HR: 1400h
AN: H33B-07    [Abstracts]
TI: Rain-Induced Bursts Of Nitrous Oxide May Account For Differences In Dissolved Nitrogen Export From Forested Catchments
AU: * Creed, I F
EM: icreed@uwo.ca
AF: Department of Biology, The University of Western Ontario, London, ON N6A 5B7, Canada
AU: Casson, N J
EM: ncasson@uwo.ca
AF: Department of Biology, The University of Western Ontario, London, ON N6A 5B7, Canada
AU: Enanga, E
AF: Department of Biology, The University of Western Ontario, London, ON N6A 5B7, Canada
AB: Despite nearly 30 years of research, we are unable to account for differences in dissolved nitrogen (N) export among catchments in the sugar maple forest of the Turkey Lakes Watershed. Neighboring catchments with similar N inputs show major discrepancies in dissolved N (nitrate + ammonium + dissolved organic nitrogen) export. In this study, we hypothesized that gaseous N export from wetland soils accounts for this discrepancy. To test this hypothesis, soil nitrous oxide (N₂O) efflux was measured during the snow free season (May 1 to October 30) in 2006, 2007, and 2008. Minimal N₂O efflux (<1 g N/ha/day) was observed on days without rain. However, on days with rain, soil N₂O efflux was significant from wetland area soils, with a linear increase of 0.016 g N/ha/day per millimeter of rain (r² = 0.60, p<0.001); N₂O efflux from upland soils was not significant. Process based monitoring of the wetland soil profile suggests that rain delivers water to the surface layers of the wetlands creating an oxygen poor environment where accumulated nitrate is first transformed to N₂O and then to dinitrogen (N₂). We could not measure N₂. However, if we assumed a N₂:N₂O ratio of 10:1 from the literature, the discrepancy in dissolved N export among the catchments could be explained. Our findings suggest that rain can produce substantial bursts of N₂O and N₂ from forest soils and that failure to account for gaseous N export may lead to an underestimation of N loss from forested catchments.
DE: 0469 Nitrogen cycling
DE: 0490 Trace gases
DE: 1865 Soils (0486)
DE: 1879 Watershed
SC: Hydrology [H]
MN: 2009 Joint Assembly