Hydrogeochemical investigations and spatial variations studies on the distribution of water isotopes and radiocarbon in the groundwater of Žitný Island (Rye Island) were carried out. Žitný Island represents the largest groundwater reservoir in Central Europe (about 10 Gm3). The chemical composition of the groundwater of Žitný Island depends mainly on the chemical composition of Danube water, as well as on the length of its infiltration from the Danube River. The groundwater is characterized by potamogenic mineralization, and its chemical composition is influenced by anthropogenic contamination. Sub-surface water profiles showed enriched δ18O levels up to around 20 m water depth, and depleted values for deeper waters. The observed isotopic composition of the groundwater is similar to Danube water, suggesting that the Danube River is the main source of the Žitný Island groundwater. The core of the sub-surface 14C profile represents contemporary groundwater with 14C values above 80 pMC.

INTRODUCTION

Hydrogeochemical and isotope studies of groundwater have been carried out in the past with the aim to better understand its origin, formation, dynamics, climatic impacts, its vulnerability and protection against anthropogenic impacts in the world (Gonfiantini et al. 1999; Kendall & McDonnell 1999; Aggarwal et al. 2006a, b), and specifically in Central Europe (Rank et al. 1995; Deák 2003; Povinec et al. 2006; Schiavo et al. 2009). Recently, new geostatistical tools have been developed to integrate isotope data into a relational database covering also hydrogeology and hydrochemistry of groundwater. Using geographical information system, it has been possible to create temporal-spatial isotope maps of groundwater (Bowen et al. 2005; Aggarwal & Araguás-Araguás 2006).

Isotope data together with hydrographic data have been used for better characterization of specific groundwater regions, for studying groundwater ages, infiltration areas, recharging characteristics of groundwater reservoirs, impact of climatic changes and a danger of groundwater contamination (Vitvar et al. 2007; Ockenden et al. 2014; Szczucinska 2014; de la Torre et al. 2015). These have been important studies for the protection and sustainable exploitation of groundwater from the long-term perspective.

Although several isotope hydrology studies were carried out in Central Europe (Rank et al. 1995, 1998, 2009; Deák 2003; Vitvar et al. 2007; Miljević et al. 2008), including Slovakia (Malík et al. 1995; Michalko 1999; Franko et al. 2005, 2008; Povinec et al. 2010), information on temporal and spatial groundwater variations, and specifically isotope depth profiles, have been missing. Development of an isotope groundwater database for Central Europe is underway which will identify regions with limited data sets, where new sampling campaigns and isotope analysis will be carried out. It is believed that with recently developed geostatistical tools the evaluation, assessment and management of groundwater resources in the region will be improved.

In this paper we present a first attempt to apply geostatistical tools in studying spatial and vertical distribution of isotopes in the groundwater of Žitný ostrov (Rye Island) in South-West Slovakia. The territory of Žitný Island is of great economic significance as it represents the largest reservoir of groundwater in Central Europe (about 1010m3, which represents potential ∼18 m3 s−1). In 1987 the territory of Žitný Island was declared as the national protected water resources territory of Slovakia. The groundwater sources at Žitný Island are delivering drinking water to Bratislava as well as to many other places in South-West Slovakia. Žitný Island is also, because of its location, good soil and climatic conditions, the most important agricultural region of Slovakia. There is also located the largest Slovak water power plant (Gabčíkovo, established in 1992), which is producing 720 MW of electricity. The Gabčíkovo water system considerably influences the hydrology of the region, as well as the Danube River shipping conditions. The Gabčíkovo plant with the reservoir, and the inlet and outlet canals has a positive impact on regional groundwater conditions. Owing to the back water effect of the reservoir, the level of groundwater in the region of Bratislava has increased by about 2 m, with an important positive impact on all ecosystems in the region.

HYDROGEOLOGY OF ŽITNÝ ISLAND

Žitný Island, with an area of 1,200 km2, covers the territory South-East of Bratislava (Figure 1), which is bordered on the north by the Small Danube River, and on the east by the Váh River. Žitný Island belongs to the Danube Plain where several wetplains are located. The relief is made of bottom lands, consisting mainly of fluvial, proluvial-wetplain and eolic-fluvial relief. The territory represents a flat terrain 129–136 m above sea level. The average annual precipitation during 1951–1980 was between 528 and 580 mm. The average annual evaporation from the soil surface at Žitný Island for the time interval between 1961 and 1990 was 450–500 mm. The total potential annual evaporation was between 700 and 800 mm.

Figure 1

Map of Slovakia with topography and the main river system (Žitný Island is SE of Bratislava).

Figure 1

Map of Slovakia with topography and the main river system (Žitný Island is SE of Bratislava).

The territory of Žitný Island is located in the Danube basin with the core of the Gabčíkovo depression, bordered at the North-West by Small Carpathians, and from the South-East by a system of faults. There are three strata in the Quaternary filling: (i) bottom strata which is formed mostly by fine-grained sand gravel with frequently occurring clayey or silt sands up to clays with 10–350 m thickness; (ii) middle strata (the Danube gravel formation) from middle up to course-grained sandy gravels with sporadic intermediate layers of fine sediments up to a thickness of 160 m in the center of the depression; and (iii) top strata (bottom-land facies), mostly fine-grain Holocene sediments from 0.5 to 3 m thickness. The Quaternary sub-base is made of ruman, dak and pont sediments, mostly of gray up to gray-green weakly calcinated mica clays and dust with varying admixture of sand. The territory of Žitný Island is formed by terraces of fluvial sediments – clayey sands, sands, gravels, sand gravels and residual sands – and by bottom lands of fluvial sediments – sandy clay, clays, clayey sands and clayey gravels (Maglay et al. 2009). Quaternary sediments of Žitný Island may be allocated to lower, middle and upper Pleistocene and Holocene. The Pleistocene sediments have a thickness from 10 to 20 m south of Bratislava, 8–12 m at Komárno, and in the center of the depression at Gabčíkovo it is about 160 m. The sediments are mostly made of coarse gravels, sand gravels and sands without fine fractions, which indicate a dominance of stream-bed facies over bottom-land sediments. The Holocene sediments are formed by a diluvium enclosure of river bottom lands with admixture of gravel, and recent and fossil soils.

On the basis of statistical evaluation of the hydrographic data from 812 boreholes, the Žitný Island territory has been divided into four regions with the following hydraulics parameters: (i) a right-riverside of the Danube – a high value of median flow capacity (2.03 × 10−2m2 s−1), and median filtration coefficient (4.06 × 10−3 m s−1), and an average value of specific strength (12.6 L s−1); (ii) an upper part – a lower value of median flow capacity (5.01 × 10−2 m2 s−1), and median filtration coefficient (1.00 × 10−2 m s−1), and an average value of specific strength (28.0 L s−1); (iii) a middle part – a highest value of median flow capacity (1.55 × 10−1m2s−1), and median filtration coefficient (3.1 × 10−2 m s−1), and an average value of specific strength (93.25 L s−1); and (iv) a lower part – a lowest value of the median flow capacity (7.95 × 10−3 m2 s−1), and median filtration coefficient (1.59 × 10−3 m s−1), and an average value of specific strength (5.4 L s−1).

A general trend in the flow of groundwater is mostly following the main rivers in the region (Danube, Small Danube and Váh). The Danube River during all its water levels in Žitný Island feeds groundwater in the region. Precipitation is influencing the groundwater regime of Žitný Island indirectly via elevated flow rates in rivers (as will be discussed later using isotope data). Increasing river flow rates have also been increasing the groundwater level, with different delays depending on the distance from the river. The groundwater regime of Žitný Island is thus mainly determined by interactions between Danube water (and other surface waters in the region) and groundwater in the region.

