October 11, 2010

Climate-Friendly Status Of Hydroelectric Power Questioned

Scientists from the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) have discovered greenhouse gas emissions from reservoirs in Switzerland, raising questions about the climate-friendly status of hydroelectric power.

In a study of Lake Wohlen in central Switzerland, EAWAG environmental chemist Tonya Del Sontro and her PhD supervisor Professor Bernhard Wehrli discovered daily methane emissions of 150mg per square meter of surface area or 150 metric tons per year. In a statement, the researchers said that those figures were equivalent to the annual methane output of 2,000 cows, making it "by far the highest emission rate recorded to date for a temperate reservoir."

"Hydropower isn't quite as climate-neutral as people have assumed in the past," Del Sontro said, noting that during the summer months, "the water in Lake Wohlen sometimes looks like champagne with masses of gas bubbles rising to the surface."

The emissions discovered by the EAWAG "indicate that run-of-the-river reservoirs can also be significant sources of methane emissions in temperate regions," they said in an October 11 press release.

However, Del Sontro and Wehrli are quick to point out that, even if the nearby Aare hydropower plant is responsible for the greenhouse gas emissions, it is still a greener alternative to other power sources. For example, they claim that a nearby coal-fired power station produces 40-times the amount of gases in the form of CO2 without producing an additional energy as a result.

Their findings have been published in the journal Environmental Science and Technology.

"Preliminary studies there had found 'very high' inflows of carbon-rich material, forming sediment in the reservoir that released greenhouse gases," French news agency AFP said Wehrli told them as part of a Monday article. "However, he underlined that the complex process was highly dependent on temperature, depth and the amount of carbon rich organic material--such as vegetation--that accumulated in the sediment on the reservoir floor."


Image Caption: Eawag researchers deploying funnel-shaped gas traps to study methane bubbles rising to the surface of Lake Wohlen.


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