Effects of Climate on Lakes – from Amazonas to the forest lakes of Sweden

13 May 2014

The sediment on the bottom of lakes accumulates tremendous amounts of organic material. Some of it is stored a very long time. Other parts are broken down into carbon dioxide and methane, which leave the water and rise into the atmosphere. In a study recently published in the journal Nature Climate Change a group of Swedish and Brazilian scientists show how these processes are impacted by the temperature in tropical and temperate regions.

Just as milk turns sour more quickly in room temperature than in the refrigerator, the degradation of organic material in sediment is temperature dependent – the break down is faster in warmer climates. In collaboration with colleagues in Brazil, a team of researchers at Uppsala University and Linköping University in Sweden have compared the effects of temperature on the degradation activity of bacteria in the sediment of lakes in tropical and Nordic forest areas.

"We took samples at the same time in the Amazonas region and in lakes of the forest landscape of Sweden and ran experiments simultaneously and in the same laboratory in Uppsala – 2,500 gas-tight containers at once. By exposing the sediments to different temperatures and measuring the production of carbon dioxide and methane, we were able to compare the temperature sensitivity of the various processes in the different environments", says Lars Tranvik, professor of limnology at Uppsala University.

Regardless of differences in the composition of the sediments, their temperature sensitivity was the same in tropical and Nordic sediments. But the associations are not linear, and the starting point in the warmer water in Amazonas produces a stronger response when the temperature is increased further.

"We combined the temperature sensitivity we measured with scenarios for increases in temperature in the coming century in the different climate zones. The absolute increase in temperature is expected to be lower in the tropics than in the north, but the result is nevertheless that the production of greenhouse gases will increase more in the tropics", says Cristian Gudasz, formerly a doctoral candidate at Uppsala University, and now a post-doctoral fellow at Princeton University in the US.

"This is partly owing to the fact that methane production rises considerably with a change in the temperature under tropical conditions. Methane is a substantially more potent greenhouse gas than carbon dioxide. Small differences in temperature in the tropics can thus have a greater effect than greater changes in temperature in the Nordic region", claims David Bastviken, a senior lecturer at Linköping University.

This research is part of a collaborative between Swedish and Brazilian universities, funded by STINT, the Swedish Foundation for International Cooperation in Research and Higher Education.

Reference: H. Marotta, L. Pinho, C. Gudasz, D. Bastviken, L. J. Tranvik and A. Enrich-Prast. Greenhouse gas production in low-latitude lake sediments responds strongly to warming. Nature Climate Change. Advance Online Publication (AOP).