There are three types of hydrogeological boreholes at Žitný Island (Figure 2): (i) a basic monitoring network; (ii) boreholes in use for water supply; and (iii) presently not used boreholes. Boreholes of the basic monitoring network have piezometers located from 1 to 6 levels, enabling thus to study vertical distribution of contaminants (and isotopes) in groundwater (L'uptáková et al. 2007).

Figure 2

Groundwater monitoring and sampling sources in Žitný Island (circles indicate the sampling sites).

Figure 2

Groundwater monitoring and sampling sources in Žitný Island (circles indicate the sampling sites).

GROUNDWATER SAMPLING AND ANALYSIS

Groundwater sampling

The sampling sites were identical with groundwater sources regularly monitored by the Slovak Hydrometeorological Institute in Žitný Island (Figure 2). The sampling strategies were determined by development of a relational isotope database of groundwater of Slovakia (which will cover hydrogeological, hydrochemical and isotope data), determination of the catchments areas of groundwater at Žitný Island and contribution to the protection of groundwater against contamination from surface waters (e.g. from the Gabčíkovo water system), from agricultural fertilizers and industrial products (e.g. oil products from the Slovnaft refinery located in Bratislava). Two sampling campaigns were carried out, one in November 2008 and the second one in June 2009. Altogether 38 boreholes were visited. Groundwater samples were taken from different horizons. A description of the sampling wells is presented in Table 1.

Table 1

Groundwater sampling sites at Žitný Island

St. no. SHMUa number Number of area Locality Sampling year GPS position Probe depth (m) Lower perfor. (m) Upper perfor. (m) Sampling level 
16 603091 51 ČUŇOVO 2008 N48 02 42.8 E17 11 32.0 66.91 67.00 65.00 
601393 52 KALINKOVO 2008 N48 03 42.4 E17 12 31.6 57.06 58.00 55.00 
724891 52 ŠAMORÍN – ČILISTOV 2008 N48 00 29.9 E17 18 47.0 88.46 89.50 86.50 
726591 52 ŠAMORÍN – MLIEČNO 2008 N48 00 20.1 E17 20 53.1 69.92 68.00 65.00 
10 601092 52 DOBROHOŠŤ 2008 N47 59 35.6 E17 20 38.2 80.50 80.00 78.00 
11 727491 52 VOJKA 2008 N47 58 39.1 E17 22 57.5 30.64 64.00 61.00 
12 603291 52 GABČÍKOVO 2008 N47 53 08.0 E17 33 49.6 25.14 24.00 20.00 
29 736591 52 SAP – PALKOVIČOVO 2009 N47 48 40.5 E17 38 00.4 46.45 45.00 42.00 
17 601691 53 ROVINKA 2008 N48 06 28.2 E17 13 31.3 62.26 55.00 40.00 
18 720092 53 PODUNAJSKÉ BISKUPICE 2008 N48 07 46.1 E17 13 22.8 23.65 50.00 47.00 
724191 54 VYDRANY – KVETOSLAVOV 2008 N48 02 39.9 E17 20 42.0 72.70 71.50 68.50 
601191 54 OL'DZA 2008 N48 05 39.8 E17 25 16.2 67.33 67.00 61.00 
727791 54 ROHOVCE – ŠTRKOVEC 2008 N47 58 44.3 E17 25 14.4 83.28 84.50 81.50 
733691 54 VRAKÚŇ 2008 N47 55 18.2 E17 38 00.6 78.50 77.00 74.00 
15 725491 54 HORNÁ POTÔŇ 2008 N48 04 09.5 E17 31 54.7 35.78 34.00 31.00 
37 729492 54 ORECHOVÁ POTÔŇ 2009 N48 02 15.8 E17 33 43.8 20.80 19.00 16.00 
36 729394 54 VEL'KÉ BLAHOVO 2009 N48 03 03.5 E17 36 17.2 28.71 28.00 25.00 
33 603391 54 MLIEČANY 2009 N47 57 44.1 E17 35 40.3 24.24 24.00 20.00 
34 66490 54 DVORNÍKY N. OSTROVE 2009 N47 59 49.4 E17 39 34.6 8.90 – – 
13 736691 55 KL'ÚČOVEC 2008 N47 47 28.3 E17 41 56.8 50.33 52.00 50.00 
14 264791 55 KLIŽSKÁ NEMÁ 2008 N47 45 22.5 E17 47 43.0 26.90 25.00 23.00 
31 600491 55 VEL'KÝ MEDER 2009 N47 52 07.2 E17 45 30.2 35.14 33.00 30.00 
30 64090 55 PARAŠ – MILINOVICE 2009 N47 51 42.1 E17 40 08.8 7.80 – – 
32 263190 55 HORNÝ ŠTÁL-ŽEL. STANICA 2009 N47 56 57.8 E17 44 04.1 11.01 – – 
24 61890 55 ZEMIANSKA OLČA 2009 N47 49 03.8 E17 53 00.9 6.32 – – 
25 61790 55 ZEMIANSKA OLČA 2009 N47 51 17.3 E17 54 15.9 6.01 – – 
23 738191 55 ZLATNÁ NA OSTROVE 2009 N47 45 59.8 E17 57 12.9 15.60 – – 
21 605990 55 ČALOVEC-KAMENIČNÁ 2009 N47 49 36.5 E18 00 38.5 10.89 9.50 8.50 
22 260790 55 KAMENIČNÁ 2009 N47 49 12.2 E18 02 13.2 7.93   
26 261190 55 KAMENIČNÁ-PIESKY 2009 N47 51 01.3 E17 59 14.8 15.22 9.00 5.00 
19 260290 55 KOMÁRNO 2009 N47 45 20.9 E18 07 56.0 7.91 – – 
20 260490 55 KOMÁRNO 2009 N47 46 22.1 E18 05 39.7 9.75 – – 
721593 56 MALINOVO 2008 N48 08 47.7 E17 18 30.7 54.66 49.50 44.50 
601291 56 VLKY 2008 N48 08 50.0 E17 21 26.0 30.48 29.50 27.50 
38 603191 56 JELKA 2009 N48 09 45.9 E17 29 55.4 25.42 24.00 20.00 
35 600592 56 JAHODNÁ 2009 N48 03 51.1 E17 41 17.2 34.92 34.00 31.00 
28 264290 56 OKOČ-ASZÓD 2009 N47 55 50.4 E17 52 25.6 15.53 14.00 10.00 
27 262890 56 KOLÁROVO 2009 N47 55 53.6 E17 57 27.4 8.98 – – 
St. no. SHMUa number Number of area Locality Sampling year GPS position Probe depth (m) Lower perfor. (m) Upper perfor. (m) Sampling level 
16 603091 51 ČUŇOVO 2008 N48 02 42.8 E17 11 32.0 66.91 67.00 65.00 
601393 52 KALINKOVO 2008 N48 03 42.4 E17 12 31.6 57.06 58.00 55.00 
724891 52 ŠAMORÍN – ČILISTOV 2008 N48 00 29.9 E17 18 47.0 88.46 89.50 86.50 
726591 52 ŠAMORÍN – MLIEČNO 2008 N48 00 20.1 E17 20 53.1 69.92 68.00 65.00 
10 601092 52 DOBROHOŠŤ 2008 N47 59 35.6 E17 20 38.2 80.50 80.00 78.00 
11 727491 52 VOJKA 2008 N47 58 39.1 E17 22 57.5 30.64 64.00 61.00 
12 603291 52 GABČÍKOVO 2008 N47 53 08.0 E17 33 49.6 25.14 24.00 20.00 
29 736591 52 SAP – PALKOVIČOVO 2009 N47 48 40.5 E17 38 00.4 46.45 45.00 42.00 
17 601691 53 ROVINKA 2008 N48 06 28.2 E17 13 31.3 62.26 55.00 40.00 
18 720092 53 PODUNAJSKÉ BISKUPICE 2008 N48 07 46.1 E17 13 22.8 23.65 50.00 47.00 
724191 54 VYDRANY – KVETOSLAVOV 2008 N48 02 39.9 E17 20 42.0 72.70 71.50 68.50 
601191 54 OL'DZA 2008 N48 05 39.8 E17 25 16.2 67.33 67.00 61.00 
727791 54 ROHOVCE – ŠTRKOVEC 2008 N47 58 44.3 E17 25 14.4 83.28 84.50 81.50 
733691 54 VRAKÚŇ 2008 N47 55 18.2 E17 38 00.6 78.50 77.00 74.00 
15 725491 54 HORNÁ POTÔŇ 2008 N48 04 09.5 E17 31 54.7 35.78 34.00 31.00 
37 729492 54 ORECHOVÁ POTÔŇ 2009 N48 02 15.8 E17 33 43.8 20.80 19.00 16.00 
36 729394 54 VEL'KÉ BLAHOVO 2009 N48 03 03.5 E17 36 17.2 28.71 28.00 25.00 
33 603391 54 MLIEČANY 2009 N47 57 44.1 E17 35 40.3 24.24 24.00 20.00 
34 66490 54 DVORNÍKY N. OSTROVE 2009 N47 59 49.4 E17 39 34.6 8.90 – – 
13 736691 55 KL'ÚČOVEC 2008 N47 47 28.3 E17 41 56.8 50.33 52.00 50.00 
14 264791 55 KLIŽSKÁ NEMÁ 2008 N47 45 22.5 E17 47 43.0 26.90 25.00 23.00 
31 600491 55 VEL'KÝ MEDER 2009 N47 52 07.2 E17 45 30.2 35.14 33.00 30.00 
30 64090 55 PARAŠ – MILINOVICE 2009 N47 51 42.1 E17 40 08.8 7.80 – – 
32 263190 55 HORNÝ ŠTÁL-ŽEL. STANICA 2009 N47 56 57.8 E17 44 04.1 11.01 – – 
24 61890 55 ZEMIANSKA OLČA 2009 N47 49 03.8 E17 53 00.9 6.32 – – 
25 61790 55 ZEMIANSKA OLČA 2009 N47 51 17.3 E17 54 15.9 6.01 – – 
23 738191 55 ZLATNÁ NA OSTROVE 2009 N47 45 59.8 E17 57 12.9 15.60 – – 
21 605990 55 ČALOVEC-KAMENIČNÁ 2009 N47 49 36.5 E18 00 38.5 10.89 9.50 8.50 
22 260790 55 KAMENIČNÁ 2009 N47 49 12.2 E18 02 13.2 7.93   
26 261190 55 KAMENIČNÁ-PIESKY 2009 N47 51 01.3 E17 59 14.8 15.22 9.00 5.00 
19 260290 55 KOMÁRNO 2009 N47 45 20.9 E18 07 56.0 7.91 – – 
20 260490 55 KOMÁRNO 2009 N47 46 22.1 E18 05 39.7 9.75 – – 
721593 56 MALINOVO 2008 N48 08 47.7 E17 18 30.7 54.66 49.50 44.50 
601291 56 VLKY 2008 N48 08 50.0 E17 21 26.0 30.48 29.50 27.50 
38 603191 56 JELKA 2009 N48 09 45.9 E17 29 55.4 25.42 24.00 20.00 
35 600592 56 JAHODNÁ 2009 N48 03 51.1 E17 41 17.2 34.92 34.00 31.00 
28 264290 56 OKOČ-ASZÓD 2009 N47 55 50.4 E17 52 25.6 15.53 14.00 10.00 
27 262890 56 KOLÁROVO 2009 N47 55 53.6 E17 57 27.4 8.98 – – 

