5 April 2018

Clearing tropical peat releases much more laughing gas than previously thought

Peat bogs hotspots for emission of ultra-powerful greenhouse gas

Palm oil plantation (photo: dr Taavi Pae)

Peat bogs converted to agricultural use, especially those in the tropics, are hotspots for the emission of laughing gas, an extremely powerful greenhouse gas. These areas must be protected in order to prevent the earth from warming even more rapidly. That is the conclusion of a global field study published recently in Nature Communications, with important contributions from Utrecht landscape ecologist Jos Verhoeven.

As a greenhouse gas, laughing gas is 260 times as potent as CO2. Draining wet peat bogs dramatically increases the emission of this gas. A recent study has shown that emissions of laughing gas are greatest when peat bogs are drained in warm areas, with a soil moisture percentage of around 50 percent.

Risk of clearing

Tropical peat bogs have been cleared for agriculture for decades, especially for use as oil palm plantations. The moisture content of the soil in these bogs mean that they are a potential risk for high emissions of laughing gas. This development continues as we speak, and is causing considerable environmental damage, including high emissions of CO2.

Predicting laughing gas formation

An international team of 37 biologists and geoscientists has studied the emission of laughing gas (nitrous oxide, N2O) and the factors that drive these emissions in organic soils at 58 locations around the world. The study is led by the University of Tartu in Estonia. Professor Emeritus of Landscape Ecology Jos Verhoeven from Utrecht University advised the researchers on techniques suitable for analysing the massive global dataset. This in turn allows them to determine the influence of many important factors, such as soil moisture and the nitrogen content of the soil, in order to calculate the emission of laughing gas.

Directly into the atmosphere

Jos Verhoeven: “Peat bogs are naturally very wet, which prevents oxygen from penetrating into the soil. When a bog is drained, as was the case in the Netherlands over the past few centuries, then a lot of oxygen can suddenly enter the soil. This not only allows microorganisms to decompose the peat, it also forms nitrates. The organisms use the oxygen and nitrate to decompose the peat, and during this process of de-nitrification, some of the nitrate is converted into nitrous oxide. That laughing gas then disappears directly into the atmosphere.”

Proportion of laughing gas emissions from organic soils

Influential variable

Until now, scientists knew much less about the role played by N2O in global warming than about the greenhouse gases carbon dioxide and methane. This is because the latter two gases are much more common, so their total effect as greenhouse gases are equivalent to 72 per cent and 19 per cent, respectively. Nitrous oxide is currently responsible for 6 per cent of greenhouse gas emissions. Verhoeven: “Despite its relatively low percentage, laughing gas is already a greenhouse gas to reckon with. Current trends in peat draining will only cause that percentage to increase.”

Recommendation: do not drain

The researchers therefore advise governments to stop the drainage of tropical peat bogs that are still intact. “This is of course a difficult recommendation, because we in Europe have drained many of our peat bogs over the centuries. But we absolutely advocate protecting these areas”, according to landscape ecologist Verhoeven. “If we drain them, then the earth will warm up even faster than it is already doing.”