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Guru
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Shades of Green?

10/12/2010 10:46 AM

Geneva - 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 greenhouse gas, the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) said on Monday.

The 150 000 tons 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 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 gas bubbles rising to the surface," she added.

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

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.

- - - - -

Only 2000 cows? - WOW - The paper used for the report may have caused more damage than 2000 cows.

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#1

Re: Shades of green?

10/12/2010 11:10 AM

The sediment that they reported wouldn't it already have been in the water? Which if the dam was not there carried down stream and deposited else where to decompose giving off the same amount of green house gases. This is a natural process of organic matter. Does it really make any difference whether it happens in a man made lake or in any natural body of water. It still would have happen. Still would be expelled into the atmosphere.

Sounds like someone looking to attack the feasibility that hydroelectric is the least damaging to our environment. Maybe to fight a dam being built. Sound like they trying to baffle them with bull####.

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Guru

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#3
In reply to #1

Re: Shades of green?

10/12/2010 11:04 PM

I think the problem with the methane/carbon dioxide is an initial phenomenon with most dam flooding. The vegetation that grows in the pre-flooded area is not the sort that would decompose suddenly. Trees, brush, etc would maintain a lock on the carbon but all would eventually die and decompose to release the carbon locked up. So when you flood an area the initial year or two will see a spike of gases released by the decomposing land vegetation. The aquatic vegetation will take over eventually and lock up the carbon as before. It is only during the change that you will see such effervescing of gases. I have seen such phenomenon in a new dam site flooded area that was particularly strong just as the ice was thawing. It only happened once and stabilized in subsequent years.

You are correct that the carbon would come out of its locked position in the vegetation but slowly and not sudden as the flooded area will cause.

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#11
In reply to #3

Re: Shades of green?

10/13/2010 8:32 AM

That is understandable but is a short term effect. These dams are built to last 50 years or more. So to classify the green house gas output on the the first years is falsifying the data to what end.

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#12
In reply to #1

Re: Shades of green?

10/13/2010 11:36 AM

The redox conditions at the bottom of a lake are different than the surface where oxygen is available. Under the reductive conditions in the bottom of the lake they are generating methane rather than carbon dioxide. Methane has a much higher CO2 equivalence than CO2. It is not the carbon released as much as the form of carbon compound that has to be considered.

Also, I would not believe anyone who claimed hydroelectric was the least damaging form of energy generation for the environment. That on the face is just not going to hold in comparison to other green energy generations forms, solar, wind turbine, nuclear, etc.. Hydroelectric substantially changes the environment.

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#2

Re: Shades of Green?

10/12/2010 4:37 PM

WOuldn't the methane just bubble up anyway, regardless if the dam was there or not? Anyways, interesting post, something to think about!

www.mylocalhvac.com

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Guru
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#4

Re: Shades of Green?

10/13/2010 12:28 AM

There is nothing new here. The original UN Climate Change report discussed the contribution to greenhouse gases from both man-made reservoirs and natural wetlands. What is worrisome is that the focus on greenhouse gases tends to hide the real negative impact of hydro plants:

1. It takes roughly 5 hectares of land to generate one megawatt of electricity (better, of course, than wind, at 50 hectares per megawatt, or solar at 20 hectares per megawatt). These numbers are based on an analysis of five projects currently under development in Panama, and it is likely that the number of hectares per megawatt is highly dependent on geography. In many, many cases, this means that each megawatt of electrical generating capacity results in the destruction of forests, which once were carbon sinks.

2. I know first hand of at least one case where the installation of a hydro generating facility (a rather small one, actually) resulted in a negative impact on the recharge rates of fresh water wells down stream from the dam. The trees were no longer available to slow down the runoff and allow the water to soak in to the ground. The dam essentially reconfigured the watershed to the point where six wells had to be abandoned, and water had to be piped in from several miles distant.

3. The Three Rivers Dam in China bears watching- there is evidence suggesting that projects on this scale have a significant negative seismic impact. The jury is still out on this one.

I do not mean by this post to denigrate any particular approach to the generation of energy. What I would REALLY like to see is people being honest about what the real trade-offs are. Methane from the reservoir is NOT the major impact of hydroelectric...

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Guru

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#6
In reply to #4

Re: Shades of Green?

10/13/2010 1:14 AM

One of the problems with studies generated at universities is that often some very bright kids are looking for an answer to something - what they don't know.

Spectacular results like the OP generate attention from professors, green girls maybe and so on.

Probably their study really has nothing to do with science at all but is more looking for a tea cup to start a tempest.

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#5

Re: Shades of Green?

10/13/2010 1:09 AM

First let me say I believe dams are beneficial, but that better emvironmental precautions need to be taken.

Now for a quick note on the effects of dams.

2.5 Water Temperature and Water Quality Changes

Dams can modify thermal and chemical characteristics of river water : the quality of dam-releases is determined by the limnology of the impoundment, with surface-release reservoirs acting as nutrient traps and heat exporters and deep-release reservoirs exporting nutrient and cold-waters (Petts, 1988). This can affect fish species and populations downstream.

