gasoline (Mikac and Branica 1994). This conclusion is well supported by the

historical trend of Pb in dated sediment core from the lake Kozjak (Mikac et al. 2011),

which showed an increase in Pb concentration in recent sediments.

PC3 was correlated only with Cd (\-0.8), indicating some unique feature regarding the

prevalent source and distribution of this element in sediments. As for Pb, Cd was also not

correlated with Al and the highest concentrations were found in the Matica River and the

lake Prosce. Water analyses showed that the main source of Cd is the spring Bijela Rijeka.

Obviously, a part of Cd is removed from the dissolved phase already in the Matica River

and further steady removal continues in the lakes, resulting in a clear decreasing gradient

going from the Upper to the Lower Lakes (Fig. 2). A similar distribution pattern was also

apparent for Zn, Tl and Ni (Fig. 2), which all originate predominately from the source

Bijela Rijeka.

The principal component scores for sediments from different locations, displayed in the

planes of the components 1 and 2, are shown in Fig. 4d. Like previously shown for the

water samples, multielemental compositions of all lake sediments were rather similar

(encircled on the figure). The only exception was the Gradinsko Lake (location 12), where

high concentration of U, Mo, Cu and Cr were obtained (Fig. 3 and Fig. S1). However, it

should be pointed out that this sediment was probably not representative for the whole lake

Gradinsko. Unlike other sediments collected in the Plitvice Lakes, its color was black,

suggesting anoxic conditions and high organic matter content typical for the marginal

marsh part of the lake. Large score on PC1 for the spring Crna Rijeka (location 2) and all

tributaries (locations 4, 7 and 8) confirmed that they represented principal sources of all

elements having terrigenic origin, as commented earlier in the text.

PCA analysis of water and sediment data indicated significant differences in the dis-

tributions of elements in the two compartments of the Plitvice Lakes system. The corre-

lation analysis based on the entire data set failed to show any correlation between element

concentrations in the sediments and their water counterparts, except for Al. The results

were more consistent in the lake part of the system, where significant correlations

(P \ 0.05) were found for Cd and Mn.

Mo

Cd

Pb

U

V

Cr Ni

Cu

Zn

Al, Li, Fe Ba, As, Tl, K

Mn

Sr

Na, Co

-1,0 -0,5 0,0 0,5 1,0

Factor 1 : 71,04%

-1,0

-0,5

0,0

0,5

1,0

Fac

tor

2 :

9,95

%

910

11

12

13

16

15

7

12

4

17

8

3

-10 -8 -6 -4 -2 0 2 4 6 8

Factor 1: 71,04%

-4

-3

-2

-1

0

1

2

3

4

5

6

Fac

tor

2: 9

,95%

(a) (b)

Fig. 5 Principal component analysis of elements in sediment of the Plitvice Lakes system: a correlationsbetween elements in the projection of principal components 1 and 2; b biplot of sites projected to principalcomponents 1 and 2

Aquat Geochem (2014) 20:19–38 33

123

3.4 Autopurification Processes of Trace Elements in the Lakes

Significantly decreased concentrations of all elements in the lake waters imply that

removal processes, which involve association with settling particles and transport to the

sediment, must have been efficient. These processes may be related to several major

biogeochemical cycles in the lake water column, including formation of authigenic cal-

cium carbonate, cycling of redox sensitive elements Fe and Mn and photosynthetic pro-

duction (Sigg et al. 1987). We assessed the removal of selected metals in the Plitvice Lakes

by considering four different sections: (a) lake Prosce, (b) smaller Upper Lakes between

the lakes Prosce and Kozjak, (c) lake Kozjak and (d) the Lower Lakes (Table 3). For each

section, the relative removal of metals was estimated by comparing the average concen-

trations in the inflow and outflow water. Average concentrations, standard deviations and

coefficients of variations of the concentrations obtained for each location and element are

given in Table S2. From the presented data, it is evident that the variations for some

elements are significant and therefore the estimated elimination rates have relatively wide

error margins. Nevertheless, the calculated removals in various sections of the lakes are in

a good agreement with the intensity of the presumed key removal mechanisms. The

assessment was performed for elements which can be regarded as potential scavengers for

Table 3 Estimation of the removal of elements from the dissolved phase in different sections of the PlitviceLakes and the contribution of the removed (precipitated) metal to the total concentration in sediment of thelake Prosce

Element Removal (%)a Relative contribution of theprecipitated dissolved metalsto the total metal in sedimentof the lake Prosceb

