Restored cut-away peatland as a sink for atmospheric CO.

In a field study, we examined the relationship between vegetation, abiotic factors and the CO 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 CO 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 ) and increased gross photosynthesis (P ), which resulted in a higher incorporation of CO into the system. The seasonal CO balance for the almost continuously submerged section of the rewetted site became positive 2 years after rewetting (9.1 g CO-C m), and it was still higher in the 3rd year (64.5 g CO-C m), 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 CO-C m 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 CO-C m 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 CO balance of the ecosystem can reach the compensation point of no net C change (P = R ) only if weather conditions are favourable, but with a high WT the seasonal CO 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 CO.