Determining the best management practices of non-point pollutants using ArcSWAT model (Case study: Dashte Bozorg catchment)

The best management practices are solutions to reduce non-point pollution in catchments. In many cases, the use of these solutions requires knowing the features of the watershed and investing in this sector. Accordingly, the use of computer models to simulate real catchment conditions can be an effective way to reduce time and cost. This research aimed to investigate the effect of different management scenarios on non-point source pollution losses in Dashte Bezorg catchment in Iran using the ArcSWAT model. To collect observational data, river water was sampled from September 2020 to June 2021. Calibration data were selected from September to March and validation data from April to June. After identifying critical areas, three non-structural scenarios and five structural scenarios were simulated using the model. The results revealed that the ArcSWAT model provides a good prediction in estimating non-point source pollution loads (nitrate, total nitrogen, and total phosphorus). The "wheat-potato-tomato" and "wheat, rice-wheat, mung bean-wheat" rotation scenarios showed the highest total nitrate and nitrogen loss, while the lowest total phosphorus loss was observed in the "wheat-potato-tomato" rotation. The terracing and buffer strip methods were recognized as the best methods of reducing the load of non-point pollution. The findings showed that the application of management practices in dominant land use and reduc the degree of slope can significantly reduce the non-point source pollution loads.