Hydrochemical Evolution Characteristics and Salinization Processes of Groundwater in a Coastal Plain Area, Southeast China

ABSTRACT A comprehensive understanding of groundwater hydrochemical characteristics and its evolution mechanisms that control the salinization process is essential for sustainable groundwater management, particularly in coastal plains with intensive anthropogenic activities. In this study, a combination of hydrochemical analysis, stable isotope tracing, PCA, and HFE‐D methods was used to identify the spatial characteristics of groundwater hydrochemistry and assess the processes controlling its evolution associated with groundwater salinization in the Wenhuang Plain, Southeast China. The results indicate that rock weathering dominated the hydrochemical evolution of groundwater in conjunction with cation exchange, and silicate weathering was the dominant weathering type controlling the chemical composition of surface water and groundwater. The weathering of evaporites was a major contributor to salinity in deep groundwater (DGW) II, related to lateral runoff recharge with the long‐term water–rock interaction. Seawater intrusion, induced by groundwater over‐exploitation, caused an imbalance in mineral saturation. This provided favorable conditions for reverse cation exchange, consequently leading to an excess of Ca 2+ and Mg 2+ in the DGW, particularly for the samples adjacent to the estuary and coastal zones. The salinization of surface water and shallow groundwater was primarily controlled by evaporation and anthropogenic inputs. Freshwater–saltwater mixing was the dominant process controlling groundwater salinization in DGW I, accounting for 25.8% of the samples identified as being in the intrusion phase. Principal component analysis (PCA) confirmed that water–rock interactions, anthropogenic activities, and seawater intrusion are the key factors governing groundwater geochemistry, explaining 82.62% of the total variance. These findings can help improve groundwater utilization and management for sustainable development in coastal areas and reveal the negative impacts of seawater intrusion on groundwater quality.