Hydrochemical and Isotope (18O, 2H and 3H) Characteristics of Karst Water in Central Shandong Province: A Case Study of the Pingyi-Feixian Region

Karst water serves as an important water supply source in northern China. Hydrochemical and isotope (18O, 2H, and 3H) characteristics are invaluable tools to identify water–rock interaction activities in karst water systems. In this study, the investigation of hydrogeological conditions, hydrogeochemistry, and hydrogen and oxygen isotopes of karst water revealed: (1) HCO3-Ca-type water is widely distributed throughout the study area, while HCO3-Ca·Mg-type water appears in the direct recharge areas and the discharge areas; karst water of the HCO3−·Cl−, Cl−·HCO3−, and Cl− types is scattered in low-land areas; (2) karst water has high δ18O, which may be due to the dissolution and exchange of 18O from the surrounding carbonate rocks in the western discharge zone; and (3) the 3H concentration of karst water is strongly correlated with the content of major ions (Ca2+, Mg2+, HCO3−, SO42−, and Cl−) and it increases along the flow path. It was also revealed that the karst water in the discharge areas is mixed with lateral recharge (infiltration recharge from surface water).