## 3 Results
### Bacterial Community Structure  
The taxonomic data on bacteria in the samples was obtained from the taxonomic analysis of the OTU data. The taxonomy was specified as a total of 47 phyla and 736 genera. The percentages of species at the phylum level are shown in Figure 2a, and the phyla with less than 0.5% were combined as Others. Proteobacteria was the dominant phylum in the soil samples, and the percentage of species in Proteobacteria increased with depth, ranging from 58.8% to 96.0%. The other dominant phyla in the surface soil samples were more evenly distributed, with 7.4% of species in Actinobacteria, 6.2% in Bacteroidetes, 6.2% in Acidobacteria, 5.8% in Gemmatimonadetes and 4.4% in Chloroflexi. In the middle and deep samples, most of the phyla were inhibited except Proteobacteria, Bacteroides (5.5% and 2.7%, respectively), Firmicutes (4.3% and 5.4%) and Chloroflexi (3.7% and 1.1%). Proteobacteria, Bacteroides and Chloroflexi accounted for relatively higher percentages than other phyla in the middle and deep samples, but were still decreased compared to the topsoil. However, the percentage of species in Firmicutes increased from the surface layer to the deep layer. In the ultra-deep samples, only Proteobacteria, Bacteroides (1.6%) and Firmicutes (1.0%) accounted for more than 1.0%. In the groundwater (GW) sample, only Proteobacteria and Bacteroides accounted for more than 1.0%. The \(\alpha\)-diversity of river water were higher than that of groundwater; Proteobacteria, Bacteroides, Acidobacteria, Chloroflexi, Cyanobacteria and Planctomycetes were more evenly distributed in the river water compared to groundwater. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample No**} & \multirow{2}{*}{**Name**} & **Depth** & **N-NH\({}_{4}\)\({}^{*}\)** & **N-NO\({}_{3}\)\({}^{-}\)** & **N-NO\({}_{2}\)\({}^{-}\)** & **N** & **C** & **S** & **C/N** & **pH** & **LOI** \\  & & **m** & **mg/kg** & **mg/kg** & **mg/kg** & **\%** & **\%** & **\%** & **\%** & **\%** & **\%** \\ \hline \multirow{4}{*}{S} & W1-1 & \multirow{4}{*}{0-2} & 2.64 & 2.66 & 0.39 & 0.04 & 0.92 & 0.15 & 25.46 & 7.58 & 3.71 \\  & W2-1 & & 0.07 & 0.33 & 0 & 0.04 & 0.91 & 0.12 & 25.29 & 7.67 & 3.81 \\  & W3-1 & & 0.21 & 0.53 & 0.12 & 0.05 & 1.02 & 0.09 & 21.22 & 7.62 & 4.12 \\  & W4-1 & & 0.27 & 0.88 & 0.19 & 0.08 & 1.63 & 0.07 & 21.57 & 7.69 & 5.23 \\  & W1-2 & & 5.40 & 1.25 & 0.52 & 0.03 & 0.92 & 0.15 & 27.49 & 7.78 & 3.47 \\  & W2-2 & & 6.83 & 0.81 & 0.27 & 0.04 & 1.02 & 0.14 & 26.18 & 7.41 & 4.12 \\  & W3-2 & & 91.23 & 0.19 & 0.01 & 0.07 & 1.36 & 0.15 & 18.26 & 7.06 & 4.55 \\  & W4-2 & & 10.96 & 0.17 & 0 & 0.04 & 1.13 & 0.08 & 30.05 & 7.89 & 3.94 \\  & W1-3 & & 2.89 & 0.09 & 0.01 & 0.01 & 0.85 & 0.14 & 57.77 & 8.02 & 2.22 \\  & W2-3 & & 79.42 & 0.27 & 0 & 0.02 & 0.80 & 0.11 & 38.25 & 8.16 & 2.17 \\  & W3-3 & & 4.55 & 0.13 & 0 & 0.02 & 1.01 & 0.11 & 42.51 & 7.93 & 2.70 \\  & W4-3 & & 26.78 & 0.35 & 0.06 & 0.02 & 0.83 & 0.11 & 49.56 & 8.01 & 1.87 \\  & W2D-1 & & 6–7.5 & 3.12 & 0.17 & 0 & 0.01 & 0.78 & 0.05 & 66.49 & 8.35 & 1.80 \\ U & W2D-2 & 9–10.5 & 23.97 & 0.10 & 0 & 0.03 & 1.02 & 0.06 & 32.47 & 8.52 & 4.60 \\  & W2D-3 & 13.5–15 & 51.16 & 0.18 & 0 & 0.07 & 1.19 & 0.30 & 16.90 & 7.74 & 6.71 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical and physical characteristics of soil samples. The percentage of the community at the genus level is shown in Figure 2b. Genera with less than 0.5% were combined as Others. Others accounted for >60% of the community in topsoil and river water samples--63.2% and 72.6%, respectively. The dominant genus in the topsoil was _Thiobacillus_ of Proteobacteria, accounting for 11.8%, and which was also widely present in the subsurface soil samples. In the river water samples, the dominant genus was an unclassified genus under the ACK-M1 family of Actinomycetes, which accounted for 17% of river water. In this study, this genus only appeared in the river water samples.