From the Cary Institute of Ecosystem Studies
Greenhouse gas impact of hydroelectric reservoirs downgraded
Site design and location can minimize carbon dioxide, methane emissions
An international team of scientists has amassed the largest data set to date on greenhouse gas emissions from hydroelectric reservoirs. Their analysis, published today in the online version of Nature Geoscience, posits that these human-made systems emit about 1/6 of the carbon dioxide and methane previously attributed to them.
Prior studies based on more limited data cautioned that hydroelectric reservoirs could be a significant and large source of both carbon dioxide and methane to the atmosphere.
Through an analysis of 85 globally-distributed hydroelectric reservoirs, the authors revealed that these systems emit 48 million metric tons of carbon annually, a downgrade from earlier estimates of 321 million metric tons. Further putting things in perspective, hydroelectric reservoirs are responsible for less than 16% of the total carbon dioxide and methane emissions from all types of human-made reservoirs combined.
“Our analysis indicates that hydroelectric reservoirs are not major contributors to the greenhouse gas problem,” comments Dr. Jonathan Cole, a limnologist at the Cary Institute of Ecosystem Studies and one of the paper’s authors. “But there are some caveats. To date, only 17% of potential hydroelectric reservoir sites have been exploited, and impacts vary based on reservoir age, size, and location.”
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  IMAGE: Located in the State of Mato Grosso, the APM Manso Dam impounds the Manso River and has a capacity of 5,600,000,000 m3 and a surface area of 357 km2….
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Carbon dioxide and methane are two of the main greenhouse gases created by human activities. Carbon dioxide is produced during the combustion of nearly any organic material; methane has a variety of industrial sources. Both gases are also produced naturally, particularly in wetlands and lakes.
When rivers are dammed to make the reservoirs needed for hydroelectricity, flooding creates lake-like conditions that generate carbon dioxide and methane. Emissions are the highest following reservoir construction, due to decomposing vegetation and soil organic matter. As reservoirs age, emissions decline, with cold-water systems stabilizing more rapidly than their warm-water counterparts.
Lead author MSc. Nathan Barros, of the Federal University of Juiz de Fora further explains, “The bottom line is that per unit of energy, hydroelectric generation produces much less carbon dioxide and methane emissions than previously thought, but impacts are not equal across all landscapes.”
The amount of greenhouse gases generated by hydroelectric reservoirs depends on where they are built, with the team’s analysis indicating that emissions are correlated with latitude and the amount of biomass in the watershed. With Barros adding, “Reservoirs in tropical locations, such as the Amazon, emit more methane and carbon throughout their lifecycles.”
Hydroelectricity supplies an estimated 20% of the world’s electricity and accounts for more than 85% of electricity from renewable sources. Future development is expected globally.
The paper’s authors urge careful consideration of site location and design. “During the environmental impact phase, it should be a goal to minimize the amount of carbon dioxide and methane emitted per unit of energy generated,” Cole notes.
To truly tease apart the emissions generated by hydroelectricity, the authors also call for a study that assesses a site’s carbon budget before and after reservoir construction. Pre- and post flooding analysis would clarify the net carbon impact of hydroelectric reservoirs.
Other contributors to the paper included Drs. Lars J. Tranvik, Yves T. Prairie, David Bastviken, Vera L. M. Huszar, Paul del Giorgio, and Fábio Roland.
The work was supported by grants from FURNAS Centrais Elétricas and from the Swedish Foundation for International Cooperation in Research and Higher Education (STINT).
The Cary Institute of Ecosystem Studies is a private, not-for-profit environmental research and education organization in Millbrook, N.Y. For more than twenty-five years, Cary Institute scientists have been investigating the complex interactions that govern the natural world. Their objective findings lead to more effective policy decisions and increased environmental literacy. Focal areas include air and water pollution, climate change, invasive species, and the ecological dimensions of infectious disease. Learn more at www.caryinstitute.org
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dp says: August 2, 2011 at 7:41 am
I have to bet the farm here that the largest volume of emitted GHG you’re going to get from a reservoir is water vapor. It wasn’t mentioned in the article, but water vapor really is in the top tier of climate affecting gases. I get the feeling sometimes that people just like to talk about CO2 rather than science.
Can you imagine them trying to cap and tax H2O? what a riot!? (probably a double entendre)
government funded nonsense …
One of the things that’s always interested me is the amount of dissolved CO2 that will be released just by simple agitation as the water flows through the gates and turbines. Try as I might, I’ve never been able to find any figures for this. I don’t suppose anyone else has had any similar idle wonderings that might have borne a bit more fruit than my own?
