Application of isotope techniques in investigation of water resources and
water protection in the Karst area of Croatia (IAEA TC CRO/8/006)
2005-2006
Final Report
(Internal no. IRB-ZEF-2007/58)
Nada Horvatinčić, Zvjezdana Roller-Lutz, Sanja Kapelj
1.
INTRODUCTION
The karst area of Croatia (app. 50% of Croatia is karst) comprises very important groundwater
storage reservoirs of the Dinaride belt, mostly situated in the regions of Dalmatia, Lika,
Gorski kotar, Hrvatsko primorje and Istrian peninsula (Fig. 1). Extensive applied studies of
ground- and surface waters, aquifers, springs, recharge characteristics as well as pollutant
impacts (karst area is very sensitive to any pollution) have to be performed to determine the
groundwater potential for the use for water supply. Beside classical hydrogeological and
geochemical methods isotopic methods (2H, 3H, 13C, 14C,18O) are very important tools in such
investigation.
In the frame of the IAEA TC Project “Application of isotope techniques in investigation of
water resources and water protection in the Karst area of Croatia” in period 2005-2006, we
investigated two areas important for water supply: springs in the drainage area of the Gacka
River, Lika region and springs in one of the subdrainage areas of the Vransko Polje
(important for water supply of the town of Biograd and surrounding settlements, Middle
Dalmatia).
The aim of the project was to determine the origin of groundwater discharging at particular
springs with respect to its drainage area, recharge conditions and anthropogenic influence. In
this sense, application of isotope techniques and methods within the project has the main role
to upgrade present hydrogeological knowledge about protection of groundwater resources.
The obtained data can be very useful for determination of sanitary protection zone as well as
for managing the quality of groundwater resources.
For mentioned purposes, knowledge about hydrodynamic conditions within the aquifer is of
crucial importance especially the mean residence time of groundwater in karstified aquifer
system and a degree of water mixing within the aquifer. For both areas most important
questions can be summarized as follows: If there is any accidental event (traffic or industrial
sources) or long-term pressure of agricultural activity or farming jeopardize groundwater
quality, when we can expect the evidence of this events on discharge point and how long
these potential contamination can be delayed in aquifer?
We used hydrochemical measurements including in situ measurements of temperature, pH,
conductivity and oxygen as well as laboratory measurements of Ca, Mg, Na, K, HCO3¯, SO42-,
Cl-, NO3, NH3, PO43-. The isotope measurements included 2H, 3H, 13C and 18O. For
determination of the mean residence time (MRT) of spring waters we also used CFC
measurements performed in the IAEA Isotope Hydrology Laboratory. Spring waters from
three main springs and precipitation water at each area were collected monthly in the period
2005-2006. During this period we also occasionally performed measurements in some
additional springs in both areas. It the Project the following institutions have been involved:
Rudjer Bošković Institute, Radiocarbon and Tritium Laboratory, Zagreb (for 3H
measurement), University of Rijeka, Faculty of Medicine, Stable Isotope Laboratory, Rijeka
(for stable isotope measurements), and University of Zagreb, Geotechnical Faculty,
1
2
Environmental Geochemical Laboratory, Varaždin (for sampling and geochemical
measurements) and Hydrogeochemical Laboratory of Croatian Geological Survey.
2.
SITE DESCRIPTION
Two investigated areas are situated in the Dinaric Karst (Fig. 1) that comprises very important
groundwater storage reservoirs in Croatia, but in the same time this area is very sensitive to
any kind of pollution. Study sites are very important for water supply in these areas. In spite
of the fact that both areas are located in the Dinaric Karst, their hydrogeological features are
different due to their physiographical and climate conditions.
Upon a time, Croatian inland part of Dinaric Karst was less inhabited, with few large and
many dispersed small settlements. But today, large water potential of its aquifer is seriously
exposed to new development trends of different types mainly waste water of settlements,
industry and traffic.
Fig. 1. Position of the investigated area of Gacka River and Vransko Polje,
Croatia.
2.1. Gacka River spring area
The spring zone of the Gacka River (Fig. 2) consists of a number of karst springs situated
along the edge of the Gacko polje, which present one of the strategic reserves of the drinking
water due to its quantity and quality. The climate is typical continental, sometimes under
Mediterranean influence. Altitudes vary between 600 m to more than 1000 m a.s.l. Springs
drain water from the large recharge area of approximately 480 km2, consisting of a mountain
parts and few smaller karst poljes, Vrhovine polje from the north-east and Perušić polje from
the southwest. Groundwater direction was confirmed by previous tracing tests by sodium
fluorescein (Figure 2) [1].
3
South and west part of the catchment area is mainly built of well permeable deposits EoceneOligocene limestone breccias, conglomerates and limestones while in the eastern and northern
part of catchment within the Jurrasic and Cretaceous limestone complex of rocks, dolomites
are more abundant. However, the structural-tectonic relations have the crucial part in
disposition and groundwater flow. Considering the tracing results, it is obvious that
groundwaters flow from the specific part of the catchment area (Lipovo polje and Vrhovine
polje) towards individual spring or group of springs, connected with an arrangement of
structural-tectonic units, structures and tectonic blocks (Figure 2).
The spring Pećina gets the water mostly from the western part of the catchment area
composed mostly of limestone breccias and limestones, where structures separated by parallel
vertical faults prevail. The strong oscillations of discharge, from several tens in the maximum
to only 0.06 m3/s in the minimum point out on smaller retention and well drained area.
Tonkovića vrelo, the main spring of the River Gacka, gets the major part of the water from the
structural unit in the immediate hinterland of the spring and in the middle part of the
catchment area. This reflects on the hydrogeological properties of the spring: permanency and
high discharge, which is connected partly to presence of dolomite rocks in composition of the
aquifer and partly to large drainage area. Dolomites in composition of karst aquifers cause
higher retention capabilities because of less cavernousity in comparison with limestone parts
of terrain. In spite of mentioned, the groundwater outflow regime on Majerovo vrelo is
determined by the existence of open joints and karst channels that enable fast inflow of huge
amounts of water drained from the mountain area and Vrhovine polje.
Before the construction of a new highway, the whole region was scarcely inhabited, with
some small industrial facilities and insignificant agriculture. Today, traffic infrastructure
enables increased touristic activities and all accompanying facilities. Also, every accident in
quarries situated within this part of catchment and some industry facilities in Ličko Lešće
could also influenced on spring water quality. But, existing Croatian legislative regulate very
rigorous conditions for its work and monitoring procedures.
4
Description of legend:
1 – well permeable carbonate rocks (Eocene-Oligocene karstified limestone breccias, conglomerates
and limestones); 2 – medium permeable carbonate rocks (Jurassic limestone and dolomites,
Cretaceous limestone and dolomites); 3 – intergranular porosity sediments (Quaternary deposits of
karstic polje); 4 – geological boundary; 5 – erosion boundary; 6 – dip and strike of bed, 7 – normal
fault; 8 – photo-geologically observed fault; 9 – relative down thrown side (vertical); 10 – captured
karst spring, 11 – perennial karst spring; 12 – swallow hole (ponor); 14 – general groundwater
direction; 15 – proven connection between karstic loss and resurgence; 16 – water dividing zone
periodically changing; 17 – borehole.
Fig. 2. Simplified hydrogeologic map of the Gacka river catchment.
