ACTA CARSOLOGICA 29/1 6 93-105 LJUBLJANA 2000 COBISS: 1.08 INVESTIGATION OF GROUNDWATER INFILTRATION TO SEAWATER IN PUNAT BAY, CROATIA, BY MEASUREMENTS OF CONDUCTIVITY AND STABLE ISOTOPES IN WATER RAZISKAVE ODTEKANJA PODTALNICE V MORJE V PUNATSKEM ZALIVU (HRVA©KA) S POMOČJO STABILNIH IZOTOPOV IN MERITEV PREVODNOSTI VODE N. HORVATINČIC1 & M. GROENING2 & N. MIKULIC3 & J. OBHODA©1 & V. VALKOVIC1 1 Ruder Boškovic Institute, Bijenička 54, 10000 ZAGREB, CROATIA 2 International Atomic Energy Agency, P.O.Box 100, A-1400 VIENNA, AUSTRIA 3 State Directorate for Protection of Nature and Environment, Vukovarska 78, ZAGREB, CROATIA Prejeto / received: 31. 1. 2000 Izvleček UDC: 556.14(497.5) 551.463(497.5) N. Horvatinčic & M. Groening & N. Mikulic, J. Obhodaš & V. Valkovic: Raziskave odtekanja podtalnice v morje v punatskem zalivu (hrvaška) s pomočjo stabilnih izotopov in meritev prevodnosti vode Mesta odtekanja sladke vode v Punatski zaliv so bila določena na osnovi prostorske porazdelitve prevodnosti in izotopske sestave vodika fH/H) in kisika (18O/16O) v morski vodi. Meritve so opravljali v treh obdobjih -poleti (25 vzorčevalnih mest), jeseni (12) in pozimi (20). Analizirali so tudi vzorce sladke vode iz sedmih izvirov in dveh akumulacij na otoku Krku. Koordinate vzorčevalnih mest so določene z GPS. In-situ so določali prevodnost, slanost, temperaturo in pH vzorcev. Povečan dotok sladke vode je bil zaznan poleti in pozimi na severni in vzhodni obali zaliva, jeseni pa le na severni obali. Izotopska sestava izvirov na Krku kaže na hitro kroženje podtalnice, predvsem v deževnem zimskem času. Ključne besede: onesnaženje morske vode, prevodnost, stabilni izotopi, Hrvatska, Krk, Punatski zaliv. Abstract UDC: 556.14(497.5) 551.463(497.5) N. Horvatinčic & M. Groening & N. Mikulic, J. Obhodaš & V. Valkovic: Investigation of groundwater infiltration to seawater in Punat Bay, Croatia, by measurements of conductivity and stable isotopes in water Locations of freshwater infiltration from the coast to the seawater of the Punat Bay were determined based upon the distribution of conductivity and hydrogen (2H/1H) and oxygen (18O/16O) stable isotope signatures of the seawater. Seawater samples in Punat Bay were measured and collected in three seasons: summer (25 sites), autumn (12 sites) and winter (20 sites). Freshwater samples from 7 springs and 2 accumulations on Krk Island were also collected. The position of each sampling site was determined by GPS. Conductivity, salinity, temperature and pH were measured in situ. Higher freshwater input was defined on the east and north coast of Punat Bay in the summer and winter seasons, and on the north coast in autumn. Stable isotope composition of freshwater from springs on Krk Island indicated fast circulation of groundwater, particularly in the wet winter season. Key words: seawater pollution, conductivity, stable isotopes, Croatia, Krk Island, Punat Bay. INTRODUCTION The coastal region of Croatia is a highly touristic area. The rocky terrain of the coastal area is mainly characterized by water-permeable karst carbonate. Because of this waste management re-presents a very complex problem that needs to be properly managed in order to minimize negative effects on the environment. The potential sources of pollution in Punat Bay, Krk Island, Adriatic Sea, include the marina in Punat, fertilizers and herbicides used for agriculture in the coastal environment, as well as the waste disposal site located uphill of the town (Figs. 1 and 2). The pollution of Punat Bay has been