Spatial-Temporal Dynamics of Anthropogenic Nitrogen Inputs in the Rapid Developing Chaohu Lake Basin

Due to the agricultural and industrial activities in rapidly urbanized basins, nitrogen (N) inputs have increased significantly, causing a variety of environmental issues. These challenges require an accurate assessment of the contributions of the driving factors, particularly in the Chaohu Lake Basin, which faces the double pressures of urban expansion and agricultural production. The research shows: (1) From 1990 to 2018, the trajectory of net anthropogenic N inputs (NANI) exhibited a three-stage pattern (uptrend stage, fluctuation stage, and downtrend stage), with an average value of 13,482 kg N km(-2) year(-1). The primary source was fertilizer N application, which made up approximately 79% of the NANI. Human food and animal feed imports, biological nitrogen fixation, and atmospheric N deposition composed 8%, 6%, and 6%, respectively. (2) Rapid urbanization enhanced the NANI in a short time stage. However, long-term analysis had shown a declining trend in nitrogen inputs, indicating that urbanization could improve fertilizer efficiency and introduce cleaner energy sources. (3) The NANI in urban watersheds were estimated at 20,700 kg N km(-2) year(-1), which was 3.4 times higher than in agricultural watersheds. Fertilizer N application was used in urban watersheds, as well as human food and animal feed imports. Urbanization drove the N input of food and feed mainly in urban watersheds but had no influence in agricultural watersheds and mixed watersheds. Since urban basins were the main source of nitrogen inputs, it was crucial to support environmental management efforts to reduce N pollution.