Rewetting effects on the spatial variability and partitioning of carbon fluxes in a drained boreal peatland

Fennoscandia has a long history of draining peatlands to increase forest production. Since these areas are potentially large sources of carbon dioxide (CO 2 ), rewetting is considered as a strategy for mitigating these emissions. However, empirical data on how rewetting affects the spatial variability and partitioning of the carbon (C) cycle components, including production, respiration and methane (CH 4 ) fluxes, are largely missing, in particular for minerogenic boreal peatlands. In this study, we addressed this knowledge gap by conducting chamber measurements of C fluxes over one growing season prior (2020) and two following (2021–2022) the rewetting of a minerogenic drained peatland forest in boreal Sweden. Our results show that higher water table level (WTL) following rewetting led to increased daytime net CO 2 uptake, driven by increased gross primary production, as well as to enhanced CH 4 emissions. Furthermore, heterotrophic respiration decreased in the second year after rewetting, whereas total forest-floor respiration remained similar due to a concurrent increase in its autotrophic component. We further found that rewetting impacts on CO 2 and CH 4 fluxes were highest closest to the ditch, however, no consistent gradient with distance from the ditch was observed. Instead, spatial variations of C fluxes were more closely related to specific local environmental conditions. Thus, our study highlights a spatially non-uniform response of all C cycle components during the initial years following rewetting. This poses a challenge for process-based modelling and the application of default emission factors for evaluating rewetting effects on the peatland C cycle. • Rewetting of a boreal peatland forest increased net CO 2 uptake and CH 4 emissions. • Flux partitioning revealed increased GPP and lower peat respiration after rewetting. • Rewetting effects on carbon fluxes were strongest near the filled ditch. • No consistent spatial gradient in carbon flux variations with ditch distance. • Spatial variability in carbon fluxes was driven by microtopography.