Abstract
In-situ oil extraction activities impact the vast mosaic of boreal wetlands and uplands. Peatland restoration in these regions aims at reestablishing crucial peatland functions, such as peat accumulation and carbon (C) sequestration. In order to assess the success of fen restoration, we evaluated the biogeochemical conditions, the seasonal carbon balances via carbon dioxide (CO2) fluxes and methane (CH4) emissions, and addressed the global warming potential following different restoration techniques at two restored in-situ oil sands well pads, during two consecutive growing seasons. Restoration work involved: 1) the partial or complete removal of introduced well pad construction materials, and spontaneous revegetation, or 2) the partial removal of foreign clay, in addition to reintroduction of typical fen plant species such as Larix laricina, Salix lutea and Carex aquatilis. Comparisons were done with regional reference ecosystems (REF) consisting of three peatlands: a wooded bog, a wooded rich fen and a wooded extreme-rich fen. While the average electric conductivity of restored sectors (946 μS cm−1) was higher compared to REF (360 μS cm−1), the pH was quite similar (pH 5.8 REF, pH 6 restored). Dissolved organic carbon concentration was lower in all restored sectors (5–11 mg L-1 restored sectors, 15–35 mg L-1 REF), presumably due to the still incomplete recovery of vegetation and lower organic matter content associated with remnant well pad material. Re-establishment of shrub and brown moss species improved significantly the C uptake. However, the active introduction of plant species was no crucial restoration step, in order to return species beneficial for C uptake. Restoration treatments that were leveled closest to the surrounding REF showed the most similar seasonal C balance to REF. In shallow open water areas resulting from the complete removal of all construction materials, we measured the highest methane emissions making these flooded sites net C sources to the atmosphere with elevated global warming potential. The partial removal of the well pad’s mineral soil to near the water table level and the surface elevation of the surrounding ecosystem seems to be the most effective site management method to sequester carbon efficiently. However, further research is needed to evaluate the suitability of this restoration method for the recovery of biodiversity and possible impacts of residual foreign materials on fen ecosystems.
Highlights
In the boreal biomes of the northern countries, industrial activities are constantly increasing within the last decades, including the sector of oil sands mining, crude oil and gas extraction
After eight to eleven years following restoration, the rates of C exchange in the restored sectors were comparable with the rates of long-time established reference wetlands, the soil and water chemistry still remained quite different due to the residual mineral soil layer
We conclude that the C uptake in restored mineral wetlands is most similar to reference peatlands, when vegetation has established and when regional wetland typical shrub species have colonized
Summary
In the boreal biomes of the northern countries, industrial activities are constantly increasing within the last decades, including the sector of oil sands mining, crude oil and gas extraction. We investigate the carbon (C) dynamics of disturbed northern peatlands impacted by oil and gas extraction infrastructure, following restoration with a variety of different techniques after in-place (in-situ) bitumen extraction has ended. The goal is to evaluate the impact of fen restoration on different ecosystem attributes, such as greenhouse gas emissions and the return of the carbon sequestration function, compared with conditions prior to disturbances. Undisturbed peatlands are recognized as the most effective C storing ecosystems on earth, which, globally, cover an area of more than 3 million km and store an estimated 644 to 1,105 Pg C (Leifeld and Menichetti 2018; Nichols and Peteet 2019). Restoration and rewetting of disturbed peatlands is recognized as a natural climate solution and allows countries to improve their C emission balance according to the national climate action plan under the UN Framework Convention on Climate Change (UNFCCC 2009)
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