Effects of climate-driven shallow groundwater fluctuations on heavy metal redistribution and migration:...

Climate change-induced shallow groundwater level fluctuations significantly alter the spatiotemporal distribution of heavy metal concentrations in aquifers. However, the influence mechanism by which these fluctuations affect changes in heavy metal concentrations has not been explicitly determined. This study developed a three-dimensional coupled SWAT-MODFLOW-MT3DMS model to simulate regional water balance and contaminant transport processes under climate change. The results show that shallow groundwater levels in the study area exhibit seasonal fluctuations, with an annual variation range of 0.1-0.4 m and a distinct response lag to rainfall. In contrast, heavy metal concentrations show an inverse response to water level fluctuations, particularly during periods of rising water levels, when the concentrations of Cd, Zn, Pb, and As significantly decrease. These concentration variations are likely attributed to changes in the hydrodynamic and soil-groundwater hydrochemical fields caused by water table fluctuations. Under the combined influence, the areas exceeding the standards for Cd, Zn, Pb, and As expanded to 4.75, 2.46, 1.59, and 2.26 times by 2029. This poses a severe threat to the downstream area of the site and necessitates the urgent implementation of effective remediation measures.