Environmental Isotopes and Cl/Br Ratios Evidences for Delineating Arsenic Mobilization in Aquifer System of the Jianghan Plain, Central China

Environment isotopes(δ18O and δ2H) and Cl/Br ratios in surface water and groundwater are combined to investigate arsenic mobilization in aquifer system of the Jianghan Plain. The groundwater has relatively high arsenic concentrations, ranging from 3.6 to 1 055.3 μg/L with an average of 102.2 μg/L, which exceeds China's drinking water standard（10 μg/L）. The arsenic content of surface water samples is quite low with the range of 6.0–14.3 μg/L, averaging 9.5 μg/L. δ18O and δ2H values for surface water and groundwater samples plot close to the local meteoric water line（LMWL）, reflecting their meteoric origin; a subset of the samples（shallow wells, 10 m） shows a shift to LMWL, commensurate with mixing with surface water and evaporation. The correlations between δ18O values and Cl concentration and Cl/Br ratios as well as arsenic concentration demonstrated that surface water and groundwater interactions, including active exchange between river/pond water and groundwater and vertical infiltration from agricultural and aquacultural soils, were dominated processes affecting arsenic mobilization in shallow groundwater system and lateral recharge was the main process controlling arsenic behavior in deep groundwater system. The results of this study will be beneficial to understanding the causes of arsenic mobilization in Jianghan groundwaters at different depths.