The transport mechanisms of sediment and phosphorus in agricultural drainage ditches in the presence of vegetation

Understanding the mechanisms by which vegetation influences phosphorus transport in agricultural drainage ditches is crucial for accurately assessing non-point source pollution loads and ecosystem restoration in irrigation areas. This study conducted experiments in outdoor artificial ditches to comprehensively analyze the effects of vegetation density, hydraulic characteristics, and suspended sediment properties (with three settings for each) on suspended sediment and phosphorus transformation and transport. Particular emphasis was placed on sediment-water interface dynamics. Building on the adsorption-desorption properties of phosphorus and particles, this study examined suspended sediment movement and phosphorus adsorption capacities across varying sizes within ditches. As vegetation density increased from 0 to 1800 stems/m 2 , the phosphorus interception rate increased from 0.11 to 0.358, particularly through the capture of fine particles with higher adsorption capacities. Vegetation was found to intercept suspended sediment with particle sizes smaller than 73 μm more effectively than gravitational settling, and this size threshold increases to 124 μm with increasing flow velocity. Under high flow velocity conditions, more than 90% of phosphorus is intercepted by plant interception. The initial concentration of suspended sediment influences the distribution of phosphorus and sedimentation. As the initial concentration increases, dissolved phosphorus concentration decreases from 0.86 to 0.757. This study provides a theoretical basis for managing phosphorus emissions in agricultural ditches under diverse environmental conditions. • Particle size affects the transport of suspended sediment and phosphorus • Vegetation facilitate the interception of more fine suspended sediment • Outdoor simulated ditch reliably replicates key processes of phosphorus transport • Plant interception is more important for phosphorus removal