Importance of drainage ditches in emissions of methane from mires drained for forestry

Methane (CH4) fluxes from drainage ditches and adjoining strips between the ditches were measured in fall 1995 at a drained mire in Finland. The fluxes were measured at different mire sites using static chambers (diffusion and plant-mediated transport) and inverted funnels (ebullition). The emissions (chamber measurements) of CH4 from drainage ditch bottoms, ditch sides, and strips between ditches ranged from 0 to 595 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 10% of the CH4 flux measured by the chambers. As the proportion of ditches of the total peatland area is rather small, the inclusion of methane fluxes from ditches would not considerably change the previous estimates of the effect of drainage on the greenhouse gas balance of Finnish peatlands.