REWET (REstoration of WETlands to minimise emissions and maximise carbon uptake – a strategy for long-term climate mitigation) – Carbon and methane fluxes at the peatland Ylpässuo in Kiuruvesi, Finland

Ylpässuo is an aapa-mire peatland complex dominated by oligo-mesotrophic Sphagnum fen vegetation, located in the middle boreal zone in the North-Savonia province, Finland. In the past decades, some marginal areas were drained due to forestry activities, changing the carbon pools and possibly triggering the shifting of dominant species, which is little known. Since 2020, Ylpässuo has been protected by the Natural Heritage Foundation with a donation from the University of Eastern Finland, aiming to restore the original watery mire characters. In 2022, Ylpässuo was developed as an open lab under the REWET/EU-Horizon project (2022-2026). To better understand the capacity of carbon sequestration and the impact of species shifting on greenhouse gases at Ylpässuo. In 2023, the eddy covariance monitoring system was successfully established, and greenhouse gas fluxes, including carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes, have been successfully collected since August of 2023. Results from 2024 showed that the eddy covariance system has a good energy closure, and the coefficient of determination between energy in and out was 0.92 (Fig. 1), indicating the good quality of carbon flux measurements at Ylpässuo (Mauder et al. 2024). Moreover, variations of CO 2 fluxes show that the maximum gross primary productivity (GPP) and ecosystem respiration (Reco) occurred in the middle of June, whereas the minimum net ecosystem exchange (NEE) occurred in the mid of July (Fig. 2). In the beginning of May, when the long winter finished and snow was melted, CH 4 flux was already active as a source until the end of the growing season (September) (Fig. 2). In conclusion, our preliminary results indicate that Ylpässu was a CO 2 sink and CH 4 source. However, overall, the carbon released as methane can still be offset by wet peatlands acting as carbon sinks, highlighting the importance of peatland restoration to mitigate climate warming. The impact of species composition and species shift on greenhouse gas emissions needs long-term continuous monitoring.