title: Nitrous oxide dynamics in a braided river system, New Zealand.
abstract: Recently the Intergovernmental Panel on Climate Change (IPCC) emission factor EF5-r was revised downward to a value of 0.0025 kg N₂O-N per kg NO₃-N leached. It was not reduced further due to the continued uncertainty surrounding the dynamics of N₂O in river systems. There have been few studies where river system N₂O yields and fluxes have been measured. In this study, we examined the relationship between NO₃-N and N₂O-N fluxes at 10 sites along a braided river system (84 km) over a 397-d period. Isotopic analysis of NO₃-N river water samples and the potential agricultural nitrogen (N) sources demonstrated that the NO₃-N came from agricultural or sewage sources. Percent saturation of N₂O varied with site and date (average, 114%) and correlated with river N₂O-N concentrations. Modeled N₂O fluxes (16-30 μg m(-2) h(-1)) from five sites were strongly related to river NO₃-N concentrations ( r² = 0.86). The modeled N₂O-N fluxes ranged from 39 to 81% of the IPCC-derived emissions based on the NO₃-N load in the river over 397 d and do not support further lowering of the EF5-r. Further in situ river studies are required to verify the N₂O-N fluxes and the calculated gas transfer velocity values for these braided river systems.
authors.affiliation: Agricultural & Life Sciences Division, Lincoln Univ., New Zealand. clought@lincoln.ac.nz
authors.forename: T J
authors.initials: TJ
authors.lastname: Clough
authors.forename: L E
authors.initials: LE
authors.lastname: Buckthought
authors.forename: K L
authors.initials: KL
authors.lastname: Casciotti
authors.forename: F M
authors.initials: FM
authors.lastname: Kelliher
authors.forename: P K
authors.initials: PK
authors.lastname: Jones
mesh_terms: D003124:Colorimetry; D005618:Fresh Water / Q000737:chemistry*; D055904:Meteorology; D009520:New Zealand; D009609:Nitrous Oxide / Q000032:analysis*
chemical_list: D009609:Nitrous Oxide