Dams have long been seen as a source of green energy. But the cost of providing that energy has not been studied, until now. And the jump in methane gas that happens during water-level changes has emerged as a potential factor in climate change with a new study.
Measuring gases dissolved in the water column of Lacamas Lake, Clark County, Washington State University–Vancouver doctoral student Bridget Deemer has found that when water levels were drawndown, methane emissions leapt up twentyfold, the university announced in a media release on August 8.
"Reservoirs have typically been looked at as a green energy source,” Deemer said in the statement. "But their role in greenhouse gas emissions has been overlooked.”
In addition, fellow student Maria Glavin sampled bubbles rising from the mud in the lake to find a 36-fold methane increase when the water levels were drawn down, the statement said.
Methane is one of the infamous greenhouse gases that trap heat in the atmosphere. It is 25 times more efficient at doing so than carbon dioxide, another greenhouse gas, the release noted. This means that dams and the water they hold back can produce effects much stronger than the relatively small proportion of space they occupy on the planet, the university said.
There are 80,000 dams in the U.S. alone, the university said, quoting the U.S. Army Corps of Engineers National Inventory of Dams.
John Harrison, an assistant professor of earth and environmental sciences and the two students’ adviser, said this could lead to alterations in the way water drawdowns are managed. Deemer will soon examine three reservoirs in Oregon and the Klamath basin of northern California.