Predicting particulate phosphorus removal efficiency in vegetative filter strips: A particle size-based model coupled with VFSMOD-W in black soil region of northeast China

The black soil region in Northeast China, a key agricultural base, faces significant soil erosion and particulate phosphorus (PP) export due to long-term intensive farming and concentrated summer rainfall events. Vegetative filter strips (VFS) are effective best management practices (BMPs) for intercepting sediment and trapping the PP attached to it. However, current VFS models (e.g., VFSMOD-W) fail to represent the mechanisms of PP transformation and migration, and they struggle to quantify the critical factor of concentrated flow (CF). To address these issues, this study established runoff plots with varying slopes on typical black soil hillsides. Field monitoring during natural rainfall events was conducted to collect runoff and soil samples for analysis of hydrological, sediment, and phosphorus dynamics. In combination with laboratory experiments on phosphorus adsorption kinetics, sediment static settling, and laser particle size-shape analysis, the mechanisms of PP adsorption and settling were revealed. Based on these findings, an area-weighted PP removal efficiency algorithm was developed using sediment particle size distribution (NSE = 0.96, RMSE = 0.03). This algorithm was then coupled with the calibrated VFSMOD-W hydrological sediment model, demonstrating excellent applicability. The simulation results indicate that the concentrated flow ratio (CFR) is the most dominant factor in suppressing VFS performance, contributing 29.5%. When the CFR reaches 90%, the PP removal rate (ΔP) can drop sharply to nearly 0, a reduction of over 96% compared to uniform flow conditions. Intense rainfall exacerbates this negative effect. To address pollution control challenges in areas with high concentrated flow risk, it is recommended to prioritize the installation of grass-shrub composite vegetation systems (e.g., grass hedge-grass strip combinations) and to increase VFS width where appropriate. This approach will enhance runoff dispersion and pollutant retention efficiency, leading to effective management of agricultural non-point source pollution.