Study on formation mechanisms and synergistic control strategies of agricultural runoff non-point source pollution under simulated rainfall conditions

Abstract

[Objective] To mitigate the adverse impacts of non-point source pollution on the aquatic environment, it is crucial to accurately elucidate the dynamic formation mechanisms of such pollution and the synergistic control strategies within the precipitation-soil-crop system. [Methods] A multi-dimensional dynamic comparative precipitation simulation experiment was designed by controlling three key variables: crop type(wheat and maize), growth stage(growing and mature), and management practice(fertilized and unfertilized). Differences in runoff pollution characteristics under different scenarios were quantified through high-frequency runoff monitoring and soil physicochemical analysis. [Results] Runoff formed 2 hours after precipitation, and pollutant concentrations decreased over time. In maize fields with a plant height of 85 cm, runoff concentrations of chemical oxygen demand(COD), ammonium nitrogen(NH₄~+-N), total nitrogen(TN), nitrate nitrogen(NO₃~--N), and total phosphorus(TP) were 210.3%, 38.0%, 188.5%, 275.4%, and 128.1% higher, respectively, than those in wheat fields. For maize at 200 cm plant height, runoff fluxes of NH₄~+-N, TN, NO₃~--N, and TP decreased by 68.8%, 79.3%, 88.5%, and 62.5%, respectively, compared to those at 80 cm plant height. Fertilization during the wheat growing stage increased runoff concentrations of COD, TN, NO₃~--N, and TP by 43.9%, 15.9%, 57.5%, and 56.1%, respectively, compared to unfertilized plots. In contrast, fertilization during the maize growing stage reduced runoff concentrations of COD, NH₄~+-N, TN, and NO₃~--N by 18.2%, 68.2%, 25.6%, and 60.7%, respectively, compared with unfertilized plots. [Conclusion] Runoff pollution is triggered only when rainfall intensity exceeds a critical threshold, and pollutant fluxes show a pronounced decay over the rainfall duration, reflecting a “scouring threshold” effect in the surface soil. Compared to the 80 cm plant height stage, enhanced canopy interception and root uptake significantly reduced nitrogen and phosphorus loss fluxes during the mature maize stage.

Keywords

non-point source pollution / agricultural runoff / precipitation / scouring threshold / fertilization / water environment / total nitrogen / canopy structure