aSlovak Hydrometeorological Institute.

The sampling of water from boreholes was carried out in such a way that inflows were isolated from their overlying and/or underlying strata. All pipes of each borehole are cemented above perforation, so the wells are technically protected from inflows of waters into the borehole from its sealed part. This, however, cannot prevent mixing of waters during their flow in aquifers. Such cases can occur especially in discharge areas, when waters of deep flow may be influenced by a shallow groundwater.

During groundwater sampling in situ measurements of basic physical and chemical parameters (groundwater temperature, air temperature, pH, electrical conductivity, oxidation-reduction potential, concentration of dissolved oxygen and oxygen saturation) were carried out as well. Water samples for radiocarbon analysis (∼50 L) were collected directly from the source. Bicarbonates were extracted as soon as possible by precipitation with barium chloride. Produced BaCO3 was stored in polyethylene containers and transported to the laboratory.

Laboratory analyses

Laboratory analyses included analysis of stable isotopes (18O, 13C), preparation of gas fillings for proportional counters and 14C activity measurements. A few mL of carbon dioxide liberated from the BaCO3 sample was used for the determination of the isotopic ratio of 13C/12C. The δ13C values are expressed relative to the Vienna Pee Dee Belemnite standard (in ‰). 18O/16O isotopic ratio was analyzed directly in water samples. The δ18O data are reported relative to Vienna Standard Mean Ocean Water (in ‰). Relative uncertainties were below 0.2‰ (at 1 σ). Stable isotope analyses were carried out using mass spectrometers at the Dionýz Štúr Geological Institute in Bratislava.

The radiocarbon measurements were carried out in the Department of Nuclear Physics and Biophysics of the Faculty of Mathematics, Physics and Informatics of the Comenius University in Bratislava. For 14C analysis of groundwater samples, carbon dioxide was released from barium carbonate by addition of H3PO4. Methane (Povinec 1972) synthesized from carbon dioxide was used as a filling gas of the low-level proportional counter (Povinec 1978). Measuring time of methane samples was from 40 to 60 h. In addition to each water sample, samples of background and of radiocarbon standard (National Institute of Standards and Technology (NIST)) oxalic acid standard were also measured (Usačev et al. 1973). 14C results are expressed as percent modern carbon (pMC) relative to the NIST 14C standard. All 14C data were corrected for δ13C. Relative uncertainties of 14C measurements were below 10% (at 1 σ). Quality management of all analyses has been assured by analysis of reference materials, and by participation in intercomparison exercises.

Isotope data evaluation

The spatial isotope maps have been constructed using the Ocean Data View software, which reproduces well surface, as well as depth distributions of isotopes in the aquatic environment (Povinec et al. 2011). The present spatial resolution of the obtained maps is 5 km in the horizontal plane, and 10 m in the vertical plane.

RESULTS AND DISCUSSION

Hydrogeochemistry

The physical, chemical and isotopic characteristics of the collected groundwater samples are presented in Tables 2 and 3. The chemical composition of the groundwater of Žitný Island depends on the chemical composition of Danube River water (and also of Small Danube and Váh river waters), as well as on the length of infiltration of rivers waters into the groundwater. Although the groundwater samples were collected during summer and winter (however, at different sampling sites during different seasons), we did not observe a statistical difference in the stoichiometry of the samples collected during different sampling periods. The groundwater is characterized by potamogenic mineralization, and its chemical composition is influenced by anthropogenic contamination. The Quaternary environment, especially the alluvial sediments of the Danube, Small Danube and Váh rivers, has mostly silicate character (gravels, sand gravels and sands).

