Exploring the Hydrogeochemical Formation and Evolution of the Karst Aquifer System in the Yufu River Based on Hydrochemistry and Isotopes

Jinan, renowned as the “Spring City” in China, relies significantly on karst groundwater as an indispensable resource for socio-economic development, playing a crucial role in ecological regulation, tourism, and historical and cultural aspects. The Yufu River basin, situated within Jinan’s karst region, represents a vital riverine leakage zone. Therefore, investigating the evolutionary characteristics and causative mechanisms of surface water and groundwater at different aquifer levels in the Yufu River basin can provide a scientific foundation for the protection of Jinan’s springs. This study, based on hydrogeochemical and isotopic data from the river water, shallow groundwater, deep groundwater, and springs in the Yufu River basin, explored the hydrogeochemical evolution in this region. The findings revealed significant spatial variations in the hydrochemical parameters of the Yufu River basin. Groundwater received contributions from surface water, while springs represented a mixture from both surface water and various recharge aquifers. Dominant ions include Ca 2+ and HCO 3 − , with prevailing hydrochemical types being HCO 3 ·SO 4 -Ca and HCO 3 -Ca. Atmospheric precipitation served as the primary source of recharge for surface water and groundwater in the Yufu River basin, albeit influenced by pronounced evaporation processes. The hydrochemical composition in the Yufu River basin was primarily attributed to water–rock interactions, mainly driven by the combined effects of carbonate rock, silicate rock, and gypsum weathering and dissolution. Among these, the weathering and dissolution of carbonate rocks played a dominant role, with human activities exerting a relatively minor influence on the hydrochemistry of the Yufu River basin.