A paper published a week ago in JGR finds a single hydroelectric dam produces as much CO2 as ~10 million people burning fossil fuels in Sao Paulo
http://hockeyschtick.blogspot.com/2011/07/oh-no-single-hydroelectric-dam-produces.html
“When rivers are dammed… flooding creates lake-like conditions”.
I always thought it actually created a lake ?
@ur momisugly Bystander and Dan Santo
============================
Yes, the different way things decompose is acknowledged. And I don’t wish to generate any angst, however, a few things should be pointed out. Regardless of whether we add water or not, we still don’t create matter nor energy. Secondly, while the mechanisms are different, decomposition underwater also contributes to growth of life underwater. While there may be some quicker decomposition, there isn’t more decomposition. And while some materials will be discarded underwater, others that would, will not be.
As it is, there are few things I can think of that could better waste more time and money as to attempting to quantify GHGs from building a hydro-electric dam. What the hell? After the dam is built and put in to use for generating electricity, what do we believe the net effect is vs. traditional electricity generation? We should do a study on how much GHG’s are released to the atmosphere by creating national parks and the maintenance required for such ventures.
Sorry if there is confusion about my moniker….. I forget where I’m at sometimes.
James ‘suyts’ Sexton
Excellent, ask and ye shall receive… many thanks for the hockeyschtick link. That’s one of the things that I love about this place…. for those not interested enough to click the link above, the answer would appear to be a resonable amount 😉
We paid for this claptrap?
It is really silly to worry about CO2 from dams or anything else for that matter.
James S;
Exactly. Quicker, a one-time burst. Then that’s all she wrote.
All aside, of course from the inherent inanity of fearing either CO2 or methane. The bleedin’ biosphere developed from those two resources.
I’m not sure why there would be any additional methane or CO2 coming from dams since the vegetation in question would eventually die off and rot, anyway?
So they’re trying to tell us an acre of lake (or pond) produces more CO2 and methane than an acre of forrest, swamp, farm, marsh, or grassland? My BS meter is pegged.
Mike Bromley, indeed you did. 44% of their budget comes from Federal grants! The real problem does not seem to be CO2 but a higher education system which has run out of control. A Phd can be gained by putting ones name to a pointless piece of, as you say, claptrap like this. then you have your food ticket for life. A previous posting states that tides have not always been the same! The mind boggles. Another bunch have discovered that it is dryer in Texas than it was 12 years ago! I deeply resent paying taxes to keep these morons off the street when they would actually achieve more with a broom and a wheely cart on the street than they do now with their X-box and Nintendo computer models.
. The next victims of this recession should be the “scientists” who pump out pointless research on government money. Each and every “scientist” should be made to work for a minimum of 10 years in a commercial industry before being granted a PhD, and then only if they can demonstrate a level of achievement or innovation above and beyond the norm.
Sounds like we’re dammed if we do and dammed if we don’t.
vboring says:
August 2, 2011 at 8:00 am
“They seem to ignore the CO2 emissions avoided by preventing floods…”
Exactly ! Can you imagine what happened whenever the Colorado river flooded before the Hoover Dam? Lake-like conditions again, and again, and again…..Whole areas was flooded, ruining peoples lives. But who care about people…..
Kaboom says (August 2, 2011 at 9:41 am): “I’m not sure why there would be any additional methane or CO2 coming from dams since the vegetation in question would eventually die off and rot, anyway?”
Presumably a hypothetical forest on the reservoir site would be in carbon equilibrium, i.e. trees dying, decaying, and emitting CO2 and CH4 would be replaced by new trees sequestering new carabon. Covering the forest with water would lead to a one-time unbalanced release of carbon.
I assume, though, that reservoirs have some biological activity, e.g. algae, peripheral marshland, fish, underwater plants, etc. which eventually reaches an equilibrium of its own. Not sure how that compares with the land ecosystem it replaces. As the article points out, your mileage may vary depending on what the reservoir replaces.
And if the hydro installation replaces a coal-burning power plant…
To put this into some sort of perspective, shouldn’t they have stated what the area of hydro-electric dammed lakes is compared with naturaly occuring lakes?
This news comes as a real relief. I have been very worried about this. Finally, I can get some sleep.
Any news on the Three Gorges Dam in China? Not from the the CO2 it might release, just the effect of the increasing mass of water on the ground underneath.
