Hydrochemical characteristics and water quality dynamic analysis of shallow groundwater in Huaibei Plain

Shallow groundwater is the most important source of agricultural water supply in Huaibei Plain, and its water quality has attracted wide attention. In this study, mathematical statistics, Shukarev classification, Piper diagram, and comprehensive evaluation of water quality were used to obtain the Hydrochemical characteristics of shallow groundwater in Huaibei Plain. The sources of water chemicals were analyzed by Gibbs diagram and ion ratio relationship, while principal component analysis (PCA) was used to screen key factors influencing water quality. The spatiotemporal evolution of groundwater quality was further examined. The results show that the shallow groundwater in Huaibei Plain is mostly weakly alkaline fresh water, with pH values of 6.6–8.6 and total dissolved solids (TDS) ranging from 192 mg/L to 5302 mg/L. The groundwater exhibits eight hydrochemical types, with \begin{document}${\mathrm{HCO}}_3^- $\end{document}as the dominant anion and Na+ and Ca2+ as the primary cations, and is primarily classified as Class IV water in terms of quality. The water-rock interaction is mainly affected by the weathering of silicate-carbonate rocks. From the upper reaches of the Huaibei Plain to the middle reaches of the Huaibei Plain, the water-rock interaction of dissolved rock weathering evolves from carbonate rocks to silicate-carbonate rocks and then to evaporative rocks. Through principal component analysis, total dissolved solids, oxygen consumption, and nitrate were identified as key indicators for analyzing groundwater quality dynamics. From 2010 to 2021, groundwater quality showed significant improvement, followed by a slight decline. However, different key indicators exhibited varied trends. Due to the natural geological environment, the total amount of soluble substances in shallow groundwater in the Huaibei Plain tends to be distributed in a planar pattern, and the high value points increased, and most of them are distributed in the middle reaches of the Huaibei Plain. The redox condition changes from reducing environment to oxidizing environment. From 2010 to 2018, agricultural activities increased in the upper reaches of the Huaibei Plain, but notable improvements have been observed since 2018. This study provides technical support for the prevention and control of shallow groundwater pollution and protection of groundwater resources in Huaibei Plain area.