American Chemical Society Podcast: Small Dams Create Greenhouse Gas 'Hot Spots'

The latest episode in the American Chemical Society's (ACS') award-winning Global Challenges/Chemistry Solutions podcast series questions the "green" reputation of small hydroelectric dams.

Based on a report by Andreas Maeck, Ph.D., in the ACS journal Environmental Science & Technology, the new podcast is available without charge at iTunes and from http://www.acs.org/globalchallenges.

Maeck explains that the large reservoirs of water behind the world's 50,000 large dams are a known source of methane. Like carbon dioxide, methane is one of the greenhouse gases, which trap heat near Earth's surface and contribute to global warming. Methane, however, has a warming effect 25 times more powerful than carbon dioxide. The methane comes from organic matter in the sediments that accumulate behind dams. That knowledge led to questions about hydroelectric power's image as a green and nonpolluting energy source. Maeck's team decided to take a look at methane releases from the water impoundments behind smaller dams that store water less than 50 feet deep.

They describe analysis of methane release from water impounded behind six small dams on a European river. "Our results suggest that sedimentation-driven methane emissions from dammed river hot spot sites can potentially increase global freshwater emissions by up to 7 percent," said the report. It noted that such emissions are likely to increase due to a boom in dam construction fostered by the quest for new energy sources and water shortages.