studied by measurements of heavy metals in marine sediment, the water column and benthos. The results of the analysis for lead, zinc and copper pollution were published in Legovic et al., 1990b. Estimation of diffuse inputs to the coastal sea using a two-dimensional transport model, and mea-surements of total concentrations of lead were made by Legovic et al., 1990a. The concentrations of more than 20 elements (from K to Pb) in sediments were determined using PIXE and XRF techniques (Valkovic and Bogdanovic, 1996). Limic and Valkovic (1996) showed that a modelling approach based on the interpretation of pollutant concentrations in sediments can be utilized for determination of the contribution from each individual source of pollution. Input of freshwater by infiltration of precipitation and groundwater from the coast to Punat Bay can be significant due to the karst terrain on Krk Island. No significant direct runoff from streams into the bay exists. In order to identify locations of freshwater input into the bay we used conduc-tivity and salinity measurements as well as hydrogen (2H/'H) and oxygen (18O/16O) stable isotope Fig. 1: a) Location of Krk Island in the northern Adriatic Sea, b) Map of Krk Island with springs and accumulations of freshwater, and location of Punat Bay. Sl. 1: a) Lega otoka Krka v Severnem Jadranu, b) zemljevid Krka z izviri, akumulacijami in Punatskim zalivom. 30.08.1998. 25.10.1998, 21.01.1999. ^ roa d fheavy Irafìcs) hi!! with seulement Waste deposi! (500m) 'lili wiltv bus ni I yaht anchor age ___> Puñal IfflfflfMg town ^ road (heavy trafics) hlll with seltlemert Waste deposit (500m) hi il witt J biish J ► yaht anchor age shipyard Cond IS « S 49 4Ü 40 Pgnat ™ town I yaht anclioragö í-can-a?» ¡ï.K.O ut # i*, ají .raj thte o ser s . Punat 1 town Fig. 2: Distribution of conductivity of seawater in Punat Bay in August and October 1998 and January 1999. The number at the sampling site represent s Sample No. from tables 1, 2 and 3 and number s in parenthese s represent and Ô180 values. Sl. 2: Porazdelitev prevodnosti morske vode v Punatskem zalivu avgusta in oktobra 1998 in januarja 1999; v oklepajih so vrednosti S2H in 5I80 na posameznih vzorcevalnih mestih. composition of the seawater. Additionally, temperature and pH values were measured. The same parameters were also measured in the freshwater of springs and accumulations at the Krk Island. AREA DESCRIPTION Krk Island is situated in the karst area of the northern Adriatic Sea. The geological structure of Krk Island is composed of carbonate rocks of Cretaceous and Eocene age, breccia of Tertiary age and Quaternary sediment. The hydrogeology of Krk Island is mainly characterized by Quaternary sediments with aquifers of poor transmisivity, and carbonate rocks with aquifers of good and ave-rage permeabilty (Hydrology and geology map of Krk Island with protection zones of springs, Faculty of geology, mining and petroleum engineering). Groundwater movements are very com-plex and depend upon the tectonic structure of rocks of different permeability. Punat Bay on Krk Island in the northern Adriatic Sea has an area of 2.4 km2, an average depth of 3.2 m and a volume of 7.7 x 106 m3 (Figs.1 and 2). The bay is connected to the sea through a narrow mouth, 200 m wide. The Bay is surrounded by hillocks that slope slightly toward the bay. The small town of Punat, a shipyard, and a marina are located on the coast of the bay. A potential source of pollution is also the waste disposal site located uphill of the town. SAMPLING