Nitrogen budget, projection and management in the Three Gorges Reservoir Area

This study investigates the spatiotemporal dynamics of nitrogen (N) and its driving factors in the Three Gorges Reservoir Area (TGRA) from 2000 to 2021, projects N budgets for 2035 under alternative scenarios, and proposes targeted control measures. The results show that fertilizer application and industrial emissions are the primary contributors to N input, whereas agricultural products, livestock production, and water loss are the main factors shaping N output. The TGRA currently exhibits an annual N surplus of approximately 187.84×10³ t a^-1, accounting for 12.72% of total N input. Overall, N input exceeds output, yielding a net N surplus flux of 32.75 kg ha^-1 a^-1. Nevertheless, these surplus displays marked temporal and spatial heterogeneity. Temporally, it declined gradually from 2000 to 2010, then increased rapidly from 2010 to 2021. Spatially, the N surplus is more pronounced in the middle section of the reservoir area than in the head or tail regions. Under a business-as-usual scenario, the N surplus is projected to continue rising. Isolated measures focusing solely on reducing fertilizer use or emissions are unlikely to significantly mitigate the surplus. Achieving a balanced N budget by 2035 will require an integrated strategy that combines reduced fertilizer application, emission controls, and mitigation of regional atmospheric N deposition. This study provides a theoretical basis for managing and controlling N pollution in the TGRA.