## 5 Conclusions  
The water quality parameters, chemical indicators, and surface sediment productivity distribution of four typical urban water body types (Canal, Pond, Lake, and River) in Shaoxing City were qualitatively and quantitatively analyzed using the C/N ratio and \(\delta^{13}\)C and \(\delta^{15}\)N values. The key results are summarized as follows:  
1. Urban water bodies exhibit subtle differences in water quality parameters. Artificial water bodies, particularly canals and lakes, exhibit higher DO and EC contents than natural water bodies. Canals have the highest DO contents, while lakes have the highest EC and TDS contents (1.52 times higher than those in rivers). Natural water bodies have a slightly stronger ORP and lower pH values than artificial water bodies. Overall, stationary water bodies, such as lakes and ponds, tend to have higher TDS and EC than flowing water bodies, such as rivers and canals.
2. All four urban water body types slightly exceed China's Class-V water quality standard for TN, with Canal, Lake, Pond, and River averaging 1.29, 1.22, 1.23, and 1.23 times the standard, respectively. TD and TDN values vary significantly among the water bodies, with ponds showing the highest TDN. NH\({}_{4}\)+N and NO\({}_{3}\)\({}^{-}\)-N levels are relatively consistent across all water bodies, except for the slightly lower NO\({}_{3}\)\({}^{-}\)-N of Lake. Chl-a and COD\({}_{\text{Mn}}\) values indicate higher organic matter in Canal and Lake and lower organic matter in Pond and River, suggesting less eutrophication. These findings highlight the need for targeted water management strategies.
3. TON content in sediments is relatively uniform across all water bodies, with lakes and rivers showing slightly higher values. TOC content is highest in lakes, 1.51 times that of canals. C/N ratios vary, with ponds and lakes having the highest averages. Source quantification using isotopic analysis (\(\delta^{13}\)C and \(\delta^{15}\)N values) reveal distinct sources of organic matter: phytoplankton sources dominate in rivers and canals, whereas terrestrial sources dominate in lakes and ponds. Sewage sources contribute considerably to rivers and canals. This study underscores the importance of phytoplankton and sewage as organic matter sources in urban water bodies, highlighting the need for targeted pollution control strategies in the urban water environment.  
S.X.: writing--original draft, conceptualization, investigation, writing--review and review and editing; S.Y.: conceptualization, data curation; Y.D.: investigation, writing--review and editing; H.X., Y.Z. and S.L.: investigation and methodology, H.Z. and F.Y.: investigation and project administration; C.W.: funding acquisition and resources. All authors have read and agreed to the published version of the manuscript.  
This study was financially supported by the Guangdong Basic and Applied Basic Research Foundation (Grant No. 2022A1515110930, 2022A1515110718, 2022A1515110325), Open Foundation of State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences (No. SKLECRA2022 OFF04), National Natural Science Foundation of China (Grant No. 42407288, 42307288), and the Laboratory of Lingnan Modern Agriculture Project (NZ201206).  
Not applicable.  
The data presented in this study are available on request from the corresponding author due to privacy.  
The authors would like to thank the anonymous reviewers for their comments and suggestions, which contributed to the further improvement of this paper.  
The authors declare that they have no conflicts of interest.