# Evaluation and Prediction of Ecological Benefits in Song-Liao River Basin
## 2 Materials and Methods
### Ecosystem Service Index
#### 2.4.3 Soil Conservation  
Soil erosion is one of the leading causes of global land degradation, and the ecological and environmental problems caused by it have attracted much attention. It is essential to evaluate the soil conservation capacity [40]. Quantitative assessment of regional soil conservation is an essential prerequisite for regional Soil and water conservation and ecological restoration [41]. This study used the Revised Universal Soil Loss Equation (RULSE) to evaluate soil conservation in SRB from 1990 to 2020. This method is widely used in the quantitative evaluation of regional soil erosion and conservation, and its evaluation effect is good. The input parameters of this evaluation method mainly include the Digital Elevation Model (DEM), Rainfall erosion factor (\(R\)), Soil erodibility factor (\(K\)), Land use cover change (LUCC), Vegetation coverage factor (\(C\)), and Soil and water conservation factor (\(P\)). The evaluation of soil conservation is completed with Equations (14)-(25), and the calculation process is completed in ArcGIS 10.8:  
\[R=0.53\times P^{1.655} \tag{14}\]  
where \(R\) is the interannual rainfall erosivity; and \(P\) is the interannual precipitation in the study area.  
\[r=0.2+0.3\times exp(-0.256\times S_{a})\times\left(\frac{1-S_{a}}{100}\right) \tag{15}\]  
\[s=\left(\frac{S_{l}}{C_{l}+S_{l}}\right)^{0.3} \tag{16}\]  
\[t=\frac{1-0.25\times C}{C+exp(3.72-2.95\times C)} \tag{17}\]  
\[u=\frac{1-0.7\times\frac{1-S_{a}}{100}}{\frac{1-S_{a}}{100}+exp\left(-5.51+22. 9\times\frac{1-S_{a}}{100}\right)} \tag{18}\]  
\[K=r\times s\times t\times u \tag{19}\]  
where \(K\) is a soil erodibility factor; \(S_{a}\) is the sand content; \(S_{l}\) is the powder content; \(C_{l}\) is clay content; and \(C\) is organic carbon content [42].  
\[L=\left(\frac{I\times cos\alpha}{22.12}\right)^{m} \tag{20}\]  
where \(L\) is the slope length factor; \(I\) is the length of surface water flow along the flow direction; \(\alpha\) is the slope value of the water flow area; and \(m\) is a variable slope index, if:  
\[m=\begin{cases}0.2\ (0.00^{\circ}\leq\theta<0.57^{\circ})\\ 0.3\ (0.57^{\circ}\leq\theta<1.72^{\circ})\\ 0.4\ (1.72^{\circ}\leq\theta<2.86^{\circ})\\ 0.5\ (2.86^{\circ}\leq\theta<45.0^{\circ})\end{cases} \tag{21}\]  
Then, the calculation equation of slope is:  
\[S=\left\{\begin{array}{l}10.80\times sin\theta+0.03\ (0^{\circ}\leq\theta<5^{ \circ})\\ 16.80\times sin\theta-0.50\ (5^{\circ}\leq\theta<10^{\circ})\\ 21.91\times sin\theta-0.96\ (10^{\circ}\leq\theta<45^{\circ})\end{array}\right. \tag{22}\]  
where \(S\) is the slope factor; and \(\theta\) is the slope.  
\[c=\frac{NDVI-NDVI_{s}}{NDVI_{\tau}-NDVI_{s}} \tag{23}\]  
\[C=\left\{\begin{array}{c}1\ (c=0)\\ 0.6508-0.3436\times lg(c)\ (0\leq c<78.3\%)\\ 0\ (c>78.3\%)\end{array}\right. \tag{24}\]  
where \(C\) is the vegetation coverage factor; \(c\) is the vegetation coverage; \(NDVI\) is normalized difference vegetation index; \(NDVI_{s}\) is the \(NDVI\) of the area without vegetation cover; and \(NDVI_{v}\) is \(NDVI\) completely covered by vegetation.  
\[SC=R\times K\times LS\times C\times P \tag{25}\]  
where \(SC\) is soil conservation; \(R\) is the rainfall erosion factor; \(K\) is a soil erodibility factor; \(LS\) is the slope and aspect factor; \(C\) is the vegetation coverage factor; and \(P\) is the factor of soil and water conservation factor.