Resolving Spatial and Temporal Greenhouse Gas Dynamics across a Heterogeneous Arctic Tundra Landscape in the Western Canadian Arctic

The Arctic region is currently warming twice as fast as the rest of the world. Accelerated permafrost thaw unlocks large pools of currently immobile carbon (C) and nitrogen (N) and ultimately increases the atmospheric burden of the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). However, Arctic GHG dynamics and their hydrological controls are poorly understood. Whether the Arctic acts as a net GHG source or sink depends on the complex and spatially varying interactions between hydrology, active layer thickness, topography, temperature, vegetation, substrate availability and the microbial world.

Our study site, Trail Valley Creek (68°44' N, 133°29' W), is an upland tundra site characterized by small-scale (<10 m) land cover type heterogeneity with interspersed shrub, tussock, and lichen patches, polygonal tundra areas, wetlands, lakes, and streams. To understand the large spatial and temporal variability of GHG dynamics across these terrestrial and aquatic landcover types we use a nested observational approach at plot- (<1 m²), ecosystem- (~10 m²), landscape- (~100 m²) and regional (~50 km²) scale. Existing ecosystem- scale eddy covariance (EC) measurements of net CO₂ and CH₄ exchanges are complemented with landscape-scale EC measurements and plot-scale automated and manual chamber measurements within the EC tower footprint and beyond. To constrain the processes governing aboveground GHG exchange we complement these multi-scale GHG flux measurements with a wide array of auxiliary measurements including soil profilce dynamics of CO₂, CH₄ and N₂O, lake and soil pore nutrient concentrations, oxygen, temperature and moisture profiles, thaw depth, leaf area index (LAI), normalized difference vegetation index (NDVI), lake catchment characteristics, and quality and microbial degradability of aquatic dissolved organic matter.

Preliminary results indicate that at ecosystem-scale upland tundra is a negligible net source of CH₄. High CH₄ emissions from emission hotspots such as lakes and wetlands in our study region (9.09 ± 2.38 mg CH₄ m^-2 h^-1) are compensated through net CH₄ uptake by uplands. Our study highlights the need to combine belowground, plot-, ecosystem- and landscape-scale measurements to understand biosphere-atmosphere interactions in Arctic ecosystems.