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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Finally! We finally have something we can use! Thank you Lord! Oh, thank you!… wait a minute… uhoooh… that means the Warmistas will want to build Arks, well at least one, and seed the atmosphere, and they probably wont let two Coolists on board… WE’RE DOOMED!!!! We just can’t win. Oh well, what’s on TV Martha?
Re: Mike Rossander, August 2, 2011 at 2:20 pm,
Thanks for that info.
I now see why the hydro would probably produce a more efficient transfer of the existing biomass into CO2, and why there would be a net decrease in sequested CO2 from any reservoir.
Not sure why this is a big issue, but I suppose until it was studied, no one really knew how big of an issue it could be.
Anyway, thanks again.
On second inspection, however, the paper seems to indicate that they are concerned with ongoing emissions from hydro-electric. I can see the one time effect of converting a certain terrestrial biomass to an aquatic state and lowering the overall amount of CO2 sequestered (in trees for example), but the amount of CO2 and methane actually generated by the hydro-plant’s ongoing operation should be near nil, except for the before mentioned maintenance requirements.
Still not sure why this has any validity whatsoever.
Let’s say you could instantly convert a free flowing river to a hydo-capable impoundment with a mature biomass; the difference in CO2 content from state 1 to state 2 would be the only difference, as the hydro dam doesn’t actually produce CO2 or methane in it’s operation.
“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.”
Now I don’t get where either the 48 or 321 metric tons comes from, once the existing vegetation becomes flooded and releases its CO2. That should be the end of it; beginning state minus end state equals total amount of emmission, not an annual figure, but a total figure divided over a period of one or two years and then done.
Their paper still doesn’t make much sense. Once the landscape is changed the CO2 state should remain at equilibrium, producing no additional CO2, hydro or not.
At last I can compare a Hydro electric lake to an SUV. Now all we need to do is convert to a rate for electic cars and we’ll have a universal measuring system to compare buses to swimming pools.
Obviously, we’re damned if we do and damned if we don’t, so the only thing that’s going to make the environmentalists happy is for us plebes to kindly report to the suicide booths. Our remains can go to make soylent green.
re: Bob Kutz’ “On second inspection…”
I concur and was assuming that the researchers were ‘amortizing’ the one-time hit over some unspecified period to show a per-annum rate. I can’t find anything in the paper to confirm it, though. I do find several comments about hydro dams encouraging more mixing and therefore being less effective as carbon sinks than the more static water bodies behind a non-hydro dam but that doesn’t challenge your first assumption that at equilibrium it should approximate the original free-moving river.
Their main point, however, is merely that the analysis done on temperate-climate dams will be significantly different from the analysis on a dams in a tropical climate. Given the difference in total flooded biomass (much greater in tropical areas) and the difference in ratio of leaf biomass (which rots readily) to trunk biomass (which doesn’t), this is unsurprising. But now it’s a bit better quantified.
The sahara loses more heat at night than it gains during the day – the only reason it stays warm is wind. Why do deserts lose so much heat at night – simple, lack of water – the GHG that accounts for 99% of all warming
“…flooding creates lake-like conditions that generate carbon dioxide and methane.”
So, why didn’t the EPA outlaw the recent flooding of the Mississippi River?
Perhaps reading the following post, “Carbon sequestration through hydroelectric generation: A variable never considered.” show first ever written about the problem. But there’s only one problem, it is written in Portuguese (but now with the Google translation !)
Lost Link for comment
http://engenheiro.blogspot.com/2010/08/captura-de-carbono-via-geracao.html
Google “Lake Nasser,” and “Aswan Dam,” and “Toshka Lakes,” and “New Valley Project.”
What fun it would be to get paid for trying to figure out how all this diversion of the Nile River is adding and subtracting to levels of H2O, Methane and CO2 in the atmosphere, and is adding and subtracting to the world’s stored carbon supply.
Great work, if you can get it.
It’s simple. If studies show that hydroelectric power is responsible for producing greenhouse gasses, it can be taxed in the future.
The only anomaly of this theory is that there isn’t taxation yet on greenhouse gasses, but can be explained that the last attempt to introduce a global tax system luckily failed. The idea of a global co2 tax is still an orgasmatic solution of a non-existent problem by leftish thinkers.
I believe the following paper is of relevance:
http://www.un.org/esa/sustdev/sdissues/energy/op/hydro_tremblaypaper.pdf
Highlights:
Temperate and boreal hydroelectric reservoirs produce far below the average of traditional thermal alternatives (8% max, Full Energy Chain, in gCO2 equiv./ kWh(e).h).
Dams in tropical regions vary significantly, from 1% to 200% of traditional thermal alternatives.
Much of the average emissions come from the initial decay of organic matter; It is expect that emissions will decline over time.
Hydro-electric generation is on average comparable in total average emissions with other renewables in tropical regions; There exists however a considerable variance. In temperate and boreal regions however, hydro-electric generation is by far the lowest in total average emissions /kwh )
Interesting that Nuclear also fares favorably compared to renewables (probably due to manufacturing processes).