CO2 and CH4 fluxes and processes in a boreal bog and surroundings: a chilling tale of cold-season greenhouse gas emissions

Cold season processes and emissions can be critical for determining annual budgets of CO₂ and methane (CH₄) in Arctic and other high-latitude ecosystems but there are relatively few measurements of winter fluxes and corresponding soil processes. In this talk, we will present results from investigating seasonality in greenhouse gas fluxes and processes controlling them, with a special emphasis on CH₄ emissions from a boreal peatland. We measured CO₂, CH₄, and N₂O fluxes for more than a year from an upland forest, dry bog, and wet bog at a site in boreal Finland using automated and manual chambers. Net CO₂ uptake and CH₄ emissions were highest in summer while N₂O fluxes were nearly always below detection. Plant transport and oxidation of CH₄ played an important role in CH₄ fluxes during the summer as well as into the fall. CH₄ emissions were enhanced throughout the fall due to plant transport and showed little seasonality in the fall in drier bog microtopographies. Net CO₂ and CH₄ emissions from the wet bog continued into December until snowpack formation, which led to an icy layer at the top of the peat profile. In the spring as snow melted and soils thawed, we saw an emissions pulse of CH₄. Additional measurements showed the highest concentrations of CH₄ in the peat porewater in the spring, indicating the accumulation of microbially-produced CH₄ in the unfrozen peat under the snowpack during the winter. Furthermore, potential decomposition in Sphagnum peat showed little temperature sensitivity in laboratory experiments, indicating microbial adaptation to cold temperatures not seen in the dry bog or upland forest soils. Sustained biological activity in peat can continue at low temperatures over winter and lead to substantial enhancements in CH₄ and CO₂ emissions, although the timing of emissions is controlled by interactions in physical environment: snow melt, soil thawing, and plant-mediated transport.