81
microscopic benthic animals, such as rotifers,
tardigrades, protozoans and nematodes. Some of
them are able to withstand being frozen every night
and revive again each morning. Further, as in Arctic
lakes, in the Antarctic lakes also, the phytoplankton
tends to be dominated by small, motile species
whose production is less than that of the benthic
algae. Of particular interest is the fact that they can
continue to fi x carbon in darkness under the ice.
6.4
Deepest Lakes
One of the key features which determines the
structure and function of lake ecosystem is depth.
Light, temperature, oxygen, etc. vary with depth
depending on time of the year. However, the
actual depth of a lake depends very much on the
modus operandi of its basin formation.
Nevertheless, most of the very big lakes owe their
origin to movements of earth’s crust. It is said that
basins of the Rift Valleys of Africa and Crater
Lake Oregon could have been formed in this way.
Most of the lakes are <500 m in depth. However,
two lakes, namely, Lake Baikal in Siberia and
Lake Tanganyika in East Africa, are >1,000 m
deep. Both these lakes are also very ancient. They
have allowed time for evolution of species to
occur within the lake basins. The communities of
both these lakes contain many endemic species.
The enormous basins of very deep lakes contain immense volume of water. Most of these
water remains within the lakes for a very long
period of time. This makes the water vulnerable
to pollutants. Lakes like Caspian Sea and Crater
Lake have no outfl ow. Hence, all the incoming
substances are destined to remain within the
basin, except the water which evaporates from
the surface. The combination of large number of
endemic species and the vulnerability to pollution make it extremely important that these lakes
are treated with utmost care.
6.4.1 Lake Tanganyika
At the cost of repetition, it has been discussed as
one of the deepest lakes in the world. It is one of
the biggest lakes in the world which is much
warmer than Lake Baikal. It has certainly never
been frozen in all its long history. Lake
Tanganyika (8° S–32° E, altitude 773 m MSL,
lake area 33,000 km
2 , catchment area
250,000 km
2
, lake volume 19,000 km
3 , max.
depth 1,470 m, mean depth 600 m) is situated in
Tropical Africa.
In this lake, the abyssal zone is uninhabitable
because it is totally and permanently devoid of
oxygen. So, majority of the endemic species are
found in the littoral and pelagic zone of the lake.
Nine-tenth of the depth of water of this lake contains no oxygen because the lake was never completely mixed. The Lake Tanganyika is younger
(1.5–6 million years) than Lake Baikal (50–75
million years). The lake is more than 600 km
long and has two major basins and a smaller middle one. The Ruzizi River enters at the north end
of the river, carrying rather saline water from
Lake Kivu. The other infl ows, except the
Malagarasi River, are rather short and precipitous
as they drain the adjacent mountain ranges. The
lake water generally shows high conductivity
(600 μS cm
−1 ). The present outfl ow which drains
to the Zaire River has not always been open ever
since the fi rst European explorers had arrived.
Lake Tanganyika contains many endemic
species. There are 60 species of molluscs in contrast to 27 in Lake Malawi. Thirty of the gastropod species of Lake Tanganyika are endemic.
Other endemics include, amongst others, two
species of aquatic snakes (cobra and krait). The
aquatic insects include the caddis fl y. It is interesting to note here that similar species of caddis
fl y had also been reported from Lake Baikal and
Lake Titicaca in Andes. In Tanganyika, many
molluscs have thick shells and long spines. Some
marine animals with shell-like structures also
inhabit the lake. These characteristics are now
thought to be adaptations to similar environmental conditions rather than evidence of a past connection between Lake Tanganyika and the sea.
Earlier connections have some indications that
Lake Tanganyika was remnant of the sea or it
could once have connection with the sea. When a
jelly fi sh was found in the open water, the case
seemed to be proved although there are many
6.4 Deepest Lakes
microscopic benthic animals, such as rotifers,
tardigrades, protozoans and nematodes. Some of
them are able to withstand being frozen every night
and revive again each morning. Further, as in Arctic
lakes, in the Antarctic lakes also, the phytoplankton
tends to be dominated by small, motile species
whose production is less than that of the benthic
algae. Of particular interest is the fact that they can
continue to fi x carbon in darkness under the ice.
6.4
Deepest Lakes
One of the key features which determines the
structure and function of lake ecosystem is depth.
Light, temperature, oxygen, etc. vary with depth
depending on time of the year. However, the
actual depth of a lake depends very much on the
modus operandi of its basin formation.
Nevertheless, most of the very big lakes owe their
origin to movements of earth’s crust. It is said that
basins of the Rift Valleys of Africa and Crater
Lake Oregon could have been formed in this way.
Most of the lakes are <500 m in depth. However,
two lakes, namely, Lake Baikal in Siberia and
Lake Tanganyika in East Africa, are >1,000 m
deep. Both these lakes are also very ancient. They
have allowed time for evolution of species to
occur within the lake basins. The communities of
both these lakes contain many endemic species.
The enormous basins of very deep lakes contain immense volume of water. Most of these
water remains within the lakes for a very long
period of time. This makes the water vulnerable
to pollutants. Lakes like Caspian Sea and Crater
Lake have no outfl ow. Hence, all the incoming
substances are destined to remain within the
basin, except the water which evaporates from
the surface. The combination of large number of
endemic species and the vulnerability to pollution make it extremely important that these lakes
are treated with utmost care.
6.4.1 Lake Tanganyika
At the cost of repetition, it has been discussed as
one of the deepest lakes in the world. It is one of
the biggest lakes in the world which is much
warmer than Lake Baikal. It has certainly never
been frozen in all its long history. Lake
Tanganyika (8° S–32° E, altitude 773 m MSL,
lake area 33,000 km
2 , catchment area
250,000 km
2
, lake volume 19,000 km
3 , max.
depth 1,470 m, mean depth 600 m) is situated in
Tropical Africa.
In this lake, the abyssal zone is uninhabitable
because it is totally and permanently devoid of
oxygen. So, majority of the endemic species are
found in the littoral and pelagic zone of the lake.
Nine-tenth of the depth of water of this lake contains no oxygen because the lake was never completely mixed. The Lake Tanganyika is younger
(1.5–6 million years) than Lake Baikal (50–75
million years). The lake is more than 600 km
long and has two major basins and a smaller middle one. The Ruzizi River enters at the north end
of the river, carrying rather saline water from
Lake Kivu. The other infl ows, except the
Malagarasi River, are rather short and precipitous
as they drain the adjacent mountain ranges. The
lake water generally shows high conductivity
(600 μS cm
−1 ). The present outfl ow which drains
to the Zaire River has not always been open ever
since the fi rst European explorers had arrived.
Lake Tanganyika contains many endemic
species. There are 60 species of molluscs in contrast to 27 in Lake Malawi. Thirty of the gastropod species of Lake Tanganyika are endemic.
Other endemics include, amongst others, two
species of aquatic snakes (cobra and krait). The
aquatic insects include the caddis fl y. It is interesting to note here that similar species of caddis
fl y had also been reported from Lake Baikal and
Lake Titicaca in Andes. In Tanganyika, many
molluscs have thick shells and long spines. Some
marine animals with shell-like structures also
inhabit the lake. These characteristics are now
thought to be adaptations to similar environmental conditions rather than evidence of a past connection between Lake Tanganyika and the sea.
Earlier connections have some indications that
Lake Tanganyika was remnant of the sea or it
could once have connection with the sea. When a
jelly fi sh was found in the open water, the case
seemed to be proved although there are many
6.4 Deepest Lakes