permaculture

[Dianne Forster <dforster@metz.une.edu.au>]

Wouldn't this be good for converting into usable energy??????



At 11:34 2/06/00 -0700, Jeffrey Newman wrote:
>RAISING A STINK
>By Fred Pearce
>New Scientist magazine
>03 June 2000
>
>Rotting vegetation in hydroelectric dams stokes global warming
>
>http://www.newscientist.com/nl/0603/stink.html
>
>FAR from being "green", many hydroelectric power schemes release more
>greenhouse gases into the atmosphere than large coal-fired power stations,
>because of the rotting vegetation they contain. So says the World Commission
>on Dams, a group of scientists, engineers and environmentalists supported by
>the World Bank, the world's biggest funder of large dams.
>
>The report comes just as engineers are arguing that dams should qualify for
>support as a "clean" technology under the Kyoto Protocol agreed in 1997. The
>commission will report its findings later this month at a meeting in Bonn to
>discuss the Clean Development Mechanism, a key part of the Protocol aimed at
>reducing carbon emissions worldwide.
>
>One surprise finding is that organic matter washed into a reservoir from
>upstream generates much of the greenhouse gas. The decay of forests
>submerged when the reservoirs fill up creates "only a fraction" of the gas.
>This means that the emissions don't disappear when the flooded forest has
>rotted away, but may continue for the lifetime of the reservoir.
>
>Hydroelectric reservoirs cover an area of the world the size of France. They
>release carbon dioxide and methane. Stagnant water produces the worst
>emissions because the decaying vegetation generates methane. This is 20
>times as potent a greenhouse gas as CO2, which is produced when there is
>oxygen in the water. So a reservoir will produce more methane than the river
>did before the dam was built.
>
>Warnings about the gas emissions from reservoirs surfaced in the mid-1990s
>(New Scientist, 4 May 1996, p 29). But what appeared at first to be a
>problem for a handful of reservoirs now looks much more general.
>
>"Tropical reservoirs that are shallow and uncleared of biomass [before
>flooding] appear most at risk," says the commission. It names two rainforest
>reservoirs as major planet-warmers. One is Balbina in Brazil, which is just
>four metres deep in parts. Its generating capacity is 112 megawatts and it
>is estimated that it will produce 3 million tonnes of carbon per year over
>its first 20 years. A coal-fired power station of the same capacity would
>produce 0·35 million tonnes per year. Petit-Saut in French Guyana, which has
>a similar capacity and powers the launch site for Europe's Ariane rocket,
>will produce 0·9 million tonnes per year in its first 20 years.
>
>The report's authors have only studied a handful of reservoirs so far, in
>just four countries, so they believe there may be many more offenders. They
>warn, however, that emissions from reservoirs seem erratic and
>unpredictable: one study of nine reservoirs in Brazil found that their
>emissions per unit of electricity vary by a factor of 500.
>
>"Greenhouse gases are emitted for decades from all dam reservoirs in the
>boreal and tropical regions for which measurements have been made. This is
>in contrast to the widespread assumption that such emissions are zero," says
>the commission. "There is no justification for claiming that
>hydroelectricity does not contribute significantly to global warming."
>
>Jamie Skinner, environmental adviser to the commission, which is based in
>Cape Town, South Africa, says the report is significant because both dam
>engineers and environmentalists agree on its conclusions.
>
>
>
>--
>
>                       *******************************
>Jeffrey Newman
>
>JN Web Design
>http://www.jnweb.com/
>Phone: 1 250 791-9206
>Fax:   1 250 791-9207
>E-Mail: newman@bcinternet.net
>ICQ: 9879310
>
>
>
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