## 3 Results and Discussion
### Bottom Sediment Characterization
\begin{table}
\begin{tabular}{l c c c c c c c} \hline \hline \multirow{2}{*}{**Sediment Characteristic**} & \multirow{2}{*}{**Unit**} & \multicolumn{3}{c}{**Average Concentration**} & \multicolumn{3}{c}{**Student’s \(t\)-Test (S1; S3)**} \\ \cline{3-8}  & & **S1** & **S2** & **S3** & **Mean Difference** & \(t\) & \(p\)**Value** \\ \hline pH & – & 6.09 & 6.59 & 6.52 & \(-\)0.43 & \(-\)1.02 & 0.37 \\ \hline Oxidation reduction potential (ORP) & mV & \(-\)219.67 & \(-\)206.07 & \(-\)217.30 & \(-\)2.37 & \(-\)0.02 & 0.99 \\ \hline Organic carbon (OC) & \% & 9.61 & 14.93 & 13.59 & \(-\)3.98 & \(-\)0.83 & 0.49 \\ \hline Organic matter (OM) & \% & 16.57 & 25.74 & 23.43 & \(-\)6.86 & \(-\)0.83 & 0.49 \\ \hline Clay & \% & 46.29 & 45.25 & 27.19 & 19.10 & 7.00 & 0.00 \\ \hline Slit & \% & 13.65 & 16.77 & 8.35 & 5.30 & 3.62 & 0.02 \\ \hline Sand & \% & 40.06 & 37.97 & 64.47 & \(-\)24.41 & \(-\)8.20 & 0.00 \\ \hline Aluminium (Al\({}_{2}\)O\({}_{3}\)) & wt \% & 5.19 & 5.87 & 4.55 & 0.64 & 1.29 & 0.29 \\ \hline Iron (Fe\({}_{2}\)O\({}_{3}\)) & wt \% & 4.36 & 4.79 & 4.41 & \(-\)0.05 & \(-\)0.08 & 0.94 \\ \hline Manganese (MnO) & wt \% & 0.06 & 0.03 & 0.07 & \(-\)0.02 & \(-\)2.24 & 0.11 \\ \hline Sulfur (SO\({}_{3}\)) & wt \% & 0.64 & 0.56 & 0.63 & 0.00 & 0.21 & 0.85 \\ \hline \hline \end{tabular} Note: wt % = weight percentage.  
\end{table} 
Table 3: Bottom sediment characteristics of each site and Student’s \(t\)-test results to compare the inflow (S1) to the far middle (S3) of the wetland. rated soils. Carbon fixation typically exceeds decomposition, leading to the accumulation of carbon and organic matter [3; 67]  
In a study by [68], the effects of plant litter decomposition on wetland sediment were examined. Their research demonstrated that litter decomposition leads to changes in the OM, pH, EC, ORP, and the bioavailability of metals in both the sediment and the surrounding water. Figure 4 in the current study illustrates the relationship between the OM%, pH, and ORP. The highest percentages of OM were observed at S2 and S3, which also showed the highest ORP and pH values. This correlation suggests the significant impact of organic matter on the chemical properties of the wetland sediment. Another critical indicator of soil's physical, chemical, and biological properties, and consequently of the biogeochemical reactions within wetland bottom sediment, is the soil particle size distribution [69]. Ref. [70] found a predominance of clay in the bottom sediment, especially concentrated downstream in a wetland affected by AMD. Contrarily, the present study observed an increase in the sand content at downstream sites (Figure 5). Ref. [8] documented sediment textures in an ecologically engineered wetland, primarily composed of sand particles. However, in the current study, clay particles constituted 46.29%, 45.25%, and 27.19% of the sediment textures at S1, S2, and S3, respectively (Table 3). The differences in the particle size distribution among these studies could be attributed to variations in the surface water velocity at different points within the wetland [3]. Clay minerals are essential for cation-anion exchange and pH buffering, contributing to the relatively stable pH values observed in the bottom sediments at each site, regardless of the surface water pH [70]. Additionally, clay particles' large surface area and cation-anion exchange capacity enhance the soil reactivity and facilitate interactions with OM [3]. However, in this study, the relationship between the OM% and clay content showed an inverse trend. S1 had the highest clay content but the lowest OM%. This discrepancy could be due to the higher water flow rate at the inflow site (S1), resulting in a shorter residence time and consequently transporting OM farther into the wetland, toward the middle (S2 and S3). Water pollutants have a strong affinity for organic materials, leading to the accumulation of metals and sulfur compounds within the bottom sediment layers of wetlands affected by AMD [5; 71].