Table 2

Groundwater sampling sites – water parameters, stable isotopes and radiocarbon data

St. no. SHMU number N. area Locality Sampling date Bottom depth (m) T (°C) EC (mS m−1pH O2 (mg L−1CO2 (mg L−1HCO3 (mg L−1δ18O (‰) δ13C (‰) pMC (‰) 
16 603091 51 ČUŇOVO 19.11.2008 54.65 12.1 55.4 7.61 1.7 4.32 189.53 −10.548 −19.224 84.81 
601393 52 KALINKOVO 11.11.2008 60.00 11.7 45.4 7.58 2.2 8.72 204.48 −10.618 −15.165 105.51 
724891 52 ŠAMORÍN – ČILISTOV 10.11.2008 90.00 12.8 44.9 7.56 1.6 4.32 238.43 −10.863 −15.201 97.17 
726591 52 ŠAMORÍN – MLIEČNO 11.11.2008 69.92 11.5 48.4 7.56 2.0 9.81 250.66 −10.702 −14.793 76.47 
10 601092 52 DOBROHOŠŤ 11.11.2008 80.50 11.8 44 7.87 1.6 6.54 235.38 −10.800 −10.656 78.88 
11 727491 52 VOJKA 12.11.2008 66.91 11.4 47.3 7.67 2.2 6.54 195.64 −10.669 −15.738 98.69 
29 736591 52 SAP – PALKOVIČOVO 15.6.2009 46.45 12.2 44.7 7.54 1.2 5.49 194.10 −11.034 −10.791 90,36 
17 601691 53 ROVINKA 19.11.2008 62.26 10.5 43.1 7.75 2.0 2.18 235.38 −11.018 −13.060 90.76 
18 720092 53 PODUNAJ. BISKUPICE 19.11.2008 55.00 10.5 59.4 7.56 6.0 5.45 290.40 −10.820 −15.244 72.86 
601191 54 OL'DZA 11.11.2008 67.33 11.7 47 7.69 4.2 5.45 244.55 −10.825 −16.810 91.24 
727791 54 ROHOVCE – ŠTRKOVEC 10.11.2008 83.28 11.2 52.2 7.70 2.2 4.32 238.43 −10.657 −15.557 80.44 
733691 54 VRAKÚŇ 11.11.2008 78.50 11.8 35.6 7.79 2.0 2.18 201.75 −11.119 −13.510 97.11 
15 725491 54 HORNÁ POTÔŇ 12.11.2008 35.78 11.3 70.4 7.52 3.9 9.81 275.12 −10.585 −14.393 82.52 
37 729492 54 ORECHOVÁ POTÔŇ 16.6.2009 20.88 13.1 77 7.43 1.8 12.08 282.04 −10.916 −11.608 84.99 
36 729394 54 VEL'KÉ BLAHOVO 16.6.2009 28.71 14.2 67.2 7.39 2.2 16.47 251.72 −10.460 −12.664 89.41 
33 603391 54 MLIEČANY 15.6.2009 23.84 12.4 61.2 7.54 2.5 12.08 245.65 −11.312 −11.502 83.95 
34 66490 54 DVORNÍKY N. OSTROVE 16.6.2009 8.55 12.8 97 7.31 3.5 20.86 321.47 −10.612 −12.692 93.85 
13 736691 55 KL'ÚČOVEC 12.11.2008 50.33 15.8 34.5 7.93 3.6 1.09 201.75 −10.917 −11.728 86.48 
14 264791 55 KLIŽSKÁ NEMÁ 12.11.2008 26.90 11.7 70.2 7.16 2.3 32.71 452.42 −10.275 −17.529 43.81 
31 600491 55 VEL'KÝ MEDER 15.6.2009 35.14 12.8 40 7.63 2.6 3.29 224.42 −11.056 −10.621 63.02 
30 64090 55 PARAŠ – MALINOVICE 15.6.2009 9.60 12.7 93.9 7.21 2.1 5.49 373.03 −10.712 −11.600 82.24 
32 263190 55 HORNÝ ŠTÁL – ŽEL. ST. 15.6.2009 11.01 12.5 83.8 7.34 2.0 294.18 −10.659 −12.053 89.62 
24 61890 55 ZEMIANSKA OLČA 11.6.2009 9.27 13.9 223 7.07 2.6 34 618.68 −10.273 −12.150 93.59 
25 61790 55 ZEMIANSKA OLČA 11.6.2009 15.51 13.2 137.3 7.07 1.5 34 464.01 −9.279 −12.541 86.62 
23 738191 55 ZLATNÁ NA OSTROVE 10.6.2009 16.50 14.7 103.6 7.39 1.5 530.73 −11.041 −11.485 72.92 
21 605990 55 ČALOVEC – KAMENIČNÁ 10.6.2009 10.91 15.2 58 7.48 1.2 29.65 351.80 −12.219 −11.080 31.54 
22 260790 55 KAMENIČNÁ 10.6.2009 5.98 15.6 98.1 7.32 1.7 21.96 606.55 −9.102 −15.859 90.05 
26 261190 55 KAMENIČNÁ-PIESKY 11.6.2009 10.00 13.8 91.3 7.09 2.2 36.23 476.14 −10.276 −12.044 69.86 
19 260290 55 KOMÁRNO 10.6.2009 7.91 15.7 98.5 6.88 3.5 6.5 582.29 −10.584 −15.849 86.83 
20 260490 55 KOMÁRNO 10.6.2009 9.76 13.2 88.8 7.34 1.4 17.57 464.01 −10.094 −14.134 80.22 
721593 56 MALINOVO 10.11.2008 54.65 12.1 55.4 7.61 1.7 4.32 189.53 −10.954 −15.406 93.47 
601291 56 VLKY 10.11.2008 30.50 12.4 53.6 7.46 1.5 10.79 250.05 −10.553 −15.406 89.62 
38 603191 56 JELKA 16.6.2009 25.40 12.7 87.3 7.47 2.1 23.06 291.14 −10.727 −12.986 79.49 
35 600592 56 JAHODNÁ 16.6.2009 34.92 12.7 51 7.59 1.2 5.49 248.68 −11.148 −11.250 80.80 
28 264290 56 OKOČ-ASZÓD 11.6.2009 15.51 12.4 63.1 7.17 1.5 27.45 351.80 −10.423 −12.623 81.16 
27 262890 56 KOLÁROVO 11.6.2009 9.00 13.7 73 7.28 1.4 13.18 327.54 −10.927 −13.933 99.58 
St. no. SHMU number N. area Locality Sampling date Bottom depth (m) T (°C) EC (mS m−1pH O2 (mg L−1CO2 (mg L−1HCO3 (mg L−1δ18O (‰) δ13C (‰) pMC (‰) 
16 603091 51 ČUŇOVO 19.11.2008 54.65 12.1 55.4 7.61 1.7 4.32 189.53 −10.548 −19.224 84.81 
601393 52 KALINKOVO 11.11.2008 60.00 11.7 45.4 7.58 2.2 8.72 204.48 −10.618 −15.165 105.51 
724891 52 ŠAMORÍN – ČILISTOV 10.11.2008 90.00 12.8 44.9 7.56 1.6 4.32 238.43 −10.863 −15.201 97.17 
726591 52 ŠAMORÍN – MLIEČNO 11.11.2008 69.92 11.5 48.4 7.56 2.0 9.81 250.66 −10.702 −14.793 76.47 
10 601092 52 DOBROHOŠŤ 11.11.2008 80.50 11.8 44 7.87 1.6 6.54 235.38 −10.800 −10.656 78.88 
11 727491 52 VOJKA 12.11.2008 66.91 11.4 47.3 7.67 2.2 6.54 195.64 −10.669 −15.738 98.69 
29 736591 52 SAP – PALKOVIČOVO 15.6.2009 46.45 12.2 44.7 7.54 1.2 5.49 194.10 −11.034 −10.791 90,36 
17 601691 53 ROVINKA 19.11.2008 62.26 10.5 43.1 7.75 2.0 2.18 235.38 −11.018 −13.060 90.76 
18 720092 53 PODUNAJ. BISKUPICE 19.11.2008 55.00 10.5 59.4 7.56 6.0 5.45 290.40 −10.820 −15.244 72.86 
601191 54 OL'DZA 11.11.2008 67.33 11.7 47 7.69 4.2 5.45 244.55 −10.825 −16.810 91.24 
727791 54 ROHOVCE – ŠTRKOVEC 10.11.2008 83.28 11.2 52.2 7.70 2.2 4.32 238.43 −10.657 −15.557 80.44 
733691 54 VRAKÚŇ 11.11.2008 78.50 11.8 35.6 7.79 2.0 2.18 201.75 −11.119 −13.510 97.11 
15 725491 54 HORNÁ POTÔŇ 12.11.2008 35.78 11.3 70.4 7.52 3.9 9.81 275.12 −10.585 −14.393 82.52 
37 729492 54 ORECHOVÁ POTÔŇ 16.6.2009 20.88 13.1 77 7.43 1.8 12.08 282.04 −10.916 −11.608 84.99 
36 729394 54 VEL'KÉ BLAHOVO 16.6.2009 28.71 14.2 67.2 7.39 2.2 16.47 251.72 −10.460 −12.664 89.41 
33 603391 54 MLIEČANY 15.6.2009 23.84 12.4 61.2 7.54 2.5 12.08 245.65 −11.312 −11.502 83.95 
34 66490 54 DVORNÍKY N. OSTROVE 16.6.2009 8.55 12.8 97 7.31 3.5 20.86 321.47 −10.612 −12.692 93.85 
13 736691 55 KL'ÚČOVEC 12.11.2008 50.33 15.8 34.5 7.93 3.6 1.09 201.75 −10.917 −11.728 86.48 
14 264791 55 KLIŽSKÁ NEMÁ 12.11.2008 26.90 11.7 70.2 7.16 2.3 32.71 452.42 −10.275 −17.529 43.81 
31 600491 55 VEL'KÝ MEDER 15.6.2009 35.14 12.8 40 7.63 2.6 3.29 224.42 −11.056 −10.621 63.02 
30 64090 55 PARAŠ – MALINOVICE 15.6.2009 9.60 12.7 93.9 7.21 2.1 5.49 373.03 −10.712 −11.600 82.24 
32 263190 55 HORNÝ ŠTÁL – ŽEL. ST. 15.6.2009 11.01 12.5 83.8 7.34 2.0 294.18 −10.659 −12.053 89.62 
24 61890 55 ZEMIANSKA OLČA 11.6.2009 9.27 13.9 223 7.07 2.6 34 618.68 −10.273 −12.150 93.59 
25 61790 55 ZEMIANSKA OLČA 11.6.2009 15.51 13.2 137.3 7.07 1.5 34 464.01 −9.279 −12.541 86.62 
23 738191 55 ZLATNÁ NA OSTROVE 10.6.2009 16.50 14.7 103.6 7.39 1.5 530.73 −11.041 −11.485 72.92 
21 605990 55 ČALOVEC – KAMENIČNÁ 10.6.2009 10.91 15.2 58 7.48 1.2 29.65 351.80 −12.219 −11.080 31.54 
22 260790 55 KAMENIČNÁ 10.6.2009 5.98 15.6 98.1 7.32 1.7 21.96 606.55 −9.102 −15.859 90.05 
26 261190 55 KAMENIČNÁ-PIESKY 11.6.2009 10.00 13.8 91.3 7.09 2.2 36.23 476.14 −10.276 −12.044 69.86 
19 260290 55 KOMÁRNO 10.6.2009 7.91 15.7 98.5 6.88 3.5 6.5 582.29 −10.584 −15.849 86.83 
20 260490 55 KOMÁRNO 10.6.2009 9.76 13.2 88.8 7.34 1.4 17.57 464.01 −10.094 −14.134 80.22 
721593 56 MALINOVO 10.11.2008 54.65 12.1 55.4 7.61 1.7 4.32 189.53 −10.954 −15.406 93.47 
601291 56 VLKY 10.11.2008 30.50 12.4 53.6 7.46 1.5 10.79 250.05 −10.553 −15.406 89.62 
38 603191 56 JELKA 16.6.2009 25.40 12.7 87.3 7.47 2.1 23.06 291.14 −10.727 −12.986 79.49 
35 600592 56 JAHODNÁ 16.6.2009 34.92 12.7 51 7.59 1.2 5.49 248.68 −11.148 −11.250 80.80 
28 264290 56 OKOČ-ASZÓD 11.6.2009 15.51 12.4 63.1 7.17 1.5 27.45 351.80 −10.423 −12.623 81.16 
27 262890 56 KOLÁROVO 11.6.2009 9.00 13.7 73 7.28 1.4 13.18 327.54 −10.927 −13.933 99.58 
Table 3

