Evolution of Palsas and Peat Plateaus in the Hudson Bay Lowlands: Permafrost Degradation and the Production of Greenhouse Gases

Peatlands in the Hudson Bay Lowlands (HBL) extend from the sporadic to the continuous permafrost zones. They store ~30 Pg of soil carbon, ~10% of which is sequestered in permafrost. Palsa fields and peat plateaus are dominant features in the HBL of northern Ontario, but pronounced warming trends in the area are associated with accelerated degradation of these features. This research investigated greenhouse gas production potential (CO₂ and CH₄) from HBL peatlands near Peawanuck, ON, in the context of rapid palsa degradation. Active layer and permafrost samples from palsas, and samples from fens adjacent to the palsas were collected at sites exhibiting different degradation rates and patterns, identified via the sequential analysis of historical aerial photographs and recent satellite imagery. The samples were incubated anaerobically at 4°C and 14°C to assess CO₂ and CH₄. In general, CO₂ production potential was higher than CH₄, however the production of CH₄ was extremely sensitive to increased temperatures. Between 4°C and 14°C CH₄ production increased by factors ranging from 6 to 90, whereas CO₂ production consistently increased by a factor of ~2. The production of both gases was higher from fen peat then from permafrost and active layer peat at either temperature when incubated in anaerobic conditions for 225 days. This suggests that higher production rates of CO₂ and CH₄ from thermokarst features compared to intact permafrost landscapes are not only the result of environmental conditions such as wetness and increased temperatures, but also likely a result of organic matter chemistry and bioavailability associated with increased sedge growth following permafrost degradation.