Carbon Cycling in Permafrost Aquatic Systems of Bylot Island, Eastern Canadian Arctic

Abstract:

Aquatic systems are widespread in permafrost environments and play a crucial role in biogeochemical cycles, especially in GHG emissions (CO₂, CH₄). Amount, rate and age of carbon released from permafrost thawing can be strongly influenced by local geomorphology, which affects the biogeochemical dynamics of ponds and lakes.

Bylot Island (Nunavut) is located in the heart of the Eastern Canadian Arctic and comprises numerous glacial and periglacial aquatic landscapes. Several glacial valleys of the island represent highly dynamic biogeosystems rich in permafrost ground ice, peat, and aquatic environments. We aimed at characterizing the influence of geomorphology and permafrost degradation processes on aquatic system biogeochemistry. We sampled gas, water, permafrost and lacustrine sediment in different types of aquatic systems: polygonal ponds, collapsed ice-wedge trough ponds, and larger lakes overlying unfrozen soil (‘talik’).

Preliminary results and field observations indicate a relationship between pond/lake morphology, processes of permafrost degradation, and the age of carbon processed – ultimately released as GHG – in these aquatic systems. Small and shallow ponds produced modern or young (< 500 yr BP) CO₂ and CH₄, whereas larger and deeper lakes released older (< 2000 yr BP) gases. We also observed a substantial difference in gas fluxes between similar ponds of comparable size and depth. When pond margins were actively eroding (eroded and collapsed peat blocks), fluxes were several orders of magnitude higher than when their margins were stabilized.

Such findings underscore the strong impact of local geomorphology and permafrost degradation processes on aquatic system biogeochemistry. Upscaling of GHG emissions at the watershed scale requires a better understanding of the emissions from different types of ecosystems.