Turns out hydropower may not be as low-carbon as we thought

Dams squeeze methane out of river water 11

There is a major controversy brewing on how carbon neutral large scale hydroelectricity really is. It has been known for a long time that dams emit both methane and CO2. The question has always been, how much of those emission are net? According to the International Rivers Network (PDF), studies by ecologist Philip Fearnside of the National Institute for Research in the Amazon (INPA) have shown that net methane emissions from hydropower are slightly higher than those from burning natural gas.

Rivers generally have organic matter trapped in their silt and mud. This rots in the dark, wet environment, producing methane that's dissolved in the water. In undammed rivers, bacteria consume the methane, converting it to CO2. (CO2 is a much less potent greenhouse gas than methane.) According to Fearnside's research, the higher pressure created by large-scale dams forces the dissolved methane out.

As an analogy, he points to fizzy soft drinks. The CO2 in soft drinks is under pressure. Let an opened can sit, and within a day or less the soft drink will be flat. The same thing happens to methane in dams, only the "can" is already open.

Fearnside suggests that net emissions from all this are very high -- probably higher than from burning natural gas. The hydroelectric industry contends most of the dissolved methane in river water would have escaped into the atmosphere in any case, before bacteria had time to convert it into CO2. Clearly this is an area where the IPCC needs to fund more research, quickly. If hydroelectricity is a major greenhouse gas emitter, that is very bad news -- and we need to know about it quickly so we can take appropriate action.

Gar Lipow, a long time environmental activist and journalist with a strong technical background has spent years immersed in the subject of efficiency and renewable energy. He has written extensively on the economics of solving the global warming, and why pricing externalities (though important) cannot be the main driver of such solutions.

His on-line reference book compiling information on technology available today, “No Hair Shirt Solutions to Global Warming”, is available at http://www.nohairshirts.com.

His articles on the economics and politics of solving the climate crisis have been published in Z magazine and a number of small journals.

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  1. Laurence Aurbach Posted 3:20 am
    13 Nov 2006

    concreteThen there's the energy embodied in all those square yards of concrete used to build the dam. I don't know exactly how much energy that is, only that it's got to be a huge amount.

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  2. TariffDude Posted 3:51 am
    13 Nov 2006

    SorryDammed if we do, dammed if we don't..

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  3. JMG's avatar

    JMG Posted 4:33 am
    13 Nov 2006

    ConcreteI recall running across a stat that making concrete is responsible for 7% of greenhouse gas emissions, but I can't find it right now.  
    Also, whatever the absolute value of post-construction emissions are, it's worth keeping in mind that methane is 20 times more potent in trapping heat than an equivalent molarity of CO2 . . .

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  4. Gar Lipow's avatar

    Gar Lipow Posted 4:55 am
    13 Nov 2006

    Methane>Also, whatever the absolute value of post-construction emissions are, it's worth keeping in mind that methane is 20 times more potent in trapping heat than an equivalent molarity of CO2 .
    Sure, but no one is arguing that methane and CO2 are equivalent. The argument IS over net methane. That is X amount of methane is emitted from dams. (There may be some dispute over X, but not a lot.) The question is how much methane would have been emitted if the dam was not there.
    In other words, would most of the methane have been released in any case? Or would it have stayed in the water long enough for bacteria to convert it to CO2 - as you say a greenhouse gas 1/20th the  intensity of methane.
    In short the question is not total emissions, it is total METHANE. Do dams result in LESS methane being converted to CO2 than natural rivers, and thus emit MORE methane?
    So far we have answers from Fearnside and from the Hydroelectric industry. While I'd back Fearnside any day as the more credible source, science works based first on peer reviewed work then on replication. Both Fearnside and the industry have published peer reviewed papers on the subject. What we need are third parties to do independent studies - so we can see which set of results are replicated.

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  5. Bart Anderson's avatar

    Bart Anderson Posted 6:22 am
    13 Nov 2006

    Moot point?I wonder if this is a moot point, in terms of new dams, since as I understand it, most of the sites for hydroelectric power have already been exploited. The dams have been built, the concrete manufactured and the end of the dam's lifetime is in sight (due to silting up).
    Also, if the climate effects of dams are comparable to burning natural gas, then that would argue for maintaining or even extending hydroelectric power, since natural gas is one of the cleaner sources of power.  (Not taking into consideration the other environmental effects of dams.)
    I await your corrections!

