title: Oxygen and nitrogen isotopic composition of nitrate in commercial fertilizers, nitric acid, and reagent salts.
abstract: Nitrate is a key component of synthetic fertilizers that can be beneficial to crop production in agro-ecosystems, but can also cause damage to natural ecosystems if it is exported in large amounts. Stable isotopes, both oxygen and nitrogen, have been used to trace the sources and fate of nitrate in various ecosystems. However, the oxygen isotope composition of synthetic and organic nitrates is poorly constrained. Here, we present a study on the N and O isotope composition of nitrate-based fertilizers. The δ(15)N values of synthetic and natural nitrates were 0 ± 2 ‰ similar to the air N2 from which they are derived. The δ(18)O values of synthetic nitrates were 23 ± 3 ‰, similar to air O2, and natural nitrate fertilizer δ(18)O values (55 ± 5 ‰) were similar to those observed in atmospheric nitrate. The Δ(17)O values of synthetic fertilizer nitrate were approximately zero following a mass-dependent isotope relationship, while natural nitrate fertilizers had Δ(17)O values of 18 ± 2 ‰ similar to nitrate produced photochemically in the atmosphere. These narrow ranges of values can be used to assess the amount of nitrate arising from fertilizers in mixed systems where more than one nitrate source exists (soil, rivers, and lakes) using simple isotope mixing models.
authors.affiliation: a Department of Earth, Atmospheric, and Planetary Sciences , Purdue University , West Lafayette , IN , USA.
authors.forename: Greg
authors.initials: G
authors.lastname: Michalski
authors.forename: Michelle
authors.initials: M
authors.lastname: Kolanowski
authors.forename: Krystin M
authors.initials: KM
authors.lastname: Riha
mesh_terms: D005308:Fertilizers / Q000032:analysis*; D007202:Indicators and Reagents / Q000032:analysis*; D017942:Nitric Acid / Q000032:analysis*; D009584:Nitrogen / Q000032:analysis*; D009587:Nitrogen Isotopes / Q000032:analysis; D010100:Oxygen / Q000032:analysis*; D010103:Oxygen Isotopes / Q000032:analysis; D012492:Salts / Q000032:analysis*
chemical_list: D005308:Fertilizers; D007202:Indicators and Reagents; D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D012492:Salts; D017942:Nitric Acid; D009584:Nitrogen; D010100:Oxygen
keywords: fertilizer; nitrate; nitric acid; nitrogen-15; oxygen-17; oxygen-18