AND METHODS Seawater samples from Punat Bay were measured and collected in three seasons: in summer (August 30, 1998) at 25 sites, in autumn (October 25, 1998) at 12 sites and in winter (January 21, 1999) at 20 sites. (Tables 1, 2 and 3). Sampling was performed between 10 and 12 a.m. during high water tide. Tidal range in this region is 20-50 cm depending upon winds. The position of each sampling site was determined by GPS. Conductivity, salinity, temperature and pH were measured in situ 2 m below the surface (in August and October) and 0.5 m below the surface (in January). Measurements of seawater conductivity and temperature at the same locations, but at different depths, showed the same values at 2 m, 1 m and 0 m from the surface (Table 1, samples No. 23, 24 and 25). Samples for measurement of stable isotope concentrations (2H/1H and 18O/16O) were col-lected and stored in plastic bottles and measured by a mass spectrometer at the IAEA Isotope Hydrology Laboratory. Freshwater samples from 7 springs and 2 accumulations at the Krk Island were also collected (Fig. 1b). Samples were collected during July and August 1998 at 8 sites (Table 4) including 1 seawater sample (sample No. 7) close to Vela voda spring, and during January 1999 at 8 sites (Table 5). A sample of water from a small water pond found on the hill, ~ 50 m above sea level, was also analyzed (Table 5, sample No. 7). RESULTS AND DISCUSSION The conductivity and salinity of seawater (conductivity: 46.8-55.0 mS/cm; salinity: 29.2-35.3%o) (Tables 1, 2 and 3) was much higher than that in freshwater (conductivity: 0.5-0.9 mS/cm; salinity 0.3-0.5%c) (Tables 4 and 5). The exceptions were Vela voda spring (Table 4, sample No. 6, con- Table 1: Seawater samples collected in Punat Bay on 30. 08. 1998, between 10 and 12 a.m. (measured at 2 m below the surface). Latitude and longitude are given in degrees, minutes and thou-sandths. Samples No. 23, 24 and 25 are at the same location but at different depths from the surface, 2 m, 1 m and 0 m. Tabela 1:Vzorci morske vode pobrani v Punatskem zalivu 30.8.1998 (2 m pod gladino). Vzorci {t. 23, 24 in 25 so pobrani na istih mestih v različnih globinah (2m, 1m, 0m). Sample No Location T (°C) Conductivity (mS/cm) Salinity (fe) ô2H (fe SMOW) Ô18O (fe SMOW) Latitude (N) Longitude (E) 1 45-00-876 14-37-383 18.6 46.8 29.2 10.8 1.25 2 45-00-926 14-37-452 18.5 48.4 30.2 3 45-01-013 14-37-516 18.5 48.4 30.2 10.7 1.22 4 45-01-131 14-37-546 18.5 48.7 30.4 5 45-01-224 14-37-505 18.7 48.5 30.3 9.3 1.24 6 45-01-355 14-37-513 19.1 48.5 30.3 7 45-01-453 14-37-508 19.2 48.5 30.3 7.5 1.11 8 45-01-550 14-37-482 19.3 48.6 30.4 9 45-01-680 14-37-484 19.4 48.7 30.4 8.8 1.12 10 45-01-790 14-37-434 19.4 48.8 30.5 11 45-01-932 14-37-401 19.6 48.9 30.6 9.5 1.14 12 45-02-061 14-37-376 19.7 49.0 30.6 13 45-02-253 14-37-326 19.8 49.1 30.7 7.6 1.20 14 45-02-368 14-37-264 19.5 49.1 30.7 15 45-02-220 14-37-129 19.8 49.2 30.7 9.7 1.24 16 45-02-030 14-37-141 19.7 49.3 30.8 17 45-01-856 14-37-157 19.7 49.4 30.9 9.7 1.25 18 45-01-722 14-37-251 19.7 49.5 30.9 19 45-01-697 14-36-873 19.8 49.5 30.9 20 45-01-480 14-36-942 19.5 49.5 30.9 21 45-01-438 14-37-322 19.7 49.6 31.0 22 45-01-449 14-37-637 19.1 49.8 31.1 23 45-01-464 14-37-680 19.3 49.8 31.1 8.6 0.87 24 45-01-464 14-37-680 19.3 49.8 31.1 25 45-01-464 14-37-680 19.3 49.8 31.1 26 45-00-735 14-37-292 18.8 50.8 31.7 27 45-00-682 14-37-124 18.8 50.8 31.7 Table 2: Seawater samples collected in Punat Bay on 25.10.1998, between 10 and 12 a.m.. (meas-ured 2 m below the surface). Latitude