非点源污染河流的水环境容量估算和分配

通过河流相应集水区内氮磷的各污染源分析(包括农地、畜禽养殖和生活排污等),利用输出系数模型估算各非点源的氮磷投(排)放量和入河量;采用河段氮磷输入-输出平衡关系分析方法,估算河流对氮磷的每月自净量.以此为基础,参照水功能区划所要求的水质目标,提出了水质未超标河段相应集水区的氮磷剩余水环境容量按月估算模型,和水质超标河段相应集水区内氮磷投放削减量的按月估算模型,及其在各污染源之间的分配方案.结果表明,长乐江的总氮和总磷自净量分别达到775.9 t·a^-1和30.9 t·a^-1,自净率分别为28.8%和51.2%.河流对氮磷的自净量不仅受水文生态条件的影响而表现出较大的季节性变化,而且随着污染负荷量本身的增加而提高.按照水功能区划中Ⅲ类水的水质要求,长乐江总氮含量全年超标;各非点源的总氮投(排)放量均须不同程度的削减,削减总量应达到1 581.0　t;氮源削减量分配结果表明,化肥是应削减的最大氮源,要求在河流相应集水区内的化肥氮投放削减量为1 047.4 t·a^-1;而与各种氮源的投排放现状相比,要求削减比例最高的是畜禽养殖的氮排放量,达32.4%.长乐江流域尚有一定的总磷剩余水环境容量(2 335.7 t·a^-1).根据目标水质要求,平水期是各污染源总氮投放需要削减的量最大的时期,丰水期则是总磷剩余水环境容量最小的时期.

Estimation and Allocation of Water Environmental Capacity in Nonpoint Source Polluted River

Based on the investigation of the application and emission quantities (QAE) of total nitrogen (TN) and total phosphorus (TP) for nonpoint sources in river catchment's area, included fertilizer applications, livestock and living pollutants emissions, the quantities of TN and TP entered the river were computed by means of export coefficient model in Changle River, southeast China. Self-purification capacities of TN and TP in the reach were also estimated in terms of input-output balance analysis method. According to the provisions of water function planning in the river, the water environment residual capacity (WERC) or the demand for reducing the application and emission (DRAE) of nitrogen and phosphorus in the corresponding catchment were monthly estimated, and WERC and DRAE were respectively allocated among the pollution sources. Results indicated that about 28.8% of TN loads and 51.2% of TP loads could be self-purified respectively in the reach, i.e., purification of 775.9 t·a^-1 for TN and 30.9 t·a^-1 for TP. Seasonal variations of the self-purification for the pollutants not only resulted from riverine hydrological and ecological conditions, but also affected by the pollution loading. According to the demand of the water quality protection in the reach, about 1581.0 t·a^-1 QAE of TN had to reduce in Changle catchment. The maximum demand for the reducing QAE of TN was the fertilizer application (1 047.4 t·a^-1), and the highest ratio for the reducing QAE of TN was livestock-poultry breeding (32.4%). There was about 2 335.7 t·a^-1 WERC for TP in the reach. The largest DRAE of nitrogen was during mid-water season and the least WERC of TP was during higher-water season.