The carbon (C) dynamics of boreal coniferous swamps are a largely understudied component of wetland carbon cycling. We investigated the above- and below-ground carbon stocks and growing season carbon dioxide (CO2) and methane (CH4) fluxes from a representative wooded coniferous swamp in northern Alberta, Canada in 2022. Tree inventories, understory vegetation biomass and peat cores were collected across three sub-sites within the broader swamp, with gas flux collars placed in the dominant plant communities present. Alongside the C flux measurements, environmental variables such as water table depth, soil temperature and growing season understory green leaf phenology were measured. Our results show that these wooded coniferous swamps store large volumes of organic C in their biomass and soil (134 kg C m-2), comparable with other wetland and forest types, although 95% of the total C stock at our site was within the soil organic carbon. We also found that understory CO2 and CH4 fluxes indicated that the ground layer of the site is a source of greenhouse gases (GHG) to the atmosphere across the growing season. However, we did not measure litterfall input, tree GHG fluxes or net primary productivity of the overstory, therefore we are not able to say whether the site is an overall source of C to the atmosphere. This study provides a much-needed insight into the C dynamics of these under-valued wetland ecosystems and we highlight the need for a coordinated effort across boreal regions to try to improve inventories of C stocks and fluxes.

Linear disturbances within boreal Canada (e.g., seismic lines) have the potential to significantly alter carbon cycling in Canada’s northern peatlands, creating the potential to switch these significant carbon stocks from long term carbon sinks to carbon sources. While efforts have been made to quantify the impacts of linear disturbance on ecosystem, vegetation, soil composition and GHG emissions, little is currently known about the specific interactions between the disturbance to peat hydrophysical structure and composition and the resulting alterations to CO 2 and CH 4 dynamics. To this end, 16 poor fen peat cores representing the top 10 cm of the peat profile were collected on and adjacent to a seismic line reflecting four degrees of disturbance complete mulch covering, partial mulch covering, mechanical roughing only, and undisturbed. In controlled laboratory conditions cores were then subjected to two subsequent static water table conditions (3 and 8 cm below core surface) for a period of ~30 days each with GHG flux measurements occurring 2-3 days. Cores were then subdivided into 5 cm segments and underwent detailed hydro physical (i.e., bulk density, porosity, water retention) and compositional (i.e., C:N, vegetational assemblage) analysis. Results show that both peat composition and hydrophysical structure were strong predictors of greenhouse gas emissions. Higher CO 2 emissions were related to both peat with high bulk density, low total and effective porosity and low C:N ratios, which occurred at depth in the undisturbed cores and at the surface where mechanical mulching and mixing occurred. Increased CH 4 emissions occurred in disturbed cores characterized by a reduction in macropores and effective porosity near the surface; these emissions were episodic in nature and occurred where trapped gas was released during pore desaturation when water tables were lowered. Additional work should therefore be conducted at field scale to further assess the interrelationships between direct changes to hydrophysical structure and these other impacts, to better determine the long-term changes to carbon cycling in systems disturbed by seismic line creation.