Microbial and environmental controls of methane emissions across Arctic permafrost landscapes

Permafrost thaw releases previously frozen organic carbon making it vulnerable to microbial transformation into carbon dioxide (CO₂) and methane (CH₄). While CO₂ emissions dominate in terms of total carbon emissions, CH4 has 35-times the warming potential of CO₂ over a 100-year period, so has a pronounced effect on future warming and permafrost thaw feedback. Understanding the microbial drivers behind CH₄ emissions is complicated by the high spatial heterogeneity of the permafrost landscape. Features such as polygonal mires and thermokarst lakes change the physical and chemical conditions of soils and freshwaters even across small spatial scales. The related impacts on microbial community structure have important implications on microbially mediated transformation of organic carbon.

Here, we propose ideas to investigate 1) how physical and chemical changes across diverse features of permafrost environments impact microbial community 2) how this impacts microbial CH₄ metabolism, and 3) whether considering microbial community improves the interpretation of controls on CH₄ emissions, through the integration of in situ CH₄ flux measurements with metagenomic analyses. We completed sampling across two polygonal mires and ten permafrost lakes in a region of continuous permafrost around the Trail Valley Creek site in the Northwest Territories, Canada. Active layer soil was collected for metagenomic analysis and air-soil CH₄ fluxes were measured across polygonal mires using a static chamber method. At each lake, water, sediment, and surface microlayer samples were collected for metagenomic analysis and air-water CH₄ fluxes were measured around the shoreline using a floating chamber.

Preliminary results suggest that diffusive CH₄ fluxes did not significantly differ between lakes but found several occasions of CH₄ ebullition. We also found that CH₄ fluxes vary widely across different structural parts of polygonal mires, ranging from -0.28 to 7.54 mg CH₄ m² h^-1, and can be largely explained by physical soil properties, namely soil moisture at 12cm depth and soil temperature at 20cm depth. We will analyse metagenomes to determine microbial taxonomic composition, identify relevant methane metabolism genes and study how these correlate with soil and freshwater properties across the permafrost environment. This will provide insight to the microbial processes driving CH₄ emissions and how these may change as permafrost environments change under continued warming.