title: Using 15N, 17O, and 18O to determine nitrate sources in the Yellow River, China.
abstract: Many previous studies have used δ(15)N and δ(18)O of nitrate (δ(15)NNO3 and δ(18)ONO3) to determine the nitrate sources in rivers but were subject to substantial uncertainties and limitations, especially associated with evaluating the atmospheric contribution. The Δ(17)O of nitrate (Δ(17)ONO3) has been suggested as an unambiguous tracer of atmospheric NO3(-) and may serve as an additional nitrate source constraint. In the present study, triple nitrate isotopes (δ(15)NNO3, Δ(17)ONO3, and δ(18)ONO3) were used for the first time to assess the sources and sinks of nitrate in the Yellow River (YR) basin, which is the second longest river in China. Results showed that the Δ(17)ONO3 of the water from the YR ranged from 0‰ to 1.6‰ during two normal-water seasons. This suggested that unprocessed atmospheric nitrate accounted for 0-7% of the total nitrate in the YR. The corrected δ(15)NNO3 and δ(18)ONO3 values with atmospheric imprints being removed indicated that the main terrestrial sources of nitrate were sewage/manure effluents in the upstream of the YR and manure/sewage effluents and ammonium/urea-containing fertilizer in the middle and lower reaches which made comparable contributions to the nitrate. In addition, there was a significant positive relationship between δ(15)NNO3 and δ(18)ONO3 values of river water (p < 0.01) which may signal the presence of denitrification. This study indicates that the triple nitrate isotope method is useful for assessing the nitrate sources in rivers, especially for the measurements of atmospheric nitrate contribution.
authors.affiliation: School of Environment, Beijing Normal University/State Key Laboratory of Water Environment Simulation , Beijing, 100875, China.
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.forename: Fan
authors.initials: F
authors.lastname: Wang
authors.forename: Greg
authors.initials: G
authors.lastname: Michalski
authors.forename: Xinghui
authors.initials: X
authors.lastname: Xia
authors.forename: Shaoda
authors.initials: S
authors.lastname: Liu
mesh_terms: D002681:China; D058440:Denitrification; D004784:Environmental Monitoring / Q000379:methods; D005308:Fertilizers; D008372:Manure; D008962:Models, Theoretical; D009566:Nitrates / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D012722:Sewage; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D005308:Fertilizers; D008372:Manure; D009566:Nitrates; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D012722:Sewage; D014874:Water Pollutants, Chemical