http://story.news.yahoo.com/news?tmpl=story&u=/afp/20030813/sc_afp/climate_africa_030813192909
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Climate
change destroying Lake Tanganyika: study
Wed Aug 13, 2003, 3:29 PM ET
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)
PARIS (AFP)
- Global warming is wrecking Africa's Lake Tanganyika,
inflicting a catastrophic decline in fish catches, a study says.
Since the mid-1950s,
catches of sardines and other food species
in one of the world's largest and most productive lakes have
plummeted, prompting some environmentalists to point the finger
at overfishing.
But the newest research,
published Thursday in the British weekly
Nature, says local fishermen are not to blame.
Instead, it points
the finger at the greenhouse effect,
a finding that strengthens accusations that reckless burning
of fossil fuels is changing the Earth's weather system.
According to the study,
warmer atmospheric temperatures
have slackened the winds which blow during the cool
May-September season, stir up the water layers and
play a vital role in the lake's ecological health.
These strong south-to-north
breezes haul algae and other
nutrients from the lake's colder lower layers towards
the warmer surface levels, thus providing food for the
sardine population and other species.
University of Arizona
researcher Catherine O'Reilly and
colleagues looked at years of data about atmospheric and
water temperatures and wind speed, and measured carbon
isotope levels in cores drilled into the lake sediment.
The local temperature
has risen by 0.5-0.7 Celsius
(0.9-1.25 Fahrenheit) over the last half century
-- a figure in line with a global increase of 0.4-0.8 Celsius
(0.7-1.4 Fahrenheit) inflicted by global warming.
Wind velocities, meanwhile,
have declined by 30 percent
since the late 1970s, which is also considered a threshold
when planetary temperatures suddenly shot up.
The core sediments
were checked for levels of carbon isotopes,
which give a reliable indicator of phytoplankton, the basic
nutrient at the bottom of the food chain.
They were stable until
the start of the 20th century,
then started to decline, with a precipitant plunge from
1950 onwards.
That decline points
to a fall of 20 percent in algae availability,
a phenomenon that reverberates up the food chain and eventually
translates into a fall of some 30 percent in fish yields,
according to O'Reilly's estimate.
Scientists have already
predicted East Africa's Great Lakes
region faces a temperature increase of up to 1.7 Celsius
(3.06 Fahrenheit) for over the next 80 years, and this
suggests Tanganyika's food mechanism faces even worse
damage.
"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 authors say.
Tanganyika, a rift
valley lake around 650 kilometers
(400 miles) long by 50 kilometers (30 miles) wide and up
to 1,470 metres (4,777 feet) deep, is bordered by Burundi,
Tanzania, Zambia and the Democratic Republic of Congo.
It is the world's second
deepest lake, the second largest
by volume and a treasure store of biodiversity.
Fishing provides up
to 40 percent of the animal protein
supply for local people, but catches have fallen by between
30 and 50 percent, to 165,000 to 200,000 tonnes per year,
since the late 1970s.
