Novel insights into the mechanisms controlling the heterogeneous distribution of arsenic-rich groundwater in the Yangtze River Basin from evolutionary analysis of sedimentary environment and groundwater flow systems

In the alluvial-lacustrine Jianghan Plain (JHP), the distribution of widespread but heterogenous arsenic(As)-contamination of groundwater is determined by the evolution of the groundwater flow system (GFS) since the Last Glacial Maximum (LGM), under the influence of progressively changing climate. Whereas, as a critical driving factor for As enrichment, the evolution of GFS has been largely overlooked. Based on the systematical integration of basin sedimentology, paleohydrogeology, and modern hydrogeochemical environment, this study establish a macro-scale theoretical framework linking “sedimentary evolution–GFS driving–geochemical field formation” in the JHP. Sedimentary environment of the aquifer system shaped by paleo-climatic changes has significantly influenced both GFS evolution and As-rich groundwater enrichment since the LGM. Beyond the reductive dissolution of amorphous As-rich minerals under favorable sedimentary conditions, the spatio-temporal GFS evolution plays a crucial role in As heterogeneity. Deep incision of the ancient Yangtze River channel leads to the most potent GFSs driving during the LGM. Rapid burial and weathering As-rich minerals provide the ample provenance during the late deglaciation period (LDP). The formation of an overlying clay cover during the Holocene warm period (HWP) ensures a reducing environment for underlying aquifer. These factors collectively lay the foundation for As-rich groundwater formation. Additionally, the continuous convergence of As-rich groundwater towards the regional discharge are is driven by the multiple-hierarchical GFS pattern alongside a gradually sluggish flow and upward discharge under a sustained hydraulic gradient, which contributed to the stable occurrence of As.