# Influence of Vegetation Filter Strip on Slope Runoff, Sediment Yield and Nutrient Loss
## 3 Results
### The Effects of the VFS on Nutrient Loss  
3.2.1. The Effects of the VFS on TP Loss  
According to the content of TP in runoff and sediment, the main way of TP loss on slope was sediment carried. When the slope was 5\({}^{\circ}\), 20\({}^{\circ}\), and 35\({}^{\circ}\), the reduction effects of VFS1 and VFS2 on TP in runoff were 39%, 30%, 20% and 23%, 40%, 45%, respectively. As the slope increased, the effects of the two vegetation filter strips showed opposite trends. With the increase of slope, the effect of the two VFS show an opposite trend, which was not completely consistent with the research conclusion that the slower the slope, the better the removal effect of pollutants in the vegetation filter strips [42]. When the rainfall intensity was 30 mm/h, 60 mm/h, and 90 mm/h, the reduction effects of VFS1 and VFS2 on runoff TP were 28%, 33%, 28% and 45%, 33%, and 30%, respectively. It can be seen that the influence of rainfall intensity on the two vegetation filter strips was not synchronous. As shown in Figure 6, on a 5\({}^{\circ}\) slope with a rainfall intensity of 30 mm/h, the TP content of runoff produced by the bare land control group was 0.19 mg/L, while the two VFSs were 0.13 and 0.18 mg/L, respectively. It can be clearly seen that the effect of VFS1 on reducing the TP loss in runoff was more significant. When the slope increased to 20\({}^{\circ}\) and 35\({}^{\circ}\), the effect of the VFS1 was 37% and 15%, respectively, while that of VFS2 was 61% and 68%, respectively. Similarly, on a slope of 5\({}^{\circ}\), when the rainfall intensity was 60 and 90 mm/h, it was better to set VFS1 to reduce TP loss in slope runoff. However, the situation was different for slope gradient of 20\({}^{\circ}\): when the rainfall intensity was 60 mm/h, VFS1 reduced the TP loss in runoff by 6% more than VFS2; but VFS2 can help to reduce the loss of TP more with rainfall intensity of 90 mm/h. When the slope continued to increase to 35\({}^{\circ}\), it was more significant to set VFS2 on the slope to reduce TP loss with rainfall intensity of 60 mm/h; while VFS1 can be more effective with rainfall intensity of 90 mm/h. Less phosphorus than nitrogen loss in the soil due to low content in coarse soil particles. The loss of phosphorus is mainly dominated by particulate phosphorus. However, inorganic phosphorus, which accounts for a high proportion of total soil phosphorus, is mainly present in the mineral state, which combines with cations to form insoluble salts (Table 2). The effect of VFS on reducing the TP in sediment was different from that in runoff. Vegetation stems can intercept granular nitrogen and phosphorus during sediment production, and plants can absorb and utilize available phosphorus to reduce total phosphorus loss. When slope was 5\({}^{\circ}\), 20\({}^{\circ}\), 35\({}^{\circ}\), VFS1 and VFS2 reduced TP in sediment by 12%, 12%, 19% and 10%, 17%, 20%, respectively. When rainfall intensity was 30 mm/h, 60 mm/h, 90 mm/h, VFS1 and VFS2 reduced TP in sediment by 6%, 16%, 20% and 11%, 17%, 18%, respectively. It can be seen that with the increase of slope and rainfall intensity, VFS1 and VFS2 had a more significant effect on reducing TP loss in sediment, which was contrary to the experimental conclusion of [9]. This may be due to the fact that with the increase of slope and rainfall intensity, surface runoff flows through the VFS at a faster speed, and the TP in the soil are not easily released into the VFS. Moreover, the TP content can be reduced through the adsorption of the surface soil, so that the reduction rate increases slightly. According to the Figure 6, when the rainfall intensity was 30 or 60 mm/h, the two types of VFSs set in 5\({}^{\circ}\) slope had the same effect. The difference was that the effect of VFS at 60 mm/h was better than that at 30 mm/h, the former reduced by 10%, while the latter only reduced by 2%. As the rainfall intensity added to 90 mm/h, the content of TP in sediment could be more effectively reduced by VFS1 on a 5\({}^{\circ}\) slope.