Scenario Analysis of Agricultural Nonpoint Source Pollution Risks in Chengdu-Chongqing Economic Zone

Identifying evolving trends of agricultural nonpoint source pollution (ANSP) risks is of great practical meaning for pollution control. Land use types and nutrient application levels are key factors affecting risk conditions of ANSP. In this study, a Patch-generating Land Use Simulation (PLUS) model was used to simulate the land use types for the Chengdu-Chongqing Economic Zone (C-C E Zone) from 2030 to 2050, and an improved output risk model was constructed by introducing topographic factors and distance factors to compensate for the shortcomings of traditional models in expressing pollutant transport. Based on these 2 models, evolving trends were analyzed to assess ANSP risks in the future. The results showed that the PLUS model could accurately simulate large-scale land use. The overall risk of ANSP in this area showed a decreasing trend, with the proportion of risk grade VII-X levels decreasing from 27.68% to 23.06% during 2000-2020, and from 16.66% to 14.02% during 2030-2050. The proportion of strict control areas of risk also showed a consistent decreasing trend, with 9.75%, 9.57%, 8%, 6.73%, 5.86%, and 5.36% in 2000, 2010, 2020, 2030, 2040, and 2050, respectively. A significant positive association was observed between risks of ANSP and the adjustment of nutrient application levels, with strict control areas increasing by 9.46% and 12.05% when the output coefficients in 2030 increased by 5% and 10%, respectively. Region strategies should be applied in the future, with focus on areas with high risks/control levels, as well as areas that are sensitive to nutrient changes.