5
2.2. Vransko Polje spring area
The Vransko Polje (Fig. 3), situated near the town of Biograd, physiographically and
geologically belongs to the outer Dinaric Karst region. The climate is typical Mediterranean
with an average air temperature of approximately 14.5 oC. Altitudes vary between a few
meters and 100 m a.s.l.
The terrain is composed of well permeable Cretaceous and Eocene limestones, medium
permeable Cretaceous dolomite and limestones and impermeable klastic deposits of Eocene
flysch. The rocks are covered with Quaternary alluvial and diluvia deposits of karstic poljes
and smaller depressions. In the northern part of study terrain, low permeable to impermeable
carbonate rocks, Promina conglomerates, extends. From the tectonic point of view, this is a
flattened, mildly folded area.
The prevailing groundwater flow occurs parallel to the structural directions, NW-SE direction.
However, along the north edge of Vransko Polje, on the barrier of flysch deposits on several
karst springs discharge the waters from the north inland carbonate recharge area. In these
parts of the terrain, groundwater flows perpendicularly to the structures. The deep parts of
aquifer along the coastal zone and Vransko Polje are partly under sea water influence due to
deep seawater intrusion after the last glaciation period. Contribution of fresh water from the
inland part formed a fresh water layer with a mixing zone which overlays “aged” sea water.
The position of the mixing zone depends on the geometry of impermeable barriers and
hydrological conditions – contribution of fresh water from the inland. Sea water influence was
investigated through the few previous studies concerning the fresh water potential of the
coastal aquifer [2, 3].
The sea water influence is not the only source of potential groundwater contamination. A
groundwater of the karst aquifers is also strongly affected by agricultural activity, mainly by
application of fertilizers on karst polje as well as by waste waters from many inland
settlements. The influence of new highway traffic is limited by completely closed system of
dewatering within the high protection zones of catchment and constructed facilities for waste
water treatment in less vulnerable parts of terrain.
Previous studies established sporadic effects of sea water as well as fertilizers on groundwater
quality. The application of isotopes in this study is mainly focused on evaluation of mean
residence time of water of coastal aquifer to evaluate the consequences of accidental
pollutions on groundwater quality, its possible impact on whole stored water and duration –
transit time or mean residence time.
6
Description of legend:
1 – well permeable carbonate rocks (Eocene limestones: E1,2, Cretaceous limestones: K23); 2 – medium
permeable carbonate rocks (Cretaceous dolomite and limestones K21,2); 3 - low permeable carbonate
rocks; 4- impermeable klastic rocks – flysch deposits: E2,3); 5 - intergranular porosity sediments
(Quaternary deposits of karstic polje: Q1, Q2); 6 – geological boundary; 7 – erosion boundary; 8 – dip
and strike of bed, 9 – normal fault; 10 - reverse fault; 11 – anticline; 12 – syncline; 13 – overthrust
anticline; 14 - sinking of anticline; 15 – captured karst spring; 16 – perennial karst spring; 17 swallow hole (ponor) ; 18 - proven connection between karstic loss and resurgence; 19 – general
groundwater direction; 20 – proven connection between karstic loss and resurgence; 21 – water
dividing zone periodically changing; 22 – monitoring borehole.
Fig. 3. Simplified hydrogeologic map of the Vransko Polje catchment.
7
SAMPLING AND MEASUREMENTS
2.3. Sampling
6
250,00
Tonkovića vrelo Q
(m3/s)
Pećina Q (m3/s)
5
200,00
Precipitation (mm)
4
150,00
3
100,00
2
50,00
1
December, 2006.
October, 2006.
November, 2006.
August, 2006.
September, 2006.
July,2006.
June, 2006.
May, 2006.
April, 2006.
March, 2006.
January, 2006.
February, 2006.
November, 2005.
December, 2005.
October, 2005.
September, 2005.
July, 2005
August, 2005
May, 2005
June, 2005
0,00
April, 2005.
0
Monthly precipitation (mm)
Average monthly discharge (m 3/s)
Water samples in recharge areas of Gacka River springs and Vransko Polje springs were
collected monthly in the period April 2005 – October 2006. Spring waters were collected
regularly at three main springs at each area. Springs in Gacka River: Tonkovića vrelo,
Majerovo vrelo and Pećina (Fig. 2). Precipitation was collected in the rain-gauge near
Tonkovića vrelo. Discharge on Tonkovića vrelo during the 2005. was at minimum 1.95 m3/s
(09.03.2005.) and 7.27 m3/s during the maximum (01.12.2005.). Average discharge was 3.98
m3/s. During the same year, in Pećina spring maximum discharge was 8.26 m3/s
(07.12.2005.), minimum 0.157 m3/s (22.11.2005.) and average discharge was 1.53 m3/s.
There are not data about discharge values for Majerovo vrelo for observed period.
Unfortunately, discharge values for other two springs in 2006. will be completed during the
second part of 2007. Monthly values of precipitation and mean monthly values of springs’
discharge are shown on Fig. 4.
Fig. 4. Average monthly values of springs’discharge and monthly precipitation of the Gacka
River catchment.
Sporadically, samples were collected at the following springs: Jaz, Marusino vrelo,
Knjapovac, Klanac and Živulja (Fig. 2), and Begovica, Krbavica, Crno vrelo, Hajdukovac,
Trnovac, Pećina Korenica, Dežmino vrelo and Mlakvena greda that are located in neighboring
catchments out of presented map.
Springs in Vransko Polje recharge area: Turanjsko jezero, Kakma and Biba (Fig. 3)
Sporadically, samples were collected at the following locations: irrigation channel Kotarka
and monitoring borehole B-1 (samples were taken from borehole at depth of 20 and 40 m) and
spring Selakovo vrelo which is the natural overflow of captured Kakma spring.
Monthly precipitation amount was observed on meteorological station in Benkovac, town
located in the central part of catchment (Fig. 5).
160
Precipitation (mm)
140
120
100
80
60
40
20
October, 2006.
September, 2006.
August, 2006.
July, 2006.
June, 2006..
May, 2006.
April, 2006
March, 2006
February, 2006.
January, 2006
December, 2005
November, 2005
October, 2005
September, 2005.
August, 2005
July, 2005
June, 2005.
0
May, 2005.
Average monthly precipitation (mm)
8
Fig. 5. Monthly precipitation of the Vransko Polje catchmen area.
Water samples were taken for the following analyses: 3H activity, stable isotope analyses H,
18O and 13C, CFC analyses and chemical analyses (Ca, Mg, Na, K, HCO3¯, SO42-, Cl-, NO3,
NH3, PO43-). Temperature, pH values and conductivity were measured in the field.
For collecting the monthly precipitation samples we put the rain-gauge close to the spring
Tonkovića vrelo at the Gacka River and close to the spring Kakma at the Vransko polje area.
Precipitation samples were collected in the period November 2005 - November 2006.
All data on the collected samples are presented in Appendix 1, Tables 1 and 5.
2.4. Measurement techniques
For the field measurement of temperature, pH and conductivity we used portable instruments
(WTW).
Tritium activity was measured at the Radiocarbon and Tritium Laboratory at the Rudjer
Bošković Institute by a gas proportional counter (GPC) technique. From water sample (50 ml)
CH4 is obtained by reaction of water with aluminium carbide at 150°C [4], purified and used
as a counting gas in a multi-wire GPC. The counting energy window is set to energies
between 1 keV and 10 keV to obtain the best figure of merit. Gas quality control has been
performed by simultaneous monitoring of the count rate above the tritium channel, i.e., above
20 keV. The lowest tritium activity that can be distinguished from the background, i.e., the
limit of detection is 2 T.U.
