Assessment of effects of best management practices on agricultural non-point source pollution in Xiangxi River watershed

Agricultural non-point source pollution (ANSP) is considered a major contributor to local water degradation in the Three Gorges Reservoir Area (TGRA) of China. The Xiangxi River, which is a first level anabranch of the Yangtze River, was selected for investigation of the effectiveness of selected best management measures (BMPs) to alleviate water pollution through analysis of several scenarios by SWAT (Soil and Water Assessment Tool). Specifically, changes in land use, fertilizer management and tillage management measures were simulated in SWAT because they were shown to be the primary factors influencing non-point source (NPS) pollution in the Xiangxi River watershed. The results revealed that when farmland was returned to forests, both runoff and NPS pollution loads showed a clear downward trend and the NPS pollution loads in the Xiangxi River watershed decreased by 20% or more when compared with the status of 2007. Furthermore, conservation tillage and contour farming can help reduce runoff by 15.99% and 9.16%, total nitrogen (TN) by 8.99% and 8%, and total phosphorus (TP) by 7% and 5%, respectively. Conservation tillage has a greater effect in controlling the losses of soil, water and nutrients than contour farming. Based on the fertilizer conditions of 2007, changing the fertilizer application resulted in little change in local runoff; however, for NPS pollution loads, various forms of nitrogen (N) and phosphorus (P) pollution loads were directly proportional to the amount of chemical fertilizer applied. Overall, the results of this study can facilitate development of environmental friendly land use plans by local managers, and enable farmers to manage agriculture and fertilizer more efficiently, ultimately achieve the goal of reduce water pollution.