ABSTRACT
Slovenia’s carbonates represent an ideal research polygon for the karst and fractured aquifers, as the limestone and dolomite sedimentation persisted almost continuously from the Upper Permian to the end of the Mesozoic. This process resulted in deposition of carbonate rocks which are several kilometers thick. A database of 430 boreholes in dolomite and limestone aquifers has been constructed, out of which 90 boreholes used for public water supply systems, were chosen for hydrogeochemical and isotopic analyses. Results indicate several differences between individual dolomite and limestone aquifers for most of analyzed geochemical parameters. Total alkalinity ranges from 2.1 mM to 8.6 mM. The study is focused on calcium and magnesium concentrations within aquifer and revealed, that the average value for Ca2+ in all aquifers is 63.8 mg/l (ranging from 22.7 to 313 mg/l), while for Mg2+ is 30.8 mg/l (ranging from 6.7-72.0 mg/l). Mg2+/Ca2+ molar ratios lie mostly in the range 0.20 to 1.84, indicating weathering of pure dolomites; however large value spans occur for different aquifers, which can be explained by the composition and origin of dolomite rocks. The highest values of Mg2+/Ca2+ ratio appear for late-diagenetic Cordevolian dolomites, while the lowest for relatively impure Lower Triassic dolomites. δ13CDIC range from −14.6 to −8.2‰ and reveal the contribution of organic matter and dissolution of carbonates within aquifer. According to mass balance calculation it was estimated that contribution of organic matter within aquifer ranged from 41.0 to 62.2% and dissolution of carbonates from 37.8 to 59.0‰.
