SPATIAL ACCUMULATION FEATURES AND ENVIRONMENT EFFICIENCY OF HEAVY METALS IN INTRA-TIDAL SURFACE SEDIMENTS OF GUANHE ESTUARY, NORTHERN JIANGSU

In northern Jiangsu coastal zone area, Guanhe is the biggest river and has the best navigation conditions among rivers which flow into the Yellow Sea. The grain sizes show gradually increasing from the high intra-tidal zone to the low intra-tidal zone. The heavy metal values have slight changes along both sides of the river mouth, but show an evident change perpendicular to the tidal flat. In the latter case, they show a good correlation with grain size fluctuation, that is,the heavy metal values gradually decline when the grain sizes increase from the high intra-tidal zone to the low intra-tidal zone.Analysis results of heavy metal elements show that in the Guanhe estuary surface sediments,contents of Hg,As and Cu are beyond background values; Pb and Zn are rather close to the background values; and Cd less than the values.Element Hg comes out to be harmful to ecological environment, while elements Cr,As,Cu,Pb,Zn,and Cd fall in a safe range of MPL. On the whole,Guanhe estuary tidal flat is not seriously ecological harmful due to the heavy metals.