Identification Of Critical Source Areas (CSAs) For Non-point Source Pollution In Miyun Watershed

As an important water source,Miyun Reservoir plays a crucial role in Beijing,China.The water quality of Miyun reservoir is at medium-eutrophication situation,which is mainly caused by the non-point source pollution(NPS) in the watershed,and Phosphorus(P) is the limited factor.So,it is important to study on sensitivity of P loss in this watershed.In this paper,Chaohe River basin,the one of two biggest upstreams of the Miyun Reservoir,is chosen as the studying area.By analyzing hydrological and meteorological data,land use,soil,soil conservation,and farmland management,P index is build up based on the local characteristics to identify critical source areas(CSAs) non-point source pollution.The critical source areas are identified and the management strategies were brought forward according to the analysis on the distribution characteristics of the critical source areas.The main conclusions are followed:(1) The basic database for P index in the study area has been established by using the GIS and Access technology.The watershed spactial parameterization is discretized,which has laid a base for the identification of CSAs and further research.(2) A modified phosphorus index scheme is developed for agricultural NPS() in Chaohe River basin.This frame of P index includes the source factors and the transport factors.Livestock pollution and rural domestic pollution were two maincontributors of local non-point source pollution,so the two factors livestock pollution and population density are added to the scheme as source factors firstly.The final classification of phosphorus index is adjusted to suitable size of CSAs area for assigning the existing resource reasonably and drawing up the target-oriented.control measure(3) Infiltration runoff equation and SCS runoff curve method are not used to calculate the runoff factor.By analyzing rainfall probability during 33 years of the watershed ourlet site,0-25%, 25-75%,75-100%probability of rainfall and runoff are linear fitted respectively.At last,runoff factor is estimated based on the three regression equations.Determination of other factors are based on the latest research results,reflecting the phosphorus index in the watershed with credible data.(4) At the scale of the whole watershed,the Phosphorus loss of CSAs only cover 7.95%,the mediume-risk areas 19.63%,and 72.43%of the watershed are low-risk areas 73.93%of the CSAs locates beside the stream,throughout the basin,where most high or relatively high soil available phosphorus or fertilizer P application rate;the other scatter the lower reaches,where most high or relatively high population desity or livestock & poultry excretion.(5) Best Management Practices(BMPs) are proposed to the critical source areas(CSAs).It is noted that conservation tillage is effective way to reduce soil erosion,which is the best choice to balance economy and efficiency.Rural families digesters are designed for livestock & poultry pollutionto reduce 19.88%of the total phosphorus loss.According to soil testing and fertilizer recommendation,67.09 ton fertilizer P could be saved.As a comprehensive pollution control measures,riparian buffer zone can effectively intercept sediment,1 nitrogen and phosphorus.