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  6. Gar Lipow's avatar

    Gar Lipow Posted 2:11 pm
    13 Nov 2006

    Not quite mootWhile undeveloped Hydropower represents an extremely tiny percent of current world consumption, there are some extremely large projects under consideration - especially in Africa. Many of these projects would displace large numbers of people. One of the big arguments for going ahead with them is carbon neutrality. So it remains an important question to answer. As far as existing dams go, the question is not quite so clear. But in many cases they have really  horrible additional effects.
    Also, though natural gas is less carbon intensive than coal or oil as an electricity source, ultimately we are going to have to phase out all major carbon emitting sources. If existing dams are part of this, we may not have to shut them down right away, but it is not good news for the future - especially since dams are use for more than electricity. We depend on them for drinking water and flood control. (I'm not clear on whether it is dams in general or only those producing hydroelectricity which have this affect. I hope for better information in the coming week.)
    Also hydro-electric power is one of the few forms of renewable energy that is fully dispatchable. It is useful for base power, load following and peaking. It can be used to shape wind electricity and make it dispatchable (up to a point).

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  7. amazingdrx's avatar

    amazingdrx Posted 11:34 pm
    13 Nov 2006

    Dam alternative!This is another great reason to modify water power, maybe this way?
    http://amazngdrx.blogharbor.com/blog/_archives/2005/7/15/...
    To restore wetlands, control flood damage, generate clean electric power, restore aquifers, and stop the eco-destruction of regular dams that block fish and wildlife from their natural migration.

    http://amazngdrx.blogharbor.com/blog

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  8. willa Posted 11:52 pm
    13 Nov 2006

    TariffDude,Ouch. :)

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  9. amazingdrx's avatar

    amazingdrx Posted 11:54 pm
    13 Nov 2006

    OhI forgot, by restoring wetlands the carbon sink effect will actually sequester a huge amount of greenhouse gases.
    That problem of methane emission from organic matter in silt is due mainly to high nitrogen concentrations in lakes and rivers from agrichem and manure runnoff from farms, lawns, golf courses, and feedlot farming.
    The manure can be digested and the methane consumed in fuel cell/turbine generators (75% efficient)to back up the grid that eventually will be mainly supplied with renewable energy.  The cO2 recycled through algae solar systems that make more fuel.
    The chemical fertilizer can be entrapped out of the watershed by filtering algae from the lake or river into bioreactors that float on the water and produce extra methane to feed the solid oxide fuel cell/turbine generators.  
    This water bourne algae is a huge energy source, and using it would allow the removal of pollutants along with the algae.  Heavy metals can be separated from the bioreactor sediment using renewable energy.
    The bioreactor filter would allow everything but the algae to escape digestion into biogas, clean water, and fertilizer.

    http://amazngdrx.blogharbor.com/blog

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  10. swozniak Posted 2:31 pm
    14 Nov 2006

    Sequestering?Is there an environmentally friendly way, for the short-term, that we might capture the methane and use it for energy, such as in a digester?

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  11. amazingdrx's avatar

    amazingdrx Posted 2:59 am
    15 Nov 2006

    Well yeah swozniak.But unless all the silt is run through a digestor, the methane already dissolved in the water will be released at the dam from the turbulence.  It might be too difficult to extract the methane and trap it in the dam itself.  
    That would take a huge structure over the dam outflow.  And gas separation, normally a very energy intensive process.  It might be possible with nanotech filtration though.
    That's why I think stopping the nitrogen from fertilizer runnoff is the way to go.  Digestion of organic material and release of methane is facilitated by the proper ratio of carbon to nitrogen.
    Cellulose, the main carbon containing element will not break down into methane without enough nitrogen.  Wetlands and lakes with naturally low levels of  nitrogen tend to store carbon underwater.  When fertilizer runnoff increases the nitrogen the methane is released through bacterial digestion.
    Algae and other plants in the water ecosystem incorporate nitrogen into their structure. If that algae were filtered out of the water and digested the nitrogen from the fertilizer is removed from the ecosystem, along with a lot of pollutants like heavy metals.

    http://amazngdrx.blogharbor.com/blog

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