Methane fluxes from a patterned fen of the northeastern part of the La Grande river watershed, James Bay, Canada

Abstract

In northeastern Canada, at the ecotonal limit of the forest tundra and lichen woodland, a rise of the regional water table in the peatland systems was registered since Little Ice Age resulting in increasing pool compartment at the expense of terrestrial surfaces. We hypothesized that, with a mean water table closer to peat surface and higher pool density, these ecosystems would be great CH4 emitters. In summers 2009 and 2010, methane fluxes were measured in a patterned fen located in the northeastern portion of the La Grande river watershed to determine the contribution of the different microforms (lawns, hollows, hummocks, string, pools) to the annual CH4 budget. Mean seasonal CH4 fluxes from terrestrial microforms ranged between 12.9 and 49.4 mg m−2 day−1 in 2009 and 15.4 and 47.3 mg m−2 day−1 in 2010. Pool fluxes (which do not include ebullition fluxes) ranged between 102.6 and 197.6 mg CH4 m−2 day−1 in 2009 and 76.5 and 188.1 mg CH4 m−2 day−1 in 2010. Highest fluxes were measured in microforms with water table closer to peat surface but no significant relationship was observed between water table depth and CH4 fluxes. Spatially weighted CH4 budget demonstrates that, during the growing season, the studied peatland emitted 66 ± 31 in 2009 and 55 ± 26 mg CH4 m−2 day−1 in 2010, 79 % of which is accounted by pool fluxes. In a context where climate projections predict greater precipitations in northeastern Canada, these results indicate that this type of peatlands could contribute to modify the methane balance in the atmosphere.