The alluvial plain (Anqing section) of the lower reaches of the Yangtze River basin is facing increasing groundwater pollution, not only threatening the safety of drinking water for local residents and the sustainable development and utilization of groundwater resources but also the ecological security of the Yangtze River Basin. Therefore, it is necessary to conduct a preliminary analysis on the hydrochemical characteristics and evolution law of groundwater in this area. This study aimed to evaluate potential hydrogeochemical processes affecting the groundwater quality of this area by analyzing major ions in groundwater samples collected in 2019. Compositional relationships were determined to assess the origin of solutes and confirm the predominant hydrogeochemical processes controlling various ions in groundwater. Moreover, factors influencing groundwater quality were evaluated through the factor analysis method, and the control range of each influencing factor was analyzed using the distribution characteristics of factor scores. Finally, reverse hydrogeochemical simulation was carried out on typical profiles to quantitatively analyze the hydrochemical evolution process along flow paths. The Piper trilinear diagram revealed two prevalent hydrochemical facies, Ca-HCO3 type (phreatic water) and Ca-Na-HCO3 type (confined water) water. Based on the compositional relationships, the ions could be attributed to leaching (dissolution of rock salt, carbonate, and sulfate), evaporation and condensation, and cation exchange. Four influencing factors of phreatic water and confined water were extracted. The results of this study are expected to help understand the hydrochemical characteristics and evolution law of groundwater in the alluvial plain (Anqing section) of the lower Yangtze River basin for effective management and utilization of groundwater resources, and provide basic support for the ecological restoration of the Yangtze River Basin.

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Riverbank filtration (RBF) is increasingly being used as a relatively cheap and sustainable means to improve the quality of surface water. Due to the obvious differences in physical, chemical, and biological characteristics between river water and groundwater, there are strong and complex physical, chemical, and biogeochemical effects in the process of bank filtration. In this paper, multivariate statistical analysis was used to identify the spatial variation of hydrogeochemical groundwater in the process of bank filtration. Firstly, the evolution process of groundwater hydrochemistry during the filtration process was identified through factor analysis. According to the results, the evolution of groundwater hydrochemistry in this area is attributable to four main types of reactions: (1) Leaching; (2) Regional groundwater influence; (3) Aerobic respiration and denitrification; and (4) Mn (IV)/Fe (III)/SO42− reduction. According to the similarity of the geochemistry, the flow path could be divided into four different hydrochemical zones through cluster analysis, revealing the evolution law of groundwater hydrochemistry and its main influencing factors during riverbank infiltration. Large hydraulic gradient in The Zone Strongly Influenced by River Water (The first group) resulted in a weak effect of leaching on groundwater chemistry. Reoxygenation and microorganism respiration occurred in The Zone Moderately Influenced by River Water (The second group), The Zone Weakly Influenced by River Water (The third group), and The Zone Strongly Influenced by Regional Groundwater (The fourth group), resulting in fluctuations in Eh and pH values of groundwater. As a result, sulfate reduction and Mn (IV) and Fe (III) reduction alternated along the flow path. The Zone Strongly Influenced by Regional Groundwater (The fourth group) groundwater chemistry was mainly affected by regional groundwater.