84
but has an average depth of only 8.9 m; Lake
Chad expands to form one of the biggest lakes
in Africa but is never more than about 8 m deep;
and Lake Balaton in Hungary, one of the
Europe’s biggest lakes, is no where >11.0 m
deep. Further, all the deep lakes have at least
some shallow areas. But since shallow lakes do
not have any deep water, one might wonder
whether they still contain all the usual lake life.
As such, they cannot of course contain specialised abyssal communities, but they do have littoral, pelagic and benthic communities. But the
population of benthic community often depends
on the area of the lake bottom. Further, much of
the lake may contain submerged and fl oating
macrophytes and a primarily littoral community. However, vascular plants may not grow
below about 10 m deep even in the clearest
water. It is because the pressure of the water
causes the spaces between their cells to collapse. The lake water may be turbid, either
through the growth of algae or because the lake
is shallow enough that sediments are stirred up
from the bottom as the wind mixes the lake
water. The littoral community may be restricted
and most of the lake area then contains open,
turbid water. In such cases, there may be a truly
planktonic community in the open water and a
benthic community in the underlying mud. If
the mud is soft and constantly disturbed, it is not
a suitable habitat for animals that dwell in permanent tubes. Further, the open water of some
shallow lakes may be so turbid, due to silt, that
the penetration of light is obstructed, thus reducing phytoplankton productivity. In turn, this also
infl uences rest of the food chain.
The shallow lakes support plants, invertebrates and large varied population of piscivorous birds. These generalisations have been
modifi ed by circumstances on particular lakes,
such as, altitude, latitude and degree of exposure to wind.
6.5.1 Lake Balaton
This is considered to be a shallow lake. It has
been dealt with in detail under Sect. 6.2.6 .
6.5.1.1 Neusiedlersee
This shallow lake is situated on the AustroHungarian border. It has been dealt with under
Sect. 6.2.6 .
6.5.2 Lake Chilwa
Lake Chilwa (15° 30′ S, 35° 30′ E; altitude
622 m; catchment area 7,500 km
2 ; maximum
depth 3 m approx.) is situated in Malawi in
Africa. Great variations occur in the area, volume
and depth of this lake. The maximum area of
open water is approx. 700 km
2 while the total
area of this shallow lake including marshland is
approx. 1,400 km
2. The principal infl ows are the
Domasi, Likangala, Thondwe, Namadzi and
Phalombe rivers. There is no outfl ow of this shallow lake. This lentic body is shallow, endorheic
and slightly saline and is surrounded by reed
swamp. However, this lake is under the infl uence
of tropical climate with a cool dry period between
May and October. The water level of this wetland
fl uctuates by up to 1.5 m each year. In 1968, the
lake had dried up completely for a few months. It
was known to do so at least twice before in this
century. The depth of the lake does not generally
exceed 3 m even in the wettest periods. The
whole lake is surrounded by swamps dominated
by Typha domingensis and covers a total of about
552 km
2 . During the wet season, the water level
rises each year and fl oods c 575 km
2 of marsh and
grassland beyond the permanent swamp.
The swamps play an important role in the
functioning of the lake ecosystem. The larger
sediment particles are trapped by them as they
are washed from the surrounding land and only
fi ne silts enter the open water. These are constantly churned up by wind mixing of the shallow
water, which is consequently very murky. As a
result, the development of rooted submerged AM
outside the sheltered swamp area is prevented.
Hence, the transition from swamp to open water
is quite abrupt. There is no wind inside the
swamp and the sediment settles out, leaving the
water much clearer. However, there is much
greater variability of different factors, e.g . in
conductivity and in oxygen availability, within
6 Lakes of the World
but has an average depth of only 8.9 m; Lake
Chad expands to form one of the biggest lakes
in Africa but is never more than about 8 m deep;
and Lake Balaton in Hungary, one of the
Europe’s biggest lakes, is no where >11.0 m
deep. Further, all the deep lakes have at least
some shallow areas. But since shallow lakes do
not have any deep water, one might wonder
whether they still contain all the usual lake life.
As such, they cannot of course contain specialised abyssal communities, but they do have littoral, pelagic and benthic communities. But the
population of benthic community often depends
on the area of the lake bottom. Further, much of
the lake may contain submerged and fl oating
macrophytes and a primarily littoral community. However, vascular plants may not grow
below about 10 m deep even in the clearest
water. It is because the pressure of the water
causes the spaces between their cells to collapse. The lake water may be turbid, either
through the growth of algae or because the lake
is shallow enough that sediments are stirred up
from the bottom as the wind mixes the lake
water. The littoral community may be restricted
and most of the lake area then contains open,
turbid water. In such cases, there may be a truly
planktonic community in the open water and a
benthic community in the underlying mud. If
the mud is soft and constantly disturbed, it is not
a suitable habitat for animals that dwell in permanent tubes. Further, the open water of some
shallow lakes may be so turbid, due to silt, that
the penetration of light is obstructed, thus reducing phytoplankton productivity. In turn, this also
infl uences rest of the food chain.
The shallow lakes support plants, invertebrates and large varied population of piscivorous birds. These generalisations have been
modifi ed by circumstances on particular lakes,
such as, altitude, latitude and degree of exposure to wind.
6.5.1 Lake Balaton
This is considered to be a shallow lake. It has
been dealt with in detail under Sect. 6.2.6 .
6.5.1.1 Neusiedlersee
This shallow lake is situated on the AustroHungarian border. It has been dealt with under
Sect. 6.2.6 .
6.5.2 Lake Chilwa
Lake Chilwa (15° 30′ S, 35° 30′ E; altitude
622 m; catchment area 7,500 km
2 ; maximum
depth 3 m approx.) is situated in Malawi in
Africa. Great variations occur in the area, volume
and depth of this lake. The maximum area of
open water is approx. 700 km
2 while the total
area of this shallow lake including marshland is
approx. 1,400 km
2. The principal infl ows are the
Domasi, Likangala, Thondwe, Namadzi and
Phalombe rivers. There is no outfl ow of this shallow lake. This lentic body is shallow, endorheic
and slightly saline and is surrounded by reed
swamp. However, this lake is under the infl uence
of tropical climate with a cool dry period between
May and October. The water level of this wetland
fl uctuates by up to 1.5 m each year. In 1968, the
lake had dried up completely for a few months. It
was known to do so at least twice before in this
century. The depth of the lake does not generally
exceed 3 m even in the wettest periods. The
whole lake is surrounded by swamps dominated
by Typha domingensis and covers a total of about
552 km
2 . During the wet season, the water level
rises each year and fl oods c 575 km
2 of marsh and
grassland beyond the permanent swamp.
The swamps play an important role in the
functioning of the lake ecosystem. The larger
sediment particles are trapped by them as they
are washed from the surrounding land and only
fi ne silts enter the open water. These are constantly churned up by wind mixing of the shallow
water, which is consequently very murky. As a
result, the development of rooted submerged AM
outside the sheltered swamp area is prevented.
Hence, the transition from swamp to open water
is quite abrupt. There is no wind inside the
swamp and the sediment settles out, leaving the
water much clearer. However, there is much
greater variability of different factors, e.g . in
conductivity and in oxygen availability, within
6 Lakes of the World