New research questions hydroelectric emissions

Oct 11, 2010
The Sayano-Shushenskaya hydroelectric power dam in southern Siberia is seen from a helicopter. Scientists have found that some reservoirs formed by hydroelectric dams emit more greenhouse gases than expected, potentially upsetting the climate-friendly balance of hydroelectric power.

Scientists have found that some reservoirs formed by hydroelectric dams emit more greenhouse gases than expected, potentially upsetting the climate-friendly balance of hydroelectric power.

A scientific study of Lake Wohlen in central Switzerland found "unexpectedly high" emissions of methane, a powerful , the Swiss Federal Institute of Acquatic Science and Technology (EAWAG) said on Monday.

The 150,000 tonnes of methane bubbling up from sediment in the retention lake on the river Aare over a year are the equivalent of emissions from 2,000 cows, or 25 million kilometres (15.5 million miles) travelled by cars, EAWAG added in a statement.

"So hydropower isn't quite as climate-neutral as people have assumed in the past," said one of the scientists involved, Tonya Del Sontro.

"In the summer, the water in Lake Wohlen sometimes looks like champagne with masses of rising to the surface," she added.

The peer-reviewed research by scientists at Swiss, German and Israeli institutes was published in the US journal .

Joint author Bernhard Wehrli, a professor of aquatic sciences at Zurich's Federal Institute of Technology (ETHZ), said the study mirrored initial findings in research on tropical reservoirs, notably at the Kariba dam in Zambia.

Preliminary studies there had found "very high" inflows of carbon-rich material, forming sediment in the reservoir that released greenhouse gases, Wehrli told AFP.

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.

"We have done a study of high Alpine reservoirs that are in a better state in terms of ," he added. High altitude mountain reservoirs are generally in colder, more rocky and sparsely vegetated surroundings.

In the shallow Lake Wohlen, on the populated 500-metre (1,640 foot) high plateau near the Swiss capital Berne, the reservoir captures large amounts of organic material that would flow along the rive Aare.

"It's not the fault of the reservoir builders that there are emissions, but because the flow of the river is slowed down," Wehrli explained.

That allows the to ferment and produce gas that bubbles up to the surface.

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User comments : 10

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Jimbaloid
5 / 5 (2) Oct 11, 2010
I'm curious to know if it is possible to estimate (and so subtract) the effect this organic material might have had if the reservoir was not there? Presumably it would still have been deposited somewhere and then decayed? If the reservoir had not been built, would it all have reached the sea? Would that change things? Would any have then got sequestered to the sea bed or would carbon have released in a form other than methane?
northwest
not rated yet Oct 11, 2010
This report came to another conclusion:
"In sub-tropical Laos, SINTEF has taken measurements from a 30 year-old HEP reservoir. They reveal that the organisms in the water and on the reservoir floor take up more CO2 from the atmosphere than the reservoir itself releases in the form of climate gases, converted to CO2 equivalents."

http://www.scienc...4454.htm
or http://www.sintef...-clean2/

So to generalize like Mr Del Sontro does here "So hydropower isn't quite as climate-neutral as people have assumed in the past," is perhaps a bit too early.
Modernmystic
1 / 5 (1) Oct 11, 2010
We should do a study to see if we "should" be allowed to use stone knives and bear skins.
apex01
not rated yet Oct 11, 2010
We should do a study to see if we "should" be allowed to use stone knives and bear skins.


Yeah no kidding. I read the first couple of paragraphs and got fed up. There's no possible way i can believe that hydroelectric dams produce CO2 EXCEPT when being built, just like wind mills, solar panels, and the power lines to connect them. They equate the CO2 emissions to x number of cows... Yes cows create CO2 but should we just get rid of them and eat like vegetarian kings instead? Everything on Earth emits some level of CO2 whether dead or alive. Maybe we should try to teach them to hold their breath/gas... I think they'd corrupt any chart or any study to rationalize shrinking the economy and creating 50% nation wide unemployment so they'd be happy as clams!
david_42
not rated yet Oct 11, 2010
Jimbaloid has the correct question. If you read the entire article, it explains where the CO2 (and methane) comes from.
TAz00
not rated yet Oct 12, 2010
If the lakes bubbles like champagne in the summer.... Why is no one capturing this methane? Sure its a large surface area, but suspended underwater funnels should be possible?
Drumsk8
not rated yet Oct 12, 2010
Ok I was so shocked at the numbers here regarding cows that I had to look them up else where.

The 150,000 tonnes of methane bubbling up from sediment in the retention lake on the river Aare over a year are the equivalent of emissions from 2,000 cows, or 25 million kilometres (15.5 million miles) travelled by cars, EAWAG added in a statement.

150,000 / 2000 = 75 tons per cow per year

Here is some other very different figures from a news paper article linked below.

The average cow emits between 80kg and 120kg of methane a year, equivalent to the annual carbon emissions from an average family car.

What's going on here? is this article seriously that wrong? 75tons per cow is ridiculous.

article from newspaper: http://www.guardi...ilk-cows
delsontro
not rated yet Oct 12, 2010
@Drumsk8 - you are correct - physorg actually quoted the press release wrong - it is 150 tons, not 150,000 tons (here's one source with the correct number: http://www.swissi...8515842)

@TAz00 - yes, it bubbles a lot for a few months of summer, but it is not enough to capture and utilize. the reservoir is only 2.6 km2 (about 6 km long and no more than 300 m wide) - it would not be cost-effective at all to do such a thing, although it is being done in other areas, such as where I used to work offshore Santa Barbara, CA: http://www.venoco...eps.html
delsontro
not rated yet Oct 12, 2010
@modernmystic and apex01 - Physorg also chose NOT to use another quote from the press release in which we state that we do not wish to dramatize these findings and that a coal-fired power plant would still emit at least 40x more CO2 than the hydropower reservoir does. We are simply filling a gap in the knowledge regarding hydropower on mainland Europe. And as it turns out, these findings are extraordinary within the much debated topic of hydropower reservoirs and highlights an important and somewhat overlooked pathway - ebullition (bubbling). Considering I come from a blue collar family from New Jersey where my mother is still struggling to find a job during the recession, the last thing I desire is higher unemployments rates anywhere. Frankly, I don't know about the researchers you know personally, but the ones I have worked with, as well as myself, would never corrupt any research in such a manner. You know that old phrase about assuming...
delsontro
not rated yet Oct 12, 2010
@Jimbaloid and northwest - both great comments! Determining the overall carbon balance of a system BEFORE and AFTER dam construction is the ideal scenario and this idea is being pushed through a specialized UNESCO committee. Unfortunately, even within the community there is controversy regarding the ultimate funding behind research (i.e., hdyropower-backed projects vs conservation-backed projects). Again, we were merely presenting our interesting results from a very small reservoir in Switzerland. Without having done a biomass consumption estimate specifically at the reservoir, I would guess that the CO2 uptake does not balance out the CH4 emissions, but again that is just a guess. As always, more research is needed (but the funding is over). As for where would the organics have gone, it would most likely be distributed over the former river channel and not highly concentrated in the reservoir as it is now, which is more conducive to bubbling. And p.s. it's Miss Del Sontro