Reducing emissions by halving drainage depths would equal 1% of all anthropogenic greenhouse gases – Science

Substantial reductions in global greenhouse gas emissions could be achieved by increasing water levels in agricultural peatlands, according to a new study published in the journal. Nature.

Peatlands occupy only 3% of the world’s land area but store a similar amount of carbon for all terrestrial vegetation, while supporting unique biodiversity.

In their natural state, they can mitigate climate change by continuously removing CO2 atmosphere and store it safely under waterlogged conditions for thousands of years.

But many areas of peatlands have been significantly altered by human activity, including drainage for agriculture and forest plantations. This results in the release from drained peatlands of the equivalent of about 1.5 billion tonnes of carbon dioxide (CO2) into the atmosphere each year – equivalent to 3% of all global greenhouse gas (GHG) emissions caused by human activities.

A team of scientists, led by the UK Center for Ecology and Hydrology (UKCEH), estimated the potential reduction in emissions by restoring all of the world’s agricultural peatlands. However, as large populations depend on these areas for their livelihoods, it may not be realistic to expect that all agricultural peatlands will be fully re-wetted and returned to their natural state in the near future.

The team therefore also analyzed the impact of halving the current drainage depths in cropland and grassland on peat – which covers more than 250,000 km.2 globally – and has shown that it can still deliver significant benefits for climate change mitigation. The study estimates that this could reduce emissions by around 500 million tonnes of CO2 per year, which is equivalent to 1 percent of all global GHG emissions caused by human activities.

Much of the world’s peatland greenhouse gases are produced in Europe and South East Asia, with the total land area of ​​many countries, including the UK, now a net source, not a sink , GHGs due to degraded peat emissions.

The study authors say there is growing recognition of the importance of peatlands to the global climate system, with efforts to reduce emissions through the conservation of undrained peatlands and rewetting of drained sites intensifying. .

UKCEH Professor Chris Evans, who led the research, said: “Widespread degradation of peatlands will need to be addressed if the UK and other countries are to meet their goal of net zero greenhouse gas emissions. greenhouse by 2050, as part of their contribution to the Parisian climate. objectives of the agreement.

“Concerns over the economic and social consequences of rewetting agricultural peatlands have prevented large-scale restoration, but our study shows that the development of locally appropriate mitigation measures could still lead to substantial reductions in emissions.

Professor Evans and his fellow authors recognize the practical challenges, for example controlling water levels and storage, as well as growing crops suited to the waterlogged conditions of peatlands, called “malaria”. Research on crops suitable for wetlands is ongoing but does not yet provide large-scale commercially viable alternatives to conventional agriculture.

However, scientists point out that there are many possibilities to partially rewet agricultural peatlands without seriously affecting production because many sites are over-drained – sometimes over two meters – and often in the absence of cultivation.

In addition to increasing emissions, drainage from peatlands causes land subsidence and soil compaction, which affects soil health and exposes low lying areas to increasing flood risk. It also deprives rare plants, insects and mammals adapted to wetlands of important habitats.

Professor Sue Page of the University of Leicester, co-author of the study, said: “Our results present a challenge but also an excellent opportunity. Better water management in peatlands offers a win-win potential – reduced greenhouse gas emissions, improved soil health, extended agricultural life and reduced flood risk. “

Scientists say the potential greenhouse gas reductions resulting from halving the drainage depth in agricultural peatlands are likely to be greater than estimates, since they do not include changes in greenhouse gas emissions (N2O) which, like CO levels2, are also likely to be higher in agricultural peatlands with deep drainage.

The study in Nature involved authors from UKCEH, Swedish University of Agricultural Sciences, University of Leeds, James Hutton Institute, Bangor University, Durham University, Queen Mary University of London, the University of Birmingham, the University of Leicester, Rothamsted Research and the University of Frankfurt.

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