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Simulation of non-point source pollution load in the Xiangtan Stream basin through swat model

Xiangtan Stream basin, a typical hilly country in the Sichuan Basin, is adversely affected by overuse of chemical fertilizer on the slope farmland and pig manure produced by intensive pig breeding farm located in the upper watershed. The nitrogen and phosphorus compounds in the runoff, sediment and manure contaminate the soil and water bodies. SWAT (Soil Water and Assessment Tool) was applied to characterize hydrologic processes in the watershed and to evaluate the reduction effect of non-point source pollution (NPSP). Field data including flow and concentration (total phosphorus (TP), total nitrogen (TN) and nitrate-nitrogen (NO3-N)) were measured for the time period from March 2012 to March 2013. The result of comparison showed that SWAT model performed satisfactorily for simulating runoff and water quality in the study area. TN and TP load was found to be concentrated in the upper parts of the watershed, critical areas with the pig breeding farm. Contribution rate analysis suggested that livestock was the major contributor for TN and TP load, which should be the key factor for NSPS. Temporal analysis showed, monthly output of TN and TP was higher in June and July.