and longitude are given in degrees, minutes and thou-sandths. Tabela 2: Vzorci morske vode pobrani v Punatskem zalivu 25.10.1998 (2 m pod gladino). Sample Location Conductivity Salinity ô2H Ô18O No Latitude (N) Longitude (E) (mS/cm) « (%0 SMOW) (%0 SMOW) 1 45-00-864 14-37-395 51.0 31.4 3.0 0.38 2 45-00-997 14-37-517 50.7 31.9 3.2 0.38 3 45-01-205 14-37-535 52.5 32.5 3.8 0.37 4 45-01-380 14-37-538 53.3 33.0 1.3 0.30 5 45-01-560 14-37-520 51.8 32.1 0.6 0.16 6 45-01-715 14-37-491 50.1 31.0 0.3 0.10 7 45-01-925 14-37-445 49.1 30.4 -0.4 0.09 8 45-02-085 14-37-401 49.1 30.4 2.1 0.18 9 45-02-260 14-37-281 48.0 29.7 1.0 0.17 10 45-01-867 14-37-228 51.2 31.7 3.0 0.17 11 45-01-583 14-36-852 53.0 32.8 2.6 0.38 12 45-01-462 14-37-664 52.5 32.5 0.5 -0.14 ductivity 6.74 mS/cm) and a small water pond (Table 5, sample No. 7, conductivity 1.19 mS/cm). Vela voda spring is very close to the sea shore (~10 m) and the water is partly mixed with seawater. The water pond originated from precipitation that percolated through the soil, and the higher concentration of dissolved salts increased the conductivity of the water. The water pond was found only in the wet winter season. A significant difference in precipitation between the dry summer and wet winter seasons at Krk Island was observed. At the meteorological station Malinska-Krk, ~20 km from Punat Bay, there was 27.7 mm of rain in August 1998, and the five-month average, AprilAugust 1998, was 61.8 mm. In January there was 105.8 mm of rain, and the five-month average, September 1998-January 1999, was 189.9 mm (Meteorological and Hydrological Service, Zagreb). Some discrepancy between conductivity and temperature in different seasons was noticed. For example, during the dry summer (August measurements) with seawater temperatures of 18.5-19.8°C, the conductivity was lower (46.8-50.8 mS/cm) (Table 1) than during the wet winter (January measurements) with seawater temperatures of 5.7-10.4°C and conductivity of 50.5-55.0 mS/cm (Table 3). We expected just the opposite because higher freshwater input during the wet season decreases the conductivity of seawater. The possible explanation for this discrepancy was different conditions of conductivity measurements. For summer and autumn measurements we used a measuring cell with a 50 m long cable and all measurements were done 2 m below the surface, and for winter measurements we used another measuring cell with a 2 m long cable and the measurements were Table 3: Seawater samples collected in Punat Bay on 21.01.1999, between 10 and 12 a.m.. (measured at 0.5 m below the surface). Latitude and longitude are given in degrees, minutes and thou-sandths. Tabela 3:Vzorci morske vode pobrani v Punatskem zalivu 21.01.1999 (0,5 m pod gladino). Sample No Location T (°C) pH Conductivity (mS/cm) Salinity (fe) 82H (fe SMOW) 818O (fe SMOW) Latitude (N) Longitude (E) 1 45-00-745 14-37-310 10.4 7.98 55.0 35.3 7.3 0.90 2 45-00-875 14-37-396 8.3 8.00 53.1 33.9 5.2 0.66 3 45-01-012 14-37-525 8.5 8.16 53.3 34.0 5.2 0.70 4 45-01-143 14-37-534 8.7 8.15 53.4 34.0 6.2 0.77 5 45-01-225 14-37-551 8.0 8.19 53.2 33.9 3.4 0.77 6 45-01-310 14-37-640 9.3 8.16 51.5 32.2 3.4 0.39 7 45-01-458 14-37-676 9.2 8.23 53.5 33.3 2.5 0.62 8 45-01-488 14-37-428 5.7 8.21 50.5 32.7 -0.8 -0.07 9 45-01-631 14-37-663 9.7 8.20 53.2 34.3 1.8 0.42 10 45-01-838 14-37-590 8.4 8.22 53.3 34.2 2.4 0.47 11 45-02-080 14-37-470 8.3 8.26 53.6 34.2 4.9 0.84 12 45-02-330 14-37-406 8.2 8.25 53.7 34.2 6.0 0.83 13 45-02-333 14-37-216 7.2 8.25 53.0 34.0 1.1 0.24 14 45-02-000 