REGIONAL DISTRIBUTION OF HEAVY METALS IN SURFACE SEDIMENTS OF DAFENG COASTAL WETLANDS IN YANCHENG, JIANGSU AND ITS ECOLOGICAL IMPLICATIONS

The regional distribution patterns of seven heavy metals in the surface sediments of the Dafeng coastal wetlands in Yancheng, Jiangsu Province are carefully studied by the authors in this paper. The results show that the mean values of Hg, Cd, As, Cu, Pb, Cr and Zn in the surface sediments are 0.05, 0.25, 7.21, 25.5, 20.3, 67.79 and 68.09 mg/kg respectively, and the mean values in tidal flat wetlands are obviously higher than those in man-made wetlands. The site JST-02 of the tidal flat wetland near the first-phase of Dafeng Port has the highest content of heavy metals, showing a pollution pattern by a single point source. The regional distribution of heavy metals is positively correlated with particle size, suggesting that the clay content plays a critical role on the enrichment and distribution of heavy metals. The average values of single factor pollution indices show an ordered pattern from high to low in the surface sediments of the study area as Cd > Cr > Cu > Zn > Pb > As > Hg, and the maximum value of Cd, the main pollution element of the study area is as high as 1.57. The comprehensive potential ecological risk index varies between 15.70 and 184.91, with a mean of 27.41, in an order of Hg > Cd > as > Cu > Pb > Cr > Zn, which is higher than that of man-made wetland. Hg and Cd are the main potential ecological risk factors. Our data further suggests that though the whole region has lower potential ecological risk indices and remains under the level of environmental pollution, the concentration of single pollutant may be too high already in some local areas.