Roaring water at hydro dams produces more than just electricity, a new study from Brazil shows. All that furiously bubbling water also produces greenhouse gas emissions by liberating methane once trapped in the depths of reservoirs. A peer-reviewed article by Ivan Lima and other scientists from the Brazilian National Institute for Space Research published in the journal Mitigation and Adaptation Strategies for Global Change indicates that dams may be responsible for 25 percent of worldwide anthropogenic methane emissions. That’s the equivalent of about 4 percent of humanity’s impact on earth’s climate. Methane is 23 times more powerful as a greenhouse gas than carbon dioxide. The source of the methane is organic matter on the bottom of reservoirs, which rots and releases methane into the water. In a lake or the ocean, the methane would remain at the bottom under the pressure of the overlying water. However, dams with deep inlet pipes release the water. As it is aerated upon exit from the turbines, the methane is released to the atmosphere. Space Institute scientists compare this methane release to the fizz of carbon dioxide when opening a can of soda, which suddenly lowers the pressure in the can. Emissions may be highest in tropical nations where there is more organic matter in water. However, the study examined 52,000 dams around the world. One possible solution is to move dam intakes higher up in reservoirs, since water near the surface does not contain sizable amounts of methane. Meanwhile, methane at the bottom of reservoirs can be tapped by pumping up deep water and aerating it in an enclosure to capture the gas. It then can be burned in turbines to create additional power. Space Institute scientists are planning to test this control technology at a suitable hydropower dam in Brazil.
