Carbon dynamics of a controlled peatland rewetting experiment in the Norwegian boreal zone

A controlled peatland rewetting experiment was conducted on two adjacent drained peatland sites in southeastern Norway. Eddy covariance monitoring of CO₂ and CH₄ fluxes at both sites began in 2019. In 2021, the Treatment Site was rewetted while the Control Site remained drained. Using nine environmental variables and the processed flux data as training data, Bayesian Additive Regression Tree (BART) models were used to generate annual flux balances for CO₂ and CH₄. The 4-year mean annual flux at the Control Site was 17.3 ± 10 g CO₂-C m^{- 2} yr^{- 1} and 4.6 ± 0.1 g CH₄-C m^{- 2} yr^{- 1}. At the Treatment Site, the 2-year mean annual flux before the rewetting was 12.2 ± 3.8 g CO₂-C m^{- 2} yr^{- 1} and 1.8 ± 0.04 g CH₄-C m^{- 2} yr^{- 1}. In the first year after rewetting the annual flux was 53.3 ± 13 g CO₂-C m^{- 2} yr^{- 1} and 3.8 ± 0.3 g CH₄-C m^{- 2} yr^{- 1}, and in the second year after rewetting the annual flux was 41.2 ± 18 g CO₂-C m^{- 2} yr^{- 1} and 3.4 ± 0.4 g CH₄-C m^{- 2} yr^{- 1}. BART counterfactual modeling was able to estimate the effect of the rewetting on CO₂ and CH₄ fluxes. Two years after the rewetting, the BART counterfactual modeling estimated that the cumulative fluxes had increased by 80.3 ± 49 g CO₂-C m^{- 2} and 3.4 ± 0.47 g CH₄-C m^{- 2} because of the rewetting. Carbon flux monitoring of both sites is ongoing as the Control Site remains drained and the soil and vegetation at the Treatment Site continues to adjust to the altered hydrological regime after rewetting.