Evolution of hydrochemistry and water quality of karst groundwater under the effects of intense anthropogenic activities

Intense anthropogenic activities in a karst area will inevitably change the regional groundwater environment and affect the characteristics of the karst groundwater, such as the hydrochemistry and water quality. It is of great importance to study the evolution characteristics of the hydrochemistry and water quality of karst groundwater under intense anthropogenic activities to ensure the stability and sustainable development of karst ecosystems. In this study, a representative synclinal basin-type karst groundwater system in northern China was used as the study object, and the effects of intense anthropogenic activities on the evolution of the hydrochemistry and water quality of the karst groundwater were analyzed using a comprehensive application of a groundwater quality assessment, a multivariate statistical analysis, a hydrogeochemical analysis, and multi-factor regime monitoring of the karst groundwater quality. The results showed that during the time scale from 1991 to 2019, major ion components, such as Na++K+, Ca2++Mg2+, Cl-, SO42- , NO3- , HCO3 -, and total dissolved solids (TDS), in the karst groundwater in discharge area increased by 1.73-4.59 times. In addition, the ion component contents primarily displayed a fluctuating equilibrium state from 2019 to 2023. At the spatial scale, the primary ion components in the karst groundwater in the discharge area were considerably higher than those in the recharge and runoff areas, and they also showed a gradual increasing trend from upstream to downstream and from the surrounding to the middle. Conclusion: Intense anthropogenic activities changed the circulation conditions of karst groundwater and deteriorated the karst groundwater quality. The primary human activity factors that controlled the evolution of the karst groundwater during the different periods were different. The large-scale exploitation of karst groundwater and other human activities primarily affected the karst groundwater quality. The construction of the Zhuangli Reservoir had a positive impact and improved the karst groundwater quality downstream, but its long-term impact on the karst groundwater environment requires long-term monitoring and study.