Sediment behind small dams contributing to greenhouse gas emissions, finds study
There are reports from scientists that indicate more methane than previously believed is emerging out of the water behind small dams.
A study by Andreas Maeck and colleagues, published in ACS Publications' journal Environmental Science & Technology, describes 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.
The report points out that the large reservoirs of water behind the world's 50,000 large dams are already 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. This 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.
With the "green" reputation of large hydroelectric dams already in question, scientists are finding that millions of smaller dams on rivers around the world make an important contribution to the greenhouse gases linked to global climate change.