Data on Seasonal variations in the Interaction Between Surface Water, Groundwater, and Thermal water at Čateško Polje, SE Slovenia
Description
Herein, we present a dataset of geochemical data (pH, temperature, conductivity, dissolved oxygen) from two sampling seasons (winter - February 2021 and summer - June 2021) to evaluate geochemical processes in the thermal water-groundwater-river water system before the construction of a hydrothermal power plant at Čateško polje, SE Slovenia. The samples were taken from surface water (a Krka tributary) on the right bank of the river. Deep groundwater samples (V-2/07 and V-1/07) were collected using a Solinst discrete interval sampler, while shallow groundwater samples (M-29/84, PM-3/07) were obtained using a Model 12.04 SA-250 ml bailer sampler set. Thermal water samples (V-16/97, V-3/69, V-15/88, and K-1/69) were collected by opening the pumps two hours before sampling in cooperation with the company Terme Čatež d.d. from the pipe, and the Terme Čatež fountain was sampled directly from the pipe. Field parameters were measured with a WTW MultiLine 3510 IDS, alkalinity by Gran titration, δ13CDIC by CF-IRMS, elemental concentrations by ICP-MS, and 87Sr/86Sr by MC-ICP-MS, while TOC and anions were analyzed by infrared spectrometry and ion chromatography. PHREEQC modeling showed groundwater is generally oversaturated with CO₂ (except V-2/07) and with calcite/dolomite, except in some thermal waters. Groundwater is dominated by HCO₃⁻, Ca²⁺, Mg²⁺, Na⁺, and K⁺, with trace elements following the order B > Li > Mn > Zn > Al > Rb > Mo > Fe > Ni > Cu > V > Cr; δ13CDIC ranges from −13.8‰ to −5.7‰ and 87Sr/86Sr from 0.70858 to 0.70934. Soil CO₂ dominates shallow wells and river water, carbonates prevail in deep and thermal waters, and only well V-2/07 shows a higher silicate contribution. Data from field and laboratory work were used to calculate saturation indices and CO₂ sources/sinks (SIcalcite, SIdolomite, pCO₂), followed by statistical analysis in R (PCA, t-tests, correlations), which identified four clusters. The Water Quality Index (WQI), calculated according to Meng (2016), ranked the sites as: V-1/07 > Terme Čatež wells > M-29/84 > PM-3/07 > V-2/7 > Terme Čatež fountain > River Sava after the Krka confluence. The data provides valuable background information on aquatic geochemistry and biogeochemical processes, which will be crucial for the future management of hydropower plant construction at Čateško polje, SE Slovenia, as well as for the broader Sava River system.
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Sampling was performed in two seasons: February 2021 (winter) and June 2021 (summer). Sampling was conducted at pre-existing drilled piezometers and a fountain (Table 1), which were specifically established for long-term water monitoring related to the construction of hydropower plants (HPPs) in the middle and lower reaches of the Sava River. Samples were collected from: a) Surface water from the Sava River after the confluence with the Krka tributary at the Slovenian Environmental Agency (SEA) gauging station on the right bank of the river b) Deep groundwater samples (V-2/07 and V-1/07) using a Solinst discrete interval sampler c) Shallow groundwater samples (M-29/84, PM-3/07) using a Model 12.04 SA-250 ml bailer sampler set d) Thermal water samples (V-16/97, V-3/69, V-15/88, and K-1/69), collected after operating the pump for two hours prior to sampling, in cooperation with Terme Čatež d.d. e) Fountain water sampled directly from the pipe. Temperature (T), pH, dissolved oxygen (DO), and conductivity were measured in the field using a WTW MultiLine® Multi 3510 IDS portable meter. Water samples for the determination of major and trace elements, as well as the 87Sr/86Sr isotope ratio, were stored in plastic (PET) bottles and acidified with 0.1 mL of concentrated HNO₃ (suprapure, Carlo Erba, Italy). Samples for total alkalinity were collected in 60 mL HDPE bottles after filtration through Macherey-Nagel 0.45 µm Chromafil® Xtra PVDF -45/25 filters using a Chirana gas tight syringe. These bottles were pre-washed twice with the sample water prior to collection. Element concentrations were determined by inductively coupled plasma mass spectrometer (ICP-MS) (7900x Agilent Technologies, Tokio, Japan). On the basis of total Sr concentrations, to prepare a sample for the determination of 87Sr/86Sr by multi-collector ICP-MS (Nu II, Nu Plasma, Ametec, Wrexham, Great Britain). Total alkalinity was determined within 24 hours of sample collection using the Gran titration method (Clesceri et al., 1998). Continuous-flow IRMS (Europa Scientific 20–20) with an ANCA-TG preparation module was used to measure δ13CDIC. TOC was measured using infrared spectrometry (SIST ISO 8245:2000), and anions (NO₃⁻ and SO₄²⁻) were measured using an ion chromatograph 881 Compact IC pro. For thermodynamic modeling to evaluate the log pCO2 and the saturation state of calcite (SIcalcite) and dolomite (SIdolomite), the PHREEQC speciation program (Parkhurst, 1999) was used. The WQI reflects water quality parameters of trace elements and their weightings (Wi) which were assigned according to the relative importance of different water quality parameters in the overall quality of water for drinking purposes. Statistical analyses and accompanying visualizations were conducted in the R environment (R Core Team, 2021). To visualize correlations between different parameters, a correlation matrix was created using the R package corrplot.
Institutions
- Jožef Stefan InstituteLjubljana, Ljubljana