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

The Arctic is currently warming faster than the rest of the world. Warming and associated permafrost thaw in Arctic landscapes may mobilize large pools of carbon (C) and nitrogen (N) and ultimately increase the atmospheric burden of the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Arctic GHG dynamics and their environmental and hydrological controls are poorly understood. Whether Arctic landscapes act 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 microbial dynamics.

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 and soil type (mineral and organic) heterogeneity consisting of different land cover types: shrub, tussock and lichen patches, polygonal tundra and thermokarst-affected 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 (since 2013) 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 increase process-based understanding we complement these multi-scale GHG flux observations with a wide array of auxiliary measurements including soil profile dynamics of CO₂, CH₄, N₂O, and oxygen, lake and soil pore nutrient concentrations, soil 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 from manual chamber measurements show that tussocks were the largest net CO₂ sink during the growing season. While the majority of terrestrial landcover types showed small but consistent and seasonally varying CH₄ uptake, lake shore and thermokarst-affected areas displayed high nutrient loads and were hotspots of CH₄ emissions. Therefore, capturing the landscape heterogeneity, areal coverage and hydrological connectivity of terrestrial and aquatic landcover types is important and our study highlights the need to combine belowground, plot-, ecosystem- and landscape-scale measurements to understand biosphere-atmosphere interactions in the Arctic.