Land use around lakes seen as critical factor in greenhouse gas equation
The world’s lakes already emit carbon dioxide equivalent to about 25 percent of the CO2 produced by fossil fuel combustion, and that amount could grow significantly in a warming world.
Researchers came to that conclusion after studying a huge amount of data from more than 5,000 lakes in Sweden, and tracking the origins of CO2 releases. The study, published in Nature Geoscience, shows that the amount of CO2 produced in the lakes by micro-organisms, and from the influx of CO2 from surrounding lands, both increase in warmer and nutrient-rich climate zones.
“In most Swedish lakes, the carbon dioxide originates from the surrounding land from where it is washed into water courses and then into lakes which then release CO2 into the atmosphere,” said study leader professor Gesa Weyhenmeyer, with the department of ecology and genetics of Uppsala University.
“There is a considerable risk that carbon dioxide emissions from lakes and water courses, especially those in northern Scandinavia, Canada and Russia, will increase as the climate warms up. And it is in these areas that most of the lakes are located,” said Weyhenmeyer.
The findings highlight the crucial role of land use in climate studies — small lake in southern Sweden surrounded by farmland releases twice as much CO2 as small lake in northern Sweden surrounded by forest.
There are two main carbon dioxide sources in water. It can either be produced by micro-organisms, especially in lakes, or it can be washed into the water from the surrounding area. The study findings will help refine climate models, accounting for the difference between those sources.
Earlier test results from individual aquatic systems showed that CO2 is mainly produced by micro-organisms in the lake itself. In the present study, researchers show for the first time that this applies to less than half of all Swedish lakes.