The new Laboratory for stable isotope measurement has been set up recently at Rijeka
University. Part of mass spectrometry system, Dual inlet system, has been obtained by the
IAEA TC Project (CRO/8/006). MS system consists of Thermo-Finnigan Delta+XP mass
spectrometer, fitted with a gas bench, an autosampler (96 sample positions) and a dual inlet.
In-house water-standards have been produced in fairly large quantities (approx. 35 litres each)
by collecting various types of waters with different δ-values, stored in stainless-steel barrels
under argon gas pressure. Their 18O values (VSMOW) have been determined in interlaboratory comparisons. For each measurement the autosampler tray is filled to approximately
50% with vials of standards and 50% of unknown samples in predefined positions, each vial
9
containing 0.5 ml. The δ-values (standard deviation generally below 0.1‰) of the unknown
samples are used as references, one serves as quality control. The latter is required to lie
within 0.1 ‰ of its VSMOW values.
The hydrochemical measurements were performed partly in the Laboratory of environmental
geochemistry of Faculty of Geotechnical Engineering – University of Zagreb (Biograd springs
and the Gacka River springs) and Hydrogeochemical laboratory of Croatian Geological
Survey (Gacka River springs) by techniques and methods common in hydrogeochemical
studies: by titrimetric method were determined alkalinity, chloride, calcium and magnesium
concentrations (HACH titration unit). Sulphate, nitrate, nitrite, ammonia and orthophospate
concentrations were measured partly by ion chromatography (LabAlliace) and partly by
spectrophotometer using appropriate colorimetric methods (HACH) while sodium and
potassium were determined using atomic absorption technique (Perkin Elmer 800) (ASTM,
2006).
3.
RESULTS
3.1. Gacka River springs
3.1.1. Hydrochemical results
The results of physico-chemical measurements for 3 main springs of Gacka River (Majerovo
vrelo, Tonkovića vrelo and Pećina) are presented in Figures 6 – 16. All results are presented
in relation with sampling date to show the seasonal variation of measured values. The
numerical data for all measured values are presented in the Appendix 1, Tables 2 and 3.
Majerovo vrelo
Tonkovića vrelo
Pećina
11,0
10,5
7,5
10,0
0
Temperature ( C)
Majerovo vrelo
Tonkovića vrelo
Pećina
7,6
9,5
pH
7,4
9,0
7,3
8,5
7,2
8,0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2005
Month
2006
Fig. 6. Temperature of spring waters of
Gacka River.
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
7,1
7,5
2005
Month
2006
Fig. 7. pH values of spring waters of
Gacka River
Temperature of spring waters (Fig. 6) with mean values of 9.1°C (variation 8.7-10.4°C) for
Majerovo vrelo, 9.7°C (9.4-10°C) for Tonkovića vrelo and 9.1°C (7.5-10°C) for Pećina reflect
the temperature of continental climate in this area. Slight seasonal fluctuation is observed in
Majerovo vrelo and Pećina while Tonkovića vrelo has very stable temperature during the
year.
Usually, groundwater temperature of a region is similar to average annual air temperature of
predominant recharge area. Due to specific hydrodynamic regimes of karst springs, observed
fluctuations of spring water temperature reflect the aquifer with dominant channel and large
fracture discharge where each seasonal contribution of infiltrated water could be noticed
(Pećina and Majerovo vrelo). Seasonal fluctuation of temperature is higher on Pećina spring
10
because of artificial barriers built many years ago for fish breeding. It partly retard discharge
from the spring and cause spring water warming during the summer and cooling during winter
time.
Different conditions were observed on Tonkovića vrelo which has the largest catchment
comparing with others. Abundant dolomite content in composition of aquifer create
conditions suitable for better homogenization of new infiltrated water (precipitation, fast flow
component) with existed groundwater (base flow) and larger retention capabilities.
pH values (Fig. 7) vary between 7.1 and 7.6 for all springs without seasonal fluctuation.
These values are typical for the karst springs.
Fig. 8. Conductivity of spring waters of
Gacka River.
Jan
Dec
Oct
Nov
Sep
Jul
Aug
Apr
Jun
Mar
Jan
Feb
Oct
May
2005
Dec
2006
Month
Sep
2005
Feb
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
450
Nov
460
Jul
470
Aug
-
480
Apr
490
Jun
500
Mar
510
HCO3 (mg/l)
Conductivity (S/cm)
520
Majerovo vrelo
Tonkovića vrelo
Pećina
335
330
325
320
315
310
305
300
295
290
285
280
275
270
265
260
May
Majerovo vrelo
Tonkovića vrelo
Pećina
530
2006
Month
Fig. 9. Alkalinity of spring waters of
Gacka River
106
104
102
100
98
96
94
92
90
88
86
84
82
80
78
76
Majerovo vrelo
Tonkovića vrelo
Pećina
14
12
8
2+
Mg (mg/l)
10
Majerovo vrelo
Tonkovića vrelo
Pećina
6
4
Month
2006
Fig. 10. Concentration of calcium in
spring waters of Gacka River.
Month
Jan
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Dec
Oct
Nov
2005
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Dec
Oct
Sep
Nov
Jul
Aug
Apr
Jun
Mar
May
Jan
Feb
Oct
Dec
Nov
2005
Sep
Jul
Jun
Aug
Apr
May
Mar
2
Feb
2+
Ca (mg/l)
The conductivity of spring waters (Fig. 8) is slightly different for different springs: mean
value for Majerovo vrelo is 461 μS/cm, for Tonkovića vrelo 500 μS/cm and for Pećina spring
482 μS/cm, indicating higher concentration of total dissolved salt in Tonkovića vrelo with
higher concentration in winter time. Concentrations of bicarbonates in all springs (Fig. 9) are
similar for all springs, in the range 265 – 330 mg/l HCO 3 that is typical for karst water. No
seasonal fluctuation was observed.
2006
Fig. 11. Concentration of magnesium in
spring waters of Gacka River
Concentrations of calcium (Fig. 10) and magnesium (Fig. 11) do not show any seasonal
fluctuation in all springs and their concentrations are typical for the karst hydrogeochemical
environment. The molar ratios nCa/nMg will be discussed later.
11
Month
2006
Fig. 12. Concentration of sodium in
spring waters of Gacka River.
Jan
Oct
Dec
Nov
Sep
Jul
Aug
Jun
Apr
Mar
Month
May
Jan
Feb
Oct
Dec
2005
Nov
Feb
Jan
Oct
Dec
Nov
Sep
Jul
Aug
Jun
Apr
Mar
May
Jan
Feb
Dec
Oct
Nov
Jul
2005
Sep
Aug
Jun
Apr
May
Mar
Feb
1,0
Jul
1,5
Sep
2,0
Aug
+
2,5
Jun
3,0
Majerovo vrelo
Tonkovića vrelo
Pećina
Apr
3,5
K (mg/l)
+
Na (mg/l)
4,0
2,0
1,9
1,8
1,7
1,6
1,5
1,4
1,3
1,2
1,1
1,0
0,9
0,8
0,7
0,6
0,5
0,4
May
Majerovo vrelo
Tonkovića vrelo
Pećina
4,5
Mar
5,0
2006
Fig. 13. Concentration of potassium in
spring waters of Gacka River
Majerovo vrelo
Tonkovića vrelo
Pećina
6,5
6,0
5,5
5,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
0,0
Majerovo vrelo
Tonkovića vrelo
Pećina
18
16
2-
SO4 (mg/l)
14
12
10
8
6
4
2
2005
Month
2006
Fig. 14. Concentration of chloride in
spring waters of Gacka River.
