Boreal lakes emit an increasing amount of carbon dioxide in a warming world
A Swedish boreal lake. Image: Erik Jeppesen
The world’s lakes, rivers and reservoirs naturally emit carbon dioxide as part of the global carbon cycle. Recent scientific studies suggest that annual carbon dioxide emissions from inland freshwaters roughly equate to the total uptake of carbon by the world’s oceans.
However, a new study using extensive ecological data from 5,000 Swedish lakes suggests that ongoing changes in land use and climate are causing increased levels of dissolved inorganic carbon in northern boreal lakes, which in turn is causing the lakes to emit increasing amounts of carbon dioxide into the atmosphere.
Writing in Nature Geoscience, Gesa Weyhenmeyer from Uppsala University and colleagues observed that small lakes in southern Sweden emitted twice as much carbon dioxide as equivalent small lakes further north. The team documented that carbon dioxide emissions were highest in lakes with a significant number of ice-free days each year and high dissolved oxygen and nutrient concentrations (often as a result of agricultural runoff).
Co-author, and MARS partner, Erik Jeppesen from Aarhus University explains,
“Our work indicates that the release of carbon dioxide from lakes in Sweden will increase as the climate gets warmer, and as areas adjacent to lakes is used for agriculture in the place of forests.”
The burning of fossil fuels releases carbon dioxide, and scientific consensus is that the resulting increase in atmospheric CO2 concentrations is causing increased global temperatures and other ongoing climatic changes.
The new study by Weyhenmeyer and colleagues shows that dissolved carbon from such emissions can travel through a watershed and ‘supersaturate’ lakes, which in turn causes them to emit carbon dioxide into the atmosphere. They suggest that carbon emissions from some of the boreal lakes in southern Sweden have reached levels comparable to lakes in tropical regions. In effect, this is a climatic feedback loop, where climate change drives further increases in CO2 emissions from freshwaters.
As a result, boreal lakes in northern latitudes of the world may become increasing sources of atmospheric carbon dioxide, a prospect that has consequences for global climate change, as Erik Jeppesen outlines,
“The findings worry us. There is great risk that as the climate warms in coming years, carbon dioxide emissions from lakes will increase significantly in the northern parts of Scandinavia, Russia and Canada. And, of course, these regions are where the vast majority of the world’s lakes are.”
For lead author Gesa Weyhenmeyer, the team’s findings have important implications for how we understand, and manage, boreal freshwater ecosystems as part of increasingly human-altered global climate systems,
“When we assess future emissions of carbon dioxide to the atmosphere, it is important to know where the carbon dioxide comes from. Only with this knowledge can we find ways to reduce the release.”
Weyhenmeyer, G. A., Kosten, S., Wallin, M. B., Tranvik, L. J., Jeppesen, E., & Roland, F. (2015). Significant fraction of CO2 emissions from boreal lakes derived from hydrologic inorganic carbon inputs. Nature Geoscience, advance online publication.
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