Freshwaters are underestimated sources of greenhouse gases. In a study published in Science of The Total Environment, researchers with the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB) have now shown that even dry water bodies can release considerable amounts of methane. An overview of the causes and magnitudes of methane emissions from freshwaters and an outlook on future developments in climate change make this evident.

Methane is produced when organic material decomposes in the absence of oxygen. It can be released for example during the mining of coal, oil or natural gas. It is produced in cows’ stomachs—but also in inland waters and oceans.

“Among the types of freshwaters that release greenhouse gases, reservoirs and lakes are major emitters,” explained IGB researcher Professor Hans-Peter Grossart. “This is because organic material from dead plants and animals sinks to the oxygen-poor water bottom of lakes and reservoir more than it sinks in flowing waters. This methane release is intensified by higher temperatures. In small gas bubbles, the methane then rises from the bottom to the water surface and thus enters the atmosphere.”

For a long time, researchers assumed that methane is only formed in water bodies where there is no oxygen. “Recent studies show that this greenhouse gas is also produced in the oxygen-rich water column: for example, various phytoplankton species—cyanobacteria, diatoms and haptophytes—emit methane during their photosynthesis,” said IGB researcher Dr. Mina Bizic, who compiled the knowledge on methane formation by phytoplankton in a scientific article.

The full article can be read here.