Restored cut-away peatland as a sink for atmospheric CO2

In a field study, we examined the relationship between vegetation, abiotic factors and the CO₂ exchange dynamics of a cut-away peatland 20 years after production had ended. The main objective was to determine the effect of rewetting on the CO₂ exchange dynamics, measured separately in Eriophorum vaginatum tussocks and intertussocks (almost non-vegetated surfaces) using closed-chamber techniques, one growing season before and three growing seasons after the rewetting treatment. Rewetting lowered total respiration (R _TOT) and increased gross photosynthesis (P _G), which resulted in a higher incorporation of CO₂ into the system. The seasonal CO₂ balance for the almost continuously submerged section of the rewetted site became positive 2 years after rewetting (9.1 g CO₂-C m⁻²), and it was still higher in the 3rd year (64.5 g CO₂-C m⁻²), i.e. the system accumulated carbon. In the driest section of the rewetted site the seasonal balance increased strongly, but the balance was still negative during the 3 years following rewetting with losses from the system of 44.1, 26.1, 38.3 g CO₂-C m⁻² in 1995, 1996 and 1997 respectively. At the control site seasonal balance during 1995–1997 varied between ecosystem C losses of 41.8 and 95.3 in an area with high Eriophorum cover and between 52.1 and 109.9 g CO₂-C m⁻² with lower cover. Simulation of a cut-away peatland with dense Eriophorum vegetation (Eriophorum cover 70%) showed that if the water level (WT) is low, the seasonal CO₂ balance of the ecosystem can reach the compensation point of no net C change (P _G = R _TOT) only if weather conditions are favourable, but with a high WT the seasonal CO₂ balance would be positive even under varying weather conditions. It can be concluded that with dense Eriophorum vegetation a restored cut-away peatland acts as a functional mire and becomes a sink for atmospheric CO₂. Received: 21 September 1998 / Accepted: 18 May 1999