Peatland hydrology in boreal Sweden: Modelling, long-term data analysis, and experimental rewetting

Peatlands are the dominant type of wetland in boreal ecosystems and they are thought to play a major role in moderating hydrological extremes such as floods and droughts. Despite the valuable ecosystem services that they provide, a large proportion of peatlands around the globe has been degraded by human activity. Notably, in Sweden, peatlands have been subjected to drainage for the purposes of forestry. As awareness of the detrimental effects of climate change on boreal ecosystems has grown, the rewetting of drained peatlands has emerged as a naturebased solution for mitigating floods and droughts. However, the science behind this strategy is scant and the question of whether its potential benefits, in terms of alleviating extreme weather impacts, outweigh the costs of rewetting remains unanswered. Using a unique collection of hydrological field observations and modelling, this thesis provides a comprehensive analysis of the hydrological functioning of peatlands, at both local and stream network scale, within a heterogeneous boreal landscape (Paper I and Paper II) and addresses the question of whether peatland rewetting is more effective at mitigating both flooding events and low flow conditions than leaving historically drained peatlands as they are (Paper III and Paper IV). Our findings indicate that the moderating effect of peatlands on flow responses can primarily be found at the local scale. We also demonstrated that peatland rewetting successfully raised the groundwater table level, increased baseflow, and enhanced the overall storage capacity within the study site. During storm events, peatland rewetting effectively attenuated peak flow, reduced the runoff coefficient, and mitigated hydrograph flashiness. In conclusion, peatland rewetting is shown to be an effective tool for moderating hydrological extremes. However, given the dynamic nature of hydrological systems, continuous long-term monitoring of peatland processes following rewetting is required.