Hydrogeochemical characteristics and gradual changes of groundwater in the Baiquan karst spring region, northern China

Karst groundwater in the Baiquan spring region is necessary for domestic use, agricultural irrigation, and industrial production in Xingtai City, northern China. Understanding the hydrogeochemistry of important groundwater resources and how they respond to sustained mining and agricultural activities is essential. Samples of karst groundwater and Quaternary sediment groundwater were collected and their hydrogeochemical properties were evaluated, environmental isotopes were determined, and statistical analyses were performed to reveal the geochemical processes controlling groundwater quality. The results indicate that the karst groundwater tested in this study area has a meteoric origin, the dissolution processes of dolomite and gypsum are dominant in water–rock interactions, and evaporation occurs in discharge areas where the groundwater is shallow-buried and slow-flowing. The preferential flows of karst groundwater in the northern region are characterized by the chemical compositions of HCO 3 –Ca·Mg type, while concentrated mining activities in the southern region increase the concentration of SO 4 2− in karst groundwater, and SO 4 ·HCO 3 –Ca, HCO 3 ·SO 4 –Ca, SO 4 ·HCO 3 –Ca·Mg, and SO 4 –Ca hydrochemical types of groundwater are formed. Compared to karst groundwater, the variability of the TDS and main ion concentrations in shallow Quaternary sediment groundwater is evident, and the hydrochemical types are also more diverse. In addition to mining activities, sewage from agricultural production and domestic sources have also negatively impacted the quality of groundwater in both exposed and buried carbonate areas, as evidenced by the increasing NO 3 − and Cl − contents in karst groundwater and Quaternary sediment groundwater. These results help explain the mechanisms of gradual hydrogeochemical changes and may assist the development of effective solutions to prevent groundwater pollution.