Monsoonal influence on arsenic mobilization in groundwater: Geochemical and hydrogeological perspectives
Authors: Majumder, S., Datta, S., Nath, B., Neidhardt, H., Berner, Z., Hidalgo, M. and Chatterjee, D.
Journal: Arsenic Research and Global Sustainability - Proceedings of the 6th International Congress on Arsenic in the Environment, AS 2016
In this study, we have investigated the potential role of monsoon on the hydrochemical evolution and concomitant As release using stable isotopes (δ18O and δ2H). A low-land flood plain and a natural levee have been selected for this purpose. Stable isotope signature depicts recharge of the shallow groundwater by evaporated surface water and Cl/Br molar ratio shows vertical recharge process in the wells within the flood plain area, especially during the post-monsoon season, while influences of both evaporation and vertical mixing are visible in the natural levee wells. Increase in DOC concentrations (from 1.33 to 6.29 mg/L), moving from pre- to post-monsoon season, indicates possible inflow of organic carbon to the aquifer. Simultaneous increase in AsT, Fe(II), and HCO3− during the post monsoon season highlights an ongoing reductive dissolution of As-rich Fe-oxyhydroxides. The subsequent increase in As(III) (> 200%), in both the flood plain and natural levee samples, with stable AsT concentration may refer to anaerobic microbial degradation of DOC coupled with the reduction of As(V) to As(III) without triggering additional As release from the aquifer sediments.