Mountain rivers total to about 33 percent of the global water flow. And that in the conditions in which mountains cover 25 percent of the Earth's surface. A new study revealed that mountain rivers represent a significant source of carbon dioxide. Asa Horgby from the EPFL's Stream Biofilm and Ecosystem Research Laboratory (SBER) and a team of international researchers revealed in a new study that mountain rivers emit more carbon dioxide than streams at lower altitudes. The study published earlier in the Nature Communications journal revealed how scientists reached those conclusions. Accordingly, researchers gathered environmental data on mountain rivers, concentrating on the streams' hydrologic and geomorphologic characteristics. Then, the scientists came up with a model to calculate the natural carbon dioxide emissions from about 2 million mountain rivers from around the world. Mountain Rivers Represent A Considerable Source Of Carbon Dioxide "We have known for a number of years that freshwater ecosystems emit roughly the same amount of CO2 that oceans absorb, but we had never before done rigorous studies on the role of the countless mountain streams for the global CO2 fluxes. Until now, they were aqua incognita," explained Tom Battin, the study's co-author, cited by Phys. "But our latest findings now open up exciting new research avenues, such as to better understand where all that CO2 comes from and how we can more accurately account for the world's alpine regions in our assessments of the global carbon cycle," he added. The scientists concluded that carbonate rocks, which are dominant around the world, are behind the high levels of carbon dioxide of geological sources. These rocks consist of fossilized marine microorganisms that lived on our planet tens of millions of years ago. "We are just starting to discover the role of mountain streams for the global carbon cycle. These are exciting times for environmental sciences," explained Tom Battin, who is the head of SBER.