Section ILakeProscea

Section IISmall UpperLakesa

Section IIILakeKozjaka

Section IVLowerLakesa

Allsectionsa

Ca 7 11 5 1 23 –

Mn 40 80 -122 30 81 5.6

Fe -25 83 -36 20 76 -0.2

Al 83 -26 -216 64 76 0.5

Cd 52 70 11 0 86 20

Zn 48 -45 21 -34 20 8.4

Cu 19 30 -38 21 38 14

Ni 12 26 -22 33 47 5.1

Pb 1 33 -33 25 34 0.1

Co -24 46 -38 17 23 -3

Cr 30 38 8 5 62 13

Tl 18 25 17 10 54 17

a Calculated as: Removal (%) = (Cinflow - Coutflow)/Cinflow * 100; Cinflow and Coutflow are the elementconcentrations in the inflow and outflow of a given lake section. Average concentrations (and standarddeviations to illustrate uncertainty of estimation) used for calculation are given in Table S2b The relative contribution of the metals (Mr) precipitated from the dissolved phase (Mpd) to the total metalamount (Mt) deposited in sediments during the same period was determined as: Mr (%) = Mpd/Mt 9 100;Mpd was calculated as follows: Mpd (kg year-1) = (Cinflow - Coutflow) 9 Qinlow where Qinlow is the averageannual inflow of the Matica River to the lake Prosce (67.4 9 106 m3 year-1); Mt was calculated as follows:Mt (kg year-1) = Sr 9 APr 9 CM where Sr is the sedimentation rate in the lake Prosce (1.3 kg m-2 year-1;Horvatincic et al. 2008), APr is the area of the lake Prosce (0.68 9 106 m2) and CM is the total concentrationof a given element in the sediment from the central part of the lake Prosce (data from Mikac et al. 2011)

34 Aquat Geochem (2014) 20:19–38

123

trace elements (Ca, Mn, Fe and Al) as well as for those trace metals which showed

significant removal ([10 %) within the lakes (Cd, Zn, Cu, Ni, Pb, Co, Cr and Tl). For all

trace elements which showed efficient removal in the Plitvice Lakes (except Tl), a sig-

nificant precipitation or co-precipitation with calcite was reported in the literature (Zachara

et al. 1991; Elzinga and Reeder 2002; Chada et al. 2005; Tang et al. 2007). Moreover, all

mentioned metals are also very efficiently scavenged with Mn and Fe oxyhydroxides,

which are considered to be the most powerful adsorbents of trace elements in natural

waters (Koschinsky and Hein 2003).

The removal of all elements, involved in scavenging processes, was rather efficient with

some significant differences between the individual elements. Calcium shows a continuous

decrease from the Upper to the Lower Lakes, with 5–7 % removal within the larger lakes

(Prosce and Kozjak) and the highest removal (11 %) inside the cascade series of the Upper

Lakes (Table 3), which is consistent with the intensive precipitation of calcite in the lakes.

Manganese shows high removal (40 %) inside the lake Prosce and almost complete removal

(80 %) within the smaller Upper Lakes section. However, for the lake Kozjak, the calcu-

lation resulted in a negative removal, suggesting an important additional input of Mn to this

lake. Indeed, enhanced concentration of Mn in the major tributary to the lakes Kozjak,

Rjecica creek (Fig. 2), supports this assumption. Manganese can be removed from the water

phase either by co-precipitation of Mn2? with calcite, or by precipitation in the form of Mn

oxyhydroxides. A significant correlation of dissolved Mn and Ca in samples from the

Matica River to the lake Novakovica brod (r = 0.78; P \ 0.05) suggests that Mn removal

from the water column might have been partly associated with co-precipitation with calcite.

Fe and Al did not show a clear removal pattern within the Upper Lakes, but similarly to Mn,

show negative removals in the lake Kozjak. The overall removal of oxide-forming elements

(Mn, Fe and Al), including all sections of the lakes, is very high (around 80 %).

For most of the trace elements, the removal pattern was similar to the patterns described

for Ca and Mn removal: significant removal inside the lake Prosce, the most intensive

removal within the cascade of the small Upper Lakes, small or negative removal inside the

lake Kozjak and then further removal within the Lower Lakes. It is interesting to point out

that the removal of metals in the section of the smaller Upper Lakes was much higher than

in the lake Prosce, despite the much shorter flushing time (11 days for the small Upper

Lakes vs. 41 days in the lake Prosce; see data for the renewal times in Table S1), which

indicated increased removal efficiency in the multicascade system. Study of variations in

the stable C isotope composition in waters of the Plitvice Lakes (Baresic et al. 2011)

indicated that precipitation of authigenic calcite is indeed accelerated on waterfalls bar-

riers, mainly due to enhanced outgassing of carbon dioxide from the water. In addition, the

same study suggested that some small lakes (e.g., Gradinsko Lake) have a higher primary

productivity. As biological material can be an important carrier phase for trace metals

(Sigg et al. 1987) both mechanisms may result in enhanced removal of dissolved metals in

the multicascade system of small lakes. A very low or apparently negative removal for

trace elements in the lake Kozjak, suggesting additional inputs of these elements, is

consistent with the enhanced concentrations in the Rjecica creek and generally higher

anthropogenic pressure on the lake Kozjak (Mikac et al. 2011), due to the intensive tourist

activities, including hotel accommodation. Some specific markers of wastewater, such as

anionic surfactants, suggested that it must have been a significant leakage of hotel

wastewater into the lake Kozjak (Mikac et al. 2011).