Groundwater chemical composition of the Žitný Island area

St. no. SHMU number Locality Number of area Date of sampling Chemical type TDSa HCO3 Cl SO2−4 NO3 Ca2+ Mg2+ (mg L−1Na+ K+ CO2 free CO2 aggr. Corg. 
16 603091 ČUNOVO 51 6.11.2008 Ca-Mg-HCO3 353.4 188.0 18.0 29.7 10.5 57.5 12.8 11.1 2.3 12.3 < 1.1 1.1 
601393 KALINKOVO 52 5.11.2008 Ca-Mg-HCO3 372.9 200.0 18.9 31.2 9.87 61.1 13.9 10.8 2.4 14.0 < 1.1 1.3 
724891 ŠAMORÍN-ČILISTOV 52 18.9.2008 Ca-Mg-HCO3 390.5 246.0 19.3 12.6 < 1.0 63.8 14.2 9.8 2.0 17.5 < 1.1 0.8 
726591 ŠAMORÍN-MLIEČNO 52 5.11.2008 Ca-Mg-HCO3 411.3 243.0 19.5 22.7 3.26 69.4 15.5 10.5 2.1 16.7 < 1.1 0.9 
10 601092 DOBROHOŠŤ 52 4.11.2008 Ca-Mg-HCO3 388.6 235.0 17.3 19.7 2.48 65.1 14.5 9.4 2.2 16.7 < 1.1 1.0 
11 727491 VOJKA 52 22.9.2008 Ca-Mg-HCO3 397.9 228.0 18.2 34.9 3.96 64.6 14.5 8.0 2.1 16.7 < 1.1 1.0 
12 603291 GABČÍKOVO 52 10.11.2008 Ca-Mg-HCO3-SO4 524.5 256.0 20.8 94.4 1.29 91.8 22.5 8.7 1.9 15.8 < 1.1 0.8 
29 736591 SAP-PALKOVIČOVO 52 23.9.2008 Ca-Mg-HCO3 355.0 199.0 17.3 41.7 < 1.0 52.3 12.9 7.0 1.8 13.2 < 1.1 1.2 
17 601691 ROVINKA 53 20.11.2008 Ca-Mg-HCO3 395.5 232.0 14.4 36.5 < 1.0 66.1 18.8 4.9 1.4 14.0 < 1.1 0.5 
18 601591 PODUNAJ. BISKUPICE 53 20.11.2008 Ca-Mg-HCO3-SO4 535.2 289.0 22.6 65.5 2.90 94.3 22.4 5.9 3.1 19.4 < 1.1 < 0.5 
724191 VYDRANY-KVETOSL. 54 30.9.2008 Ca-Mg-HCO3 386.8 220.0 17.6 33.7 4.56 66.2 15.4 5.0 1.1 5.28 < 1.1 0.5 
601191 OL'DZA 54 4.11.2008 Ca-Mg-HCO3 378.6 237.0 56.0 29.4 12.70 59.6 20.4 4.3 1.3 15.8 < 1.1 0.8 
727791 ROHOVCE-ŠTRKOVEC 54 23.9.2008 Ca-Mg-HCO3 435.0 231.0 22.5 48.4 5.06 70.5 16.8 8.0 1.4 15.8 6.6 0.6 
733691 VRAKUŇ 54 23.9.2008 Ca-Mg-HCO3 303.5 207.0 4.6 20.5 2.69 45.9 13.7 2.4 0.5 13.2 < 1.1 < 0.5 
15 725491 HORNÁ POTÔŇ 54 24.9.2008 Ca-Mg-HCO3-SO4 604.7 288.0 26.0 80.6 40.8 102.0 26.1 5.8 1.6 21.1 < 1.1 0.5 
37 729492 ORECHOVÁ POTÔŇ 54 24.9.2008 Ca-Mg-HCO3-SO4 678.3 293.0 37.6 117.0 33.2 104.0 30.1 11.5 3.0 9.7 < 1.1 0.6 
36 729394 VEL'KÉ BLAHOVO 54 24.9.2008 Ca-Mg-HCO3-SO4 594.5 293.0 26.2 84.1 24.2 101.0 24.6 6.0 1.8 12.3 < 1.1 0.7 
33 603391 MLIEČANY 54 20.11.2008 Ca-Mg-HCO3-SO4 534.4 256.0 24.1 85.7 14.20 87.9 25.9 6.9 2.4 5.3 < 1.1 < 0.5 
13 736691 KL'ÚČOVEC 55 22.9.2008 Ca-Mg-HCO3 290.9 209.0 3.3 12.0 < 1.0 39.2 11.8 9.9 0.9 15.8 < 1.1 < 0.5 
14 264791 KLIŽSKÁ NEMÁ 55 10.11.2008 Ca-Mg-HCO3 644.3 464.0 5.8 24.7 < 1.0 93.3 35.4 9.3 1.0 22.0 < 1.1 1.8 
31 600491 VEL'KÝ MEDER 55 20.11.2008 Ca-Mg-HCO3 341.6 226.0 5.5 23.7 < 1.0 53.7 15.5 7.6 1.3 16.7 6.6 < 0.5 
23 738191 ZLATNÁ NA OSTR. 55 24.11.2008 Na-Ca-Mg-HCO3-SO4 958.4 549.0 29.4 124.0 < 1.0 68.4 36.5 109.0 1.7 23.8 < 1.1 1.7 
21 605990 ČALOVEC-KAMENIČNÁ 55 25.9.2008 Ca-Mg-HCO3 442.3 293.0 16.4 14.8 < 1.0 35.5 20.0 38.8 1.1 0.9 < 1.1 1.1 
22 260790 KAMENIČNÁ 55 26.11.2008 Mg-Ca-K-HCO3 926.4 634.0 2.9 60.1 5.56 55.1 58.6 10.8 94.2 33.9 < 1.1 1.4 
26 261190 KAMENIČNÁ-PIESKY 55 25.9.2008 Ca-Mg-HCO3-SO4 798.2 445.0 22.9 108.0 < 1.0 125.0 36.7 24.7 1.7 39.6 42.9 1.8 
19 260290 KOMÁRNO 55 27.11.2008 Ca-Mg-HCO3 1091.5 677.0 26.8 60.1 47.90 146.0 38.7 19.0 39.4 64.7 < 1.1 2.4 
20 260490 KOMÁRNO 55 24.11.2008 Mg-Ca-HCO3 926.2 555.0 27.9 95.1 31.50 77.6 71.0 28.9 2.3 29.0 < 1.1 1.4 
721593 MALINOVO 56 24.9.2008 Ca-Mg-HCO3-SO4 489.0 238.0 21.8 98.8 10.20 70.4 22.4 3.9 1.1 14.0 < 1.1 0.6 
601291 VLKY 56 5.11.2008 Ca-Mg-HCO3 434.6 232.0 25.3 35.0 1.97 71.2 16.2 14.5 2.4 16.7 < 1.1 1.3 
38 603191 JELKA 56 30.9.2008 Ca-Mg-HCO3-SO4 803.5 305.0 57.0 133.0 35.8 140.0 38.0 16.4 3.8 9.7 < 1.1 1.0 
35 600592 JAHODNÁ 56 24.9.2008 Ca-Mg-HCO3 433.0 249.0 13.8 48.0 2.85 76.4 18.6 4.8 1.3 17.6 < 1.1 0.6 
28 264290 OKOČ-ASZÓD 56 29.9.2008 Ca-Mg-HCO3 580.5 342.0 12.7 62.9 < 1.0 107.0 23.7 7.9 0.9 26.4 2.2 2.6 
