Interannual variability in the CO2 balance of a boreal patterned fen, James Bay, Canada

Abstract

During 2 years (2009, 2010), CO2 fluxes were measured in an oligotrophic fen located at the ecotonal limit of forest tundra and lichen woodland, in northeastern Canada. Peatlands in this region have registered a rise in surface moisture since Little Ice Age, allowing an increase in their pool size and density. In the studied peatland, 83 % of the surface is covered either with pools (42 %), hollows (28 %) and lawns (13 %) all of which present a mean water table higher than 7 cm. We evaluated how these conditions might influence the CO2 balance in these poor fens located in the northeastern section of the La Grande river watershed. During the two years measurements, results indicate a net CO2 source with 404 (±287) and 272 (±250) g CO2 m−2 year−1 emitted to the atmosphere throughout the growing seasons and winters. Modeled wintertime net ecosystem exchange resulted in a net loss of 150 (±36) and 150 (±37) g CO2 m−2 year−1 in 2009 and 2010 respectively, while 248 (±248) and 124 (±195) g CO2 m−2 was emitted during 2009 and 2010 growing seasons. This high CO2 source can be attributed to three factors: (1) the length of the cold season which represented 210–214 days of net CO2 loss (2) a high pool/vegetated surface ratio since pools are a net source of CO2 and presented 38–40 % of the annual spatially weighted CO2 budget and (3) hydroclimatic conditions during the growing season as dryer and warmer conditions in 2009 reduced photosynthesis and increased respiration rates.