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
-
Cl (mg/l)
Concentration of sodium (Fig. 12) and potassium (Fig. 13) is low for all springs, without
seasonal fluctuation. The lowest concentrations for Majerovo vrelo spring and the highest
concentrations for Tonkovića vrelo spring are in good correlation with the lowest and highest
conductivity for the same springs.
2005
Month
2006
Fig. 15. Concentration of sulphate in
spring waters of Gacka River
The concentration of chloride (Fig. 14) is low for all springs (0.5 – 5.5 mg/l). Slight increase
in winter time could be caused by the use of salt on highways. Concentration of sulphate
(Fig. 15) is slightly higher in Tonkovića vrelo spring and very uniform and low in two other
springs. The sulphate in karst can originate from the gypsum of anhydrite minerals ussually
present in carbonate rocks.
12
Majerovo vrelo
Tonkovića vrelo
Pećina
1,75
1,50
1,00
0,75
-
NO3 / N (mg/l)
1,25
0,50
0,25
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
0,00
2005
Month
2006
Fig. 16. Concentration of nitrate in
spring waters of Gacka River.
The concentration of nitrate in all springs (Fig. 16) is low, between 0.25 – 1.5 NO3/N mg/l
indicating non influence of contaminated waste waters. No seasonal fluctuation is observed.
The concentrations of ammonium and phosphate in all springs (not presented in graphs) are
mainly <0.01 mg/l NH3/N and <0.01 mg/l PO43-/P, respectively.
3.1.2. Isotopic results
3.1.2.1. Tritium
Precipitation
Majerovo vrelo
Tonkovića vrelo
Pećina
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Precipitation
Majerovo vrelo
Tonkovića vrelo
Pećina
Marusino vrelo
Knjapovac
Begovica
Jaz
KLanac
16
14
12
3
H (T. U.)
10
8
6
4
2
Fig. 17. Tritium activity in three main
springs and in precipitation in Gacka
River spring area.
2005
Month
Jan
Feb
Dec
Oct
Nov
Jul
Sep
Aug
Apr
Jun
May
Jan
Mar
Feb
Dec
Oct
Sep
Nov
Jul
Apr
Jun
Aug
2006
May
Month
Mar
2005
Feb
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
3
H (T. U.)
The results of 3H activity of water in three main springs and in precipitation in Gacka River
area are presented in Fig. 17. The 3H results for all other springs in this area are presented in
Fig. 18. The numerical data for all measured values are presented in the Appendix 1, Tables 4
and 9.
2006
Fig. 18. Tritium activity in all springs
and precipitation in Gacka River spring
area.
The seasonal distribution of 3H in the precipitation in the Gacka River region is well
correlated with that in Zagreb (linear correlation coefficient r = 0.9) for the same period since
both stations are continental ones (see Fig. 46 in Discussion). The mean 3H activity in
precipitation for the Gacka River area is (6.5 ± 3.9) T.U., with a maximum of 13.6 T.U. in
13
June 2006. All three main springs in the Gacka River recharge area show similar mean 3H
concentrations as that in precipitation: Majerovo vrelo (6.6 ± 2.1) T.U., max 9.7 T.U.;
Tonkovića vrelo (6.5 ± 2.1) T.U., max 10.1 T.U.; Pećina (5.9 ± 2.2) T.U., max 9.2 T.U. This
indicates a short mean residence time and good mixing of infiltrated and ground water.
3.1.2.2. Stable isotopes H and 18O
The results of H and 18O for water in three main springs of Gacka River and for
precipitation collected in this area are presented in Fig. 19. The numerical data for all
measured values are presented in the Appendix 1, Tables 4 and 9.
-40
-45
-50
2
 H (‰)
-55
-60
Majerovo vrelo
Tonkovića vrelo
Pećina
Precipitation Gacka
LMWL
-65
-70
-75
-80
-12
-11
-10
-9
-8
-7
18
 O (‰)
Fig. 19. Correlation between H and 18O values for three main springs of
Gacka River. LMWL is related to the stable isotope composition of precipitation
collected in the Gacka River spring area.
H and 18O values of all three springs are close to the local meteoric water line (LMWL)
based on stable isotope composition of precipitation collected during 2005-2006 in the raingauge close to spring Tonkovića vrelo. Different concentrations of stable isotopes, with
highest concentration for Pećina spring and lowest for Majerovo vrelo are observed. Mean
values for H and 18O are the following: Majerovo vrelo: (-68.1 ± 0.5)‰ and (-10.11 ±
0.04)‰; Tonkovića vrelo: (-62.1 ± 0.5)‰ and (-9.51 ± 0.03)‰; Pećina: (-59.2 ± 0.3)‰ and
(-9.15 ± 0.03)‰. Mean values for precipitation collected in this area are (-58.1 ± 4.6)‰ and
(-8.74 ± 0.66) ‰ for H and 18O, respectively. Calculated LMWL is 2H = (6.84 ± 0.43)
18O + (1.7 ± 3.8) (R = 0.985, N = 10, P <0.0001).
3.1.2.3. 13C of dissolved inorganic carbon (DIC)
13C values of DIC for water in three main springs of Gacka River are presented in Fig. 20
and for all other springs in this area in Fig. 21. The numerical data for all measured values are
presented in the Appendix 1, Table 4.
-11,5
-12,0
-12,0
-12,5
-12,5
-13,0
-13,0
 C (‰)
-11,5
-13,5
-14,5
-14,0
-14,5
Majerovo vrelo
Tonkovića vrelo
Pećina
-15,0
-15,5
Majerovo vrelo
Tonkovića vrelo
Pećina
Klanac
Marusino vrelo
Knjapovac
Begovica
Krbavica
Crno
Živulja
Hajdukovac
Trnovac
-13,5
13
-14,0
13
-15,0
-15,5
-16,0
2006
Month
2005
Fig. 20. 13C of DIC for three main
springs of Gacka River
Jan
Oct
Dec
Nov
Jul
Sep
Jun
Aug
Apr
Mar
May
Jan
Feb
Dec
Oct
Sep
Nov
Jul
Jun
Aug
Apr
Mar
Feb
Jan
Oct
Dec
Sep
Nov
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
2005
Nov
Sep
Jul
Aug
Jun
Apr
May
Mar
Feb
-16,0
May
 C (‰)
14
2006
Month
Fig. 21. 13C of DIC for all springs of
Gacka River area.
13C values for three main springs are in the range -14.5 to -12.0‰ and are mostly in the same
range for all other springs. These values are typical for the Dinaric karst water, e.g. Plitvice
Lakes, Korana River [5]. The seasonal fluctuation of 13C for three main springs with
minimum values in winter is observed.
3.1.3. CFC analyses
Samples for CFC measurement were collected only once, in June 2006. Preliminary results of
CFC measurements (CFC-11, CFC-12, CFC-113, see Appendix 1, Table 4) indicate that
groundwaters from the Gacka river catchment are composed mostly of young water with
small fraction of old groundwater.