St. no. SHMU number Locality Number of area Date of sampling Chemical type TDSa HCO3 Cl SO2−4 NO3 Ca2+ Mg2+ (mg L−1Na+ K+ CO2 free CO2 aggr. Corg. 
16 603091 ČUNOVO 51 6.11.2008 Ca-Mg-HCO3 353.4 188.0 18.0 29.7 10.5 57.5 12.8 11.1 2.3 12.3 < 1.1 1.1 
601393 KALINKOVO 52 5.11.2008 Ca-Mg-HCO3 372.9 200.0 18.9 31.2 9.87 61.1 13.9 10.8 2.4 14.0 < 1.1 1.3 
724891 ŠAMORÍN-ČILISTOV 52 18.9.2008 Ca-Mg-HCO3 390.5 246.0 19.3 12.6 < 1.0 63.8 14.2 9.8 2.0 17.5 < 1.1 0.8 
726591 ŠAMORÍN-MLIEČNO 52 5.11.2008 Ca-Mg-HCO3 411.3 243.0 19.5 22.7 3.26 69.4 15.5 10.5 2.1 16.7 < 1.1 0.9 
10 601092 DOBROHOŠŤ 52 4.11.2008 Ca-Mg-HCO3 388.6 235.0 17.3 19.7 2.48 65.1 14.5 9.4 2.2 16.7 < 1.1 1.0 
11 727491 VOJKA 52 22.9.2008 Ca-Mg-HCO3 397.9 228.0 18.2 34.9 3.96 64.6 14.5 8.0 2.1 16.7 < 1.1 1.0 
12 603291 GABČÍKOVO 52 10.11.2008 Ca-Mg-HCO3-SO4 524.5 256.0 20.8 94.4 1.29 91.8 22.5 8.7 1.9 15.8 < 1.1 0.8 
29 736591 SAP-PALKOVIČOVO 52 23.9.2008 Ca-Mg-HCO3 355.0 199.0 17.3 41.7 < 1.0 52.3 12.9 7.0 1.8 13.2 < 1.1 1.2 
17 601691 ROVINKA 53 20.11.2008 Ca-Mg-HCO3 395.5 232.0 14.4 36.5 < 1.0 66.1 18.8 4.9 1.4 14.0 < 1.1 0.5 
18 601591 PODUNAJ. BISKUPICE 53 20.11.2008 Ca-Mg-HCO3-SO4 535.2 289.0 22.6 65.5 2.90 94.3 22.4 5.9 3.1 19.4 < 1.1 < 0.5 
724191 VYDRANY-KVETOSL. 54 30.9.2008 Ca-Mg-HCO3 386.8 220.0 17.6 33.7 4.56 66.2 15.4 5.0 1.1 5.28 < 1.1 0.5 
601191 OL'DZA 54 4.11.2008 Ca-Mg-HCO3 378.6 237.0 56.0 29.4 12.70 59.6 20.4 4.3 1.3 15.8 < 1.1 0.8 
727791 ROHOVCE-ŠTRKOVEC 54 23.9.2008 Ca-Mg-HCO3 435.0 231.0 22.5 48.4 5.06 70.5 16.8 8.0 1.4 15.8 6.6 0.6 
733691 VRAKUŇ 54 23.9.2008 Ca-Mg-HCO3 303.5 207.0 4.6 20.5 2.69 45.9 13.7 2.4 0.5 13.2 < 1.1 < 0.5 
15 725491 HORNÁ POTÔŇ 54 24.9.2008 Ca-Mg-HCO3-SO4 604.7 288.0 26.0 80.6 40.8 102.0 26.1 5.8 1.6 21.1 < 1.1 0.5 
37 729492 ORECHOVÁ POTÔŇ 54 24.9.2008 Ca-Mg-HCO3-SO4 678.3 293.0 37.6 117.0 33.2 104.0 30.1 11.5 3.0 9.7 < 1.1 0.6 
36 729394 VEL'KÉ BLAHOVO 54 24.9.2008 Ca-Mg-HCO3-SO4 594.5 293.0 26.2 84.1 24.2 101.0 24.6 6.0 1.8 12.3 < 1.1 0.7 
33 603391 MLIEČANY 54 20.11.2008 Ca-Mg-HCO3-SO4 534.4 256.0 24.1 85.7 14.20 87.9 25.9 6.9 2.4 5.3 < 1.1 < 0.5 
13 736691 KL'ÚČOVEC 55 22.9.2008 Ca-Mg-HCO3 290.9 209.0 3.3 12.0 < 1.0 39.2 11.8 9.9 0.9 15.8 < 1.1 < 0.5 
14 264791 KLIŽSKÁ NEMÁ 55 10.11.2008 Ca-Mg-HCO3 644.3 464.0 5.8 24.7 < 1.0 93.3 35.4 9.3 1.0 22.0 < 1.1 1.8 
31 600491 VEL'KÝ MEDER 55 20.11.2008 Ca-Mg-HCO3 341.6 226.0 5.5 23.7 < 1.0 53.7 15.5 7.6 1.3 16.7 6.6 < 0.5 
23 738191 ZLATNÁ NA OSTR. 55 24.11.2008 Na-Ca-Mg-HCO3-SO4 958.4 549.0 29.4 124.0 < 1.0 68.4 36.5 109.0 1.7 23.8 < 1.1 1.7 
21 605990 ČALOVEC-KAMENIČNÁ 55 25.9.2008 Ca-Mg-HCO3 442.3 293.0 16.4 14.8 < 1.0 35.5 20.0 38.8 1.1 0.9 < 1.1 1.1 
22 260790 KAMENIČNÁ 55 26.11.2008 Mg-Ca-K-HCO3 926.4 634.0 2.9 60.1 5.56 55.1 58.6 10.8 94.2 33.9 < 1.1 1.4 
26 261190 KAMENIČNÁ-PIESKY 55 25.9.2008 Ca-Mg-HCO3-SO4 798.2 445.0 22.9 108.0 < 1.0 125.0 36.7 24.7 1.7 39.6 42.9 1.8 
19 260290 KOMÁRNO 55 27.11.2008 Ca-Mg-HCO3 1091.5 677.0 26.8 60.1 47.90 146.0 38.7 19.0 39.4 64.7 < 1.1 2.4 
20 260490 KOMÁRNO 55 24.11.2008 Mg-Ca-HCO3 926.2 555.0 27.9 95.1 31.50 77.6 71.0 28.9 2.3 29.0 < 1.1 1.4 
721593 MALINOVO 56 24.9.2008 Ca-Mg-HCO3-SO4 489.0 238.0 21.8 98.8 10.20 70.4 22.4 3.9 1.1 14.0 < 1.1 0.6 
601291 VLKY 56 5.11.2008 Ca-Mg-HCO3 434.6 232.0 25.3 35.0 1.97 71.2 16.2 14.5 2.4 16.7 < 1.1 1.3 
38 603191 JELKA 56 30.9.2008 Ca-Mg-HCO3-SO4 803.5 305.0 57.0 133.0 35.8 140.0 38.0 16.4 3.8 9.7 < 1.1 1.0 
35 600592 JAHODNÁ 56 24.9.2008 Ca-Mg-HCO3 433.0 249.0 13.8 48.0 2.85 76.4 18.6 4.8 1.3 17.6 < 1.1 0.6 
28 264290 OKOČ-ASZÓD 56 29.9.2008 Ca-Mg-HCO3 580.5 342.0 12.7 62.9 < 1.0 107.0 23.7 7.9 0.9 26.4 2.2 2.6 

