Hydrochemical Response of Karst Groundwater to Rapid Urbanization in Xingtai, North China.

Karst groundwater is the main water source for domestic, industrial, and agricultural needs in Xingtai City, North China. The objective of this study was to comprehensively access changes in the hydrochemical characteristics and evolution of karst groundwater in response to rapid urbanization. Water samples from the late 2010s and the 1970s were compared utilizing statistical analysis, hydrochemical diagrams, and inverse simulation technology. The total dissolved solids (TDS), total hardness (TH), NO₃⁻, and Fe contents were significantly higher in the more recently obtained karst groundwater samples. Further, the dominance of HCO₃-Ca-type water decreased, with new types emerging, relative to 1970s karst groundwater. Abnormal TDS, TH, SO₄²⁻, NO₃⁻, and Cl⁻ concentrations can be attributed to sewage discharge and fertilizer. Two groundwater discharge areas around the center of Xingtai City and Yangfan Town in the south of the study area were the most significantly affected by human activities. However, inverse modeling indicated that the dissolution of gypsum and halite, as well as cation-exchange processes, occurred in the groundwater paths during both periods. Recent increases in ion concentrations of karst groundwater in the study area have caused carbonate minerals to dissolve, resulting in a further increase of ion concentrations. The hydrochemical response and evolution of karst groundwater requires further study. [ABSTRACT FROM AUTHOR]