IMPORTANCE OF DRAINAGE DITCHES IN EMISSIONS OF METHANE FROM MIRES DRAINED FOR FORESTRY

Methane (CH4) fluxes from drainage ditches and adjoining strips betwee n the ditches were measured in fall 1995 at a drained mire in Finland. The fluxes were measured at different mire sites using static chamber s (diffusion and plant-mediated transport) and inverted funnels (ebull ition). The emissions (chamber measurements) of CH4 from drainage ditc h bottoms, ditch sides, and strips between ditches ranged from 0 to 59 5 mg.m(-2).d(-1), from 0 to 78 mg.m(-2).d(-1), and from -3 to 33 mg.m( -2).d(-1), respectively. The ebullition of CH4 from ditches was rather small, ranging from 3 to 37 mg CH4.m(-2).d(-1), which was less than 1 0% of the CH4 flux measured by the chambers. As the proportion of ditc hes of the total peatland area is rather small, the inclusion of metha ne fluxes from ditches would not considerably change the previous esti mates of the effect of drainage on the greenhouse gas balance of Finni sh peatlands.