The overall removal efficiency of trace elements within the Plitvice Lakes decreases in

the following order: Cd [ Cr [ Tl [ Ni [ Cu [ Pb [ Co [ Zn. Dissolved Cd, which

showed the most efficient removal (86 %), was highly correlated with dissolved Ca

Aquat Geochem (2014) 20:19–38 35

123

(r = 0.86; P \ 0.05) and Mn (r = 0.88; P \ 0.05). Good correlations were obtained for

dissolved Cr (r = 0.81 and r = 0.56 with Ca and Mn, respectively; P \ 0.05) and Co

(r = 0.51 and r = 0.75, respectively; P \ 0.05). This suggested that co-precipitation with

authigenic calcite and Mn oxyhydroxides might have been important mechanisms of trace

metal removal from the dissolved phase in the Plitvice Lakes. At present, it is not possible

to evaluate, which of these mechanisms were more important, however, we presume that

the massive precipitation of authigenic calcite should play a major role. The extent of

binding of metals to different kinds of particles depends on the respective surface area and

on the specific affinity of the different active sites. Although the specific surface area of Mn

oxides is at least hundred times higher than that of calcite (Sigg et al. 1987), concentration

of Mn in settling particles (which may be roughly approximated by concentration in the

lake sediments) was more than 3,000 times lower than that of Ca. A more complete

assessment of the impact of different processes on the metal fluxes in the Plitvice Lakes

would require the implementation of sediment traps and better characterization of settling

particles, which should include study of the role of colloidal fraction as well as the uptake

by phytoplankton and adsorption onto organic particles.

An attempt was made to estimate the influence of the metal removal from the water

column on their total content in the lake sediments. This calculation was possible only for

the lake Prosce for which reliable data on the sedimentation rate were available (Horva-

tincic et al. 2008). The calculated contributions of precipitated dissolved metals (Table 3)

were compared with the total metal concentrations in sediment. For this purpose, data from

the sediment core taken in the center of the lake Prosce (Mikac et al. 2011) were used as

they better reflect the overall sedimentation rate in the lake. The comparison revealed that

for Cr, Cu, Tl and Cd, 10–20 % of these metals in sediment originated from the dissolved

phase, while for all other metals this contribution was much lower. Therefore, it could be

concluded that the co-precipitation of metals with authigenic calcite, which actually rep-

resents the major mineralogical component of the Plitvice Lake sediments (70–80 % in the

lake Prosce, 80–85 % in the lake Kozjak and 90–95 % in the lake Gradinsko; Horvatincic

et al. 2008) does not increase the metal concentrations in sediments but rather serves as a

geochemical dilutor of the terrigenic material. Indeed, analyses of authigenic calcite,

forming tufa barriers (which is closely related to the authigenic calcite found in the lake

sediments), showed that this material contained very low concentration of all typical

terrigenic elements, such as Al and Fe as well as trace elements associated with clays

(Cukrov et al. 2011).

4 Conclusions

Multielemental analysis of metals in water and sediments in combination with PCA was

shown to be a useful tool for the recognition of sources and processes, which govern the

metals distribution in a complex lake system. Complementary analyses of the metal dis-

tributions in water and sediments were instrumental in identifying the key processes

involved. Such an integrated approach is especially important in karst environments,

characterized by low concentration of suspended solids, where metals are transported

mainly in the dissolved phase and precipitate in the lentic parts of the system. Precipitation

of authigenic calcite in the lakes was shown to be an important mechanism determining

distribution of metals and their residence times in the dissolved phase. The results suggest

that the cascade feature of the Plitvice Lakes system enhances the removal of trace

elements.

36 Aquat Geochem (2014) 20:19–38

123

Acknowledgments The work was supported by the Ministry of Science, Education and Sport of theRepublic of Croatia. Financial support from the Royal Norwegian Ministry of Foreign Affairs to the project‘‘Mitigation of environmental consequences of the war in Croatia—risk assessment of hazardous chemicalcontamination’’ is gratefully acknowledged.

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