Early carbon recovery after cell-bunding rewetting is constrained by aerated microsites in a cutaway raised bog

Abstract. Rewetting is increasingly used to reduce greenhouse gas emissions from cutaway peatlands and support the recovery of carbon sequestration. While carbon responses of drained peatlands to rewetting are relatively well understood, few studies link ecosystem-scale carbon exchange with fluxes at restoration-created microsites during early recovery. This is particularly true for cell-bunding restoration, where whole-site fluxes are rarely linked to the microsites created by the restoration design. Here, we examined carbon dynamics at an Irish cutaway raised bog during the two years after cell-bunding rewetting. We combined ecosystem-scale eddy covariance measurements of CO₂ and CH₄ with CO₂ chamber measurements across bunds, vegetated peat, bare peat, and open water. The site remained a net CO₂-C source in both years, although net CO₂ losses declined by 39 % from 2024 to 2025. CH₄ emissions were approximately two orders of magnitude smaller than CO₂ emissions in carbon-mass terms. CO₂ exchange was strongly associated with meteorological and hydrological conditions, with lower net losses occurring during the cooler, wetter conditions of 2025. Chamber measurements revealed strong spatial heterogeneity. Bunds were persistent CO₂ hotspots. Flooded open water areas had very low emissions, whereas CO₂ efflux increased when these surfaces became temporarily exposed following water-table drawdown. Vegetated peat showed high respiration along with substantial growing-season CO₂ uptake. Overall, early post-rewetting CO₂-C dynamics at the site remained strongly influenced by aerated microsites. Restoration success should therefore be assessed using both ecosystem-scale fluxes and microsite-level measurements to capture spatial heterogeneity in carbon responses.