| Extensive areas of forest land in Sweden have been artificially drained by ditching to increase timber production. In many drained areas, no production increase has occurred, and these areas are now targeted for hydrological restoration as an efficient measure to reduce CO2 emissions from drained peat soils. However, increasing the groundwater level by wetland restoration (WR) lead to increased formation and atmospheric emission of methane (CH4). Higher CH4 emissions are estimated to offset a large share (30-90%) of the WR induced reduction in CO2 emissions. An additional, as yet unaccounted for, flux term that could further offset WR climate benefits is the effect on lateral CH4 export via runoff. In the worst case, the expected climate benefit of many of the large-scale wetland restorations that are currently made across Sweden could be lower or even non-existing. The proposed project aims to answer:
Does restoration of drained forest wetlands enhance CH4 export via runoff?
To investigate the effects of WR on CH4 export we will evaluate collected data from an established replicated and detailed WR experiment in northern Sweden called Trollberget. The infrastructure is funded through the EU program GRIP on Life in conjunction with SLU and the Swedish Forest Agency. Within this infrastructure two wetland catchments were restored during late 2020 by filling in all ditches and damming the catchment outlets. Monitoring of ground and stream water have been conducted since late 2018 resulting in that we now have in total four years of CH4 export data, two years prior to and two years after restoration. Patterns observed in the restored wetlands will be compared with two non-restored wetland catchments in order to detect any WR effects on CH4 exports via runoff.
The outcome of the project will be a unique and important knowledge contribution to the effects of WR on export of CH4 via runoff. This will in turn be central information when assessing the overall climate benefit of WR as a climate mitigation measure. Such science based knowledge is urgently needed in order to make well-founded and sustainable decisions regarding restoration of drained forest areas.
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