01 Aug 2008

Chinese acid rain may combat greenhouse gas emissions from rice paddies, new Open University research shows

Air pollution

Air pollution

As the world’s attention focuses on Beijing and China for the Olympic Games, criticism of the pollution levels around the city continues.

Now, new research, led by Dr Vincent Gauci of The Open University, indicates that related atmospheric pollution may have a beneficial side-effect – in combating methane emissions from rice, of which China is the world’s biggest producer.

Dr Gauci says: “We found that acid rain rates of sulfate pollution can reduce rice paddy emissions of methane - a gas that is 21 times more powerful than CO2 as a greenhouse gas.

“It happens during the stage of the lifecycle when the rice plant is producing grain. This period is normally associated with around half of all methane emissions from rice and we found that simulated acid rain pollution reduced this emission by 25 per cent.

“We had similar results when exposing natural wetlands to simulated acid rain but this could be more important since natural wetlands are mostly located far from major pollution sources, whereas for rice agriculture, the methane source and the largest source of acid rain are both in the same region - Asia, says Dr Gauci.

“We need to do further research but it looks like there could be a combination of processes at work. One line of investigation we’d like to confirm is that the sulfate component of acid rain may actually boost rice yields. This might, paradoxically, have the effect of reducing a source of food for the methane producing microorganisms that live in the soil.

“There is also likely to be competition between these microorganism and sulfate reducing bacteria. Normally in these conditions sulfate reducers win which results in less methane.”

Dr Gauci added a note of caution to the results.
“Acid rain is one of several pollution problems in Asia that need solving in the coming decades but we need to appreciate the potential consequences of that clean up, one of which could be an increase in methane emissions as the effect of the acid rain wears off.”



The work, funded by the Natural Environment Research Council, used rice soils and grain from Portuguese paddies, that are extremely clean in terms of acid rain pollution, so were an ideal analogue for Asian rice soils before they became polluted. The researchers then added frequent small doses of sulfate to simulate acid rain experienced in polluted areas of China.

The research, was published in the latest edition of the Journal of Geophysical Research - Biogeosciences.

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