14-37-093 8.7 8.26 53.9 34.4 5.3 0.86 15 45-01-794 14-36-834 8.2 8.29 53.6 34.2 6.6 0.87 16 45-01-711 14-36-720 8.1 8.26 53.8 34.2 17 45-01-518 14-36-924 7.9 8.23 53.0 33.7 18 45-01-273 14-37-226 7.8 8.27 53.0 34.1 19 45-01-133 14-37-440 8.2 8.26 53.1 33.8 20 45-01-098 14-37-604 9.4 8.28 52.9 34.0 performed at 0.5 m below the surface. Therefore, the absolute values of conductivity (salinity) are not comparable between different seasons. Distributions of conductivity in Punat Bay in three different seasons are presented in Fig. 2. The number at each sampling site represents the Sample No. from tables 1, 2 and 3, and the numbers in parentheses represent 82H and 818O values. Lower conductivity (light green) indicates possible locations of higher freshwater input from the coast. Some seasonal variations were evident. August and January conductivity distributions showed similar patterns with lower conductivity on the east and north coast of the bay. October measurements showed lower conductivity on the north coast. Table 4: Freshwater samples from springs and accumulations at Krk Island collected on 16.07.1998. and 30.8.1998. Sample No. 7 is a seawater from the seashore close to the Vela Voda spring. Tabela 4: Vzorci sladke vode in vode iz akumulacij na Krku zbrani 16.7.1998 in 30.8.1999; vzorec št. 7 predstavlja morska voda z obale blizu izvira Vela voda. Sample Location name T pH Conductivity Salinity 82H 818O No (°C) (mS/cm) (%.) (%0 SMOW) (%0 SMOW) 1 Ponikve accum., Vela Fontana, tap 21.3 6.97 743 0.44 -28.9 -4.21 2 Vela Fontana-closed spring 25.8 7.08 547 0.32 -24.4 -3.39 3 Ponikve accumulation- dam 26.0 7.38 469 0.27 -23.8 -3.29 4 Water station Jezero-Njivice lake 23.6 7.49 596 0.35 -22.6 -3.03 5 Njivice Lake-surface 24.9 7.67 587 0.34 6 Vela voda- spring (30.8.98.) 14.2 7.78 6.74 (mS/cm) 3.96 -34.3 -5.90 7 Vela voda-gat , sea w. (30.8.98.) 19.6 8.16 54.4 (mS/cm) 32.0 -37.1 -5.89 8 Zanac spring -42.5 -6.93 Table 5:Freshwater samples from springs and accumulations at Krk Island, collected on 20.-21. 01.1999. Tabela 5: Vzorci sladke vode iz izvirov in akumulacij na Krku, pobrani 20.-21.01.1999. Sample Location name T pH Conductivity Salinity 82H 818O No (°C) (mS/cm) (%.) (%0 SMOW) (%0 SMOW) 1 EB-2- Baska, spring (tap) 10.3 7.69 760 0.43 -40.4 -6.72 2 Vrbnik-Rogoznik, spring (tap) 9.0 7.32 667 0.38 -35.5 -5.89 3 Dobrinj-Ogreni, spring (tap) 8.5 7.61 702 0.41 -36.0 -6.01 4 Ponikve-Vela fontana, spring (tap) 9.7 7.58 751 0.43 -36.1 -5.80 5 Njivice-Vrutak, spring (tap) 13.4 7.13 896 0.52 -37.3 -6.14 6 Njivice Lake 5.8 7.94 554 0.32 -31.8 -5.09 7 Water pond above Kanajt (on hill) 9.9 7.09 1191 0.69 -30.9 -5.25 8 Ponikve accumulation -37.0 -5.87 The concentrations of stable isotopes (82H and 818O expressed in % according to the SMOW standard) were also much higher in seawater (82H: from -0.8 to 10.8%; 818O: from -0.07 to 1.25%) (Tables 1, 2 and 3) than in freshwater (82H: from -40.4 to -22.6%; 818O: from -6.9 to -3.0%). (Tables 4 and 5). Seasonal variations of 82H and 818O values were evident for both freshwater and seawater. 