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"The definitive version is available at www.blackwell-synergy.com" Keywords: denitrification, diurnal, EF5, emission factor, indirect emissions, nitrification, nitrous oxide. Corresponding author:Dr

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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.

Significant areas of ruminant-grazed pastures are simultaneously covered by excreted urine and fertiliser nitrogen (N). However, the effect of overlapping N inputs on nitrous oxide (N 2 O) emission factors has not been studied. Three rates of 15 N-labelled urea fertiliser were applied with either no urine, an autumn-urine or a spring-urine application. These treatments were applied to perennial ryegrass pasture (Lolium perenne L.) and N 2 O fluxes were determined over 373 days using standard static closed chamber techniques. Cumulative N 2 ON fluxes ranged from 766 to 4332 g N 2 ON ha-1 (0.36%-0.74% of total N applied) and were lowest in the absence of urine; however, no fertiliser rate effect occurred regardless of urine presence or season of application. Urine-elevated N 2 ON fluxes followed urine applications for up to 40 days, resulting in lower fertiliser contributions to the N 2 ON fluxes at these times. Total 15 N recoveries as N 2 ON were ≤0.04% and did not differ with fertiliser rate.