[Characteristics and Controlling Factors of Groundwater Chemical Change in a Typical Area of Groundwater Exploitation Reduction in Hebei Province]

Due to groundwater overexploitation control in Hebei Province, the significant reduction of groundwater exploitation inevitably induces changes in regional groundwater quantity and quality. How to effectively identify these changes caused by groundwater exploitation reduction （GWER） is directly related to the safety of groundwater resources in Hebei Province. The eastern plain of Handan was selected as the study area, where groundwater restoration is remarkable. Groundwater chemical changes and controlling factors were analyzed by integrating multi-statistics, graphic method, and absolute principal component-multiple linear regression receptor model （APCS-MLR）. The results showed that the variability of groundwater chemistry in this region was mainly controlled by water-rock interaction and human activities （agricultural fertilization, GWER, and inter-basin water transfer）. Although the groundwater quality in the study area still showed the vertically distributed characteristics of "Brackish water at the top and freshwater at the bottom," the GWER improved the shallow groundwater quality to some extent and resulted in the evolution from salt water to brackish water. The distributed area of salt water reduced from 872 km² to 310 km², the distributed area of brackish water increased from 4 141 km² to 4 632 km², and the distributed area of freshwater increased from 2 574 km² to 2 645 km². The main controlling factors of chemical compositions in shallow groundwater were leaching-enrichment factor based on salinity, agricultural factor, and geological factor based on alkalinity, and their contribution rates were 57%, 17%, and 16%, respectively. While the main controlling factors of chemical compositions in deep confined water were the leaching-enrichment factor based on salinity, geological factor based on alkalinity, and pollutant migration factor, and their contribution rates were 61%, 15%, and 11%, respectively. The findings deepen the understanding of changes in groundwater chemistry in GWER areas, which is of great significance to the rational development and utilization of groundwater resources in GWER areas of Hebei Province.