Acid rain reduces methane emissions from rice paddies
6 August 2008
Acid rain from atmospheric pollution can reduce methane emissions from rice paddies by up to 24 per cent according to research led by Dr Vincent Gauci of The Open University.
This is potentially a beneficial side-effect of the high pollution levels that China - the world's largest producer of rice - is often associated with. Methane is 21 times more powerful as a greenhouse gas than CO2.
"The reduction in pollution happens during a 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 24 per cent," said Dr Gauci.
The project - funded by the Natural Environment Research Council - used rice soils and grain from Portuguese paddies. Soils from these paddies have been exposed to very little acid rain and are similar to Asian rice soils before they became polluted. To test the effects of acid rain, the researchers added frequent small doses of sulphate, which simulate acid rain experienced in polluted areas of China.
"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," added 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 micro-organisms that live in the soil."
This is because some sugars produced by rice plants are lost in the soil and micro-organisms feed on these sugars. But when the rice plant is producing grain, the carbohydrates are directed into grain production and away from soil so limiting the amount of food available for micro-organisms.
"There is also likely to be competition between these micro-organisms and sulphate-reducing bacteria. Normally in these conditions sulphate-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."
Dr Vincent Gauci
Centre for Earth, Planetary, Space & Astronomical Research
The Open University
Tel: 01908 858137
Louis De La Forêt
The Open University
Tel: 01908 653256
NERC Press Office
Natural Environment Research Council
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1. 'Suppression of rice methane emission by sulfate deposition in simulated acid rain' is published in Journal of Geophysical Research, volume 113, G00A07, doi:10.1029/2007JG000501, 2008. The authors are Vincent Gauci (lead author) and Graham Howell - Open University, Nancy Dise - Manchester Metropolitan University and Meaghan Jenkins - Open University and University of New South Wales.
2. The Open University is the UK's largest university and a world leader in distance education. For nearly 40 years, it has been at the forefront of global development in designing and delivering higher education programmes that make intelligent use of combining the latest communications technologies with traditional teaching methods. It has more than 200,000 students in more than 40 countries studying for a variety of degrees and vocational qualifications ranging from short courses to PhDs. More than two million people have used the OU to gain access to university study from their homes and workplaces - many of whom would have been denied access to conventional universities (the OU has no prerequisites for its undergraduate courses).
3. The Natural Environment Research Council (NERC) funds world-class science, in universities and its own research centres, that increases knowledge and understanding of the natural world. It is tackling major environmental issues such as climate change, biodiversity and natural hazards. NERC receives around £400m a year from the government's science budget, which is used to provide independent research and training in the environmental sciences.
Press release: 41/08
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