A geochemical and stable isotope investigation of groundwater/surface-water interactions in the Velenje Basin, Slovenia

Kanduč, Tjaša; Grassa, Fausto; McIntosh, Jen; Stibilj, Vekoslava; Ulrich-Supovec, Marija; Supovec, Ivan; Jamnikar, Sergej

A geochemical and stable isotope investigation of groundwater/surface-water interactions in the Velenje Basin, Slovenia | Investigation des interactions entre les eaux de surface et les eaux souterraines dans le bassin de Velenje, Slovénie, par la géochimie et les isotopes stables de l’eau Una investigación geoquímica y de isótopos estables de la interacción agua superficial–agua subterránea en la Velenje Basin, Eslovenia 斯洛文尼亚Velenje盆地地下水–地表水相互作用地球化学和稳定同位素调查 Uma investigação geoquímica e de isótopos estáveis das interações água subterrânea–água superficial na Bacia Velenje, na Eslóvénia Geokemične in izotopske raziskave interakcij med podzemnimi in površinskimi vodami v Velenjskem bazenu, Slovenija

2014

The geochemical and isotopic composition of surface waters and groundwater in the Velenje Basin, Slovenia, was investigated seasonally to determine the relationship between major aquifers and surface waters, water–rock reactions, relative ages of groundwater, and biogeochemical processes. Groundwater in the Triassic aquifer is dominated by HCO₃–, Ca²⁺, Mg²⁺and δ¹³CDICindicating degradation of soil organic matter and dissolution of carbonate minerals, similar to surface waters. In addition, groundwater in the Triassic aquifer has δ¹⁸O and δD values that plot near surface waters on the local and global meteoric water lines, and detectable tritium, likely reflecting recent (<50 years) recharge. In contrast, groundwater in the Pliocene aquifers is enriched in Mg²⁺, Na⁺, Ca²⁺, K⁺, and Si, and has high alkalinity and δ¹³CDICvalues, with low SO₄²–and NO₃–concentrations. These waters have likely been influenced by sulfate reduction and microbial methanogenesis associated with coal seams and dissolution of feldspars and Mg-rich clay minerals. Pliocene aquifer waters are also depleted in¹⁸O and²H, and have³H concentrations near the detection limit, suggesting these waters are older, had a different recharge source, and have not mixed extensively with groundwater in the Triassic aquifer.

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