北京市北沙河小流域非点源氮、磷负荷估算与源解析

Estimation and sources apportionment of non-point source nitrogen and phosphorus loads in Beishahe sub-catchment of Beijing

选取北京市北沙河小流域为研究对象,将非点源污染物分为溶解态和吸附态2类,采用降水径流模型〔径流曲线数模型(SCS-CN)〕、土壤侵蚀模型〔修订的通用土壤流失方程(RUSLE)〕和污染物输出负荷模型,对北沙河小流域非点源氮、磷负荷进行估算,探讨不同土地利用类型产生的氮、磷负荷的空间分布特征。结果表明:北沙河小流域非点源总氮年均负荷为0.625 t/(km^(2)·a),其中溶解态氮为0.190 t/(km^(2)·a),吸附态氮为0.435 t/(km^(2)·a);总磷年均负荷为0.118 t/(km^(2)·a),其中溶解态磷为0.011 t/(km^(2)·a),吸附态磷为0.107 t/(km^(2)·a)。总氮年均负荷较高的3种土地利用类型为农村用地〔0.855 t/(km^(2)·a)〕、林地〔0.713 t/(km^(2)·a)〕和未利用地〔0.619 t/(km^(2)·a)〕;总磷年均负荷较高的3种土地利用类型为草地〔0.238 t/(km^(2)·a)〕、林地〔0.126 t/(km^(2)·a)〕和未利用地〔0.115 t/(km^(2)·a)〕。北沙河小流域氮、磷流失主要以吸附态为主,因此应重点控制流域的土壤侵蚀和水土流失,降低吸附态氮、磷负荷。

Beishahe sub-catchment of Beijing was studied for the source apportionment of non-point source(NPS)pollution.The NPS pollutants in this area were generalized into two types:the dissolved and the adsorbed.The dissolved and adsorbed nitrogen and phosphorus NPS pollution loads were estimated based on the precipitation runoff model(soil conservation service curve number,SCS-CN),soil erosion model(revised universal soil loss equation,RUSLE),and the pollutant output load model empirical equation.The spatial distribution characteristics of nitrogen and phosphorus loads produced by different land use types were also analyzed.The simulation results showed that the average annual load of total nitrogen(TN)in Beishahe sub-catchment was 0.625 t/(km^(2)·a),of which the dissolved nitrogen was 0.190 t/(km^(2)·a)and the adsorbed nitrogen was 0.435 t/(km^(2)·a);the average pollution load of total phosphorus(TP)in Beishahe sub-catchment was 0.118 t/(km^(2)·a),of which the dissolved phosphorus was 0.011 t/(km^(2)·a)and the adsorbed phosphorus was 0.107 t/(km^(2)·a).The rural area produced the most TN of 0.855 t/(km^(2)·a)among all different land use types,followed by the forest land(0.713 t/(km^(2)·a))and the unused land(0.619 t/(km^(2)·a)).For TP,the land use types with highest annual pollution load was the grassland(0.238 t/(km^(2)·a)),the forest land(0.126 t/(km^(2)·a))and the unused land(0.115 t/(km^(2)·a)).Generally speaking,the losses of nitrogen and phosphorus were mainly in the form of adsorbed in the Beishahe sub-catchment.Therefore,controlling of the soil erosion,water and soil loss should be highlighted for the reduction of the loads of adsorbed nitrogen and phosphorus in Beishahe sub-catchment.