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DAM-L Reservoirs and greenhouse emissions/LS (fwd)
----- Forwarded message from Lori Pottinger -----
From owner-irn-safrica@netvista.net Mon Oct 23 13:41:23 2000
Date: Mon, 23 Oct 2000 10:21:34 -0800
To: irn-safrica@netvista.net
From: lori@irn.org (Lori Pottinger)
Subject: Reservoirs and greenhouse emissions/LS
The Independent, London
13 October 2000
Our reservoirs are plumbing the depths of insanity
Once reservoirs and dams were the answer to pollution-free power. Now evidence
shows greenhouse gases bubbling up from them at an alarming rate
By Fred Pearce
13 October 2000
Fetid, choked with weeds and swarming with mosquitos, the
Balbina reservoir in the Amazon rainforest is a billion-dollar
boondoggle. The dam soars 50 metres above the trees. But
much of the reservoir behind it, which floods an area the size
of Warwickshire, is less than four metres deep. "From the air,
you can see brown trees beneath the water across huge
areas," says Philip Fearnside, from Brazil's National Institute
for Research in Amazonia. He has counted 1500 islands and
"so many bays and inlets it looks rather life a cross-section of
a human lung".
Even the introduction of a herd of grazing manatees has failed
to staunch the spread of weeds across the surface. Water
stagnates in the reservoir's backwaters for years before
reaching the dam's hydroelectric turbines, which have a
piffling generating capacity of 112 megawatts. That means the
reservoir needs to flood the equivalent of two football pitches
to power a one-kilowatt air conditioner in the Amazonian
capital, Manaus.
The depth of the insanity of this hydroelectric dam has only
recently emerged. Built 13 years ago to provide "green",
pollution-free electricity, it in fact produces eight times more
greenhouse gas than a typical coal-fired power station with a
similar generating capacity.
The rotting vegetation has generated millions of tonnes of two
greenhouse gases. These are carbon dioxide and methane -
a gas that, molecule for molecule, is 20 times more potent at
warming the planet than carbon dioxide.
Balbina is not alone. Recent research by Marco Aurelio dos
Santos, at Cidade University in Rio de Janeiro, suggests that
that up to half of Brazil's hydroelectric reservoirs have a
global-warming capability similar to that of a fossil-fuel power
plant. And just across the border in French Guiana, the
Petit-Saut dam, which powers Europe's Ariane rocket launch
site, produces three times as much gas as a coal-burning
equivalent.
In June, the World Commission on Dams warned that the
problem extended beyond rainforest reservoirs. It told UN
climate-change negotiators that greenhouse gases bubble up
from "all 30 reservoirs for which measurements have been
made." The message was clear: "There is no justification for
claiming that hydroelectricity does not contribute significantly
to global warming." The Commission is a blue-chip assembly
of scientists, engineers and environmentalists, and is
supported by the World Bank, the world's biggest funder of
large dams. Its findings have been corroborated by
researchers from Canada, home of some of the world's
largest hydroelectric projects.
Vincent St Louis, of the University of Alberta, has made the first
ever calculation of the total contribution of the thousands of
reservoirs round the world to global warming. In the
September issue of the journal BioScience, he says that they
produce a fifth of all the man-made methane in the
atmosphere. Add in their emissions of carbon dioxide, and
they make up 7 per cent of the man-made greenhouse effect.
That is a bigger impact than, for instance, aircraft emissions.
While probably only a handful of reservoirs - the likes of
Balbina and Petit-Saut - are turning out to be dirtier than
coal-fired power stations, almost all make a significant
contribution. "Whatever dam builders may say, reservoirs are
not greenhouse-gas neutral," says St Louis. He says all
governments should start measuring the emissions from their
reservoirs.
And scientists policing the Kyoto Protocol to halt climate
change should insist that the findings are included in national
emissions inventories.
As of now, that does not happen. Nobody thought it was
necessary. Only last year, the UN's chief scientific advisers for
the protocol, the Intergovernmental Panel on Climate Change,
dismissed reservoir emissions as "a minor source of
methane compared to other energy sector or agricultural
activities." St Louis's paper should put an end to that notion.
His startling calculations rely on three breakthroughs. First, he
has recalculated the area of the planet covered by reservoirs.
The previous estimate of 500,000 square kilometres included
only large hydroelectric reservoirs. But he has estimated the
area covered by reservoirs of all sizes and all uses -
collecting water for cities and farm irrigation, improving river
navigation and preventing flooding. The figure comes to 1.5m
square kilometres - six times the land area of Britain.
