Chemical and isotopic characteristics of groundwater-dominated Radovna River (NW Slovenia)

In order to investigate stream water, spring waters and water from a borehole facies, weathering processes, residence times and average recharge altitudes in the Radovna River valley were analysed for their concentrations of dissolved Ca²⁺, Mg²⁺, K⁺, Na⁺, HCO₃ ⁻, Cl⁻, NO₃ ⁻, SO₄ ²⁻ and for the isotope compositions of hydrogen, oxygen and dissolved inorganic carbon (DIC). All water samples show a Ca²⁺–HCO₃ ⁻ water facies with low contents of K⁺, Na⁺, Cl⁻, NO₃ ⁻ and SO₄ ²⁻. Water–rock interaction and carbonate weathering are the significant contributors to water geochemistry. Analysis of the water chemistry indicates that waters drain a monolithological terrain and non-anthropogenically influenced watershed. The δ ²H and δ ¹⁸O values are seasonally dependent on the snowmelt, precipitation and evaporation. The average recharge altitudes for all sampling locations are between 1120 and 2130 m. The average residence time for the stream water is 2.4 years and for karst springs 1.2 years. The δ ¹³C_DIC values in all samples are influenced by dissolution of carbonates, degradation of organic matter and by equilibrium with atmospheric CO₂. All geochemical and isotope analyses show changes in stream water in the downstream direction and are highly dependent on the inflow of karstic spring. Based on hydrogeological mapping, geochemical and stable isotope results, a conceptual hydrogeological model of the Radovna system, in which karstic and alluvial aquifers are in contact, was determined.