80
rates of metabolism and growth. The very low
levels of production also limit the total number of
animals which are able to exploit the small
amount of food produced.
Char Lake
It is a small Arctic lake (74° 42′ N; 94° 50′ W,
area 0.53 km
2 or 52.6 ha, lake volume 5.4 million
m
3 ) and is situated on Cornwallis Island in the
Canadian part of the Arctic Ocean. The mean
annual temperature is –15 °C at the nearby village of Resolute, which deep down to −33 °C
during winter. Concomitantly, the highest
monthly mean temperature during July is
+4.5 °C. The lake is almost circular having a
maximum depth of 27.5 m and a mean depth of
10.2 m. The catchment (area 43.5 km
2 ) is low
and undulating. All the three main inlets fl ow
into the lake from a plateau. The conductivity of
the water increases when ice forms as in other
Arctic lakes, because ions are frozen out into the
underlying water.
In most Arctic lakes, the phytoplankton (PP)
is dominated by very small cells. Their high
surface- to-volume ratio may be advantageous in
nutrient-poor waters. Many are motile. This
allows them to select the best possible niche’
amongst the rather poor light conditions available. In Char Lake, the PP biomass begins to
increase in February which goes on till May. It
declines during September. The productivity of
benthic plants (mainly mosses) is little higher,
perhaps, because they are able to retain nutrient
from the substrate. On the other hand, the zooplankton (ZP) usually consists of ciliates and few
species of copepods and rotifers, notably,
Limnocalanus macrurus and Keratella cochlearis , respectively . Perhaps, the cold and the lack
of algal food slows everything down. The benthic
fauna includes approx. 18 species, namely, 4
species of nematodes, 7 species of chironomid
larvae, few oligochaetes and one representative
each of Ostracoda and Copepoda. Fish is represented by only one species in this simplifi ed community, which is the Arctic Char ( Salvelinus
alpinus ) . It is the most widely distributed fi sh at
these latitudes, occurring in all Arctic waters
deeper than 3–4 m. The low level of production
in the Char Lake could be due to cold and lack of
much light. Low level of inputs of N and P could
also be the reasons for relatively low lake productivity of Char Lake.
The red-throated diver Gavia stellata is a typical piscivorous bird in small Arctic lakes. It
often nests on lakes which are less productive. As
such, the bird has to fl y elsewhere to feed. During
winter, the lakes are frozen. Thus, the birds
migrate out to coastal waters and unfrozen lakes.
6.3.2 Antarctic Lakes
In Antarctica, the climate is more severe than in
Arctic region and comparable latitudes. Winters
are longer and summers are colder. The main plateau of the Antarctic continent is at high altitude
and also remote from other land masses. It is
surrounded by ice-covered sea. Hence, it is isolated from possible sources of colonisation of
lakes. This has been recently unearthed by the
retreating ice resulting in the formation of very
impoverished fauna. There are relatively few
lakes in Antarctica, majority of which are found
on the nearby islands, such as the South Orkneys
or on the northern end of the Antarctic Peninsula
where there is a more maritime climate. In the
Continental interior, there are large lakes which
are permanently covered with 3,000–4,000 m of
ice. These are perhaps fed by water melting from
the base of ice sheet. There are also very salty
lakes where the glacier ice has withdrawn and
streams now feed lakes with meltwater in summer. Apart from this, most of the Antarctic lakes
have very low concentration of salts except where
colonies of birds and seals live nearby. It is
because their excretory products, guano, etc.,
drain into water. Most of the lakes are unproductive and share certain common characteristics
with the Arctic sites, e.g . Char Lake.
There are no higher plants growing in these
lakes. The principal primary producers are the
BGA which form a thick felt-like mat on the bottom. Green algae and diatoms may grow amongst
the BGA. Mosses are also important in some
Antarctic lakes and may be found growing down to
depths of 20–30 m. Within the algal mats live
6 Lakes of the World
rates of metabolism and growth. The very low
levels of production also limit the total number of
animals which are able to exploit the small
amount of food produced.
