饮用水源区小流域氮素污染负荷估算方法比较

Estimating methods for non-point source pollution of small watershed in drinking water source area

采用输出系数法、通用土壤流失方程估算法、径流试验场法和相关关系法4种方法对密云土门西沟小流域非点源氮污染负荷进行估算。结果表明:输出系数法中的Johnes模型和考虑降雨影响的输出系数模型计算值相对误差比较大,考虑流域损失的输出系数模型计算结果与实测结果相对误差仅为5%;输出系数方法适用于资料比较缺乏的地区,输出系数的确定是提高估算精度的关键。对流域非点源污染发生类型区和类型单元进行详细划分,并将对各类型采用径流试验场法的监测结果推算到小流域就能减小估算相对误差;采用径流试验场法推算密云土门西沟小流域非点源氮污染负荷相对误差仅为8%;相关关系法通过建立降雨和污染负荷的关系,其估算值相对误差达到4%,此方法需要长期的降雨-水质监测数据;通用土壤流失方程估算法主要估算流域土壤侵蚀量,没有考虑径流对污染物输移过程中的沉积、起动和交换等问题,估算值会偏大。

Nitrogen pollutant in Miyun Tumenxigou small watershed was estimated by export coefficient method, the Universal Soil Loss Equation, Runoff field experiment and relevant relationship method. The results show that： Johnes model of the export coefficient method and the export coefficient model which was considered the rainfall impact on, had large relative error. Considering the loss of watershed the of export coefficients method was the best, of which the simulation value closed to the true one and the relative error was 5 %. Export coefficient method is suitable for the region where there is no enough observation data. Export coefficient is the key to improve the accuracy of estimation. The relative error will be smaller if non-point source pollution area are divided into smaller type block and the monitoring results of runoff plot can be used for the whole small watershed. The relative error of runoff plot experiment estimation in Miyun Tumenxigou small watershed reached to 8 % by this method. Relevant relationship method needs establish the relationship between pollution load and rainfall, which requires long-term rainfall-water quality monitoring data. Relative error of relevant relationship method was approximate to 4 % . Universal Soil Loss Equation did not take into account the transport capacity of runoff, estimation error of which was relatively large.