3.2. Vransko Polje springs
3.2.1. Hydrochemical results
Turanjsko jezero
Kakma
Biba
16,6
16,4
16,2
16,0
15,8
15,6
15,4
15,2
15,0
14,8
14,6
14,4
14,2
14,0
Turanjsko jezero
Kakma
Biba
7,3
pH
7,2
7,1
Fig. 22. Temperature of spring waters
in Vransko Polje.
2005
Month
Jul
Aug
Jun
May
Apr
Mar
Feb
Jan
Dec
Oct
Nov
Sep
Aug
Jul
Jun
May
Apr
2006
Mar
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Dec
Oct
Sep
Jul
Aug
Nov
Month
6,9
Feb
2005
Jun
May
Apr
Mar
Jan
7,0
Feb
0
Temperature ( C)
The results of physico-chemical measurements for 3 main springs in Vransko Polje
(Turanjsko jezero, Kakma and Biba) are presented in Figures 22 – 34. All results are
presented in relation with sampling date to show the seasonal fluctuation/variation of
measured values. The numerical data of all measured values are presented in the Appendix 1,
Tables 5 and 6.
2006
Fig. 23. pH values of spring waters in
Vransko Polje
15
Temperature of spring waters (Fig. 22) with mean values of 15.2°C (variation 14.2-16.4°C)
for Turanjsko jezero spring, 14.8°C (14.5-15.2°C) for Kakma and 14.9°C (15.5-15.8°C) for
Biba reflect the Mediterranean warmer climate in this area (temperature are significantly
higher than for the Gacka River springs). Seasonal fluctuation is observed in Turanjsko jezero
and Biba, and in Kakma it is less expressed.
pH values (Fig. 23) vary between 6.9 and 7.3 for all springs, with lower values for Turanjsko
jezero. No seasonal fluctuation is observed. The values are lower than in Gacka River springs
(see Fig. 7).
Turanjsko jezero
Kakma
Biba
480
460
440
750
HCO3 (mg/l)
700
-
Conductivity (S/cm)
500
Turanjsko jezero
Kakma
Biba
800
650
420
400
380
360
340
320
600
300
Fig. 24. Conductivity of spring waters
in Vransko Polje.
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Sep
Jul
Aug
Jun
Apr
2005
2006
Month
May
Mar
Feb
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
2005
Nov
Sep
Jul
Aug
Jun
Apr
May
Mar
Feb
280
2006
Month
Fig. 25. Alkalinity of spring waters in
Vransko Polje.
The mean values of conductivity of spring waters (Fig. 24) is similar for Turanjsko jezero
(726 μS/cm) and Kakma (720 μS/cm) and lower for Biba (628 μS/cm). No systematic
seasonal variation is observed although high variation of conductivity in Kakma and Biba is
observed. Concentrations of bicarbonates in all springs (Fig. 25) are in the range 300 – 480
mg/l HCO 3 without seasonal fluctuation. Values, conductivity and alkalinity for all springs
are much higher than for the Gacka River springs.
2005
Month
2006
Fig. 26. Concentration of calcium in
spring waters in Vransko Polje.
2005
Month
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
80
Apr
100
Turanjsko jezero
Kakma
Biba
Mar
2+
Mg (mg/l)
120
2+
Ca (mg/l)
140
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
6
4
Feb
Turanjsko jezero
Kakma
Biba
160
2006
Fig. 27. Concentration of magnesium in
spring waters in Vransko Polje.
Concentrations of calcium (Fig. 26) and magnesium (Fig. 27) do not show any seasonal
fluctuation in all springs and their concentrations are typical for the karst hydrogeochemical
environment. The molar ratios nCa/nMg will be discussed later.
16
3,5
12
Turanjsko jezero
Kakma
Biba
11
10
Turanjsko jezero
Kakma
Biba
3,0
2,5
K (mg/l)
8
7
2,0
1,5
+
1,0
6
0,5
5
Fig. 28. Concentration of sodium in
spring waters in Vransko Polje.
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Sep
Jul
Aug
2005
2006
Month
Jun
Apr
Feb
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Sep
Jul
Aug
Jun
Apr
May
Mar
Feb
2005
May
0,0
4
Mar
+
Na (mg/l)
9
2006
Month
Fig. 29. Concentration of potassium in
spring waters in Vransko Polje.
Concentrations of sodium (Fig. 28) and potassium (Fig. 29) are similar for all springs, without
seasonal fluctuation. Concentrations of both kations are higher comparing with Gacka River
springs (Figs. 12 and 13).
35
50
Turanjsko jezero
Kakma
Biba
30
40
35
SO4 (mg/l)
25
2-
20
-
Cl (mg/l)
Turanjsko jezero
Kakma
Biba
45
15
30
25
20
15
10
10
Aug
Jul
Jun
May
Apr
Mar
Feb
2005
Month
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Nov
Oct
Sep
Aug
Jul
Jun
May
Apr
Feb
Month
Jan
Dec
Nov
Oct
Sep
Aug
Jul
Jun
Apr
May
Mar
Feb
2005
Mar
5
5
2006
2006
Fig. 30. Concentration of chloride in
spring waters in Vransko Polje.
Fig. 31. Concentration of sulphate in
spring waters in Vransko Polje.
Concentrations of chloride (Fig. 30) as well as sulphate (Fig. 31) are much higher in spring
waters of the Vransko Polje area than in the Gacka River springs (Fig. 14 nad 15). Relatively
high concentration of chloride indicates the influence of sea water throughout the mixing
zone and of maritime precipitation. The seasonal fluctuation of chloride for all springs with
higher concentration in winter time is observed. It could be a consequence of soil zone
flushing after fertilization treatment that is stronger in winter time when precipitation is higher
(Fig. 5). Also, a strong flushing of sanitary waste disposal sites and surrounding soils in
settlements without sewegae and waste water treatment could be the reason of chloride
increasing inwinter time. The highest concentration of sulphate in Kakma spring with
pronounced seasonal fluctuation (higher in summer) is probably due to the influence of
sewage waters from settlements without sewage system.
17
0,2
PO4/P (mg/l)
0,3
NH3/N (mg/l)
Turanjsko jezero
Kakma
Biba
Turanjsko jezero
Kakma
Biba
0,4
0,2
0,1
0,1
0,0
2005
Fig. 32. Concentration of ammonia in
spring waters in Vransko Polje.
Month
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Sep
Jul
Aug
Jun
Apr
May
2006
Month
Mar
Jul
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Sep
Jul
Feb
2005
Aug
Jun
Apr
May
Mar
Feb
0,0
2006
Fig. 33. Concentration of phosphate in
spring waters in Vransko Polje.
Concentrations of ammonia (Fig. 32) and phosphate (Fig 33) are very low (close to detection
limit) in winter time, and higher in summer showing the influence of agriculture activity
and/or sewage waters in this area.
5,0
Turanjsko jezero
Kakma
Biba
4,5
-
NO3 / N (mg/l)
4,0
3,5
3,0
2,5
2,0
1,5
1,0
0,5
2005
Month
Aug
Jul
Jun
May
Apr
Mar
Feb
Jan
Dec
Oct
Nov
Sep
Aug
Jul
Jun
May
Apr
Mar
Feb
0,0
2006
Fig. 34. Concentration of nitrate in
spring waters in Vransko Polje.
