[Calculation of environmental dredging depth of heavy sediments in Zhushan Bay of Taihu Lake metal polluted].

Horizontal distribution of heavy metals in surface sediments of Zhushan Bay was investigated, and core sediment samples were collected in the representative area. Core sediments were divided into oxide layer (A), polluted layer (B), upper polluted transition layer(C1), lower polluted transition layer(C2) and normal mud layer(D) from top to bottom. The change of total contents of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb and contents of biological available Cr, Ni, Cu, Zn, As, Cd, Pb with depths were analyzed. Ecological risk assessment of heavy metals in sediments was done by potential ecological risk index method. At last, environmental dredging depth was calculated. The results shows that the contents of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb are 30.56-216.58, 24.07-59.95, 16.71-140.30, 84.31-193.43, 3.39-22.30, 0.37-1.59, 0.00-0.80 and 9.67-99.35 mg x kg(-1), respectively. The average concentrations of Cr, Ni, Cu, Zn, As, Cd, Hg, Pb are 79.74, 37.74, 44.83, 122.39, 10.39, 0.77, 0.14 and 40.08 mg x kg(-1), respectively. Heavy metals in the surface sediments of Zhushan Bay mainly distribute in the west bank and the estuaries of Taige canal, Yincun Port, and Huanshan River,and Cd pollution is relatively serious. There is an accumulative effect of heavy metals in Zhushan Bay, and the contents of biological available metals decrease with depths. Ecological risk grades of Cd in layer A and B are high, and the comprehensive potential ecological risk grades of each layer are in middle or low. The environmental dredging layers are A and B, and the average dredging depth is 0.39 m.