HR: 08:20h
AN: B41D-02 INVITED     [Abstracts]
TI: Variability in Methane Emissions from a Temperate Poor Fen
AU: * Crill, P M
EM: patrick@geo.su.se
AF: Stockholm University, Department of Geology and Geochemistry, Stockholm, 106 91 Sweden
AB: Methane is the most abundant organic compound in Earth's atmosphere, where it is an efficient infrared radiation absorber. Methane influences the global climate by contributing approximately 25% to the radiative forcing of greenhouse gases. Total annual emissions of methane range from 500 to 600 Tg. Methane emissions from wetlands are the most important natural source but also one that is highly uncertain. Recent estimates vary by a factor of ca. 2.5. There is much uncertainty in our present understanding of methane dynamics. Without such knowledge, we cannot understand how the natural contribution to the global methane balance is likely to change under different climate scenarios in the future. Long term datasets are important in evaluating the responses of natural systems to climatic forcing. Methane exchange has been measured in Sallie's Fen in New Hampshire USA since 1989 using the same static chamber methodology at the same sites linked to consistent analytical standards from CMDL. Individual surface fluxes are highly variable on a daily to seasonal temporal scale indicating they are controlled by weather. The 16 year dataset shows that annual fluxes have varied by a factor of 3 (ca. 40-120 gC-CH$_{4}$ m$^{-2}$) with differing seasonal distributions of the flux. On average most of the flux is in the summer and about 4% in the winter with the spring and fall emissions dependent on weather. CH$_{4}$ emissions have been lower (ca. 40 g C m$^{-2}$) since 2000 compared to the previous decade (ca. 75 g C m$^{-2}$) probably because of a shift in nutrient status as peat accumulates and the fen grows to be more similar to a nutrient poor bog. Interpolation of a C balance model suggest that Sallie's Fen has been a sink of atmospheric CO2 from the atmosphere in with most (52 - 91 gC- CO$_{2}$ m$^{-2}$) fixed in the summer and a consistent loss of 12-19 gC- CO$_{2}$ m$^{-2}$ in the winter. However, when CH$_{4}$ emissions (48-122 gC-CH$_{4}$ m$^{-2}$) and DOC export (ca. 3 gC m$^{-2}$) are added to the total, Sallie's Fen lost C in 1994 and was only a weak sink of C in 1995-1997 demonstrating that CH$_{4}$ emissions can have a significant impact on the C balance of a natural wetland. Longer term decadal patterns in flux are controlled by the growth of the peatland and the surface hydrology or moisture regime which will be determined by climate.
DE: 1890 Wetlands
DE: 1615 Biogeochemical processes (4805)
DE: 0315 Biosphere/atmosphere interactions
DE: 0330 Geochemical cycles
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting