长江流域污染物输出对河口水质的影响

基于EFDC模型建立长江口及邻近海域三维水质模型,模拟2004—2007年不同水期的ρ(COD_Mn)、ρ(DIN)、ρ(PO₄3--P)状况,分析水质分布的变化特征,研究流域污染物输出对河口水质分布的影响. 根据GB 3097—1997《海水水质标准》,长江口门以上ρ(COD_Mn)为Ⅱ类水质,ρ(DIN)、ρ(PO₄3--P)为劣Ⅳ类,并且有明显的分层现象. 枯水期各指标等值线均向东北方向延伸,丰水期和平水期向东南延伸,丰水期流域污染物输出对河口水质的影响最大,不同类别水体的分布形态和水体面积年际变化不明显. 按不同时期ρ(COD_Mn)、ρ(DIN)、ρ(PO₄3--P)分布面积进行统计,长江口ρ(COD_Mn)、ρ(DIN)、ρ(PO₄3--P)分布与流域污染物输出之间有显著关系,河口水质分布面积与流域污染物输出之间存在定量的压力-响应关系.ρ(COD_Mn)、ρ(DIN)、ρ(PO₄3--P)达Ⅳ类以上水体面积(y)与流域污染物输出通量(x)的关系分别为:y_CODMn=2 061.4 ln x_CODMn-15 357.0,y_DIN=1 386.8 ln x_DIN-6 546.1,y_PO43--P=2 219.3 ln x_PO43--P-6 166.1. 

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 COD_Mn, 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 COD_Mn 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 COD_Mn, DIN and PO₄3--P in different seasons, contribution of COD_Mn, 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 COD_Mn, DIN and PO₄3--P which were worse than Class Ⅳ and the pollutant export from the basin (x) were y_CODMn=2 061.4 ln x_CODMn-15 357.0,y_DIN=1 386.8 ln x_DIN-6 546.1,y_PO43--P=2 219.3 ln x_PO43--P-6 166.1 respectively.