## 2 Materials and Methods
### Research Methodology
#### 2.2.3 Method for ESV Evaluation in the Unit Area  
[PERSON] et al. calculate the ESV based on estimating individuals' \"willingness to pay\" for ecosystem services and constructing regional price and supply curves between \"residual\" or \"net rent\" markets\". [PERSON] combined this with the actual situation in China to carry out a comprehensive assessment of a national-scale ESV and its dynamic changes [37]. The indirect costs and conversion to monetary units were examined using methods presented in the literature, weighted calculations, proportionality, and expert experiences [26]. The calculation method used references the evaluation method of the ESV employed by [PERSON] et al. and the ESV equivalent table per unit area of China's terrestrial ecosystems formulated by them [26]. The specific formula is shown in Equation (1):  
\[ESV_{i}=\sum_{j=1}^{m}A_{ij}\times VC_{j} \tag{1}\]  
where \(ESV_{i}\) is the ESV (CNY) of \(j\) ecosystem type in area \(i\); \(A_{ij}\) is the land use area of \(j\) ecosystem type in area \(i\) (hm\({}^{2}\)), and \(VC_{j}\) is the ESV per unit area of \(j\) ecosystem type. Since the economic value of the food production capacity per unit area of farmland without human labor is one-seventh of that with human labor [38], in order to make the calculation more real and reliable, we made the following amendments to \(VC_{j}\), excluding farmland. \[E=Q\times\frac{1}{7}F \tag{2}\]  
\[VC_{j}=E\times V_{j} \tag{3}\]  
where \(Q\) is the average grain yield in Guangdong Province in 2020, which was 590,400,000 kg/km\({}^{2}\); \(F\) is the average purchase price of rice in Guangdong Province in 2020, which was 2.66 CNY/kg; \(E\) is the value of unit equivalent (CNY/km\({}^{2}\)), and \(V_{j}\) is the equivalent value of the corresponding land use type. Most of the wetlands on both sides of the Xijiang River were farmland, fish ponds, shrimp ponds, and other pits and reservoirs used for agricultural production and still had the basic characteristics of wetlands because their surface features were characterized by large bodies of water [39]. In this study, this part of the site was divided separately from the water system as an artificial wetland, distinguishing it from the other natural wetlands that had not been artificially transformed. The equivalence factor was corrected with the shadow engineering method, with reference to a related study conducted by [PERSON] [32]. The conversion of the equivalent factor of artificial wetlands in this study is achieved through the ratio of artificial wetlands to natural wetlands, and the results are shown in Table 2 below. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Before Amendment**} & \multicolumn{2}{c}{**After Amendment**} \\ \cline{2-5}
**Ecosystem Services Classification** & \multicolumn{2}{c}{**Classification**} & \multicolumn{2}{c}{**Wetlands**} & \multicolumn{2}{c}{**Wetlands**} \\ \cline{2-5}  & **Secondary Classification** & **Natural Wetlands** & **Natural Wetlands** & **Artificial Wetlands** \\ \hline \multirow{3}{*}{Supply service/CNY \(10^{4}\)} & Food production & \(0.51\) & \(0.51\) & \(0.3\) \\  & Raw material production & \(0.5\) & \(0.5\) & \(0.3\) \\  & Water supply & \(2.59\) & \(2.59\) & \(1.7\) \\ \hline \multirow{3}{*}{Regulating services/CNY \(10^{4}\)} & Gas regulation & \(1.9\) & \(1.9\) & \(1.2\) \\  & Climate regulation & \(3.6\) & \(3.6\) & \(2.4\) \\ \cline{1-1}  & Purification of the environment & \(3.6\) & \(3.6\) & \(2.4\) \\ \cline{1-1}  & Hydrology & \(24.23\) & \(24.23\) & \(15.8\) \\ \hline \multirow{3}{*}{Support services/CNY \(10^{4}\)} & Soil conservation & \(2.31\) & \(2.31\) & \(1.5\) \\ \cline{1-1}  & Maintaining nutrient cycles & \(0.18\) & \(0.18\) & \(0.1\) \\ \cline{1-1}  & Biodiversity & \(7.87\) & \(7.87\) & \(5.1\) \\ \hline \multirow{3}{*}{Cultural service/CNY \(10^{4}\)} & Aesthetics landscape & \(4.73\) & \(4.73\) & \(3.1\) \\ \cline{1-1}  & & & & \\ \hline \hline \end{tabular}
\end{table}