The researchers estimate that the area of UK peatland used for maize cultivation, which is processed through anaerobic digesters to produce biomethane, has tripled since 2015. Despite this growth, the study highlights that the emissions associated with draining these carbon-rich wetlands for agricultural use have been largely overlooked.
Funded by the Department for Environment, Food and Rural Affairs (Defra), the study focuses on maize cultivation in the UK but suggests that similar greenhouse gas emissions would occur from any bioenergy crop grown on drained peatlands globally. "Biomethane is an important renewable energy source, but it seems unwise to use drained peatland primarily for generating bioenergy in areas where this leads to higher CO2 emissions than the fossil fuel it replaces," said Professor Chris Evans of UKCEH, who led the research published in 'Nature Climate Change'.
Impact of Peatland Drainage
The principle behind biomethane is that the carbon released during its combustion was recently absorbed from the atmosphere via photosynthesis, creating a closed carbon cycle. However, when peatlands are drained to grow crops or trees, carbon stored in the soil for centuries is exposed to oxygen and released as carbon dioxide, adding substantial additional emissions.
UKCEH's field flux measurements show that while each cubic metre of natural gas burned emits the equivalent of 2 kg of CO2, cultivating maize on drained peatland emits up to 6 kg of CO2 per cubic metre of biomethane produced. This figure excludes additional emissions from fertilisers, harvesting, transport, or the actual biomethane production process.
Surge in Maize Cultivation
The area of drained peatland used for maize cultivation in the UK increased from 6,000 hectares in 2015 to more than 11,000 hectares in 2021, with the proportion of maize grown for bioenergy rising from 20% to 34% during the same period.
However, the researchers noted that not all forms of bioenergy production on peat soils result in higher emissions. For example, growing biomass crops in agricultural peatlands with higher water levels-a method called paludiculture-could help mitigate climate change. Professor Evans also pointed out that using maize as a "break crop" within rotational farming systems is less harmful than dedicating entire areas of peatland solely to biomethane production.
The study also indicates that growing maize on mineral soils, rather than peat, leads to lower soil carbon losses, making this a more effective approach for reducing emissions.
Improving Policy Decisions
The production of biomethane in the UK has increased four-fold since 2000, supported by government initiatives like the Green Gas Support Scheme and the Renewable Heat Incentive. However, the study's findings suggest a need for more nuanced decision-making to ensure bioenergy production does not lead to unintended environmental consequences.
Dr Rebecca Rowe, co-author of the study, emphasized: "The transition to net zero won't be completely smooth. Along with the successes, there will be failures and unintended consequences. Our role, as scientists, is to support the Government, land managers, and industry by providing them with the best up-to-date knowledge on the impacts of their actions so they can make informed decisions about energy crop production and land use."
Research Report:Biomethane production from maize grown on peat soils emits more carbon dioxide than using natural gas, the study concludes.
Related Links
UK Centre for Ecology and Hydrology
Bio Fuel Technology and Application News
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