aTotal dissolved solids.

Total dissolved solids (TDS) and the contents of basic ions in groundwater depend on the intensity of anthropogenic contamination. The chemical composition of groundwater in Žitný Island changes with distance from the Danube River, as well as with the groundwater depth. The chemical analyses (Table 3, and a piper diagram presented in Figure 3) show that the basic hydrogeochemical type of groundwater is Ca-Mg-HCO3, which is dominant on the whole area of Žitný Island, mainly in deeper levels, under 25 m. An expressive sulfates contamination appears in groundwater levels up to 25 m with dominant hydrogeochemical Ca-Mg-HCO3-SO4 type. TDS of groundwater (Table 3) ranges from the lowest values in fluvial zone of the Danube River (290 mg L−1) to the highest values (1,091 mg L−1) at the South-East of the Island. The pH values were between 6.88 and 7.93, and the water temperature between 10.5 and 15.7 °C (Table 2). The basic cations are calcium (35.5–140 mg L−1) and magnesium (11.8–58.6 mg L−1). The dominant anions are represented by (188–677 mg L−1). The values of in deeper water layers are low (12.6–62.9 mg L−1) with the exception of Gabčíkovo (94.4 mg L−1). Higher values were observed in water layers up to 35 m (65.5–133 mg L−1). The Cl contents are low (2.9–56 mg L−1). Concentrations of are also low, often under the detection limit (<1.0 mg L−1). This is connected with reduction conditions in alluvial deposits, following with reduction of . The highest value of (47.9 mg L−1) is at the Komárno station (Table 3). Quality of groundwater is influenced by unfavorable oxidation-reduction conditions with high contents of Fe and Mn.

Figure 3

Piper diagram.

Figure 3

Piper diagram.

Under anthropogenically non-influenced conditions, groundwater is of Ca-Mg-HCO3 type with TDS between 400 and 600 mg L−1. In regions with anthropogenic influence, sulfites, chlorides and nitrates dominate among anions. Sodium and potassium dominate over calcium and magnesium in the cation group, and TDS is usually above 800 mg L−1.

