Objective To investigate the process and intensity of nitrogen (N) and phosphorus (P) runoff losses from paddy fields adjacent to the Three Gorges Reservoir area, and to assess the reduction effects of terraced paddy fields on N and P losses, thereby providing a scientific basis for the prevention and control of farmland non-point source pollution in the region. Methods Field experiments were conducted to monitor runoff volumes and N and P concentrations of various forms during rainfall-runoff events throughout the rice growth stages in 2017 and 2018. Results 1) The potential environmental risk of N and P runoff losses from reservoir-adjacent paddy fields was extremely high. Total nitrogen (TN) concentrations in surface runoff during each event ranged from 0.65 mg/L to 56.50 mg/L, and total phosphorus (TP) concentrations ranged from 0.06 mg/L to 0.84 mg/L. TN concentrations exceeded 2 mg/L in 47.6% of runoff, and TP concentrations exceeded 0.2 mg/L in 40.5% of runoff. 2) The concentrations and intensities of N and P losses from reservoir-adjacent paddy fields decreased gradually over the rice growth stages. The cumulative surface runoff fluxes of TN and TP during the entire growth stages were 2.89 kg/hm2 and 0.29 kg/hm2, respectively, with the highest intensity of N and P runoff losses observed during the tillering stage. 3) During the rice growing stage, the average reduction rates of TN and TP in surface runoff by terraced paddy fields were 19.18% and 18.49%, respectively. The highest TN reduction rate (34.82%) occurred during the maturity stage, while the highest TP reduction rate (26.46%) occurred during the tillering stage. Conclusion The tillering stage is a high-risk period for N and P surface runoff losses from reservoir-adjacent paddy fields. However, terraced paddy fields have a certain capacity for retention and interception, and appropriate regulation can reduce N and P inputs into the reservoir water.
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