Higher concentrations of nitrate for Turanjsko jezero and Kakma (Fig. 34), particularly during
vegetation period, could be the consequence of using the fertilizers (Turanjsko jezero spring)
and sewage water from settlements (Kakma spring).
3.2.2. Isotopic results
3.2.2.1. Tritium
The results of 3H activity of water in three main springs and in precipitation in Vransko Polje
area are presented in Fig. 35. The 3H results for all other springs in this area are presented in
Fig. 36. The numerical data of all measured values are presented in the Appendix 1, Tables 8
and 10.
18
13
12
11
Precipitation
Turanjsko jezero
Biba
Kakma
Precipitation
Turanjsko jezero
Biba
Kakma
Kotarka
Vransko jezero
Selakovo
Begovača drill hole, 40 m deep
Begovača drill hole, 20 m deep
18
16
10
14
9
12
3
A (T. U.)
H (T. U.)
8
7
6
5
10
8
6
4
4
3
2
2
1
0
2005
Fig. 35. Tritium activity in three main
springs and in precipitation in Vransko
Polje.
Month
Dec
Oct
Nov
Jul
Sep
Aug
Jun
Apr
May
Mar
Jan
Feb
Dec
Oct
Nov
Jul
Sep
Aug
Jun
Apr
May
2005
2006
Month
Mar
Feb
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
0
2006
Fig. 36. Tritium activity in all springs
and precipitation in Vransko Polje
Mean 3H activity in precipitation for the Vransko Polje area is (6.8 ± 2.5) TU. Mean and
maximum values of 3H activity for springs of Vransko Polje recharge area are as follows:
Turanjsko jezero (3.7 ± 1.7) T.U., max 7.6 T.U.; Biba (4.9 ± 1.8) T.U., max 8.4 T.U; Kakma
(4.6 ± 1.8) T.U., max 6.9 T.U. Lower 3H activity in springs than in precipitation could
indicate recharge preferentially by winter precipitation, but also the influence of sea water
infiltration.
3.2.2.2. Stable isotopes H and 18O
The results of H and 18O for water in three main springs in Vransko Polje and for monthly
precipitation collected in this area are presented in Fig. 37. The numerical data for all
measured values is presented in the Appendix 1, Tables 8 and 10.
-20
-40
2
 H (‰)
-30
Turanjsko jezero
Kakma
Biba
Precipitation Biograd
LMWL
-50
-60
-9
-8
-7
-6
-5
-4
-3
18
 O (‰)
Fig. 37. Correlation between H and 18O values for three mains springs in
Vransko Polje area. LMWL is related to the stable isotope composition of
precipitation collected in Vransko Polje.
H and 18O values of all three springs are close to the local meteoric water line (LMWL)
based on stable isotope composition of precipitation collected during 2005-2006 in rain-gauge
close to spring Kakma. Slight difference in H and 18O values for different springs is
19
observed. Mean values for H and 18O are the following: Turanjsko jezero: (-33.1 ± 0.4)‰
and (-5.74 ± 0.02)‰; Kakma: (-35.3 ± 0.4)‰ and (-5.90 ± 0.05)‰; Biba: (-37.6 ± 0.4)‰ and
(-6.33 ± 0.04)‰. Mean values for precipitation collected in this area are (-40.3 ± 3.6)‰ and (6.5 ± 0.5) ‰ for H and 18O, respectively. Calculated LMWL is 2H = (6.94 ± 0.63) 18O +
(4.8 ± 4.2), (R = 0.97, N = 10, P <0.0001).
3.2.2.3. 13C of DIC
13C values of DIC for water in three main springs in Vransko Polje are presented in Fig. 38
and for all other springs in this area in Fig. 39. The numerical data for all measured values are
presented in the Appendix 1, Tables 8.
13C values for three main springs are in the range -14.0 to -11.5‰ and are mostly in the same
range for all other springs. These values are typical for the Dinaric karst water and similar
13C values are in spring waters of Gacka River (Fig. 20 and 21). The exception is sample
taken from Begovača monitoring bore hole from depth of 40 m, deeply situated in the mixing
zone with sea water.
-11,5
-7,0
Turanjsko jezero
Kakma
Biba
-12,0
-7,5
-8,5
-9,0
-9,5
 C (‰)
-12,5
13
-13,0
13
 C (‰)
Turanjsko jezero
Kakma
Biba
Kotarka
Begovača, drill hole 40m deep
Begovača, drill hole 20m deep
-8,0
-10,0
-10,5
-11,0
-11,5
-12,0
-13,5
-12,5
-13,0
-13,5
-14,0
-14,0
Month
Jan
Oct
Dec
Nov
Jul
Sep
Aug
Apr
Jun
Mar
May
Jan
Feb
Dec
Oct
Sep
Nov
Jul
Jun
Aug
Apr
May
Mar
Feb
2005
2006
Fig. 38. 13C of DIC for three main
springs in Vransko Polje
Month
Jan
Oct
Dec
Sep
Nov
Jul
Aug
Apr
Jun
May
Jan
Mar
Feb
Oct
Dec
Nov
Jul
Sep
Jun
2005
Aug
Apr
Mar
May
Feb
-14,5
-14,5
2006
Fig. 39. 13C of DIC for all springs in
Vransko Polje.
3.2.3. CFC analyses
Samples for CFC measurement were collected two times, in May 2005 and June 2006.
Preliminary results from the Vransko Polje catchment (Appendix 1, Table 8) show the best fit
to piston flow model and obtained age of 18 years for Turanjsko jezero, 10 years for Kakma
and 25 years for spring Biba. For Biba and Kakma turnover time obtained by exponential
model and CFCs input data is in agreement with tritium content, but on Turanjsko jezero there
is not agreement with calculated tritium activity. Using binary mixing model 25% of old
water (CFC and tritium free water) with 75% of modern water is possible.
4.
DISCUSSION
Geochemical affinities of measured hydrochemical parameters were identified using cluster
analysis as a very useful multivariate pattern recognition technique [6, 7]. In this study Rmode hierarchical cluster analysis was performed. It groups different hydrochemical
parameters in clusters according to their similarities, similar geochemical source or behavior
(affinity). There are few different methods for calculating the similarities between
20
geochemical parameters and clusters which could exist in some geochemical systems. In our
case the relative similarities between the parameters were quantified using the Pearson
distance and Ward’s method for combining clusters. The results are usually presented as a
dendrogram of affinity or similarity.
Taking into account as input variables selected hydrochemical data from main springs of the
Gacka River catchment (Tonkovića vrelo, Majerovo vrelo and Pećina) and Vransko polje
springs (Turanjsko jezero, Kakma and Biba) and software package STATISTICA [7] we
obtained two different dendrograms of geochemical similarities for both study areas.
On the dendrogram of Gacka River springs (Fig. 40) two main clusters are distinguished,
lithogeochemical cluster of variables where ions mainly originated as a result of prevailing
rock mineral composition weathering (limestone and dolomites) and the geochemical cluster
which is composed of substances seepages from the soil zone reflecting the decomposed
organic part of soil composition (nitrogen forms, phosphates, sulfates, sodium and chlorides).
Within the geochemical cluster, two subgroups were formed due to present ionic form and
reactivity in well aerated karst ground water hydrogeochemical environment: reactive
components and non-reactive components (ions). Sodium, ammonia and orthophosphates
could in our case submit in different transformation (oxidation-NH3) or alteration processes
(adsorption-Na, SO42-) or can be incorporated in solid substances (precipitation-Na, SO42-,
PO43-). Chloride and nitrate ions are in aerated karst water media very stable and mobile with
negligible chance for involving in chemical or biochemical reactions which can influence its
pathway throughout the underground to discharge point.
