长江干流寸滩断面污染负荷核算及来源分析

Pollution Load Accounting and Source Analysis at Cuntan Section in Main Stream of Yangtze River

将长江干流寸滩断面以上区域划分为39个排污单元,将河道划分为63个纳污河段,建立排污单元与纳污河段之间的排污-纳污拓扑关系,并基于污染物的产生-入河-降减过程进行断面污染物通量核算.采用输出系数法核算排污单元内各类污染源的产生量,并考虑降水作用,建立污染源入河系数公式,核算排污单元点源与非点源的入河量;考虑污染物在河道内的综合降解过程,核算各纳污节点到输出断面的流达率,分析各纳污节点各类污染源对下游断面的贡献率.通过以上模式对长江干流寸滩断面2004与2005年的污染物通量进行核算,并进行各支流的贡献率分析.核算结果显示:寸滩断面CODMn和TP月通量模拟值与实测值曲线基本吻合,TN月通量模拟值与实测值曲线拟合稍差,整体偏低,可能是忽略了大气沉降的影响所致.从CODMn的贡献率核定结果可以看出,嘉陵江对寸滩断面的贡献率最小,综合贡献率为14%左右,其中点源贡献率为6%左右,非点源贡献率为8%左右,非点源与点源的比率仅为1.3;金沙江对寸滩断面的贡献率最大,综合贡献率达到49%左右,其中点源贡献率为14%左右,非点源贡献率为35%左右,非点源与点源的比率达到2.5,是流域污染控制的重点.

The area above the Cuntan section in the main stream of the Yangtze River was divided into 39 output units,and the river network was divided into 63 input rivers. In addition,a topological relationship between units and rivers was built. Based on the steps of production,arrival,and reduction of pollutants,the flux of pollutants at Cuntan section was estimated. The production of pollution from various types of pollution discharge units was checked by export coefficient method. Pollutant arrival coefficient formulas were established and checked considering the effect of precipitation and input amount from point sources and non-point sources. The established coefficients from pollutant carrying sections to output sections were checked considering comprehensive degradation of pollutants in rivers. Contribution rates were analyzed for each pollutant source for each pollutant carrying joints to downstream sections. The model was applied to account for the flux of pollutants and to analyze the contribution rate from tributaries at the Cuntan section in the main stream of Yangtze River from 2004 to 2005. The accounting results show that the monthly loading curve of CODMn and TP at the Cuntan section tallies with the measured data well,but that of TN is lower than the measured data,perhaps due to neglected atmospheric nitrogen precipitation. The CODMn contribution rate to the Cuntan section of Jialing river was smallest; the general contribution rate was about 14% ,among which 6% were from point sources and 8% were from non-point sources,therefore the ratio of non-point sources to point sources was only 1. 3. The CODMn contribution rate to the Cuntan section of Jinsha river was largest; the general contribution was about 49% ,among which 14% were from point sources,35% were from non-point sources,therefore the ratio of non-point sources to point sources was 2. 5,indicated that non-point pollution sources were more serious. As a result, control of non-point sources is more important in Jinsha river.