Kathryn Bennett
Ph.D. student
Department of geography
University of Montreal

Supervised by:

Oliver Sonnentag (Regular member)

Research project description

The impact of permafrost thaw on spatial and temporal greenhouse gas dynamics across permafrost zones

Introduction: Permafrost underlies nearly a quarter of global land area in the form of continuous, discontinuous, isolated, and sporadic permafrost and stores significant amounts of carbon (C) and nitrogen (N). Wetlands, lakes, and thaw features, such as collapse scars, located in permafrost regions are notable sources of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) to the atmosphere. Emissions which will potentially increase amid rising temperatures and increased permafrost thaw. Natural sources of CH4 emissions, including northern wetlands and lakes, currently have the largest uncertainty in the global CH4 budget. Specific research gaps contributing to this uncertainty include disturbance from thermokarst and emissions during the autumn and spring seasons. Improving scientific understanding of GHG emissions from thermokarst and aquatic features is critical to constraining C and N sources across heterogeneous permafrost landscapes. Objectives: The goal of my research is to develop a refined understanding of the influence of rapidly changing environmental conditions on C and N cycling in northern wetlands and lakes via three main research objectives. My first research objective is to constrain the impact of landscape heterogeneity on the isotopic signature of CH4 emissions from northern ecosystems, to further reduce uncertainty in the global CH4 budget. Following this effort, I will address specific spatial and temporal gaps in the northern GHG budgets. My second research objective is to determine the influence of permafrost thaw on terrestrial and aquatic fluxes of GHGs in the continuous permafrost region. My third research objective is to identify and quantify controls of understudied autumn and spring greenhouse gas emissions from peatland ponds in the discontinuous permafrost region. Study sites: My second and third research objectives are field-based studies and will be conducted at Trail Valley Creek Research Station in Inuvik, NT and in Abisko and Pulsujärvi, Sweden, respectively. Trail Valley Creek Research Station is located in the continuous permafrost region of north-western Canada. The study will be conducted about 45 km north of Inuvik, NT at the northern edge of the boreal forest-tundra transition zone in an area of tussock tundra interspersed with thermokarst lakes. Research in northern Sweden will occur in the discontinuous permafrost zone at two permafrost peatlands, Stordalen Mire and Tavvavuoma. Stordalen Mire, located in Abisko, Sweden, consists of permafrost peat plateaus, bogs, fens, ponds, and post-glacial lakes and is experiencing rapid permafrost degradation. Tavvavuoma, located near Pulsujärvi, Sweden, is the largest permafrost peatland in Scandinavia consisting of permafrost peat plateaus, bogs, fens, ponds, and thermokarst lakes. Material and methods: For my first research objective, I will conduct a data synthesis to identify signature ranges of the stable isotopes carbon-13 (δ13C-CH4) and deuterium (δD-CH3D) of CH4 for distinct wetland and lake classifications across the arctic and boreal zones. I will use classifications defined by the Boreal-Arctic Wetlands and Lakes Dataset (Olefeldt et al, 2021) and will use a database structure adapted from the International Soil Radiocarbon Database (Lawrence et al., 2019). My second research objective on thermokarst features will use terrestrial and aquatic manual flux chamber methods to measure CO2, CH4, and N2O fluxes along permafrost gradients from intact tundra across eroding thermokarst lake edges and thaw slumps into lakes. To quantify shoulder season GHG emissions in northern Sweden, I will measure ebullitive (bubble) and diffusive fluxes, microbial community composition, and environmental conditions of small peatland ponds during the autumn, spring, and summer seasons. References: Olefeldt, D., et al. (2021). The Boreal-Arctic Wetland and Lake Dataset (BAWLD), Earth Syst. Sci. Data, 13, 5127–5149, 2021, Lawrence, C. R., et al. (2019). An open-source database for the synthesis of soil radiocarbon data: International Soil Radiocarbon Database (ISRaD) version 1.0, Earth Syst. Sci. Data, 12, 61–76,

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