Controlling and Influencing Factors

Studies showed that the sediment grain size and TOC influenced the heavy metal distributions. According to the profound analysis of the heavy metal concentrations in the sediments of SYS, it was safe to reach a conclusion that the grain size of sediment was the most important factor controlling the heavy metal distributions in SYS. 

The sediments grain size is controlled by the distance from the material source, the transportation medium, transportation mode and the sediments environmental characteristics. B2 and the A line stations were near to the Han River Estuary, so that the sand and silt schlepped by the Han River contributed enormously to high concentrations. Additionally, due to the effects of the ancient Yellow River and Yangtze River in the Wiirm glaciations, a thick layer of sand sediments developed in the west coast area north of the Yangtze 

River Estuary, represented by B9, C7, C8, and C9 in the study area. Therefore, the sand concentrations of the stations mentioned above were higher than those of other stations. The finer sediments area in the SYS middle area reflected the effects of the transportation mode and sediments characteristics on the sediments t rpes. The clay sediments of the middle area in the SYS continental shelf tended to transport to the mid-north sediments area center, consistent with the cold vortex center by and large, located at about 123.5° E, 35.5° N. The weak hydrodynamic energy controlled by the cyclonic circum-fluence at the surface and cold vortex at the bottom resulted in the centrality of transportation (Shi et ah, 2002). Therefore, fine sediment particles were transported to the SYS middle area with the ocean current and settled down very tardily. 

Li (1995) pointed out that the majority of the sediments in the SYS west area and the area adjacent to the ancient Yellow River came from the ancient Yellow River. However, in the east area, the sediments originated from the modern Yellow River, and the material corralled by the ancient Yellow River had not been conveyed to the east sediments area. The Yangtze River contributed to the sediments distribution to some extent, but the material of sediments in the east of the SYS could not embody the characteristics of Yangtze River material explicitly. Therefore, the sediments in the eastern area of the SYS had several somces, partly from the Yangtze River, partly from Korean Rivers, or from the sediments formed before corrosion, resuspending, and redeposition under the complex hydrodynamic conditions (Li, 1995 Song, 1997). 

Even though fine grain size sediments were the main carriers of heavy metals, it was still possible to form certain high areas of coarse grain size sediments. Heavy metal deposition was through the sediment-seawater surface in fine sediments, heavy metals were easily released to the overlying water and the burial of heavy metals would decrease in coarse sediments the adsorption 

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