title: From the ground up: global nitrous oxide sources are constrained by stable isotope values.
abstract: Rising concentrations of nitrous oxide (N2O) in the atmosphere are causing widespread concern because this trace gas plays a key role in the destruction of stratospheric ozone and it is a strong greenhouse gas. The successful mitigation of N2O emissions requires a solid understanding of the relative importance of all N2O sources and sinks. Stable isotope ratio measurements (δ15N-N2O and δ18O-N2O), including the intramolecular distribution of 15N (site preference), are one way to track different sources if they are isotopically distinct. 'Top-down' isotope mass-balance studies have had limited success balancing the global N2O budget thus far because the isotopic signatures of soil, freshwater, and marine sources are poorly constrained and a comprehensive analysis of global N2O stable isotope measurements has not been done. Here we used a robust analysis of all available in situ measurements to define key global N2O sources. We showed that the marine source is isotopically distinct from soil and freshwater N2O (the continental source). Further, the global average source (sum of all natural and anthropogenic sources) is largely controlled by soils and freshwaters. These findings substantiate past modelling studies that relied on several assumptions about the global N2O cycle. Finally, a two-box-model and a Bayesian isotope mixing model revealed marine and continental N2O sources have relative contributions of 24-26% and 74-76% to the total, respectively. Further, the Bayesian modeling exercise indicated the N2O flux from freshwaters may be much larger than currently thought.
authors: National Water Research Institute, Canada Centre for Inland Waters, Environment Canada, Burlington, ON, L7R 4A6, Canada.
authors: David M
authors: DM
authors: Snider
authors: Department of Geography and Environmental Studies, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada; Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Jason J
authors: JJ
authors: Venkiteswaran
authors: Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Sherry L
authors: SL
authors: Schiff
authors: National Water Research Institute, Canada Centre for Inland Waters, Environment Canada, Burlington, ON, L7R 4A6, Canada; Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: John
authors: J
authors: Spoelstra
mesh_terms: D001499:Bayes Theorem; D005618:Fresh Water / Q000737:chemistry; D009587:Nitrogen Isotopes / Q000737:chemistry; D009609:Nitrous Oxide / Q000032:analysis*; D010103:Oxygen Isotopes / Q000737:chemistry; D010126:Ozone / Q000737:chemistry; D012623:Seawater / Q000737:chemistry; D012987:Soil / Q000737:chemistry
chemical_list: D009587:Nitrogen Isotopes; D010103:Oxygen Isotopes; D012987:Soil; D010126:Ozone; D009609:Nitrous Oxide