Influence of Pollutants Exported from the Yangtze River Basin on Water Quality in the Estuary

Based on the EFDC model,a three-dimensional water quality model was established for the Yangtze River estuary and its adjacent waters.Distribution and variation of CODMn,DIN and PO43——P in different seasons from 2004 to 2007 were simulated,and the contribution of pollutants exported from the Yangtze River Basin to the water quality of the estuary was studied.As defined by China's National Standard GB 3097-1997(Sea Water Quality Standard),the water quality class of CODMn in the upper entrance of the Yangtze River estuary was Class Ⅱ,while the classes of DIN and PO43——P were worse than Class Ⅳ.Furthermore,the water quality was vertically stratified.The isoconcentration lines extended to the northeast in dry seasons and to the southeast in wet and normal seasons.The contribution of pollutants exported from the whole basin to the estuary water quality was greatest in wet seasons.The distribution of different water quality classes had no obvious annual variation.According to statistical analysis of the distribution areas of CODMn,DIN and PO43——P in different seasons,contribution of CODMn,DIN,and PO43——P were significantly correlated with pollutants exported from the basin.There was a quantitative pressure-response relationship between the distribution areas of water quality in the estuary and pollutant export from the basin.The regression equations between the distribution areas(y) of CODMn,DIN and PO43——P which were worse than Class Ⅳ and the pollutant export from the basin(x) were yCODMn=2,061.4ln xCODMn-15,357.0,yDIN=1,386.8ln xDIN-6,546.1,yPO43——P=2,219.3ln xPO43——P-6,166.1 respectively.