METHANE FLUXES ON BOREAL PEATLANDS OF DIFFERENT FERTILITY AND THE EFFECT OF LONG-TERM EXPERIMENTAL LOWERING OF THE WATER-TABLE ON FLUX RATES

Methane (CH4) fluxes were measured at 17 peatland sites with different nutritional and hydrological characteristics in the southern and midd le boreal zones in Finland by a static chamber technique. Many of the natural peatlands also had counterparts drained for forestry 30-50 yea rs ago. The mean emissions from May to September were 8.0 g CH4 m(-2) for natural ombrogenous bogs and 19.0 g CH4 m(-2) for natural mineroge nous fens thus being higher than the 2 g CH4 m(-2) yr(-1) estimated fo r the Canadian peatlands. Change in the mean water table level had gre ater effect on CH4 fluxes on natural fens than on natural bogs. The me an CH4 emissions on drained bogs and fens were 3.9 g CH4 m(-2) and 0.3 g CH4 m(-2), respectively. Some drained fens even had CH4 uptake from the atmosphere. The change in the mean water table had the lowest eff ect on CH4 fluxes on drained peatlands. The CH4 fluxes on peatlands (n atural fens and bogs and drained peatlands) are associated with peat a eration, nutrient level, vegetation cover, peat compaction, peat tempe rature, and finally with microbial processes responsible for the net r elease of CH4. We could explain 67% of the variation in mean CH4 fluxe s on Finnish peatlands by measuring the mean water table, peat bulk de nsity, and peat pH. The present results can be used to predict the pos sible changes in CH4 emissions on peatlands if the climate is drying i n north. For example, lowering of the present water table by 10 cm wou ld induce a 70% reduction in the CH4 emissions from fens and a 45% red uction from bogs.