Coupled evolution of sedimentary environment and groundwater flow systems drives groundwater arsenic heterogeneity in...

In the alluvial-lacustrine Jianghan Plain (JHP), widespread but heterogeneous arsenic(As) contamination in groundwater is closely related to the evolution of the groundwater flow system (GFS) since the Last Glacial Maximum (LGM) under progressively changing climatic conditions. Approximately 72% of groundwater samples in As hotspots exceeded the WHO (World Health Organization) guideline of 10 μg/L, with concentrations up to 2620 μg/L. However, the role of GFS evolution as a key driver of As enrichment has received limited attention. Through systematic integration of basin sedimentology, paleohydrogeology, and the modern hydrogeochemical environment, this study established a macro-scale theoretical framework linking "sedimentary evolution-GFS driving-geochemical field formation" in the JHP. Paleoclimate-controlled sedimentary environment significantly influenced both GFS evolution and As-rich groundwater development since the LGM. Deep incision of the ancient Yangtze River channel during the LGM created a strong potential sink and promoted an upward discharge pattern of multi-hierarchical GFSs. Rapid burial of weathered As-rich minerals during the late deglaciation period (LDP) provided a material source. The formation of an overlying clay layer during the Holocene warm period (HWP) maintained reducing conditions in the underlying aquifer. Collectively, these processes formed the origin of As-rich groundwater. Additionally, the hierarchically nested GFS pattern characterized by a gradually sluggish flow and upward discharge, drives the continuous convergence of As-rich groundwater toward regional discharge areas, contributing to the stable occurrence and heterogeneous distribution of As. This conceptual model elucidated the control mechanisms of As-rich groundwater in alluvial-lacustrine plains, supporting effective utilization and sustainable management of regional groundwater.