GSC Logan Club Series: Dr. Roxane Maranger

“Assessing cross-regional and seasonal N2O emissions from boreal freshwater networks".

Date: Thursday, January 30, 2014

Time: 11:30

Location: 127 Marion Hall (MRN), University of Ottawa

Poster available here

Nitrous oxide (N2O), a potent greenhouse gas with over 300 times the global warming potential of carbon dioxide (CO2), is produced during microbial nitrogen (N) cycling. Inland waters, known as active sites of N processing are nevertheless poorly characterized in recent global N2O budgets, which do not consider the potential role of lakes. Although the boreal biome holds the highest density of freshwater on earth, no comprehensive evaluation of N2O emissions from boreal aquatic systems has ever been conducted. In this study, we measured N2O concentrations across a wide range of rivers, lakes, and ponds in four distinct boreal regions of Québec (Canada), and combined with piston velocity estimates, derived water-air N2O fluxes. Net fluxes ranged from -23.1 to 177.9 μmol m-2 d-1, with a large degree of cross-system, cross-regional and seasonal variability. Surprisingly, over 40% of the 322 systems sampled acted as N2O sinks during the summer, with one region’s aquatic network being an overall net atmospheric N2O consumer. Seasonally, maximum N2O concentrations were measured during winter due to gas accumulation under the ice.  Production during winter appears to be a function primarily of nitrification, although the process was measureable using isotopic tracers during the entire year. Archaea seem to be the dominant nitrifyers, but an obvious succession in species was observed. Outgassing at ice thaw accounts for approximately 20% of annual flux representing a hot-moment of emissions. Overall, lakes contributed over 90% of the annual boreal freshwater N2O emissions, and must therefore be integrated in global aquatic budgets. Globally, we estimate the aquatic boreal alone accounts for 0.12 Tg N-N2O fluxes, representing 11 to 20 % of total inland water contributions.