Tracing nitrate sources and transformations using △17O, δ15N, and δ18O-NO3− in a coastal plain river network of eastern China

Identifying the sources and transformations of riverine nitrate plays a critical role in mitigating nitrogen enrichment river networks. Several previous studies have used δ18O-NO3− to quantitatively assess contributed by atmospheric terrestrial sources, but their results great uncertainty due wide range values isotopic fractionation during nitrogen-cycling processes environment. The 17O anomaly (△17O-NO3−), as an unambiguous tracer nitrate, is promising tool effectively separate from microbially produced nitrate. However, our knowledge, △17O-NO3− approach has not been previously applied identify pollution plain networks eastern China. In this study, we multiple isotope (δD/δ18O-H2O δ15N/δ18O/△17O-NO3−) for first time hypereutrophic coastal network namely Wen-Rui Tang River located China, which region receiving high inputs deposition. precipitation water study period (April–June 2021) varied 14.83‰ 31.39‰ − 2.82‰ 9.66‰, respectively. δD/δ18O-H2O revealed that mainly originated recent with little evaporation. Moreover, δ15N/δ18O-NO3− indicated microbial nitrification, denitrification, was predominant process watershed. Based on Bayesian mixing model (Stable Isotope Analysis R, SIAR) using δ15N/△17O-NO3−, municipal sewage identified dominant source (50.5 ± 11.7%), followed soil (23.8 13.7%), deposition (14.3 2.9%), fertilizer (11.4 8.7%). Finally, analysis apportionment demonstrated greatest associated nitrogen, sewage, fertilizer, This provides important scientific information guide control/remediation strategies highlights benefits utilizing enhance apportionment.