Environmental controls and temporal trends of CO2 and CH4 emissions in a former cultivated peatland under rewetting

Rewetting drained peatlands is commonly regarded as an effective strategy to reduce greenhouse gas (GHG) emissions. In this study, we monitored the net ecosystem CO 2 and CH 4 emissions of a Danish peatland undergoing rewetting over three years (Y1–Y3) using eddy covariance (EC) measurements. As rewetting progressed, the mean annual water table rose from −12 cm in Y1 to 0 cm in Y3, although it remained highly variable, ranging from above soil surface in winter to −50 cm in summer (Y1). The net ecosystem carbon balance (NECB) of the peatland shifted from a net source in Y1 (2.30 t C ha –1 yr –1 ) and Y2 (1.13 t C ha –1 yr –1 ) to a net sink in Y3 (-0.55 t C ha –1 yr –1 ), primarily driven by cessation of biomass harvest (1.13 t C ha⁻¹ yr⁻¹ in Y1–Y2 and no harvest in Y3) and reductions in ecosystem respiration, while gross primary productivity remained stable. Total GHG emission was reduced by 7.23 t CO 2 e ha –1 yr –1 from Y1 to Y3 but remained positive in Y3 (2.66 t CO2e ha-1 yr-1) because of increased CH 4 emissions. Linear modelling identified soil temperature, global radiation, WTD, and green chromatic coordinate as drivers of net ecosystem exchange (NEE) and CH 4 fluxes. Models trained on shorter, month-year-specific intervals captured interannual flux dynamics more effectively than those trained on annual or full-period datasets. EC fluxes from Y1 were compared with chamber-based measurements within the EC footprint from a parallel study. On average, the EC-derived NEE was considerably lower than the chamber-based estimates, though they closely matched in parts of the footprint, revealing high field heterogeneity within the peatland. Overall, our results demonstrate the complex carbon dynamics of rewetted peatlands and emphasize the importance of high temporal resolution in ecosystem flux modelling. Furthermore, we show that a controlled and gradual rewetting strategy is an effective approach for reducing GHG emissions from a previously drained peatland while facilitating transition of the ecosystem from a carbon source to a carbon sink.