Freshwater lakes and rivers contributing to climate change

Posted: 26 January 2011

Author: Tom Levitt, The Ecologist

Emissions of methane from freshwater systems are now estimated to be 103 million tonnes per year - equivalent to 25 per cent of all the carbon dioxide absorbed by the world's land areas.

Methane emissions from lakes and rivers are a significant factor in the greenhouse gas cycle, claims a new study in Science which urges climate scientists and policy-makers to pay it closer attention.

The 'other' greenhouse gas, as it is sometimes known, is regularly left out of the public discourse on climate change - one usually dominated by discussions of carbon dioxide (CO2). It makes up a small portion of the atmosphere in comparison to CO2 but is 20-30 times more potent in its ability to absorb infrared energy and contribute to the global warming effect.

Methane bubbles in lake
Tiny bubbles of methane trapped in lake ice in Norway.

As well as natural sources like wetlands and lakes, methane is also emitted from industrial sources and agriculture (rice fields and livestock).

Scientists from Sweden, Brazil and the US investigated methane emissions from 474 freshwater systems and explained their 'previously neglected' role in recycling the carbon absorbed by the land. The natural landscape absorbs carbon dioxide but decaying trees, vegetation and plant matter in water systems then produce significant amounts of methane and CO2 emissions.

'Our accounting system is focussed solely on land and trees but the landscape is bigger than that and we should be taking account of the role freshwater systems play in the greenhouse gas cycle,' said lead study author David Bastviken from Lopatking University, Sweden.

The study estimated total emissions of methane from freshwater systems to be 103 million tonnes per year - the equivalent to 25 per cent of all the carbon dioxide absorbed by the world's land areas.

However, Bastviken dismissed suggestions that climate engineering solutions could be used to negate methane emissions from lakes and rivers . 'It seems much better to focus our efforts on reducing fossil fuel emissions which are the main problem. Large scale ecosystem engineering would be shifting the attention away from the real problem and is dangerous and not very cost-effective in this case,' he said.