EFFECT OF WATER-LEVEL DRAWDOWN ON GLOBAL CLIMATIC WARMING - NORTHERN PEATLANDS

Since the last deglaciation, 300-500 Pg carbon have accumulated in nor thern peatlands (346 mill. ha). While sequestering carbon dioxide (CO2 ), these peatlands release considerable amounts of methane (CH4) to th e atmosphere. The greenhouse-gas balance of peatlands may change in th e future if summers become warmer and drier, as has been predicted for high latitudes. Subsequent emissions of CH4 would decrease, whereas e missions of CO2 and nitrous oxide (N2O) would increase. Water-level dr awdown has been predicted to enhance the greenhouse impact from northe rn peatlands. The components of carbon cycling were measured both in u ndrained and drained peatlands of different trophic levels, The result s were drawn together into a single radiative forcing factor, to asses s the combined atmospheric effects of water-level drawdown. We present a hypothesis, based on the measured changes in carbon stores in soil and tree stand, and fluxes of CO2, CH4 and N2O after water-level drawd own caused by drainage for forestry. The hypothesis suggests that poss ible drying arising from climate change would, in fact, decrease the i mpact of northern peatlands on the total radiative forcing for about o ne hundred years by c. 0.1 W m(-2). This is caused by the decrease in CH4 emissions, fairly small changes in the peat carbon storage, and in crease in the tree-stand biomass storage.