Research Of Migration And Transformation Rules Of Heavy Metal Hg In Combined Constructed Wetland System

Xiaosha River is important water channel and impounded lakes in east route of Water Transfer Project from South to North.In order to improve the water quality of Xiaosha River,large-scale wetland eco-restoring project was carried out.In the cause of understanding the migration and transformation rules of heavy metal Hg in constructed wetland system,Xuecheng constructed wetland was the research object and the research carried out in May and September,2016.Sediment,Hg content in water body,plant samples were detected,and migration and transformation mechanism of mercury in sediment,water body,plant samples was discussed.The results of the content analysis which of the total mercury and three forms mercury(mobile Hg,semi-mobile Hg,non-mobile Hg)were shown that semi-mobile Hg was the main mode of occurrence,accounting for 34.12%~85.24%;the content of pH and organic matter had a significant effect on mercury speciation transformation.The total content of core sediments showed center enrichment-type in May and upper enrichment-type.Three forms mercury had no obvious correlations with basic property.In general,the content distribution of various kinds mercury of core sediments was not affected by basic property.Total mercury concentration of Xuecheng constructed wetlands ranging from 4.96 ng/L to 103.16 ng/L in May and from 2.52 ng/L to 81.26 ng/L in September.The total mercury concentration of water body showed a trend of decreasing step by step,particulate mercury accounted for the highest proportion in total mercury,the content of reactive mercury in September accounted for 60.67~68.49%,soluble mercury and reactive mercury rates were relatively low.Soluble mercury's diffusion flux to overlying water of interstitial water in May was 76.63ng·(m2·d)-1,and 55.17 ng·(m2·d)-1 were found by calculation in September.The total mercury mass ratio of dominant plants in Xuecheng constructed wetland had great difference,and there were obvious time,species and organs differences of mercury enrichment ability.Enrichment ability of wetland plants in September all greater than May to the same kind plants.Enrichment ability of wetland plants in May showed as: huanghua iris>cattail>scirpus tabernaemontani>willow herb> thalia dealbata.Enrichment ability of wetland plants in May showed as: thalia dealbata>Huanghua iri>willow herb>cattail>schoenoplectus tabernaemontani.The five kind plants had weak transport capacity in May,(TF<1),the enrichment characteristics showed root hoarding.The enrichment ability and transfer coefficient of all kinds plants had improved,shown as enrichment plants.The total mercury mass ratio of different parts in the same kind plants was discrepant.In May was: root>leaf>stem,and in September was: leaf> root>stem.Analyze the correlation between the content mercury of plants organs in May and September with total mercury and other forms mercury of sediment,finding mercury of sediment was not the principal factor to affect the mercury content of plants.