World’s largest freshwater lake under dire threat from climate change

May 4th, 2009 - 1:08 pm ICT by IANS  

Washington, May 4 (IANS) Siberia’s Lake Baikal, the world’s largest freshwater lake, faces severe ecological threats due to climate change, a new study has found.
The planet’s most biologically diverse water body, Lake Baikal is considered a treasure trove for biologists. It was designated a World Heritage Site by Unesco because a high proportion of its rich fauna and flora cannot be found anywhere else.

Perhaps the most alarming imminent threat stems from the dependence of the lake’s food web on large, endemic diatoms, which are vulnerable to expected reductions in the length of time the lake is frozen each winter.

The study was based on a joint analysis by a US-Russian team which included Marianne Moore of Wellesley College, Massachusetts, and five co-authors, including four from Irkutsk State University in Russia.

Moore and colleagues note that Lake Baikal’s climate has become measurably milder over recent decades, and that annual precipitation is expected to increase.

The average ice depth in the lake is known to have decreased, and the ice-free season has increased. Changes in the lake’s food-web composition have been documented.

Future shortening in the duration of ice cover is expected to curtail the growth of the lake’s endemic diatoms. This is because unlike most diatoms, they bloom under ice in springtime and are highly dependent on ice cover for their reproduction and growth.

The diatoms constitute the principal food of tiny crustaceans abundant in the lake, and these in turn are preyed upon by the lake’s fish.

Shortened periods of ice cover and changes in the ice’s transparency may also harm the Baikal seal, the lake’s top predator and the world’s only exclusively freshwater seal.

Because the seals mate and give birth on the ice, premature melting of the ice forces them into the water before melting and drastically reduces their fertility.

A warmer, wetter climate may be the principal threat to Lake Baikal’s unique biological heritage, but it is not the only one. The secondary effects of climate change, including greater nutrient input and industrial pollution from melting permafrost, may also exact a toll on an already-stressed ecosystem.

These findings were published in the latest issue of BioScience.

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