CHANGE IN FLUXES OF CARBON-DIOXIDE, METHANE AND NITROUS-OXIDE DUE TO FOREST DRAINAGE OF MIRE SITES OF DIFFERENT TROPHY

Northern peatlands accumulate atmospheric CO2 thus counteracting clima te warming. However, CH4 which is more efficient as a greenhouse gas t han CO2, is produced in the anaerobic decomposition processes in pear. When peatlands are taken for forestry their water table is lowered by ditching. We studied long-term effects of lowered water table on the development of vegetation and the annual emissions of CO2, CH4 and N2O in an ombrotrophic bog and in a minerotrophic fen in Finland. Reclama tion of the pear sites for forestry had changed the composition and co verage of the field and ground layer species, and increased highly the growth of tree stand at the drained fen. In general, drainage increas ed the annual CO2 emissions but the emissions were also affected by th e natural fluctuations of water table. In contrast to CO2, drainage ha d decreased the emissions of CH4, the drained fen even consumed atmosp heric CH4. CO2 and CH4 emissions were higher in the virgin fen than in the virgin bog. There were no N2O emissions from neither type of virg in sites. Drainage had, however, highly increased the N2O emissions fr om the fen. The results suggest that post-drainage changes in gas flux es depend on the trophy of the original mires.