Soil Degradation Based Nitrous Oxide Emissions and Rewetting Options for European Peatlands

Nitrous oxide (N₂O) is approximately 265 times more potent than carbon dioxide (CO₂) in atmospheric warming¹. Drained peatlands contribute substantially to N₂O emissions, however, estimating N₂O emissions from peatlands is challenging especially at a national scale. The published IPCC default emission factors for organic soils² have always been applied to estimate the N₂O emissions. However, the representativeness of these emission factors is not convincing as only a small percentage of peatlands have been monitored and usually for a short period of time only (maximum several years). One recent study³ suggests that the N₂O emissions from peatlands are closely related to the degradation stage of the peat. The more a peatland is degraded, the higher the N₂O fluxes. The bulk density of the topsoil (0–30 cm) as a proxy for peat degradation was superior to other parameters (e.g. carbon to nitrogen ratio, pH) in estimating N₂O fluxes. The distribution of soil bulk density in European managed peatlands indicates that most peatlands are highly degraded (high bulk density). Therefore, applying the IPCC default emission factors may underestimate the N₂O emissions from drained peatlands, as the majority of IPCC emission factors is from lightly or moderately degraded peatlands.

Rewetting is an effective approach to reduce N₂O emissions from peatlands, especially when the average annual water table is near or above the ground surface. In Europe, only approximately 1% of the drained peatlands have been rewetted⁴ so far. There is, however, a position developing that most of the peatlands shall be rewetted, but there is only little discussion on the rewetting strategy and which peatlands should be given priority in the rewetting endeavor. Several studies^5,6 stated that lightly degraded peatlands should be prioritized for rewetting because costs are low and the biodiversity targets can be easily achieved. However, from the viewpoint of greenhouse gas (GHG) emissions, the highly degraded peatlands should be rewetted first⁷. Most managed peatlands in Europe are highly degraded and emit most of the GHG of all peatlands. Postponing rewetting of these highly degraded soils may increase the long-term warming effect through continued GHG emissions. The debate on rewetting strategies will continue and it is important to take all aspects such as GHG emissions, biodiversity, water storage, costs, societal perception among others into consideration.

The poster image is from Micha Weil (rewetted and now intensively studied peatland, which was formerly under agricultural usage).

1. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC: Geneva, Switzerland (2014).
2. 2013 Supplement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, Wetlands, 2014).
3. Liu, H., Zak, D., Rezanezhad, F., & Lennartz, B. Soil degradation determines release of nitrous oxide and dissolved organic carbon from peatlands. Environ. Res. Lett. 14, 094009. (2019).
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5. Renou-Wilson, F., Moser, G., Fallon, D., Farrell, C.A., Müller, C., & Wilson, D. Rewetting degraded peatlands for climate and biodiversity benefits: Results from two raised bogs. Ecol. Eng. 127, 547–560 (2019).
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7. Liu, H., Wrage-Mönnig, N., Lennartz, B. Rewetting strategies to reduce nitrous oxide emissions from European peatlands. Commun. Earth Environ. (2020).