Methane emission from Swedish mires:: National and regional budgets and dependence on mire vegetation

A national land use inventory program was used to estimate the flux of methane from Swedish mires. During the snow-free season in 1994, methane fluxes were monitored at 60% (n = 619) of the total number of permanent inventory plots for the four mire vegetation classes included. The methane flux was measured only once at each inventory plot using transparent static chambers, yielding 3157 (89%) accepted flux rates. The temperature during the measurement period was close to the long-term (30 year) average in the north and much warmer in the south. The precipitation was lower than the long-term average. Average flux rates, specific for each mire vegetation class and geographical region, varied between 8 and 238 mg CH4 m(-2) d(-1). The national averages +/- SE (mg CH4 m(-2) d(-1)) were hummock communities, 24 +/- 6; transitional fens, 15 +/- 2; short sedge fens, 49 +/- 4; and tall sedge fens, 97 +/- 22. To derive the annual flux, the number of days with a daily average air temperature over 5 degreesC was used. The annual methane fluxes for each mire vegetation class and region varied between 1.5 and 40 g CH4 m(-2) yr(-1). The annual methane fluxes (average +/- SE in g m(-2) yr(-1)) for each mire vegetation class for the whole of Sweden were hummock sites, 4.9 +/- 1.3; transitional fens, 2.5 +/- 0.5; low sedge fens, 8.2 +/- 0.8; and tall sedge fens, 16.5 +/- 3.6. The methane flux (+/- 95% confidence limits) in 1994 from the monitored mire types in Sweden was 0.29 +/- 0.05 Tg CH4. The low and tall sedge mires accounted for 96% of the methane emitted.