Secondly, he has cross-checked the two standard ways of
measuring emissions from bodies of water. One is based on
physical measurements, capturing gases in a box above the
water. But because this is difficult and time-consuming,
researchers have often plumped instead for theoretical
calculations of how fast the gases will diffuse into the
atmosphere.
But according to St Louis, the theoretical calculations are often
far too low. This is because they ignore bubbles, which form
wherever the fetid reservoir water cannot dissolve methane as
it is generated. Bubbles reach the atmosphere independently
of diffusion processes.
Thirdly, St Louis has looked at how long reservoirs carry on
producing greenhouse gases. When the issue first emerged
in the early 1990s, scientists believed that the gases came
mostly from vegetation trapped underwater when the reservoir
filled. They reasoned that the rotting vegetation would soon be
gone and emissions would cease. Reservoirs would become
like natural lakes, in a rough chemical equilibrium with the
atmosphere above.
Not so, it turns out. As reservoirs round the world age, it
appears that most continue to produce significant greenhouse
gases throughout their working life. As Fearnside says, it can
take 500 years for a tree to rot in a stagnant Amazon reservoir.
And in any case, probably most rotting vegetation in a reservoir
is from elsewhere, floating down rivers that drain into the
reservoir.
Most of this vegetation would have rotted anyway, of course.
But, without reservoirs, the decomposition would occur mostly
in the atmosphere or in well-oxygenated rivers or lakes. The
presence of oxygen would ensure the carbon in the plants
formed carbon dioxide. But many reservoirs, particularly in the
tropics, contain little oxygen. Under those anaerobic
conditions, rotting vegetation generates methane instead.
Both gases have a greenhouse effect. But a molecule of
methane is 20 times as potent as a molecule of carbon
dioxide. Reservoirs thus magnify the greenhouse effect of the
rotting of a significant amount of the Earth's vegetation.
St Louis found that emissions from tropical reservoirs contain
the most methane. "We suspect this is because warmer
temperatures in sediments promote faster, more anaerobic
decomposition," says co-author Carol Kelly of the Canadian
government's Department of Fisheries and Oceans. While
only a third of the world's reservoirs are in the tropics, they
appear to produce around 80 per cent of greenhouse gas
emissions.
But in the long run, reservoirs in northern countries could be
as dangerous for the world's climate - especially those that
flood peat bogs. A thick peat bog, says Kelly, contains "large
stores of decomposable organic carbon" - far more than a
rainforest. Over the centuries, most of it will rot in a reservoir
and bubble into the air.
Scientists working for dam-builders say that reservoirs often
flood marshes and other land that is already a source of
greenhouse-gas releases to the air. So their extra emissions
are, at least in part, illusory. But equally, some flood land was
absorbing greenhouse gases from the atmosphere, says St
Louis. Many healthy peat bogs and forests fall into this
category. Some studies suggest that the surviving stands of
the Amazon rainforest are major absorbers of carbon dioxide
from the atmosphere.
The inclusion of reservoir gases could transform national
inventories of greenhouse gases. French Guiana used to be
one of the world most greenhouse-friendly nations. But
according to calculations by Robert Delmas, of the Laboratory
of Aerology Observation in Toulouse, the Petit-Saut reservoir
has turned it into one of the worst polluters. Per head of
population, French Guiana's emissions are three times those
of France and greater than those of the US.
Another secret emitter is Ghana. It has flooded a twentieth of
its land area to create the giant Akosombo hydroelectric dam.
If St Louis's average figure for emissions from tropical
reservoirs holds for Akosombo, the reservoir will emit five
times as much greenhouse gas as all the country's fossil-fuel
burning.
Industrialised countries that rely on reservoirs for much of their
electricity -- such the Canada and Norway -- could also be
embarrassed. Including reservoir gases could make it harder
for them to meet targets for cutting emissions agreed in the
Kyoto Protocol three years ago, and due to be finalised in The
Hague in November.
But the people with most to fear are the builders of dams.
They have endured constant attack from environmentalists for
damaging wildlife habitats and flooding people from their
homes. They had hoped the drive to cut greenhouse-gas
emissions would revive their industry. They have been
lobbying hard this year to have hydroelectricity included in the
Kyoto Protocol's list of greenhouse-friendly technologies that
should get international support. That drive is now in jeopardy.
::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Lori Pottinger, Director, Southern Africa Program,
and Editor, World Rivers Review
International Rivers Network
1847 Berkeley Way, Berkeley, California 94703, USA
Tel. (510) 848 1155 Fax (510) 848 1008
http://www.irn.org
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