[Spatiotemporal Changes and Multi-scale Driving Mechanism Analysis of Nitrogen and Phosphorus Export in Yunnan...

The issue of eutrophication caused by the excessive discharge of nutrients such as nitrogen and phosphorus has become a global concern. Yunnan Province, an essential part of the ecological security barrier in Southwest China, is ecologically sensitive and vulnerable. Rapid urbanization has drastically altered land use patterns, notably affecting regional nitrogen and phosphorus output. This study focused on Yunnan Province and used the InVEST model to quantitatively assess the spatiotemporal characteristics of nitrogen and phosphorus output from 2000 to 2020. It also incorporated the GCCM model to analyze the impacts and causal relationships of natural and anthropogenic drivers on nitrogen and phosphorus output. The results showed： ① There was notable spatiotemporal heterogeneity in nitrogen and phosphorus output in Yunnan Province, with an overall trend of an initial increase followed by a decrease from 2000 to 2020. Spatially, lower values predominated, with high-value areas mainly concentrated in the central urban agglomeration of Yunnan. ② The spatial distribution of nitrogen and phosphorus output exhibited significant clustering characteristics, with high-high clusters mainly in areas with high urbanization and favorable agricultural conditions and low-low clusters often in remote mountainous areas with less agricultural activity and higher forest coverage. ③ Terrain, vegetation cover, rainfall, slope, and land uses, such as cropland, forest, and water bodies were the main drivers influencing nitrogen and phosphorus output. ④ The causal relationship between nitrogen and phosphorus output and different land use types was scale-dependent, showing significant differences in the intensity and direction of impact by cropland, forest, and water bodies at different spatial scales. The study extends the application of the GCCM model in nitrogen and phosphorus attribution analysis and provides a scientific basis for watershed management and ecological conservation.