82H vs. 818O values were correlated with the Global Meteoric Water Line (GMWL: 82H = 8 818O + 10 %) (Fig. 3). The stable isotope composition of groundwater was lower in winter (mean values: 82H = -36.2 ± 2.5%; 818O = -5.94 ± 0.48%) and was very close to the GMWL. This indicated fast infiltration of surface waters caused by strong precipitation in winter. Freshwater samples collected in summer showed generally higher concentrations of 2H and 18O (mean values: 82H = -24.9 ± 2.4%; 818O = -3.48 ± 0.44%) and larger deviation from the GMWL that was caused by evaporation due to higher summer temperature. Correlation of 82H and 818O values of seawater in different seasons is presented in Fig. 4. The lowest concentrations of the heavy isotopes 2H and 18O in seawater were measured in the samples collected in October 1998 (mean values: 82H = 1.7 ± 1.3%; 818O = 0.21 ± 0.15%) and the largest fluctuations of 82H and 818O values were in winter (mean values: 82H= 4.0 ± 2.2%; 818O = 0.62 ± 0.27%). These effects are the results of the temperature variations and evaporation effect, respectively. Higher freshwater input during the wet season (autumn and winter) also has a similar influence. Fig. 3: ô2H vs. 818O values of groundwater samples from springs and accumulations collected at Krk Island and of seawater samples collected in Punat Bay, Krk Island. Samples were collected in different seasons. Stable isotope values were correlated with the Global Meteoric Water Line (MWL). Sl. 3: Zveza med ô2H in 818O v podtalnici izvirov in akumulacij na otoku Krku ter v morski vodi Punatskega zaliva. Vzorci so bili pobrani v različnih obdobjih. Vrednosti d so korelirane s splošno meteorno premico. Fig. 4: ô2H vs. ô18O values of seawater samples collected in different seasons in Punat Bay, Krk Island. Sl. 4: Zveza med §2H in ô18O morske vode v Punatskem zalivu, otok Krk, v različnih obdobjih. The relationship between conductivity and stable isotope signatures of seawater in Punat Bay is presented in Fig. 2. In most cases lower 82H and 818O values belonged to the sites with lower conductivity, particularly in winter, indicating locations with higher infiltration of freshwater. In this study we did not take into consideration the influence of water exchange driven by tides, winds and density differences within the bay that also have an important role in water circulation. CONCLUSIONS Locations of freshwater infiltration from the coast to the seawater of Punat Bay were determi-ned based on the distribution of conductivity and hydrogen (2H/1H) and oxygen (18O/16O) stable isotope composition of the seawater. Higher freshwater input was observed on the east and north coast of the bay in the summer and winter seasons, and on the north coast in autumn. Additional measurements in different seasons, particularly after heavy rains, will help for more precise determination of freshwater infiltration to the seawater. The stable isotope composition of freshwater from the springs at the Krk Island indicated fast circulation of groundwater, particularly in the wet winter season. ACKNOWLEDGEMENT The research was supported by the IAEA Technical Cooperation Project "Assessment of coastal sea water pollution in Punat Bay, Island Krk" (CR0/8/004), Municipality of Punat and State Directorate for Protection of Nature and Environment, Zagreb. REFERENCES Hydrogeology and geology map of Krk Island with protection zones of springs, Faculty of geo- logy, mining and petroleum engineering Legovic T., Limic N. and Valkovic V. (1990a) Estimation of diffuse inputs to a coastal sea: solution to an inverse modelling problem, Estuarine, Coastal and Shelf Science, 30, 619-634 Legovic T., Limic N., Valkovic V., Injuk J. and Nadj M. (1990b) Pollution of the Punat Bay by Zn, Cu and Pb, Fizika, 22, Suppl. 