Impact of soil and vegetation characteristics on CH4 fluxes in Arctic wetlands of the Northwest Territories, Canada

Arctic wetlands have been identified as significant emitters of CH₄, accounting for about 2% of the global methane budget, but the underlying processes remain poorly constrained. These wetlands show not only a considerable variability in CH₄ flux estimates, but also varying levels of emissions between different regions and even among various elements within the same wetland. The pronounced spatial variability in ecosystem characteristics across scales requires observational approaches that can cover larger landscapes while still being capable of resolving fine-scale details.

This study presents findings based on flux chamber measurements with a portable gas greenhouse analyser for CH4/CO2/H2O (LI-7810), conducted at the Trail Valley Creek research station in the Canadian NW Territories. We collected data from two polygonal mires and a small gulley, all plots organized as transects across moisture gradients. Our approach included analysing variations in CH₄ fluxes across microsites within wetland complexes, such as rims, trenches, or polygon centres. In addition to greenhouse gas signals, we examined soil parameters (pH, temperature, moisture) and vegetation (height, composition, green fraction) to understand their influence on CH₄ fluxes. Random forest models highlighted soil moisture at 12 cm as a primary control factor, explaining 41% of the predictive power and demonstrating higher accuracy compared to linear models for CH₄ flux prediction. Based on partial dependence analyses, we classified our measurements into three groups based on soil moisture at 12 cm. In the low moisture scenario, soil moisture at deeper levels (30 cm) was more influential, while in medium moisture conditions, soil temperature at 10 and 20 cm depths played a crucial role. In the high moisture category, the presence of Carex aquatilis was a key factor influencing the CH₄ flux. 

Our study also showed that the CH₄ flux varied significantly among different wetland elements. The gully area showed the lowest rate, whereas the polygonal mires had higher fluxes. Notably, within a polygonal mire, the rim exhibited lower flux compared to the wet polygonal centres and trenches, the latter showing the highest emissions. These findings underscore the complexity and variability of CH₄ fluxes in Arctic wetland ecosystems and highlight the importance of considering both soil and vegetation characteristics in understanding and predicting CH₄ emissions from these critical regions.

The authors acknowledge funding from the European Research Council (ERC synergy project Q-Arctic, grant agreement no. 951288).