## 4 Discussion  
Water quality is a key indicator of the health of aquatic ecosystems and is influenced by various natural and anthropogenic factors. The pH values for all water bodies range from slightly alkaline to neutral. Canals exhibit the broadest range (7.45-9.96), indicating a more variable environment, possibly due to agricultural runoff or industrial discharge. Lakes and ponds have similar pH ranges, with lakes showing a slightly higher mean pH (8.87) than ponds (8.65). Rivers have the narrowest pH range (7.82-9.72), suggesting a more stable environment. ORP indicates the tendency of water to gain or lose electrons and is a measure of water's ability to act as an oxidizing or reducing agent [30]. Canals have the highest mean ORP (159.77), suggesting a more oxidizing environment, attributable to higher organic matter decomposition. Ponds have the widest range (73.66-214.26) and the highest variability in ORP, indicating a more dynamic redox state. Obviously, DO is essential for the survival of aquatic life. Canals have the highest mean DO (8.83 mg/L), which is beneficial for aquatic organisms. Meanwhile, ponds have the lowest mean DO (6.94 mg/L), attributable to higher biological oxygen demand from increased organic matter [31]. The wide DO range for rivers (2.84-13.29 mg/L) suggests significant spatial and temporal variability, consistent with rivers having the strongest flow characteristics among the four types of water bodies. EC measures the ability of water to conduct electricity  
Figure 3: C and N source contributions for sediments from canals, lakes, ponds, and rivers. Figure 2: Characteristics of \(\mathrm{\SIUnitSymbolMicro}\)C and \(\mathrm{\SIUnitSymbolMicro}\)N for sediments from canals, lakes, ponds, and rivers. and is influenced by the presence of ions. Lakes have the highest mean EC (224.59 uS/cm), indicating a higher concentration of dissolved ions. Rivers have the lowest mean EC (148.13 uS/cm), suggesting a lower ionic content, attributable to more frequent water exchange. TDS is a measure of the total amount of dissolved substances in water. Lakes have the highest mean TDS (145.56 mg/L), consistent with their high EC. Rivers have the lowest mean TDS (95.83 mg/L), consistent with their low EC, indicating less dissolved material. Water chemical indicators reveal several key characteristics that distinguish these environments in terms of their nutrient content and biological productivity. The TN levels were relatively consistent among the four types of water bodies, with mean values ranging from 2.44 to 2.58 mg/L. This suggests a similar level of nitrogen input or availability across different aquatic ecosystems. The average TN contents in the four types of water bodies exceeding the surface water Class-V water quality standard (2.0 mg/L) in China showed that these bodies totally exhibited nitrogen pollution. However, there is a notable variation in TDN, which was highest in ponds (mean = 2.46 mg/L), indicating higher organic matter decomposition rates or runoff inputs in ponds [32]. NH4+-N contents were generally low across all samples, with means ranging from 0.07 to 0.10 mg/L, indicating efficient ammonification processes or rapid uptake by microorganisms within water bodies. Meanwhile, NO3\({}^{-}\)-N levels varied more significantly, with the highest mean content observed in canals (1.81 mg/L). This may reflect a greater anthropogenic influence on riverine systems through agricultural runoff or sewage discharge [33; 34]. Chl-a contents serve as an indicator of algal biomass and primary productivity. Rivers exhibited the lowest Chl-a levels (mean = 3.37 ug/L), whereas canals exhibited the highest (mean = 5.42 ug/L). This pattern is attributable to differences in light penetration, nutrient availability, and grazing pressure between these habitats [35]. CODMn provides insights into the amount of oxygen required to oxidize organic matter present in water. Lakes showed the highest CODMn values (mean = 3.47 mg/L), suggesting a higher organic pollutant load than in other water bodies.