Gacka springs
EC
Mg
Ca
HCO3
lithogeochemical cluster
-
K
Na
SO4
2-
reactive components
NH3 _N
3-
geochemical cluster
PO4 _P
Cl
-
non-reactive components
-
NO3 _N
0,0
0,5
1,0
1,5
2,0
Linkage Distance
Fig. 40. Dendrogram of geochemical similarities of hydrochemical parameters of the Gacka
River catchment
The same procedure was applied with geochemical parameters determined on main spring of
the Vransko Polje (Fig. 41). Because of few simultaneous impacts on groundwater
21
composition of natural and anthropogenic origin, obtained clusters linked together variables
of both sources. Lithogeochemical cluster contain main ions of carbonate rocks which made
aquifer but also an anthropogenically produced sulphate and nitrate ions (waste water from
settlements, fertilizers). Other cluster is composed of two subgroups, where magnesium,
chlorides and potassium indicate strongly common affinity due to their origin from two
sources: influence of sea nearness (sea aerosols) and mineral fertilizer application. In study of
coastal drainage area sodium, orthophosphates and ammonia linked together due to their
possible geochemical and biochemical reactivity.
Vransko polje springs
EC
Ca
HCO3
lithology
-
lithogeochemical cluster
2-
SO4 _
anthropogenic cluster
-
NO3 _N
Mg
Cl
-
sea influence and fertilizers impact
K
geochemical cluster
Na
anthrophogenic cluster
3-
PO4 _P
NH3 _N
0,0
0,2
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
Linkage Distance
Fig. 41. Dendrogram of geochemical similarities of hydrochemical parameters of the Vransko
polje springs.
The molar ratios of nCa/nMg are in the similar range for both areas (Fig. 42 and 43) typical
for the karst hydrogeochemical environment. The lower values of nCa/nMg for Majerovo
vrelo and Tonkovića vrelo springs (Fig 42) point to limestone with dolomite aquifers while
the recharge area of Pećina spring (higher nCa/nMg) is mainly built of limestone. In Vransko
Polje (Fig. 43) the lowest values of nCa/nMg are for Biba spring indicating the presence of
dolomites in the recharge area, while for Kakma and Turanjsko jezero springs the higher
influence of limestone is observed. The high fluctuation of nCa/nMg in Turanjsko jezero
spring can be the consequence of the calcium input from other sources, e.g. leaching from
carbonate fraction of flysch or from mineral fertilizers.
22
Majerovo vrelo
Tonkovića vrelo
Pećina
20
18
14
14
2+
12
12
n Ca /n Mg
10
10
8
2+
6
2005
Fig. 42. Molar ratio of calcium and
magnesium in spring waters of Gacka
River.
Month
Jul
Aug
Apr
Jun
Mar
May
Jan
Feb
Dec
Oct
Nov
Sep
2006
Month
Jul
Feb
2005
Aug
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
2
2
Jun
4
4
Apr
6
Mar
8
May
2+
n Ca / n Mg
2+
16
Turanjsko jezero
Kakma
Biba
16
2006
Fig. 43. Molar ratio of calcium and
magnesium in spring waters of Vransko
Polje area.
-20
-30
2
 H (‰)
-40
Majerovo
Tonkovica
Pecina
Precipitation Gacka
LMWL Gacka
Turanjsko jezero
Kakma
Biba
Precipitation Biograd
LMWL Biograd
-50
-60
-70
-80
-90
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
18
 O (‰)
Fig. 44. Correlation of H and 18O for main springs in both areas, Gacka
River and Vransko Polje (Biograd).
Comparison of stable isotope composition of spring waters from Gacka River and Vransko
Polje chatcment areas as well as composition of precipitation collected in both areas (Fig. 44)
shows the following:
- The Local Meteoric Water Line (LMWL) for Gacka River area is H = (6.9 ± 0.4)
18O + (1.7 ± 3.8) (N=10, R=0.985, P<0.0001) and for Vransko Polje area H = (6.9
± 0.6) 18O + (4.8 ± 4.2) (N = 10, R = 0.97, P<0.0001). The slope for both LMWLs
are equel and close to the slopes for two other continental stations Zagreb (LMWL is
H = (7.5 ± 0.2) 18O + (0.9 ± 1.9)) and Plitvice (LMWL is H = 7.97 ± 0.2) + (14.3
± 1.6)) showing no evaporation effect (Fig. 45). Slightly higher concentrations of H
and 18O for precipitation for Vransko Polje (Biograd) area than for Gacka River are
the consequence of different climate, Mediterranean and continental, respectively.
- Stable isotope compositions for the springs in both areas are close to the LMWL for
each area (Figs. 19, 37 and 44) but with significantly different concentrations of H
and 18O. The higher concentrations of springs in Vransko Polje than in Gacka River
area is due to the different climate. Moreover, in each catchment area the stable
isotope composition of each spring is well distinguished showing different recharge
23
conditions. This difference is result of altitude effect for springs in Gacka River area
and the influence of distance from the coast for Vransko Polje area.
Interesting results have been obtained by measurements of 13CDIC values. The seasonal
fluctuation of 13CDIC for three main springs of Gacka River with minimum values in winter is
observed (Fig. 20). Lower 13CDIC values for all three springs in winter time indicate higher
influence of organic carbon fraction, e.g. more intensive process of humus dissolution that is
due to strong vegetation and/or root respiration in autumn. Additionally, the higher discharge
of the springs as well as higher precipitation amount in winter could accelerate the process of
organic carbon dissolution. This seasonal fluctuation of 13CDIC indicates fairly fast
circulation of surface and precipitation water.
13CDIC values of springs of Vransko polje area (Figs. 38 and 39) also show some fluctuations
but not the seasonal ones. The 13CDIC values are generally more positive than for Gacka
springs indicating the influence of sea water infiltration. This is particularly observed in the
Begovača monitoring bore hole from depth of 40 m, deeply situated in the mixing zone with
seawater.
0
-10
2005 - 2006
-20
-30
Majerovo
Tonkovica
Pecina
Precipitation Gacka
Turanjsko jezero
Kakma
Biba
Precipitation Biograd
Gacka
Biograd
precipitation Plitvice
precipitation Zagreb
Plitvice
Zagreb
-50
-60
2
 H (‰)
-40
-70
-80
-90
-100
-110
-15
-14
-13
-12
-11
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0
18
 O (‰)
Fig. 45. Comparison of LMWL for Gacka River, Vransko Polje (Biograd),
Zagreb and Plitvice.
The seasonal distribution of 3H in the precipitation in the Gacka River region is well
correlated with that in Zagreb (linear correlation coefficient r = 0.9) for the same period since
both stations are continental ones (Fig. 46). The correlation is poor between the precipitation
in Zagreb and the Vransko Polje area (r = 0.4) where Mediterranean climate prevails.
24
2.4
20.0
1.8
1.6
A (Bq/L)
18.3
Zagreb-Grič
Plitvice
Vransko j.
Gacka
2.0
16.7
15.0
13.3
1.4
11.7
1.2
10.0
1.0
8.3
0.8
6.7
0.6
5.0
0.4
3.3
0.2
0.0
1.7
LOD
J
F
M
A
M
J
J
A
S
A (T.U.)