1, 126-140 Limic N. and Valkovic V. (1996) A combined experimental-modelling method for the detection and analysis of pollution in coastal zones, Nuclear Instruments and Methods in Physics Research B, 109/110, 415-418 Valkovic O. and Bogdanovic I. (1996) PIXE and XRF analysis of marine sediments, Nuclear Instruments and Methods in Physics Research B, 109/110, 488-492 RAZISKAVE ODTEKANJA PODTALNICE V MORJE V PUNATSKEM ZALIVU (HRVAŠKA) S POMOČJO STABILNIH IZOTOPOV IN MERITEV PREVODNOSTI VODE Povzetek Potencialni izvori onesnaženja v Punatskem zalivu (otok Krk, Hrvaška) so marina v Punatu, uporaba gnojil in herbicidov na kmetijskem obalnem področju in lokalno odlagališče odpadkov nad mestom (slike 1 in 2). Zaradi zakraselosti terena je dotok sladke vode v zaliv pomemben, tako s prenikanjem padavin kot tudi s podzemnimi izviri. Primes sladke vode pomembno vpliva na električno prevodnost in slanost morske vode, kakor tudi na njeno izotopsko sestavo. Lokacije možnih dotokov sladke vode v Punatski zaliv smo določili z meritvami električne prevodnosti in/ali slanosti ter izotopske sestave vodika (2H/H) in kisika (18O/16O) morske vode. Merili smo tudi temeraturo in pH. Prevodnost, tempeaturo in pH smo določili in-situ, medtem ko smo izotopske meritve opravili z masno spektrometrijo na IAEA v laboratoriju za izotopsko hidrologijo. Vzorce morske vode smo zbirali v treh obdobjih: poleti (avgusta 1998) na 25 mestih (tabela 1), jeseni (oktobra 1998) na 12 mestih (tabela 2) in pozimi (januarja 1999) na 20 mestih (tabela 3). Koordinate vzorčevalnih mest smo določili z GPS. Vzorce sladke vode iz zbirnega področja Punatskega zaliva smo vzeli na 7 izvirih in 2 akumulacijah na otoku Krku. Analizirali smo 8 vzorčevalnih mest julija 1998 (tabela 4) in januarja 1999 (tabela 5). Prav tako smo analizirali tudi vzorec vode, za katero menimo, da pronica skozi tla in morda tudi skozi deponijo (tabela 5, vzorec št. 7). Prevodnost in ustrezna slanost morske vode (prevodnost 46,8 - 55,0 mS/cm; slanost 39,2 - 35,3%o) sta bili mnogo večji v morski vodi kot v sladki (prevodnost 0,5 - 0,9 mS/cm, slanost 0,3 - 0,5%o). Porazdelitev prevodnosti vode v Punatskem zalivu v treh obdobjih je prikazana na sliki 2. Opazili smo nekatera neskladja med prevodnostjo in temperaturo; verjetno so vzrok različni pogoji ob opravljanju meritev prevodnosti. Koncentracija težkih izotopov vodika in kisika (82H in 818O, izražena v %% glede na SMOW standard) je tudi mnogo višja v morski vodi (82H od -0,8 do +10,8%, 818O od -0,07 do +1,25%) kot v sladki (82H od -40,4 do -22,6%, 818O od -6,7 do -3,0%). Sezonska nihanja vrednosti 82H in 818O so značilna tako za sladko kot morsko vodo. Zvezo med 82H in 818O smo primerjali s splošno meteorsko premico (GWML, 82H = 8 x 818O + 10%, slika 3). Podtalnica je bila izotopsko lažja pozimi (srednja vrednost 82H -36,2 ± 2,5% in 818O -5,94 ± 0,48%) in zelo blizu splošni meteorski premici, kar kaže na hitro infiltracijo površinske vode ob izdatnejših zimskih padavinah. Vzorci sladke vode, zbrani poleti, so izotopsko težji (srednje vrednosti 82H -24,9 ± 2,4% in 818O -3,48 ± 0,44%) in tudi bolj odstopajo od splošne meteorske premice zaradi izhlapevanja ob višjih poletnih temperaturah. Najvišje d vrednosti so bile izmejene oktobra 1998 (srednje vrednosti 82H 1,7 ± 1,3% in 818O 0,21 ± 0,15%), največja nihanja pa pozimi (srednje vrednosti 82H 4,0 ± 2,2% in 818O 0,62 ± 0,27%), kar je posledica temperaturnih nihanj in izhlapevanja, prav tako pa tudi večjega dotoka sladke vode v bolj vlažnem obdobju (jeseni in pozimi). Skladno s porazdelitvijo prevodnosti in izotopske sestave vodika in kisika v morju v Punatskem zalivu smo določili večji vnos sladke vode ob vzhodni in severni obali zaliva poleti in pozimi ter ob severni obali jeseni.