Water temperature changes have often been identified as a cause of reduction in native species, particularly as a result of spawning success (Petts, 1988). Cold-water release from high dams of the Colorado river has resulted in a decline in native fish abundance. (Holden and Stalnaker, 1975). The fact that Salmo spp. had replaced some twenty native species has been attributed to the change from warm-water to cold-water.

Water-chemistry changes can also be significant for fish. Release of anoxic water from the hypolimnion can cause fish mortality below dams (Bradka and Rehackova, 1964).

During high water periods, water which spills over the crest of the dam can become over-saturated with atmospheric gases (oxygen and nitrogen) to a level which can be lethal for fish. Mortality can result from prolonged exposure to such lethal concentrations downstream of the spillways. Substantial mortalities of both adult and juvenile salmonids caused by high spillway flows which produced high supersaturation (120-145%) have been observed below the John Day dam on the Columbia river (Raymond, 1979). The Yacyreta dam on the Parana river generates supersaturated levels of total dissolved gases that can affect the health condition of fish: in 1994, massive fish mortality was observed in a 100 km reach below the dam (Bechara et al., 1996).

http://www.fao.org/docrep/004/y2785e/y2785e03.htm

Have a great day.

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Guru

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#7

Re: Shades of Green?

10/13/2010 1:31 AM

"Lining" the base of the lake with the equivalent of the under-gravel filters used in large fish tanks (installed with their slots on the "down" side and then using the integrated web of tubing- feeding into small headers- to capture the methane and burn it in a small CoGeneration module for electricity and recovered heat.

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Anonymous Poster
#8
In reply to #7

Re: Shades of Green?

10/13/2010 2:58 AM

Match, strike, flame, no methane.

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Guru

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#9
In reply to #7

Re: Shades of Green?

10/13/2010 3:55 AM

That I want to see! Lining a lake of a few square miles (or much larger) and managing to not have the liner tear as natural settlement occurs.

OK for a fish tank I guess but in real life?

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Guru
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#16
In reply to #9

Re: Shades of Green?

10/15/2010 9:03 PM
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Guru

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#10

Re: Shades of Green?

10/13/2010 4:06 AM

Dams are primely meant for water& storage control-multipurpose schemes and hydropower is just an additional use. If some one is so concerned about CH4 emissions, what about the other emission outlets- transport, power plants?

Hydropower plant certainly is out of scope for direct methane gas emissions and the question of methane emission versus hydropower is ruled out.

Vegetation is the very basis of our survival on the planet- humans, cows, bulls and vegetations are integrated embodiments in the life systems.

The dumping of organic wastes, eutrophication etc are to be taken care and not hydro power plants. Some folks are deliberate about finding faults and favour nuclear it seems.

Human wisdom should come to the rescue on selective priorities and mode of actions.

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#13

Re: Shades of Green?

10/13/2010 6:20 PM

I think what this is saying is they didn't clear the valley - just flooded it.

You can sell the trees to wood people, be that for timber of chips.

You can sell the topsoil to "agriculture", including turf growers and garden supplies.

Or anything badly done has more impact that otherwise.

Or it's not about "hydro", or "irrigation", or "town supply", being "not as green" as thought - but about "doing it stupid".

Then dragging people who did it properly into the "it's all terrible" BS PR of some other lobbies arsenal.

Stupid on stupid.

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Guru

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#14
In reply to #13

Re: Shades of Green?

10/13/2010 8:03 PM

Hmm, well even in California and Oregon I have never seen a dammed reservoir where they removed all the vegetation and top soil before flooding the basin. Can find Lakes all over Oregon with dead trees in them, and run in to old dead trees in California fairly commonly. Eventually admittedly those trees disappear, but as they comprise fish habitat, it is unlikely that any environmental quality EIR would have them removed. You would likely get into a fight with the fish and wildlife biologist if a EIR suggested removing all the trees and vegetation. Heck I have had them require us to install tree stumps below water line in major rivers to re-establish habitat that wasn't present before the banks eroded.

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#15
In reply to #14

Re: Shades of Green?

10/13/2010 11:34 PM

A fight? - moi?

(Only with tree huggers that spike trees)

As in all things there is a balance.

What you want the water for, effects the 'what to leave and what to remove'.

For a purely potable supply 'clean as possible' has long term treatment cost advantages, but obviously increased vulnerability to silting is a down side.

Both above Warragamba Dam - Sydney, Australia.

Or: principally irrigation/recreation; Hume Weir - Murray Valley, Australia.

"full" is at the change of tree colour

Or Hydro; Lake Eucumbene - Snowy Mountains Scheme, NSW, Australia.

Where water levels are subject to big changes, drowning the regrowth seasonally makes for all sorts of rubbish problems. Oh, and possibly makes some methane - not unlike dead fish might make in a natural lake

(if they drop below the active thermocline )

p.s in the link above; don't miss the bit after "The accumulation of dissolved carbon dioxide in three meromictic lakes ...

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