Effect of water-level drawdown on global climatic warming: Northern peatlands

Since the last deglaciation, 300-500 Pg carbon have accumulated in northern peatlands (346 mill. ha). While sequestering carbon dioxide ( CO₂), these peatlands release considerable amounts of methane ( CH₄) to the atmosphere. The greenhouse-gas balance of peatlands may change in the future if summers become warmer and drier, as has been predicted for high latitudes. Subsequent emissions of CH₄ would decrease, whereas emissions of CO₂ and nitrous oxide ( N₂O) would increase. Water-level drawdown has been predicted to enhance the greenhouse impact from northern peatlands. The components of carbon cycling were measured both in undrained and drained peatlands of different trophic levels. The results were drawn together into a single radiative forcing factor, to assess 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 drawdown caused by drainage for forestry. The hypothesis suggests that possible drying arising from climate change would, in fact, decrease the impact of northern peatlands on the total radiative forcing for about one 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 increase in the tree-stand biomass storage.