LAUSR

The prevalence of arsenic (As)-affected groundwater in the Late Pleistocene and Holocene aquifers leads to serious arsenicosis worldwide. However, the geogenic foundational processes underlying the high As aquifers remain elusive. Here we present joint lines of evidences from chronological, sediment geochemical and geomicrobial analysis that climate change since the Last Glacial Maximum (LGM) initiates the genesis of high As aquifers in the central Yangtze River Basin, which represents Quaternary alluvial-lacustrine floodplains affected by arsenicosis occurrence. Optically stimulated luminescence-based sediments dating and grain size characterization indicate that the LGM depositional boundary also separates the Late-Pleistocene/Holocene high arsenic aquifers from the underlying arsenic-depleted aquifers. Further examination of solid-phase As/Fe/S speciation and associated microbial communities function suggests that the pre-LGM depositional environments characteristic of S metabolism engender the fixation of As in pyrite, whereas during the post-LGM period climate change to warm and humid leads to As repartitioning to Fe/Mn oxides in response to strong chemical weathering. This may have contributed to a dynamic fate of As in the post-LGM depositional environments and thus a highly variable aqueous As concentrations over depth. Our results highlight the important roles of climate change has played in the genesis of high As aquifers, with implications for other LGM-affected regions worldwide as well as for the evolution of high arsenic aquifers under future climate change.