79
6.2.10 The Alpine Lakes of New
Zealand
The mountains run northeast to southwest in the
South Island of New Zealand (NZ) and large
lakes fi ll many of the valleys.
The native aquatic fl ora seems to be very
restricted in NZ. As such, there had not been
much reports on the AM of a single typical lake
in NZ. It appears that certain species, notably,
Potamogeton cheesemanii and Myriophyllum
propinquum , are very plastic. Their ecophenes
may occupy a number of niches, which, with a
greater fl ora, would, probably, be fi lled by different species. Nevertheless, Mason ( 1969 ) had
given a general account of the AM of the
Canterbury District of South Island. Some of the
abundant AM in clear permanent waters of lakes
with little or no silting are Isoetes alpines ,
Limosella lineate , etc. Elodea canadensis is said
to go deeper than any native plant. Potamogeton
cheesemanii is dominant where silting occurs.
Some of NZ species are prone to produce
remarkable ecophenes fi lling many niches in the
absence of much fl oristic diversity. Myriophyllum
propinquum may grow as a moss-like subaerial
plant on wet mud. In small lakes with a very gently sloping margin, a littoral fl ora was found to
compose mainly of M. elatinoides , Glossostigma
elatinoides , etc. All these marginal plants may
grow under water, but some of them do not
fl ower when submerged. Some of the eulittoral
psammobiont members of the Centrolepidaceae
in NZ and Tasmania were known to contain two
sympatric species of Isoetes in Lake Taupo
(Allan 1961 ).
6.3
Polar and Mountain Lakes
The air is said to get cooler by −1 °C for every
150 m height extra as one climbs a mountain.
Similarities occur between the conditions found
in lakes at high altitudes and those at high latitudes. In both the cases, the water is very cold
being covered with ice and snow for long period.
However, the main difference lies in the pattern
of sunshine. The pattern of sunlight falling on
high mountain lakes depends on their latitudes.
The common feature of such lakes is the availability of ice, snow and cold water. They may be
shallow or deep, fresh or saline, etc.
6.3.1 Lakes of the Polar Regions
The lakes of the polar region include the Arctic
lakes and the Antarctic lakes.
6.3.1.1 Arctic Lakes
The true Arctic lakes of the northern hemisphere
(NH) are those with a mean air temperature of
<−3 °C during winter and between 0 and 10 °C
during summer. The regions include northern
land masses of Alaska, Canada, Soviet Union,
Greenland, Spitsbergen and northern fringes of
Scandinavia. In these regions, there are big areas
of land where meltwater collects in every cavity
of the bare ground and the landscape is dotted
with large number of lakes. These lakes are said
to be comparatively new. During winter, the shallow lakes are all frozen starting by the end of
September. The infl ow rivers usually freeze even
earlier, but the outfl ow rivers may continue to
fl ow below the ice for some time. Such lakes are
generally about 2.4 m deep.
Anguissaq Lake is a deep (max. 187 m) Arctic
lake in North-West Greenland. It may be noted
here that most Arctic lakes have an ice-free
period for a few weeks in summer.
During the Arctic winter, when the sun does
not rise above the horizon, there is no energy for
primary production, and living organisms have to
subsist on what remains of the previous year’s
production or spend the winter in a dormant
phase. Light is available for much longer than the
lake is free from the ice.
Arctic lakes are generally very unproductive
and contain communities composed of a very
limited number of species. Simple animals and
plants seem to occur in Arctic lakes in similar
numbers to those in temperate lakes and are
sometimes of the same species. But the diversity
of higher plants and animals is more restricted.
Only those which can function in continuous
cold may be able to thrive, but they have very low
6.3 Polar and Mountain Lakes
6.2.10 The Alpine Lakes of New
Zealand
The mountains run northeast to southwest in the
South Island of New Zealand (NZ) and large
lakes fi ll many of the valleys.
The native aquatic fl ora seems to be very
restricted in NZ. As such, there had not been
much reports on the AM of a single typical lake
in NZ. It appears that certain species, notably,
Potamogeton cheesemanii and Myriophyllum
propinquum , are very plastic. Their ecophenes
may occupy a number of niches, which, with a
greater fl ora, would, probably, be fi lled by different species. Nevertheless, Mason ( 1969 ) had
given a general account of the AM of the
Canterbury District of South Island. Some of the
abundant AM in clear permanent waters of lakes
with little or no silting are Isoetes alpines ,
Limosella lineate , etc. Elodea canadensis is said
to go deeper than any native plant. Potamogeton
cheesemanii is dominant where silting occurs.
Some of NZ species are prone to produce
remarkable ecophenes fi lling many niches in the
absence of much fl oristic diversity. Myriophyllum
propinquum may grow as a moss-like subaerial
plant on wet mud. In small lakes with a very gently sloping margin, a littoral fl ora was found to
compose mainly of M. elatinoides , Glossostigma
elatinoides , etc. All these marginal plants may
grow under water, but some of them do not
fl ower when submerged. Some of the eulittoral
psammobiont members of the Centrolepidaceae
in NZ and Tasmania were known to contain two
sympatric species of Isoetes in Lake Taupo
(Allan 1961 ).
6.3
Polar and Mountain Lakes
The air is said to get cooler by −1 °C for every
150 m height extra as one climbs a mountain.
Similarities occur between the conditions found
in lakes at high altitudes and those at high latitudes. In both the cases, the water is very cold
being covered with ice and snow for long period.
However, the main difference lies in the pattern
of sunshine. The pattern of sunlight falling on
high mountain lakes depends on their latitudes.
The common feature of such lakes is the availability of ice, snow and cold water. They may be
shallow or deep, fresh or saline, etc.
6.3.1 Lakes of the Polar Regions
The lakes of the polar region include the Arctic
lakes and the Antarctic lakes.
6.3.1.1 Arctic Lakes
The true Arctic lakes of the northern hemisphere
(NH) are those with a mean air temperature of
<−3 °C during winter and between 0 and 10 °C
during summer. The regions include northern
land masses of Alaska, Canada, Soviet Union,
Greenland, Spitsbergen and northern fringes of
Scandinavia. In these regions, there are big areas
of land where meltwater collects in every cavity
of the bare ground and the landscape is dotted
with large number of lakes. These lakes are said
to be comparatively new. During winter, the shallow lakes are all frozen starting by the end of
September. The infl ow rivers usually freeze even
earlier, but the outfl ow rivers may continue to
fl ow below the ice for some time. Such lakes are
generally about 2.4 m deep.
Anguissaq Lake is a deep (max. 187 m) Arctic
lake in North-West Greenland. It may be noted
here that most Arctic lakes have an ice-free
period for a few weeks in summer.
During the Arctic winter, when the sun does
not rise above the horizon, there is no energy for
primary production, and living organisms have to
subsist on what remains of the previous year’s
production or spend the winter in a dormant
phase. Light is available for much longer than the
lake is free from the ice.
Arctic lakes are generally very unproductive
and contain communities composed of a very
limited number of species. Simple animals and
plants seem to occur in Arctic lakes in similar
numbers to those in temperate lakes and are
sometimes of the same species. But the diversity
of higher plants and animals is more restricted.
Only those which can function in continuous
cold may be able to thrive, but they have very low
6.3 Polar and Mountain Lakes