Characteristics Of Arsenic Behaviors During Surface Water-Groundwater Interaction In Hyporheic Zones

More and more attention has been paid to study on behavior of arsenic in hyporheic zone. Two typical units were chosen in Shahai country, Hangjinhouqi, including perennial lake and dried lake(assigned as PL and DL, respectively). Along different profiles near the PL and DL, porewater, groundwater and sediments were collected and analyzed for physiochemical parameters. Chemical characteristics of porewaters and arsenic transfer and transportation has been investigated during surface water and groundwater interaction, and arsenic transport model was established for the hyporheic zone. The main conclusions and findings are summarized as follows.(1) Along the flow paths, porewater arsenic increased from the recharge area to the flow area in the zone of near the dried lake.(2) In the presence of surface water, oxic conditions were observed close to the perennial lake. Arsenic was enriched in the sediments coated by Fe/Mn oxides. This As-accumulated zone was located at depths of 3.5 m and between 6 and 8 m within the range of 25 m away from the lake. However, the adsorbed As would be mobilized in the presence of competing anions and microbes.(3) Surface water affected the arsenic cycle in hyporheic zone through biological, chemical processes, hydrodynamic conditions and redox environment. Near the lake, correlations between arsenic and dissolved iron, manganese, and bicarbonate were poor. However, there were good positive correlations between groundwater arsenic and sediment organic matter, and negative correlations between groundwater arsenic and contents of iron, manganese, the reflectance of sediments.(4) The formation of As-enriched areas was related to the fine sand with good conductivity and high concentrations of DO and low concentrations of organic matter in surface water.The major innovative advances achieved in this dissertation are shown as follows.(1) The interaction between groundwater and surface water was proved by the reflectance of sediments, showing that the interaction zone was in the range at depths of 3.5 m, 6 to 8 m, and the distance between 0 and 25 m away from the lake. The shorter distance from the lakeshore was, the stronger groundwater-surface water interaction.(2) The cycle of arsenic was complex in the areas with the surface water-groundwater interaction. In the interaction zone, arsenic was enriched in a fine sand subzone with high iron/manganese contents.