If there’s loads of methane being outgassed as the water passes through the turbines, couldn’t it be collected and used to drive a gas turbine? If this is not viable, maybe the methane could be burnt off if methane is so much worse than CO2?
“the authors revealed that these systems emit 48 million metric tons of carbon annually“ (my bold)
Blimey – what is happening to all that carbon? Are we harvesting it? Is it being burned in coal power stations?
/sarc
@ur momisugly Dan Santo,
Aug 2, 2011 @ur momisugly 6.38 am
I’m calling you out on this on, or at least any source of information that you have imparted to this thread. Please provide citations as to your claim that it takes 10-15 years for a log to decompose in H2O as to 50 years in air (with all the claimed benefits in air). If you can provide documentation as to your claims that would withstand the scrutiny of a serious review, I will apologize. DO NOT consider this an apology at this point
There is a log that I used to cross a medium size stream that was washed out on the ends by high water about 35-40 years ago and ended up creating a low dam if you will. It has long ago filled in on the upstream side but the log is still visible. Still solid as the day submerged. I know as I nailed a plank to it a couple of years ago in low water so I could cross to hunt. The other timber (trees) that were felled and ended up on the shore have long since decomposed. Also a manmade lake in my area was flooded in the very earlier 60’s with standing timber in the depths that would be completely covered when the lake was filled. These are the GO TO regions to catch fish. Fish locator shows submerged timber just as it was on maps created over 50 years ago.
I had the opportunity to float the Upper James River in Virginia, where in the very early history of this country, long before the invent of the railroad, the river was used for transportation of goods/raw materials (pig iron, coke, etc) to Richmond, Va to be used in the progress of this country. There is a series of locks (primitive by today’s standards) utilizing wooden timbers submerged in the river bottom to divert some of the river flow into the adjoining canal to get around the shallow water rapids. The timbers are still there today and not at all decomposed! I believe that President George Washington signed an appropriation bill to complete this project.
There is a place in the National Forest in Virginia that has a dam built with 4 or 5 large white pine logs to provide a pool for the transfer of water to a gravity fed pipe to an off stream pond/lake. I would guess it has been there for over 40 years Still there and looks good. The NF recently spent a couple of hundred thousand dollars above the purchase price of the property for renovations and did not replace the log dam. I would guess that if it were the least bit justified, they would have spent all they could get.
Logs are still sought for harvest from some area in the Great Lakes that were submerged and lost (I believe over a 100 years ago). They are used for exotic and specialty wood products. At one time the Japanese purchased from the USA and submerged timber for preservation (probably does not apply as to the discussion of this thread due to salt water).
Perhaps another look into the past ‘science’ is in order. Possible reservations for a spot on the chopping block of past junk science may be in order. The greens have/are burning their bridges and the above referenced post/comment just may be the match for another bonfire. Common sense and observations are going to be hard to trump.
If you are new to this site, welcome to an eye opener to the truth. Beware of what you post as Anthony has an army of many ones!
Bystander,
Once again you make bad assumptions. Nobody here is reflexively against any form of energy. What we oppose is the subsidizing of energy forms that cannot compete on their own.
This does not apply to hydro. Therefore the only people who are reflexively against it are your fellow eco warriors.
Dams were reviled for years by greens, and they made study after study to make hydro-electric look bad and as such some areas of the world to this date have not maximized their potential for what is probably the BEST source of power that is CO2 free. These studies should come as no surprise, as the original studies were at best just shoddy science.
They are also anti-nuclear, another source of power that is “CO2 free.” It just makes no sense when you look at what they advocate. This is the problem with combining science with politics. We can not learn anything of value until people learn that science has to be unbiased otherwise you get religious like pronouncements.
And I can not begin to describe how much dams (When run correctly) can stop floods in their tracks. Any flooding that occurs could easilly be stopped by a good system of large dams. This is the issue on the larger rivers in the world which still flood because we do not control them. I still do not see how the argument that allowing the rivers to flood periodically is better then just having a permanent area flooded. Just ZERO common sense…and that is why green organizations should be kept away from science.
oeman50 says:
It also matters if the flooded land for the reservoir was logged or not before it was filled. Rotting wood at the bottom of a lake can generate a lot of methane. However, most states now require saleable timber to be logged before filling, but I know of some that were filled before this became a requirement.
At least one company has developed a remote controlled mini-sub to log trees in such lakes. Since this is commercially viable it looks like wood dosn’t rot that quickly in fresh water lakes.