密云水库流域非点源污染负荷估算及特征分析

Application of improved export coefficient model in estimating non-point source nutrient load from Miyun reservoir watersheds

采用改进的输出系数模型,以研究区实测数据为基础,结合基于水文水质资料和文献数据的方法确定输出系数取值,估算了密云水库上游潮河和白河流域平水年(2000年)和丰水年(2010年)的非点源污染负荷.结果表明:①通过对降雨和地形的表征,改进的模型降低了估算误差,总氮、总磷在平水年和丰水年的模拟误差均降低20%以上,可以更精确地模拟污染负荷的时空分布情况.②总氮、总磷负荷量在平水年和丰水年分别为7505.28t、997.88t和10022.1t、1075.6t,总氮负荷量随降雨径流量的增加而有显著增大,但总磷负荷增加不大,反映出总氮负荷量在不同水文年份中变化显著.③来自流域农业非点源污染的总氮、总磷负荷量占总负荷的85%以上.总磷主要来自于农村生活污染源,占70%以上,2000年与2010年比例变化不大;总氮污染,在2000年主要来自于农村生活,占当年污染负荷总量的31.44%,而2010年主要来自禽类养殖,占当年污染负荷总量的27.27%,反映出10年间经济发展导致主要污染源发生变化.④污染高风险区空间分布的总体特点是"东高西低,局部集中,分布不均,靠近水体",密云县、赤城县以及丰宁县等人口密度较大、以农业种植和畜禽养殖为主要产业的地区为污染负荷总量较高的区县.

Export coefficient model （ECM） has been widely used to estimate non-point source （NPS） pollution loads. However the accuracy of this model is limited for basin simulation with significant spatial differences on precipitation and terrain, such as upper watershed of the Miyun reservoir. In this study, an improved export coefficient model was used to estimate the NPS pollution from upper watershed of the Miyun reservoir in a normal flow year （2000） and a high flow year （2010）. The export coefficient of different land use types was also estimated based on the hydrological and water quality monitoring data. The results showed that the relative errors of TN simulations were effectively reduced to 39.5% in 2000 and 20.5% in 2010, and those of TP simulations were reduced to 27.5% in 2000 and 25% in 2010, compared to the original model. For different pollution sources, the main pollution sources of TN in 2000 were rural life which accounted for 31.44% , while in 2010 livestock turned out to be the main source which accounted for 27.27%. For TP, the main pollution sources were constantly rural life in 2000 and 2010, accounting for 75.03% and 70.02% of total TP load, respectively. The high-risk areas were mainly concentrated in ChaoHe river watershed and the most of the CSAs were close rivers. There were significant discrepancy of TN and TP loads distribution in this area. Higher loads were in Miyun, Chicheng and Fengning counties which have high population density with crop planting and livestock as the main industries.