Distribution Characteristics And Environmental Risk Assessment Of Hg And As In Sediments Of Wuliangsuhai Lake

Wuliangsuhai Lake is a typical lake located in irrigation area of arid and cold regions, while mercury(Hg) and arsenic(As) pollution has received great attention. Under the influence of natural processes and human activities, the Hg and As emissions of the atmosphere precipitate into the water environment and transfer in air, water, sediment, organisms and other media. Wuliangsuhai Lake had selected as research object. This paper was about exploring the content of Hg、As and chemical speciation distribution characteristics.And Hg、As and its chemical forms in different physical and chemical indexes analysis were carried out by using SPSS. The following conclusions were drawn:(1) The distribution characteristics of Hg and As in the sediments of Wuliangsuhai Lake:The average contents of Hg、As in surface sediment of Wuliangsuhai Lake were 0.054mg/kg and 8.197mg/kg, and respectively 80% and 20% of the samples exceeded the soil background value of Hetao Irrigation district. In the spatial distribution, the estuaries content was relatively high, and the central and Southern region were smaller and smaller.The results of HgN As in different depths of Wuliangsuhai Lake showed that the content of THg ranged from 0.008-0.135mg/kg, As ranged from 3.081-13.948mg/kg. Vertical distribution of Hg in sediments of lake showed that the minimum Hg content of ten points in the whole lake appeared at 10cm below the surface. Then the content tended to be stable oscillationly as the depth increases. And the whole content of As gradually decreased with the increase of the depth.(2) The influencing factors of seasonal distribution on Hg and As in sediments of Wuliangsuhai Lake showed:Correlation analysis showed:In July 2014, pH, ORP and electrical conductivity were the important factors of Hg and As.In October 2014, the Organic matter and clay content influenced on the Hg content. In January 2015, organic matter was an important factor on the content of Hg. Clay and silt affected the content of As. Organic matter affected the content of Hg in April 2015, While Hg and As influenced each other. Principal component analysis showed:pH, ORP, conductivity and organic matter were main factors influenced on Hg and As contents in Wuliangsuhai Lake.(3) The chemical speciation analysis results of Hg、As in sediments of Wuliangsuhai Lake were showed:The main form of Hg in sediments of Wuliangsuhai Lake was residual form, followed by organic combination forms. The main form of As in sediments of Wuliangsuhai Lake was residual form, followed by iron manganese oxide combining form. Hg and As in various forms in vertical sediments had no obvious regularity.The correlation analysis of Hg、As chemical forms content and physical and chemical factors showed pH,ORP and organic matter had a significant correlation with the iron manganese oxide combining form and organic combination form of Hg in Wuliangsuhai Lake. The clay was an important factor on acid extractable form、organic combination form of As.(4) The geoaccumulation index and potential ecological risk index method were used to evaluate the surface sediments of Wuliangsuhai Lake, the index of geoaccumulation analysis results showed that:Hg in surface sediments of the lake was between light and moderate pollution levels, and As was in non-pollution level. The results of potential ecological index method showed that the total potential ecological risk index was between light and moderate pollution levels, which the contribution rate of Hg was the largest.