Hydrochemical characteristics and evolution processes of karst groundwater in Pingyin karst groundwater system, North China

Karst aquifer is the main source of drinking water in the world, but it usually has high vulnerability to contamination. Understanding the chemical characteristic is the precondition for the protection and management of karst groundwater. To reveal the hydrochemical process and the key factors dominating the chemical compositions of karst groundwater, 23 groundwater samples from Pingyin karst groundwater system and 3 surface water samples from the Yellow River are collected for hydrochemical and isotopic (δ 18 O and δ 2 H) analysis, and multivariate statistical analysis. Results indicate that two clusters (C1 and C2) can be generated from HCA based on groundwater samples. Samples in C2 (mainly collected in the southern hilly area) are predominantly Ca type, and samples in C1 (mainly collected in the central area) are mixed types. Chemical compositions of karst groundwater in the study area are mainly dominated by the dissolution of the dolomite minerals. However, domestic sewage has severely influenced the qualities of groundwater samples in C2. In the meantime, the chemical characteristics of karst groundwater in C1 are significantly influenced by the Yellow River. Soil media is only the basic geologic setting indirectly influencing the chemical compositions of karst groundwater. The karst groundwater samples in C2 are characterized by high level of NO 3 − and Cl − due to the seepage of domestic sewage, but the qualities of karst groundwater samples C1 turn to good due to the infiltration of the Yellow River water. The hydraulic connection between karst groundwater and surface water from the Yellow River is identified. At present, deep buried karst groundwater in the central plain along the Yellow River should be regarded as the main supply source for drinking and other purposes. In addition, government agencies should adopt some strategies to control the indiscriminate discharge of domestic sewage in the rural areas, and to further improve the water quality of the Yellow River to protect the karst groundwater environment in the lower reach of the Yellow River.