Nitrogen and Oxygen Isotope Tracing of Nitrate Concentration Sources in the Middle Reaches of the Huaihe River

The objective of this study was to examine the link between agricultural surface pollution in the central Huaihe River and nitrate sources and their transport through water bodies. Therefore, this study aimed to use the nitrogen and oxygen isotope technique and the stable isotope analysis in the R model (SIAR) to explore the NO 3 − sources in the central Huaihe research area. This indicates the following: ① The predominant form of nitrogen in the experimental area’s water masses was NO 3 − . Nitrogen levels were higher in the wet season (2.88 mg/L) compared to the dry season (1.85 mg/L). The NO 3 − /Cl − and Cl − concentrations demonstrate that the research area was affected by numerous sources of pollution, particularly agricultural activities, which account for a large share of these s sources. ② The research area’s water bodies did not experience any substantial denitrification. The contribution of various pollution sources encompassed chemical fertilizers (CF: 6.10 to 62.47%), atmospheric deposition (AP: 1.41 to 2.06%), manure and domestic sewage (MS: 7.07 to 67.36%), and soil sources (SN: 25.13 to 28.40%). MS and SN were the dominant factors influencing nitrate concentration in the dry season and CF and SN in the wet season. The primary causes of nitrate pollution in the research area’s water bodies were the use of fertilizers, cattle manure, and rural sewage. Based on the results of this study, reasonable suggestions are made for the effective reduction of nitrate pollution in the Huaihe River Basin.