Retention Efficiencies of Vegetative Filter Strips in Reducing Agricultural Nonpoint Source Pollution in Jianghan Plain: Experiments and VFSMOD Modeling

In this study, a field experiment was conducted to examine the retention efficiencies of vegetative filter strips (VFS) on agricultural nonpoint source pollutants. Furthermore, the numerical model VFSMOD was used to predict the VFS performance and linked to a simplified nitrogen transport algorithm. The results indicated that the long filter, low grass spacing, low initial soil water content, and low inflow rate had high VFS retention efficiencies for surface runoff, sediment, and N. However, shallow water table depths (> 1.8 m) had little influence on VFS retention efficiencies, suggesting that shallow WTD (> 1.8 m) need not be considered when constructing VFS. The retention efficiencies varied greatly from 16.55%, 21.15%, 24.70%, 14.57%, 21.86%, and 27.70% to 81.51%, 87.58%, 88.47%, 87.56%, 82.97%, and 89.95% for surface runoff, sediment, TN, NH₄⁺, NO₃⁻, and PN, respectively. The VFSMOD can predict hydrology and sediment transport well for the experimental events with peak outflow rate from VFS greater than 0.0004 m³/s. The good VFSMOD predictions in surface runoff (C_eff = 0.985 for TRF, C_eff = 0.969 for RDR) and sediment (C_eff = 0.998 for MSF, C_eff = 0.960 for SDR) also resulted in good predictions of N (C_eff = 0.913 for MDN). Overall, our study demonstrated that VFSMOD is a useful tool in formulating management schemes for retaining nonpoint source pollutants using VFS, provided local meteorology, rainfall intensity, agricultural fertilization policies, and other influencing factors are considered.