The Technical University of Zürich ETH has published the results of a new study dealing with the methane production in the water reservoir lake of a water power station. The results show that the green credentials of water power are less than previously thought.
Researchers and students of the Technical University of Zürich ETH have completed an in-depth study of the water reservoir Wohlensee (Lake of Wohlen). The lake is an artificial reservoir on the Aar River near Bern. It was chosen for the study because in summer large gas bubbles can be seen surfacing all over its surface. On a hot day the lake might look like an oversized champagne container.
Establishing the content of the bubbles, the researchers found that they contained methane gas. Methane is the gas emitted by cows as part of their digestion of grass and herbs. The gas in the lake is the result of a comparable process whereby organic material rots and methane is produced. The Aar River transport large amounts of organic materials. The reservoir stops the natural flow of the river and the transported materials are allowed to sink to ground where the rotting process begins.
The 150 tons of methane produced on an average day equal the output of 2,000 cows. Methane is one of the causes for global warming like carbon dioxide. The 150 tons are comparable to driving 25 million kilometres (15.5 million miles) in a car. On the other hand, compared to a coal power station of the same capacity the water power station is 40 times less damaging.
A further result of the study shows that the warmer the water the higher the amount of methane produced. As soon as the water temperature rises above 17 degrees Centigrade, the amount of methane surfacing doubles to 300 tons. The amount of methane produced at this relatively low temperature was hitherto thought to be a phenomenon of tropical waters.
The problem with this temperature level is its frequent occurrence. In rising temperatures (if global warming does what computers predict), the methane output of water reservoirs will continually rise. The University of Zürich therefore sees demand for further study on the matter.
The researchers state quite clearly that this is a preliminary study on one lake. It could be fluke due to special circumstances. The University will broaden the study to include a multitude of other reservoir lakes. As Switzerland has such reservoirs spanning the spectrum from glacier lakes to subtropical climate in the South, it should produce a reproducible and comprehensive result.
It may be assumed that the cold glacier lakes in the mountains will contribute almost no methane to the equation for several reasons: They stay cold even during summer and the water collected contains little to no organic material. It may also be assumed that warmer lakes produce more methane the more organic material is deposited by rivers flowing into it. It will be interesting to see if the depth of a lake has an influence as well.
Whatever the outcome of that research, this preliminary study shows that whatever we do it has implications on our environment. Think about it next time you leave your television set on stand-by when leaving the house.
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