Distributed Simulation of Non-Point Source Pollution in Ashi River Basin

In order to get a thorough understanding of non-point source pollution,it is essential to examine its temporal and spatial distribution. A physically-based distributed model,Soil and Water Assessment Tool( SWAT),was used in this research,to quantitatively estimate the NPS load and analyze the temporal and spatial distributions of NPS pollution in Ashi River Basin. The results indicated that SWAT was suitable to simulate stream-flow and water quality in Ashi River Basin. Total Nitrogen which was contributed by NPS( NPS-TN) accounted for 32. 47%-62. 61%,and Total Phosphorus which was contributed by NPS( NPS-TP)accounted for 22. 30%- 57. 85% of the total load respectively. In inter-annual timescale,both NPS-TN and NPS-TP were influenced by stream-flow and fertilizer. However,when compared with fertilizer,NPS pollution was more directly affected by stream-flow. In annual timescale,NPS-TN and NPS-TP mainly occurred in flood season( from May to September). In the aspect of space,spatial differences of NPS-TN and NPS-TP were extremely significant. The spatial variations of NPS pollution were mainly influenced by land use,precipitation,soil and slope.