Simulating soil atmosphere exchanges and CO₂ fluxes for a restored peatland

Abstract. Restoration of drained and extracted peatlands can potentially return them to carbon (C) sinks, thus acting as significant climate change mitigation. However, whether the restored sites will remain C sinks or switch to sources with a changing climate is unknown. Therefore, we adapted the CoupModel to simulate soil atmosphere exchanges and the associated ecosystem CO₂ fluxes of a restored bog. The study site was a peatland in eastern Canada that was extracted for eight years before restoration. The model outputs were first evaluated against three years (representing 14–16 years post restoration) of eddy covariance measurements of net ecosystem exchange (NEE), surface energy fluxes, soil temperature profiles, and water table depth data. A sensitivity analysis was conducted to evaluate the response of the simulated CO₂ fluxes to the thickness of the newly grown mosses. The validated model was then used to assess the sensitivity of changes in climate forcing. CoupModel reproduced the measured surface energy fluxes and showed high agreement with the observed soil temperature, water table depth, and NEE data. The simulated NEE varied slightly when changing the thickness of newly grown mosses and acrotelm from 0.2 to 0.4 m but showed significantly less uptake for a 1 m thickness. The simulated NEE was -95 ± 19 g C m^-2 yr^-1 over the three evaluation years, and -101 ± 64 g C m^-2 yr^-1, ranging from -219 to +54 g C m^-2 yr^-1 with an extended 28-year climate data. After 14 years of restoration, the peatland has a mean C uptake rate similar to pristine sites, but with a much larger interannual variability, and under dry years, the restored peatland can switch back to a temporary C source. The model predicts a moderate reduction of CO₂ uptake, but still a reasonable sink under future climate change conditions if the peatland is ecologically and hydrologically restored. The ability of CoupModel to simulate the CO₂ dynamics and its thermal-hydro drivers for restored peatlands has important implications for emission accounting and climate-smart management of drained peatlands.