DISTRIBUTION PATTERN AND ASSESSMENT OF HEAVY METALS IN THE SEDIMENTS OF NORTH GUANG-LI RIVER ESTUARY

Based on the data of heavy metals, grain sizes and TOC for 45 surface sediments and 2 core columns taken from the north tidal flat of the Guang-li River estuary, we studied the distribution patterns and sources of heavy metals in the sediments of the estuary. Environmental quality evaluation is made with the Nemerow comprehensive index. The results show that the 7 elements of Cu, Pb, Zn, Cr, Cd, Hg and As, are all lower than the national standard of heavy metal pollution. In the spatial distribution, a high value anomaly of heavy metals is discovered in a place to certain distance from the shore, under the influence of coastal residual current. In terms of the source, however, the Cr element is clearly injected by the Guang-li River. In the sediments taken from the surface and the Z1 and Z2 sinks, grain size has obvious controlling effect over heavy metal distribution. The pollution indices of Cr and As remain the highest in the study area, while the pollution index of Cu changes greatly. The distribution of comprehensive pollution index is in a "dumbbell-like" pattern, with a high value region near the modern Yellow River estuary and another in the Guang-li River estuary. To conclude, the heavy metal content in the north tidal flat of the Guang-li River estuary has so far not reached the level of pollution, but the trend of development towards slight pollution is observed.