Char Lake
It is a small Arctic lake (74° 42′ N; 94° 50′ W,
area 0.53 km
2 or 52.6 ha, lake volume 5.4 million
m
3 ) and is situated on Cornwallis Island in the
Canadian part of the Arctic Ocean. The mean
annual temperature is –15 °C at the nearby village of Resolute, which deep down to −33 °C
during winter. Concomitantly, the highest
monthly mean temperature during July is
+4.5 °C. The lake is almost circular having a
maximum depth of 27.5 m and a mean depth of
10.2 m. The catchment (area 43.5 km
2 ) is low
and undulating. All the three main inlets fl ow
into the lake from a plateau. The conductivity of
the water increases when ice forms as in other
Arctic lakes, because ions are frozen out into the
underlying water.
In most Arctic lakes, the phytoplankton (PP)
is dominated by very small cells. Their high
surface- to-volume ratio may be advantageous in
nutrient-poor waters. Many are motile. This
allows them to select the best possible niche’
amongst the rather poor light conditions available. In Char Lake, the PP biomass begins to
increase in February which goes on till May. It
declines during September. The productivity of
benthic plants (mainly mosses) is little higher,
perhaps, because they are able to retain nutrient
from the substrate. On the other hand, the zooplankton (ZP) usually consists of ciliates and few
species of copepods and rotifers, notably,
Limnocalanus macrurus and Keratella cochlearis , respectively . Perhaps, the cold and the lack
of algal food slows everything down. The benthic
fauna includes approx. 18 species, namely, 4
species of nematodes, 7 species of chironomid
larvae, few oligochaetes and one representative
each of Ostracoda and Copepoda. Fish is represented by only one species in this simplifi ed community, which is the Arctic Char ( Salvelinus
alpinus ) . It is the most widely distributed fi sh at
these latitudes, occurring in all Arctic waters
deeper than 3–4 m. The low level of production
in the Char Lake could be due to cold and lack of
much light. Low level of inputs of N and P could
also be the reasons for relatively low lake productivity of Char Lake.
The red-throated diver Gavia stellata is a typical piscivorous bird in small Arctic lakes. It
often nests on lakes which are less productive. As
such, the bird has to fl y elsewhere to feed. During
winter, the lakes are frozen. Thus, the birds
migrate out to coastal waters and unfrozen lakes.
6.3.2 Antarctic Lakes
In Antarctica, the climate is more severe than in
Arctic region and comparable latitudes. Winters
are longer and summers are colder. The main plateau of the Antarctic continent is at high altitude
and also remote from other land masses. It is
surrounded by ice-covered sea. Hence, it is isolated from possible sources of colonisation of
lakes. This has been recently unearthed by the
retreating ice resulting in the formation of very
impoverished fauna. There are relatively few
lakes in Antarctica, majority of which are found
on the nearby islands, such as the South Orkneys
or on the northern end of the Antarctic Peninsula
where there is a more maritime climate. In the
Continental interior, there are large lakes which
are permanently covered with 3,000–4,000 m of
ice. These are perhaps fed by water melting from
the base of ice sheet. There are also very salty
lakes where the glacier ice has withdrawn and
streams now feed lakes with meltwater in summer. Apart from this, most of the Antarctic lakes
have very low concentration of salts except where
colonies of birds and seals live nearby. It is
because their excretory products, guano, etc.,
drain into water. Most of the lakes are unproductive and share certain common characteristics
with the Arctic sites, e.g . Char Lake.
There are no higher plants growing in these
lakes. The principal primary producers are the
BGA which form a thick felt-like mat on the bottom. Green algae and diatoms may grow amongst
the BGA. Mosses are also important in some
Antarctic lakes and may be found growing down to
depths of 20–30 m. Within the algal mats live
6 Lakes of the World