Identifying Critical Source Areas and Optimizing Agricultural Management Practices to Reduce Non-Point Source Pollution in Taihu Basin

Abstract

Agricultural non-point source pollution (NPSP) has become a global concern requiring urgent attention, and high fertilizer application to cash crops often leads to more serious NPSP. We quantified the control effect of best management practices (BMPs) on total nitrogen (TN) and total phosphorus (TP) pollution in the Dongtiaoxi Watershed, with an emphasis on identifying critical source areas (CSAs), using the Soil Water Assessment Tool (SWAT) model. Although CSAs accounted for 11.78% of the whole watershed, they contributed to 23.43 and 21.72% of the TN and TP loads, respectively. In agricultural systems, planting cash crops is a key factor in the emergence of CSAs and NPSP; thus, it is necessary to improve the management of cash crops. Further, combined BMPs outperformed individual measures, achieving a 25.51% reduction in TN at the watershed scale. At the sub-watershed level (e.g., sub-watershed 27), combined BMPs reduced TN and TP by 50.11 and 20.00%, respectively. There are a large number of cash crops such as commercial bamboo forests in the study area that have been fertilized but were previously regarded as forest land. This can also lead to NPSP but may have been ignored in the past. Overall, our study classifies cash crops as agricultural land and improves the reliability of the results. The findings not only help to improve the water quality from the Taihu Basin but also provide technical support and a theoretical basis for government departments to improve the water environment.

Keywords: SWAT model, critical source area, cash crop, best management practices, Taihu Basin