Annual methane emission from Finnish mires estimated from eddy covariance campaign measurements

Measurements of landscape-scale methane emission were made over an aapa mir e near Kaamanen in Finnish Lapland (69 degrees 8' N, 27 degrees 16' E, 155 m ASL. Emissions were measured during the spring thaw, in summer and in aut umn. No effect of water table position on CH4 emission was found as the wat er table remained at or above the surface of the peat. Methane emission flu xes increased with surface temperature from which an activation energy of - 99 kJ mol(-1) was obtained. Annual emission from the site, modelled from te mperature regression and short-term flux measurements made in three separat e years, was calculated to be 5.5 +/- 0.4 g CH4 m(-2) y(-1) of which 0.6 +/ -0.1 g CH4 m(-2) y(-1) (11%) was released during the spring thaw which last ed 20 to 30 days. The effect of global warming on the CH4 budget of the site was estimated us ing the central scenario of the SILMU (Finnish Research Programme on Climat e Change) model which predicts annual mean temperature increases of 1.2, 2. 4 and 4.4 degreesC in 2020, 2050 and 2100, respectively. Maximum enhancemen ts in CH4 emission due to warming were calculated to be 18, 40 and 84% for 2020, 2050 and 2100, respectively. Actual increases may be smaller because prediction of changes in water table are highly uncertain.