Influence of changing active-layer thickness on PERmafrost PeatLand trace gas EXchanges and carbon balance (PERPLEX)

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For millennia, boreal and subarctic peatlands have been acting as long-term carbon (C) sink because annually net primary production has been exceeding respiratory losses of carbon dioxide (CO2) and methane (CH4) and lateral C losses. A large portion of Canada's northern peatlands is underlain by permanently frozen ground (permafrost) that thaws seasonally at the top over a short growing season. Increases in the thickness of this permeable and biogeochemically active top layer due to ongoing climate change will have severe consequences for peatland ecophysiological and biogeochemical processes by exposing additional organic C to microbial decomposition and by altered peatland hydrology. The impact of a deepening active layer on the fate of permafrost peatlands' CO2 and CH4 sink-source strengths is largely unknown. The proposed research project will shed light on how peatland-atmosphere interactions are affected by increasing active-layer thickness (maximum depth to frost table as it descends through the peat profile). Using two identical sets of instrumentation installed at two sites in the discontinuous permafrost zone of western Canada, the net exchanges of CO2, CH4, water and energy will be measured over a permafrost peat plateau and a nearby permafrost-free peatland with the eddy covariance technique. Recent cutting-edge developments in measurement technology resulted in new robust sensors and analyzers designed for use of this technique under harsh conditions in remote locations. Ancillary hydrological and spectral measurements in combination with regular surveys of vegetation composition and structure, snow pack, and surface and frost table topography will aid in establishing the link between continued permafrost degradation and peatlands' CO2 and CH4 sink-source strengths and C balance. This knowledge is urgently needed for including Canada's vast peatland C store in the country's greenhouse gas inventory.