Impact of sediment grain size on the distribution of organic matter in Changjiang River Estuary and East China Sea

Surface sediment samples were collected from 78 stations in East China Sea continental shelf in November 2007 and suspended matter samples were collected from Changjiang River Estuary and Zhejiang coastal mud area.The grain size,organic carbon and total nitrogen of surface sediment samples as well as some suspended samples from Changjiang River Estuary and East China Sea were analyzed,and the impact of sediment grain size on the process of transport and deposition of organic matter were explored.The results showed that the average grain size of suspended matter decreased from Changjiang River Estuary southward to the Zhejiang coastal area,and had a better correlation with the contents of suspended matter and particulate organic carbon,indicating that the grain size of suspended matter was an important factor to influence the transport of organic matter.In addition,the distribution of surface sediment grain size appeared to have an obvious area variation characteristic,and the organic carbon and total nitrogen were closely related to the distribution of surface sediment grain size.The smaller the surface sediment grain size was,the higher contents of organic carbon and total nitrogen appeared.The sand contents of surface sediments from Changjiang River Estuary and Zhejiang coastal mud area was low,while those from middle and out of the shelf were high.The sand contents gradually increased seaward.With the increase of sand contents and sediment grain size,organic matter contents gradually reduced.There was strong correlation between TOC contents and mud proportions,suggesting muddy sediments were the primary control to the organic matter distribution.Fine grained sediments were the main carrier of organic matter transport,at the same time,they controlled the distribution of organic matter.