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The Sangu Spring Basin is located in an important economic area, and groundwater is the main source of water for local life and industry. Understanding the sources of chemical components in groundwater is important for the development and utilization of groundwater. In this paper, we analyzed the origin of the chemical components of groundwater and their evolution in the Sangu Spring Basin using statistical analysis, Piper diagrams, Gibbs diagrams, ion ratios, and combined hydrochemistry–isotope analyses. The results show that the groundwater in the Sangu Spring Basin is mainly derived from atmospheric precipitation, that the groundwater in stagnant and confined environment zones was formed under colder climatic conditions, and that the surface water (SW) has a close hydraulic relation with the groundwater. Water–rock interaction is the main factor controlling the composition of groundwater. The compositions of groundwater are mainly derived from carbonate weathering, silicate weathering, and dissolution of gypsum. Na+ and K+ in groundwater mainly come from the dissolution of albite and potassium feldspar, rather than rock salt. Ion exchange occurs in karst groundwater (KGW) and fissure groundwater (FGW), and ion exchange is dominated by the exchange of Mg2+ and Ca2+ in the groundwater with Na+ and K+ in the rock or soil. Sulfate in groundwater is derived from dissolution of gypsum, infiltration of atmospheric precipitation, and leakage of SW. Groundwaters with the highest sulfate content are located in the vicinity of SW, as a result of receiving recharge from SW seepage. Groundwaters with higher sulfate contents are located in the stagnant and deeply buried zones, where sulfate is mainly derived from the dissolution of gypsum. SW seepage recharges groundwater, resulting in increased levels of Cl−, NO3− and SO42− in groundwater. These insights can provide assistance in the protection and effective management of groundwater. [ABSTRACT FROM AUTHOR]

Karst groundwater is the most important source of water supply for Shanxi province, northern China. In this study, different hydrogeochemical indices along with multiple isotope (2H, 18O, and 87Sr/86Sr) were used to identify the main factors controlling groundwater salinization and hydrogeochemical processes in the Xin'an karst groundwater system at Shanxi. The region's karst groundwater system was divided into three geologically distinct subsystems, namely, the Changzhi–Xiangyuan subsystem (C–X), Huguan–Pingshun subsystem (H–P), and Licheng subsystem (LC). HCO3–Ca·Mg was dominant chemical type for karst groundwater system. The H–P and LC subsystems experienced similar hydrogeochemical processes; from the recharge zone to discharge zone, the Sr2+ content, Sr2+/Ca2+ ratio, and TDS concentrations of karst groundwater gradually increase along the flow direction. However, for C–X subsystem, from the deep buried zone to discharge zone, the Sr2+ content, Sr2+/Ca2+ ratio, and TDS concentrations gradually decrease due to the mixing of fresh water. The main source of karst groundwater was meteoric water, and it is also recharged by surface water and shallow groundwater. The water–rock interactions in conjunction with the cation exchange absolutely predominated in hydrogeochemical evolution of karst groundwater. Major ions, such as Ca2+, Mg2+, HCO3−, and SO42−, originated from the dissolution of carbonate and sulfate minerals. Dissolution of sulfate minerals was the major process for the increase of groundwater salinity. The NO3−, Cl−, and K+ could be attributed to agricultural and human activities, and the Na+ originated from intense mining activities in the study area. The results will facilitate understanding of hydrogeochemical processes and groundwater pollution to enable effective management and utilization of karst groundwater resources. [ABSTRACT FROM AUTHOR]