Methane and carbon dioxide emissions from thermokarst lakes on mineral soils.

• Published in: Arctic Science
• Main Authors: Matveev, Alex, Laurion, Isabelle, Vincent, Warwick
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2018
• Subjects: lithalsa; methane; permafrost; subarctic; thermokarst; Arctic; Ice; Subarctic; Thermokarst
• Online Access: https://espace.inrs.ca/id/eprint/7280/; https://espace.inrs.ca/id/eprint/7280/1/P3344.pdf; https://doi.org/10.1139/AS-2017-0047

Thermokarst lakes are known to emit methane (CH₄) and carbon dioxide (CO₂), but little attention has been given to those formed from the thawing and collapse of lithalsas, ice-rich mineral soil mounds that occur in permafrost landscapes. The present study was undertaken to assess greenhouse gas stocks and fluxes in eight lithalsa lakes across a 200-km gradient of permafrost degradation in subarctic Québec. The northernmost lakes varied in their surface-water CO₂ content, from below to above saturation, but the southern lakes in this gradient had much higher surface concentrations that were well above air-equilibrium. Surface-water CH₄ concentrations were at least an order of magnitude above air-equilibrium values at all sites, and the diffusive fluxes of both gases increased from north to south. Methane oxidation in the surface waters from a northern lake was only 10% of the emission rate, but at the southern end it was around 60% of the efflux to the atmosphere, indicating that methanotrophy can play a substantive role in reducing net emissions. Overall, our observations show that lithalsa lakes can begin emitting CH₄ and CO₂ soon after they form, with effluxes of both gases that persist and increase as the permafrost continues to warm and erode.