Reservoirs tagged as global warming source

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VANCOUVER, Wash., Aug. 8 (UPI) -- Reservoirs behind dams have been identified as new culprits in global warming, releasing greenhouse gases as water levels go up and down, U.S. researchers say.

Researchers at Washington State University-Vancouver measured dissolved gases in the water column of a reservoir in Clark County and found methane emissions jumped 20-fold when the water level was drawn down, the school reported Wednesday.

Methane can trap 25 times more heat in the Earth's atmosphere than carbon dioxide, the researchers said.

"Reservoirs have typically been looked at as a green energy source," doctoral student Bridget Deemer said. "But their role in greenhouse gas emissions has been overlooked."

While dams and the water behind them cover only a small portion of the earth's surface, researchers said, they harbor biological activity that can produce large amounts of greenhouse gases.

There are some 80,000 dams in the United States, the U.S. Army Corps of Engineers National Inventory of Dams records.

The research could lead to different ways of managing reservoir drawdowns, WSU earth and environmental science Professor John Harrison said.

Emissions may be higher in summer months, he said, when warmer temperatures and low oxygen conditions in bottom waters stimulate the microbial activity that produces greenhouse gases.

"We have the ability to manage the timing, magnitude and speed of reservoir drawdowns, which all could play a role in how much methane gets released to the atmosphere."