Distribution characteristics of COD,its influencing factors and its contribution to the eutrophication in waters near the Changjiang River Estuary in spring and summer

Based on the data from the surveys in the Changjiang River Estuary in spring(May) and summer(August) of 2009,the distribution characteristics of COD and its influencing mechanism were studied and the level of pollution was evaluated.Meanwhile,its contribution to the eutrophication in the study area was analyzed,and the main source of COD,the relationship between environmental factors and COD and the seasonal variation of COD were discussed.The results showed that the concentration of COD was significantly different at the surface in spring and summer,as well as in the bottom in spring and summer,and there was no significant difference at the surface and in the bottom in spring,as well as at the surface and in the bottom in summer.The average concentration and the maximum concentration of COD at the surface and in the bottom in spring were lower than those in summer.The distribution was characterized by the tendency of decreasing from the alongshore to the open sea.The pollution level of COD in summer was lower than that in spring.The range of contribution to the eutrophication was from 39.69% to 63.58%,and the average was(46.53±4.49)%.The contribution decreased with the increase of eutrophication index.The runoff and emission from land-based sources were the main sources of COD.There was a certain relationship between environmental factors and COD.The spatial and temporal distributions of COD were regulated by the diluted water of Changjiang River,and the contribution of COD to the eutrophication was influenced by nutrients and sediment resuspension.