2.2
O
N
D
J
F
M
A
2005
M
J
J
A
S
O
N
D
0.0
2006
month/year
Fig. 46. Comparison of tritium activity in Zagreb and Plitvice precipitation
(continental stations) with precipitation in Gacka River and Vransko Polje
area.
Spring waters from both areas show smaller seasonal fluctuations (Figs. 17 and 35) and also
lower maximum 3H activities than the corresponding precipitation. All three main springs in
the Gacka River recharge area show similar mean 3H concentrations as that in precipitation
(Fig. 17) which indicates a short mean residence time and good mixing of infiltrated and
ground water. Lower 3H activity of springs in Vransko Polje recharge area than that of
precipitation could indicate recharge preferentially by winter precipitation, but also the
influence of sea water infiltration.
5.
CONCLUSION
The results of hydrogeological investigations using geochemical and isotopic measurements
in the main springs of the two areas, Gacka River (continental area) and Vransko Polje
(coastal area) showed the following:
The mean 3H activity in all main springs in the Gacka River area is similar to that of
precipitation, while in the springs of Vransko Polje the mean 3H activity is lower if compared
with precipitation due to sea water infiltration and/or recharge preferentially by winter
precipitation. There is no seasonal fluctuation of 3H activity in all springs indicating fast
circulation and good mixing of precipitation and ground waters. The results of the 3H and
CFC measurements are not completely in agreement regarding MRT determination and
additional measurements of CFC and 3H at the spring waters will be performed during 2007.
Correlation between H and 18O in both areas showed the values close to the LMWL but
with distinguish differences with lower values for Gacka river springs (higher altitude,
continental climate) and higher for Vransko Polje springs (Mediterranean climate, low
altitude).
Also the stable isotope data show only weak seasonal variations, again indicating a fairly
short mean residence time and good ground water homogenization. The 18O values allow to
deriving the catchment altitudes of the three springs. Stable as well as radioactive isotope data
indicate that both areas are very sensitive to any kind of pollution and the response to the
pollution will be very fast.
25
The chemical composition of spring waters from the Gacka River recharge area shows low
concentration of total dissolved salts. Low concentrations of nitrates, ammonium and
phosphates indicate non-polluted ground waters in this area.
Hydrochemical composition of spring waters in the Vransko Polje recharge area shows
seasonal vegetation and hydrological variations (Cl-, SO42-, NO3-) closely related with the sea
water influence and anthropogenic activities. The sewage waters from settlements and
agriculture activity affect the quality of spring waters mainly after a dry season when the
precipitation washes out soil and the unsaturated zone of karst aquifers.
The results of this project will be used in definition of protection measures for the water
supply for the recharge areas of Gacka River and Vransko polje springs and establishment of
close cooperation between hydrogeolgists from Hrvatske vode, Environmental Geochemical
Laboratory and institutions that perform the isotope analyses such as Rudjer Bošković
Institute, Zagreb and Stable Isotope Laboratory, Rijeka.
ACKNOWLEDGEMENTS
This study was financially supported by the IAEA Technical Cooperation project CRO/8/006
and by the Project 098-0982709-2741, 062-0982709-0510 and 160-0982709-1709 by the
Ministry of Science Education and Sport, Republic of Croatia. We greatly appreciate the
assistence of Dr. M. Gröning from the IAEA Isotope Hydrology Laboratory and Dr. M.
Ferrari and Dr. T. Kurttas from the IAEA Isotope Hydrology Section.
REFERENCES
[1] PAVIČIĆ, A., KAPELJ, S., LUKAČ, J., The influence of the Highway on the protected
spring of the Gacka River. 1st International Conference on Groundwater in Geological
Engineering. RMZ- Materials and Geoenvironment 50, 1 (2003) 289-292.
[2] KAPELJ, J., KAPELJ, S., BIONDIĆ B. Spatial variations of the fresh-salt water interface of
a Croatian coastal aquifer in the town of Biograd area. 24th Hydrology and Water Resources
Symposium - 1997, Auckland, New Zeland, extended abstract (1997)
[3] MARKOVIĆ, T., MIKO, S., KAPELJ, S.,BULJAN, R., LARVA, O., PEH, Z., Behaviour
of metals and nutrients in soils and groundwater of karst polje, J. Geochemical Exploration,
87 (2005).
[4] HORVATINČIĆ N. Radiocarbon and tritium measurements in water samples and
application of isotopic analyses in hydrology. Fizika 12 (S2) (1980) 201-218
[5] HORVATINČIĆ N., KRAJCAR BRONIĆ I., OBELIC B., Differences in the 14C age, 13C
and 18O of Holocene tufa and speleothem in the Dinaric Karst. Palaeogeography,
Palaeoclimatology, Palaeoecology, 193 (2003) 139-157
[6] DAVIS, J.C. ): Statistics and data analysis in geology. II ed. John Wiley & Sons, New York,
(1986) 646 p
[7] StatSoft, Inc. Statistica for Windows, Statistics 2., StatSoft, Inc. Tulsa (1995)
26
PARTICIPANTS ON THE PROJECT
Counterpart Institution
Participants
Rudjer Bošković Institute, Zagreb
Dr. Nada Horvatinčić
Dr. Bogomil Obelić
Dr. Ines Krajcar Bronić
Jadranka Barešić, M.Sc.
Andreja Sironić, B.Sc.
Medicine Faculty, Rijeka
Dr. Zvjezdana Roller-Lutz
Magda Mandić, B.Sc
Dijana Bojić, B.Sc
Geotechnical Faculty, Varaždin
Dr. Sanja Kapelj
Institute of Geology, Zagreb
Dr. Tamara Marković
External experts
Dr. Janislav Kapelj
Dr. Hans Lutz
The results of the Project CRO/8/006 have been presented at the following conferences:
Horvatinčić, N., Kapelj, S., Sironić, A., Marković, T. Geochemical and isotopic investigations
of groundwater in the karst area of Croatia, XX. Croatian Meeting of Chemists and Chemical
Engineers, Book of abstract, Zagreb, 2007. p.120
Horvatinčić, N., Kapelj, S., Sironić, A., Krajcar Bronić, I., Kapelj, J., Marković, T.
Investigation of water resources and water protection in the karst area of Croatia using
isotopic and geochemical analyses, Inter. Symposium on Advances in Isotope Hydrology and
its Role in Sustainable Water Resources Management (IHS 2007), Book of Abstracts IAEACN-151.Vienna, Austria: IAEA, 2007. p.47
Roller-Lutz, Z., Mandić, M., Bojić, D., Lutz, H. O., Kapelj, S. Installation of a laboratory for
stable isotope analysis in Croatia, Inter. Symposium on Advances in Isotope Hydrology and
its Role in Sustainable Water Resources Management (IHS 2007), Book of Abstracts IAEACN-151.Vienna, Austria: IAEA, 2007. p.46
Bojić, D., Mandić, M., Roller-Lutz, Z., Lutz, H. O., Kapelj, S., Horvatinčić, N., Krajcar
Bronić, I., Sironić, A. Isotopic composition of spring waters from Croatian karst regions:
Gacka River area, Proceedings of the European Society for Isotope Research ESIR IX, In:
Studia Universitatis Babes-Bolyai, Geologia, vol. 52, Issue 1 / Tamas, Tudor (ur.).ClujNapoca : Cluj University Press, 2007. p.9