Insights into karst groundwater hydrogeochemical characteristics and spatial evolution of in the Jinan karst aquifer system, northern China

Karst aquifers are strategically important as they supply domestic water and are a resource for irrigation and industry in northern China. The heterogeneity of the karst aquifer medium makes it vulnerable to external influences. Here, samples of surface water and groundwater in a typical karst groundwater system of Jinan (China) were collected in December 2021, and the sample data were analyzed to further elucidate the hydrogeochemical processes. Results showed that the predominant water chemical type is HCO3-Ca, with a lesser proportion of type HCO3 · SO4-Ca and SO4-Ca. The dominant water–rock interactions comprise the dissolution of carbonate minerals, gypsum, and halite and ion exchange. Dissolution/precipitation of calcite, dolomite, and gypsum determines the concentrations of Ca2+, Mg2+, HCO3-, and SO42-. In terms of spatial distribution, the indirect and direct recharge areas are dominated by calcite dissolution, followed by dolomite dissolution, and are prone to ion exchange. The hydrogeochemical formation mechanism of the discharge area is more complicated by other hydrochemical processes and anthropogenic activities. These results provide guidance for global karst groundwater resource management and pollution prevention.