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 meth ane 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 measu rement 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 a verage. Average flux rates, specific for each mire vegetation class and geo graphical 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; t ransitional 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 ave rage air temperature over 5 degreesC was used. The annual methane fluxes fo r 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.