Mass Balances Of A Drained And A Rewetted Peatland: On Former Losses And Recent Gains

Drained peatlands are important sources of greenhouse gases and are rewetted to curb these emissions. We study one drained and one rewetted fen in terms of losses-and, after rewetting-gains of organic matter (OM), carbon (C), and peat thickness. We determined bulk density (BD) and ash/OM (and C/OM) ratios for 0.5 cm thick contiguous slices from peat monoliths to calculate losses. Whereas one site has lost 28.5 kg OM m(-2) corresponding to annual emissions of similar to 10 t CO2 ha(-1) a(-1) over 50 years of effective drainage, the other site has lost 102 kg OM m(-2), corresponding to an annual loss of similar to 30 t CO2 ha(-1) a(-1) for 30 years of intensive drainage and 6 t CO2 ha(-1) a(-1) during similar to 225 years of weak drainage before that. Height losses ranged from 43 to 162 cm. In the 20 years after rewetting, 2.12 kg C m(-2) was accumulated, equaling an average annual uptake of similar to 0.4 kg CO2 m(-2) a(-1). The results indicate that rewetting can lead to carbon accumulation in fens. This sink function is only small compared with the high emissions that are avoided through rewetting.