Profile

Melanie Burnett
Ph.D. student
Department of Earth and Planetary Sciences
McGill University
melanie.burnett2@mail.mcgill.ca

Supervised by:

Peter Douglas (Regular member)

Research project description

Linking nitrogen and carbon fluxes in two permafrost affected ecosystems in northeastern Canada

Introduction: How are nitrogen (N) cycling and potential emissions related to carbon cycling and emissions in boreal and arctic ecosystems? Nitrogen cycling and gaseous losses as (N2O) are poorly studied in permafrost-affected ecosystems. Since inorganic N limits primary production, it was assumed that the potential for gaseous emissions would be minimal, but recent studies in Scandinavia and Russia have shown that permafrost-affected soils can be significant sources of N2O (Repo et al. 2009; Voigt et al. 2020; Marushchak et al. 2021). This phenomenon is very heterogeneous on the ground and justifies further study in Canada. Objectives: This project aims to: characterize the spatial and temporal distribution of carbon and nitrogen pools and gaseous fluxes in a boreal and arctic permafrost influenced ecosystem, use isotopic methods to identify the dominant microbial pathways producing nitrous oxide (N2O) emissions and characterize the relationship between the dominant pathway and relative emissions. Study sites: The research will be centred around two sites that span the extremes of permafrost extent from sporadic to continuous. The boreal site (SAS) is near Kuujjuarapik-Whapmagoostui in a palsa and thermokarst pond forming peatland above sporadic permafrost in Nunavik. The only permafrost found at this site is near the palsas which are in varying levels of disturbance, some of which are degrading rapidly due to permafrost thaw creating expanding thermokarst ponds. The arctic site is on Bylot Island, Nunavut in Sirmilik National Park in a polygonal pond landscape above continuous permafrost. This site has several different landscape features with different levels of permafrost degradation that will be encompassed in studies of carbon and nitrogen pools and fluxes. Material and methods: To characterize the spatial and temporal distribution of carbon and nitrogen pools and fluxes along permafrost disturbance gradients, aquatic and terrestrial N2O, CO2, and CH4 fluxes will be measured using static chambers and gas wells for uplands, floating chambers, ebullition capture, and dissolved gas equilibrations for ponds. Soil and water chemistry will be used to assess potential drivers of carbon and nitrogen emissions. For the temporal component, differences between summer and winter in the SAS Valley, and differences between spring snow melt into late summer on Bylot Island will be assessed. To characterize the dominant pathways of N2O production, either denitrification or nitrification, site specific 15N stable isotope measurements of the alpha and beta N atoms will be used. To complement this, 15N and 18O stable isotope measurements will be used to determine the sources and pathways producing nitrate which is used in denitrification, and the final product of nitrification. References: Marushchak ME, Kerttula J, Diáková K, et al (2021) Thawing Yedoma permafrost is a neglected nitrous oxide source. Nat Commun 2021 121 12:1–10. https://doi.org/10.1038/s41467-021-27386-2 Repo ME, Susiluoto S, Lind SE, et al (2009) Large N2O emissions from cryoturbated peat soil in tundra. Nat Geosci 2:189–192. https://doi.org/https://doi.org/10.1038/ngeo434 Voigt C, Marushchak ME, Abbott BW, et al (2020) Nitrous oxide emissions from permafrost-affected soils. Nat Rev Earth Environ 1:420–434. https://doi.org/10.1038/s43017-020-0063-9

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