In the layer up to 25 m, groundwater is characterized by three chemical types: (i) a basic distinctly A2 type (Ca-(Mg)-HCO3) with average TDS of 426 mg L−1, which is dominating in the fluvial zone of the Danube River; (ii) a basic-indistinctly A2 type (Ca-(Mg)-HCO3) with average TDS of 662 mg L−1, typical for the central part of Žitný Island, in a continuous strip from Bratislava down to Kolárovo; and (iii) a mixed type with dominance of A2 and S2(SO4) components with average TDS of 911 mg L−1, which is bordered from the south by the line Bratislava – Komárno, and from the north by the Small Danube up to the Váh River.

In the layer below 25 m, groundwater is characterized by three chemical types: (i) a basic distinctly A2 type (Ca-(Mg)-HCO3) with average TDS of 381 mg L−1, which is dominating on the territory of Žitný Island; (ii) a mixed type with dominance of A2 and S2(SO4) components with average TDS of 680 mg L−1, which is probably overlapping from the first layer; and (iii) a basic distinctly A1 type (Na-HCO3) with average TDS of 626 mg L−1, which is found in the South-East part of Žitný Island.

Spatial distribution of δ18O in groundwater

Spatial distribution of δ18O in shallow groundwater (top 25 m) with latitude and longitude of Žitný Island area is presented in Figure 4. Although the data density is still very limited, we can see regional differences in the δ18O distribution. The eastern part of Žitný Island shows enriched δ18O values (up to −9.5‰). The rest of the region shows, however, depleted values (below −10.5‰), which are in agreement with δ18O data measured for the Danube River (Pawellek et al. 2002; Michalko et al. 2011). The enriched δ18O values observed at the east may be due to larger evaporation losses (river runoff in this part of Žitný Island is small), and also due to land irrigation (Kompári et al. 2012), which has been often used in this agricultural region.

Figure 4

Spatial distribution of δ18O with latitude and longitude in groundwater of Žitný Island.

Figure 4

Spatial distribution of δ18O with latitude and longitude in groundwater of Žitný Island.

Vertical distribution of δ18O in groundwater with latitude and longitude of Žitný Island is also presented in Figure 4. While the bottom samples (below 40 m) are depleted in δ18O values, generally below −10.5‰, the sub-surface core observed at around 20 m water depth shows enriched δ18O values between −10.0 and −9.5‰. However, the sub-surface samples (up to 10 m water depth) on the north and north-east side of the island show again depleted δ18O values, close to the values observed for the Danube River system (from −12.4 to −10.2‰; Michalko et al. 2011).

The measured δ18O values in the Danube River (Bratislava) have been varying during the year showing maxima (up to −10.2‰) in winter and minima (down to −12.4‰) in June (Michalko et al. 2011). The June minimum (also accompanied by the largest river flow rates) should be associated with melting of Alpine snow. A δ18O in Alpine precipitation as low as −18‰ was observed by Pastorelli et al. (2001). The δ18O values in shallow wells situated close to the Danube River should be therefore following this temporal variation (with a time delay of a few years; Michalko et al. 2011).

On the contrary, the measured δ18O values in precipitation in south-west Slovakia varied from about −15‰ during winter to about −5‰ during summer (caused by evaporation losses of 16O), with average annual values for Bratislava of −8.83‰, and for Topoľníky (situated at the center of Žitný Island) of −9.35‰ (Holko et al. 2012). Unfortunately, we do not have δ18O sub-surface groundwater data available yet for the Žitný Island stations, which would be collected both during summer and winter seasons at the same stations at the same depth. The δ18O data presented in Table 2 do not show large differences between groundwater samples collected in summer (top horizons down to 25 m with average value of −10.54‰) and in winter (deeper horizons <25 m with average value of −10.74‰). However, for proper temporal variations studies we would need new δ18O results for top horizons in winter and bottom horizons in summer.

The obtained δ18O groundwater data are in reasonable agreement with isotope data measured for the Danube River system indicating therefore that the Danube River should be the main source of groundwater observed at Žitný Island. As we already mentioned, precipitation should be influencing the groundwater regime of Žitný Island only indirectly via elevated flow rates in rivers. We should get, however, a more-clear picture when summer/winter data are available for the same stations.

Spatial distribution of δ13C in groundwater

Distribution of δ13C with latitude and longitude of sub-surface (top 25 m) groundwater samples collected in Žitný Island is presented in Figure 5. Here we see mostly enriched δ13C levels in surface waters of the central part of Žitný Island. The depth profile of δ13C shows large variability – depleted values in the central and eastern parts of the Island at depths between 30 and 50 m (down to −19.22‰ at St. 6), but also enriched δ13C values (−10.66‰ at St. 10 at 80 m depth, up to −10.62‰ at St. 31 at 35 m depth) in the central and eastern part of the Island. Quaternary aquifers which form the main hydrogeology structure of the area (Maglay et al. 2009) are usually represented by large variations in δ13C values, which are connected with a large amount of carbonate materials, as observed, e.g. in the eastern part of the Island.

Figure 5

Spatial distribution of δ13C with latitude and longitude in groundwater of Žitný Island.

Figure 5

Spatial distribution of δ13C with latitude and longitude in groundwater of Žitný Island.

Spatial distribution of 14C in groundwater

The spatial distribution of radiocarbon in sub-surface (top 25 m) groundwater with latitude and longitude of Žitný Island is shown in Figure 6. The surface samples up to 10 m depth at the western part of the Island show 14C values above 80 pMC, representing contemporary groundwater. At the other regions, the observed values are also mostly >80 pMC, except at St. 21 (depth 10.9 m) on the east side of the Island, where a 14C value of 31.5 pMC was measured. At around 60 m water depth a sub-surface core of about 50 pMC is well allocated at the eastern part of the Island as well. Neogene clays were found there a few meters below the surface (Maglay et al. 2009), which prevent a direct infiltration of groundwater of Danube origin to deeper layers. This indicates existence of a confined aquifer formed below the layer of Neogene clay sediments.

Figure 6

Spatial distribution of 14C with latitude and longitude in groundwater of Žitný Island.

Figure 6

Spatial distribution of 14C with latitude and longitude in groundwater of Žitný Island.

CONCLUSIONS

This has been a first attempt to construct isotope maps and to study spatial and vertical distribution of isotopes in groundwater of Slovakia. Groundwater samples collected during 2008–2009 in SW Slovakia, at the area called Žitný Island, improved the data density so that geostatistical methods of data treatment could be applied.

The chemical composition of groundwater of Quaternary sediments of Žitný Island depends on the chemical composition of Danube water, and also of Small Danube and Váh river waters, as well as on the length of infiltration of river waters into the groundwater. The groundwater is characterized by potamogenic mineralization, and its chemical composition is influenced by anthropogenic contamination.

The obtained results on spatial variability of 14C, δ13C and δ18O suggest large isotopic heterogeneity in the groundwater of Žitný Island. While the bottom samples (below 40 m) are depleted in δ18O values, generally below −10.5‰, the sub-surface core observed at around 20 m depth shows enriched δ18O values between −10.0 and −9.5‰. However, the sub-surface samples up to 10 m depth on the north and north-east of the island show again depleted δ18O values, close to the values observed for the Danube River system. In the 14C profile a sub-surface core of about 50 pMC at around 60 m depth at the south-east of the island was observed, in agreement with expectations due to the presence of Neogene clay sediments there. The sub-surface samples up to about 20 m depth show 14C values above 80 pMC, representing thus contemporary groundwater mostly supplied by the Danube River system.

The obtained groundwater isotope data are in good agreement with isotope data measured for Danube water indicating that the Danube River should be the main source of groundwater observed at Žitný Island. More groundwater samples from the Žitný Island area will be collected and analyzed during forthcoming expeditions, which will help to improve the spatial density of isotope data, as well as their seasonal characteristics, and thus contribute to better understanding the groundwater system of Žitný Island.

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