CLIMATE CONTROLS ON TEMPORAL VARIABILITY OF METHANE FLUX FROM A POOR FEN IN SOUTHEASTERN NEW-HAMPSHIRE - MEASUREMENT AND MODELING

Three scales of temporal variability were present in methane (CH4) flu x data collected during a 2.5 year (mid-1990-1992) study at a small, p oor fen in southeastern New Hampshire. (1) There was a strong seasonal ity to the fluxes (high in summer); monthly average fluxes range from 21.4 mg CH4 m(-2) d(-1) (February 1992) to 639.0 mg CH4 m(-2) d(-1) (J uly 1991). Annual fluxes were 68.8 g CH4 m(-2) (1991) and 69.8 g CH4 m (-2) (1992). (2) There was interannual variability; distribution of fl ux intensity was very different from 1991 to 1992, particularly the ti ming and rapidity of the onset of higher fluxes in the spring. (3) The re was a high degree of variability in CH4 flux during the warm season ; four successive weekly flux rates in July 1991 were 957, 1044, 170, and 491 mg CH4 m(-2) d(-1). Fluxes were correlated with peat temperatu re (r(2)=0.44) but only weakly with depth to water table (r(2)=0.14 fo r warm season data). Warm season fluxes appeared to be suppressed by r ainstorms. Along with methane flux data we present an analysis of this temporal variability in flux, using a peatland soil climate model dev eloped for this site. The model was driven by daily air temperature, p recipitation, and net radiation; it calculated daily soil temperature and moisture profiles, water table location, and ice layer thickness. Temperature profiles were generally in good agreement with field data. Depth to water table simulations were good in 1992, fair in 1990, and poor in the summer of 1991. Using model-simulated peat climate and co rrelations to methane flux developed from the field data, simulated me thane fluxes exhibited the same three modes of temporal variability th at were present in the field flux data, though the model underestimate d peak fluxes in 1990 and 1991. We conclude that temporal variability in flux is significantly influenced by climate/weather variability at all three scales and that rainfall appears to suppress methane flux fo r at least several days at this site.