Groundwater quality variability with inter-basin water transfer and overexploitation control in an agriculture-dominant subregion of North China Plain

Inter-basin water transfer (IBWT) and groundwater exploitation reduction (GWER) are changing the surface and subsurface hydrological processes in the North China Plain (NCP), but groundwater quality variability with the impacts of IBWT and GWER remains unclear. To address this issue, a total of 209 groundwater samples and 26 surface water samples were collected from a typical subregion (Handan Eastern Plain) of the NCP, and major ions & trace elements were measured during three sampling campaigns (May, September, December 2023). Results showed that deep groundwater (DGW) was more suitable for drinking than shallow groundwater (SGW) in this region. Poor quality of SGW in urban areas and farmlands may result from agricultural practices and sewage from domestic and industrial sectors. Salinity control measures should be fully considered to avoid high salinity hazards, in the case of utilizing groundwater (especially SGW) to irrigate the crops. The fluctuations of water levels (below 2 m) were mostly concomitant with reduced salinity of SGW. The salts likely accumulated in the SGW and DGW once the water level increased over 2 m. Additionally, the GWER and the Water Diversion from the Yellow River to the Baiyangdian Lake in Hebei Province jointly contributed to the desalinization of shallow groundwater, while the GWER and the South-to-North Water Diversion Project triggered the salinization of deep groundwater. This study is a step forward in the knowledge of groundwater quality variability impacted by IBWT and GWER, with important implications for optimized regulation and management of multiple water sources in similar basins worldwide.