Influence Of Surface Water Recharge On Groundwater Chemical Characteristics And Arsenic Distribution

Groundwater with high arsenic concentration is widely distributed in the world,which seriously threats human health.As an important recharge source of groundwater,surface water affects arsenic concentrations in groundwater.In recent years,the dynamic change and control mechanism of arsenic in aquifer under the interaction of surface water and groundwater have attracted the attention of domestic and foreign scholars.Taking the western Hetao basin as the study area,this paper investigated the dynamic change characteristics of water level and hydrochemical compositions of surface water and groundwater,and evaluated the influence mechanism of surface water recharge on variation in groundwater arsenic concentrations,which is of theoretical and practical significance.The main conclusions are shown as follows:(1)Groundwater in the study area mainly receives the lateral recharge of the groundwater in the northern mountainous area and the surface water in the south,and the groundwater flows from the north and the south to the center.During the irrigation period,groundwater levels in the study area decrease with the pumping of irrigation wells,which enhances the infiltration recharge of surface water.(2)Water levels of the main drainage and the Shahai Lake are higher during irrigation seasons in relative to non-irrigation seasons.The groundwater near Shahai Lake is obviously affected by surface water and the groundwater level is recovered quickly after irrigation ceases,while groundwater levels in the central plain,far from the lake,are slowly recovered.(3)From the piedmont plain to the Shahai Lake plain,the study area can be divided into five zones: irrigation area I,irrigation area II,irrigation area III,the block in the south sides of Shahai Lake and the block in north sides of Shahai Lake.Each region presents different hydrogeochemical characteristics.From irrigation area I to irrigation area II,groundwater ORP decreases,salinity and concentrations of major ions increase;and these parameters also increase during the irrigation period.In irrigation area III,groundwater ORP increases slightly,and TDS and concentrations of major ions reach the highest;these parameters decrease during the irrigation period.However,compared with groundwater near the south of Shahai Lake,the area near the north of Shahai Lake has lower pH,higher ORP and TDS,where groundwater ORP decreases,TDS and concentrations of major ions decrease in the irrigation period.(4)The infiltration recharge of surface water has introduced relatively heavy stable hydrogen and oxygen isotopes,oxidant components(such as dissolved oxygen)and labile organic matters to the groundwater near Shahai Lake.During the irrigation period when the recharge from surface water is strong,arsenic concentrations in the shallow groundwater decrease slightly,which may be the result of the fact that the reductive dissolution of arsenic-containing iron/manganese oxides and arsenic desorption are weakened.