Scientists at Washington State University have reported a new source of greenhouse gas emissions: dams. When water levels dropped in reservoirs, the researchers found that methane emissions increased as much as 36-fold. The study is the first to examine the relationship between drawing water from reservoirs and greenhouse gas emissions.

Methane is a much more potent greenhouse gas than carbon dioxide, trapping 25 times more heat in the atmosphere. The EPA reports that the biggest sources of methane in the United States are waste in landfills, livestock and some forms of energy production. The new research suggests that dams and reservoirs may join that list as well.

There are around 80,000 dams in the U.S. They are often considered sustainable sources of energy, but that view may change. The ability of the Earth to store greenhouse gases may be much less than previously thought, according to another study, published last year in Science.

Scientists say emissions may vary depending on the outdoor temperature, and the speed and amount of water taken from the reservoirs. Plants and soils may also be able to help store gases from dams. As the researchers learn more, the knowledge can be used to help better manage dams.

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