| Atmospheric accumulation of nitrous oxide (N2O) is contributing to an increase in radiative forcing, with global budgets indicating that streams and rivers are important sites of anthropogenic N2O release. Direct measurement of N2O emissions from five streams in Southern Ontario, Canada indicate that although areal N2O emissions from streams are comparable to those of soils, streams are not a regionally significant N2O source because of their small area. As well, despite recent downscaling of Intergovernmental Panel on Climate Change emissions factors, a further downscaling may be required for streams of this region. Significant short-term variability in N2O and nitrogen chemistry was observable over diel periods, with increased concentrations of ammonium and N2O observed at night, concurrent with decreased concentrations of nitrate. These diel changes could bias monitoring programs where daytime-only sampling is performed. Summertime N2O emissions often exceeded N2O emissions during other seasons, and ratios of N2O:NO3 were greatest in summer months. On an annual basis N2O emissions were strongly related to concentrations of nitrate in these streams, and more broadly among all streams where annual emissions have been measured. Concentrations of N2O under ice were also strongly related to nitrate concentrations. The isotopic character of N2O was indicative of N2O production via denitrification. Flux measurements suggest that N,O consumption is an important process that limits N2O emissions from some streams, particularly when nitrate concentrations are low. This suggests that nitrogen enrichment has contributed to a decline in the strength of an aquatic N 2O sink, although more research is required to determine the generality of N2O uptake in low nitrate systems.Keywords: Nitrous oxide, Greenhouse gas, Nitrogen, Nitrification, Denitrification, Nitrate, Stream, Stable isotope, Climate, Ebullition, Diel... |
