## 3 Results and Discussion
### Analysis of Pollutant Sources
#### 3.5.2 Principal Component Analysis  
The KMO test and Bartlett's sphericity test were performed to determine the suitability of the data for factor analysis before the factor analysis was conducted. In this study, the KMO statistic was 0.57, which is generally considered to be a KMO value greater than 0.5, indicating that the data are suitable for factor analysis. The factors were extracted using the principal component analysis method, and orthogonal rotation was performed using the maximum variance method. The factors were extracted according to the principles of a cumulative contribution rate of 80% or more and an initial eigenvalue greater than 1, and four common factors were obtained (Table 6). The cumulative variance contribution rates before and after rotation did not change, indicating that these four common factors can be used to explain the basic information of the nine original variables of the Wanquan River. The factor loading matrices and the main control indicators of water quality for each common factor after rotation are shown in Tables 6 and 7. The contribution of the first principal component (F\({}_{1}\)) was 36.556%. NH\({}_{4}\)+-N, TN, TP, and BOD\({}_{5}\) had high factor loadings, indicating organic pollution sources, among which the factor loadings of TP and TN were 0.890 and 0.951, respectively, indicating the presence of nitrogen and phosphorus pollution in the water body, whereas the factor loading of NH\({}_{4}\)+-N was 0.941, whose main source was the decomposition of organic nitrogen compounds entering the water body by microorganisms [32]. Its content can reflect the degree of pollution and self-purification ability of the water body. The contribution of the second principal component (F\({}_{2}\)) is 17.007%. COD has a high factor loading, indicating the source of organic pollution. COD can reflect the amount of organic substances in the water body and, to some extent, can characterize the degree of pollution of the water body by organic substances. The third principal component (F\({}_{3}\)) has a contribution of 16.611%, with Cr\({}^{6+}\) and As having high factor loadings, indicating metallurgical and chemical pollution sources, which are mainly from the mining, smelting, and foundry industries of chromium ore and the application of chromium compounds in electroplating, alloying, printing, and dyeing, as well as in agriculture [33]. The fourth principal component (F\({}_{4}\)) has a contribution of 12.410%, and COD\({}_{\text{Mn}}\) has a high factor loading. COD\({}_{\text{Mn}}\) reflects the concentration of organic matter by measuring the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Indicators** & **F\({}_{1}\)** & **F\({}_{2}\)** & **F\({}_{3}\)** & **F\({}_{4}\)** \\ \hline NH\({}_{4}\)+-N & **0.941** & 0.222 & 0.030 & 0.060 \\ TN & **0.951** & 0.181 & 0.041 & 0.025 \\ TP & **0.890** & \(-\)0.123 & 0.019 & 0.273 \\ COD\({}_{\text{Mn}}\) & 0.146 & 0.021 & \(-\)0.013 & **0.954** \\ COD & \(-\)0.158 & **0.798** & 0.151 & 0.169 \\ BOD\({}_{5}\) & **0.713** & \(-\)0.390 & \(-\)0.244 & \(-\)0.158 \\ Cr\({}^{6+}\) & 0.081 & 0.007 & **0.844** & \(-\)0.117 \\ As & \(-\)0.101 & 0.111 & **0.834** & 0.115 \\ Hg & 0.370 & **0.795** & \(-\)0.052 & \(-\)0.218 \\ \hline \hline \end{tabular} Note: Values in bold in the table represent higher factor loadings.  
\end{table} 
Table 6: Rotated factor loading matrix. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Common Factor** & **Eigenvalue** & **Percentage of Variance** & **Cumulative Contribution of Variance** & **Main Control Indicators** \\ \hline F\({}_{1}\) & 3,33 & 37.04 & 37.04 & NH\({}_{4}\)+-N, TN, TP, BOD\({}_{5}\) \\ F\({}_{2}\) & 1.80 & 20.05 & 57.09 & COD \\ F\({}_{3}\) & 1.22 & 13.57 & 70.66 & Cr\({}^{6+}\), As \\ F\({}_{4}\) & 1.07 & 11.92 & 82.58 & COD\({}_{\text{Mn}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Extracted common factors. oxidation capacity of organic matter in a water sample and is not fundamentally different from what COD represents.