http://www.commondreams.org/headlines03/0814-05.htm
Published on Thursday,
August 14, 2003 by the lndependent/UK
[ See
the satellite photograph from the original article... ]
Global Warming is Choking the Life Out
of Lake Tanganyika
by Steve Connor
CAPTION:
"This NASA satellite file image shows Lake Tanganyika
in East Africa. Global warming is wrecking Africa's
Lake Tanganyika, inflicting a catastrophic decline
in fish catches, a study says."
(AFP-NASA/File)
Lake Tanganyika in central Africa - where Henry Stanley delivered
his immortal question, "Dr Livingstone, I presume?"
- is in ecological
crisis as a result of global warming.
Studies by two independent
teams of scientists have found local
temperature rises and climate change have dramatically altered
the delicate nutrient balance of the lake, Africa's second largest
body of fresh water.
have discovered that
the surface of the lake is getting warmer
and that has meant the mixing of vital nutrients in the lake
has diminished and cut the lake's fish population.
The effect has had
a dramatic impact on the local economy,
with fishing yields plummeting by a third or more over
the past 30 years and further decreases predicted.
Lake Tanganyika has
traditionally supplied between 25 and
40 per cent of the protein needs of the local people,
citizens of the four countries bordering the lake, Burundi,
Tanzania, Zambia and the Democratic Republic of Congo.
As a tropical lake
accustomed to high year-round temperatures,
Tanganyika was not obviously vulnerable to the effects of
global warming yet this is what the scientists have discovered.
All deep freshwater
lakes rely on nutrients in the lower depths
periodically coming to the surface where aquatic plants and
algae live. This is particularly critical in tropical lakes
which have steep temperature gradients that tend to keep
the warm, less dense layers on top of the colder, denser
water in the lake's depths where the nutrients are stored.
Lake Tanganikya is
the second-deepest lake in the world
and the second richest in terms of biological diversity;
it has 350 species of fish with new ones being discovered
regularly. Nutrient mixing has been vital for its biodiversity.
Piet Verburg, of the
University of Waterloo, in Canada, and
Catherine O'Reilly of the University of Arizona, in Tucson,
who led the studies, found warmer temperatures and less windy
weather in the region is starving the lake's life of essential
salts that contain nitrogen and sulphur.
Dr O'Reilly's study,
in the journal Nature, suggests the
lake's productivity, measured by the amount of photosynthesis
its plant life has done, has diminished by 20 per cent,
which could easily account for the 30 per decrease in fish
yields.
The scientists say
climate change rather than overfishing
is largely responsible for the collapse in Tanganyika's
fish stocks and the position is likely to get much worse.
"The human implications
of such subtle, but progressive,
environmental changes are potentially dire in this densely
populated region of the world, where large lakes are essential
natural resources for regional economies," the scientists
say.
Dirk Verschuren, a freshwater biologist at Ghent University
in Belgium, said both studies could explain why sardine
fishing has declined by between 30 and 50 per cent since
the late 1970s.
"Since overexploitation
is at most a local problem on some
fishing grounds, the principal cause of this decline has
remained unknown," Dr Verschuren writes in an accompanying
Nature article. "Taken together ... the data in the two
papers provide strong evidence that the effect of global
climate change on regional temperature has had a greater
impact on Lake Tanganyika than have local human activities.
Their combined evidence covers all the important links
in the chain of cause and effect between climate warming
and the declining fishery."
© 2003 Independent
Digital (UK) Ltd
###
