Effects Of Ecological Restoration Of Urban Water System On Transformation Of Heavy Metals In Sediments And Biological Assimilation

In order to investigate effect of benthic animals and aquatic plants on heavy metals (lead and mercury) removal and transform in sediments and offer a certain reality consult basis to aquatic vegetation remediation in urban water body, Yinchu Lake without ecological restoration, Liwa River with ecological restoration for ten years, Caoyang River with ecological restoration for twenty years Located in Putuo District of Shanghai were selected. The water quality, surface sediments, submerged plants and benthic animals in the three rivers were selected as the research objects, total content and forms characteristics of heavy metal Pb and Hg in each rever were researched, correlations analyzed by SPSS between Pb and Hg as well as two heavy metal and physical and chemical properties of water were studied, which would provide theoretical basis of heavy metals removal and transform in the sediments of urban rivers. The main results are as follows:(1) The content of Pb and Hg in the surface sediments of the three rivers are Pb> Hg in turn. The content of Pb in sediments of Caoyang River was 11-1.30 mg/g and more than that of Liwa River and Yinchu Lake,0.045-0.17 mg/g and 0.023-0.034 mg/g, respectively. The content of Hg in the sediments of Yinchu Lake, Liwa River, and Caoyang River were respectively 0.08-0.27 μg/g,0.40-1.68 μg/g and 0.37-0.94 μg/g. Moreover, The content of Pb in the interstitial water of the three rivers were 3-39 μg/L,0.5-21 μg/L and 4-53 μg/L.(2) The extracted proportion (acid solube, reducible and oxidable fractions) of Pb in the sediments of the three rivers was higher than the residual. The concentration of acid solube Pb was lowest in the three extracted fractions.(3) The content of Pb in submerged plants of Caoyang River was higer than that of Liwa River with rare exceptions. There were significantly negative correlations between the Pb content in submerged plants and organic matter, total nitrogen and total phosphorus in sediment of Liwa River and Caoyang River. However, significantly positive correlations were found between the Pb content and organic matter, total nitrogen and total phosphorus in submerged plants in the two rivers.(4) The content of Hg in submerged plants of Caoyang River was higer than that of Liwa River. There were significantly positive correlations between the Hg content in submerged plants and organic matter, and pH in sediment of Liwa River and Caoyang River. Furthermore, positive correlations were found between the Hg content and Cond, Salt and Tds in Caoyang River.(5) The content of Pb and Hg in viscera of benthonic animals were higher than that of muscle in Liwa River and Caoyang River. The Pb content of Bellamya aeruginosa was higher than that of Bellamya purificata.(6) Correlation analyses of Pb fractions in the sediments, Pb in interstitial water, Pb and Hg in submerged plants and benthonic animals in the three rivers shown that Caoyang River had the closer correlation that other two rivers, which suggested that ecological restoration was beneficial to the Pb and Hg removal and transform in sediments.