# Influence of Vegetation Filter Strip on Slope Runoff, Sediment Yield and Nutrient Loss
## 4 Discussion
### The Offset Effect of Influencing Factors on Erosion Control
Firstly, from the analysis of TN content (Figure 8e), as far as the group of No. 1 was concerned, when rainfall intensity was 30 mm/h, there was no significant difference on bare slope of any gradient, indicating that the change of slope gradient was not significant for soil TN loss under the condition of light rain intensity. However, the 5\({}^{\circ}\) slope with VFS was also distributed in the same group under the same rain intensity. We speculated that VFS had little effect on reducing soil TN loss with the same light rain intensity. The groups including No. 7 (60 mm/h, 5\({}^{\circ}\), VFS1), 13 (60 mm/h, 5\({}^{\circ}\), VFS2) and 22 (90 mm/h, 5\({}^{\circ}\), bare slope) validated a previous study by [PERSON] et al. [61], showing that soil nutrient loss increases with the increase of rainfall intensity. It can be speculated that the installation of VFS can offset the impact of rainfall intensity and significantly reduce sediment loss in surface runoff, thus effectively reducing the loss of soil TN. By analyzing the group of No. 8, 20 and 25, we knew that when rainfall intensity was fixed, slope gradient and VFS had opposite effects on TN loss on slope surface. In addition, when VFS was set in the same way, rainfall intensity and slope gradient also had opposite effects on TN loss. The analysis and summary of other groups can be concluded as follows: when slope gradient was greater than 20\({}^{\circ}\), the effect of setting VFS was not obvious, and the effect of rainfall intensity on TN loss was not signifi  
Figure 8: The groups of the phase dissimilarity of 6 evaluation indicators. (**a**) The groups of the phase dissimilarity of the runoff yield. (**b**) The groups of the phase dissimilarity of the sediment yield. (**c**) The groups of the phase dissimilarity of the TN content in runoff. (**d**) The groups of the phase dissimilarity of the TP content in runoff. (**e**) The groups of the phase dissimilarity of the TN content in sediment. (**f**) The groups of the phase dissimilarity of the TP content in sediment. cant. For gentle slopes with heavy rainfall, VFS can effectively reduce TN loss, improve runoff water quality, and thus reduce pollution to the downstream areas of the slope [62]. Then, the groups of TP content (Figure 8f) in sediment were analyzed. No. 15 (60 mm/h, 35\({}^{\circ}\), VFS1) and No. 16 (90 mm/h, 5\({}^{\circ}\), VFS1) were in the same group, indicating that the effects of rainfall intensity and slope gradient on soil TP loss were opposite. When the rainfall intensity was and there were two vegetation filter strips on the slope, the TP content of No. 25 (90 mm/h, 5\({}^{\circ}\), VFS2) was similar to that of No. 27 (90 mm/h, 35\({}^{\circ}\), VFS2), which can prove that slope nutrient losses exist critical slope gradient [63], the range of 15-25\({}^{\circ}\), the local surface slope is less than the critical value, the nutrient content in the sediment increased with the increase of slope and when the slope is larger than the critical value, the nutrient content in sediment decreases with the increase of slope. According to the group of No. 1, when rainfall intensity was no more than 60 mm/h and slope was no more than 20\({}^{\circ}\), it can be considered that setting VFS1 had no obvious effect on reducing TP loss on slope surface, and other soil and water conservation measures can be sought to reduce TP loss. By analyzing the group of No. 3, we knew that the effect of rainfall intensity was not prominent when the slope was steep (35\({}^{\circ}\)), and it was not suitable to set VFS2 on the slope under the condition of light rainfall intensity. To analysis the group including No. 7, we can also know that under the condition of strong rainfall and relatively steep slope, the difference of setting VFS1 or VFS2 was not big. However, setting VFS can eliminate the influences of increasing rainfall intensity and slope gradient on TP loss in sediment, can effectively reduce the loss of the slope of nutrients, which is beneficial to protect the ecological environment [64; 65].