76
However, Pearsall ( 1921 ), on the basis of his
works on English Lakes, had suggested that the
main factor(s) which may determine the differences in vegetation within the broad limits of
depth and fl ux is the physico-chemical nature of
the sediment. Further, Misra ( 1938 ) had worked
on the substrata required by various submerged
plants in the English Lakes in detail. He had concluded that the mud usually required for P. perfoliatus is a mixture of organic material and silt,
with a minimum C–N ratio, a high capacity to
produce NH 3 , and a low redox potential. This
suggests much bacterial activity and a high
content of exchangeable cations. Mishra, further,
following Pearsall, opined that the more highly
organic mass are formed by too rapid sedimentation to permit growth of the plant that seemingly
might not be able to raise itself in the mud as the
latter accumulates.
Loch Leven
It is situated north of Edinburgh in Scotland in
the UK. The lake has an area of 13.3 km
2 with
many large islands providing ideal national
grounds for ducks. It has a maximum and mean
depth of 23 m and 3.9 m, respectively. However
much of its area is very shallow. There are
productive farmlands around the lake. From
these farmlands, run-off-loaded fertilisers have
increased the nutrient supply to the lake. In
winter, the fi elds also provide grazing for
geese. One of the farms is now a bird reserve.
The lake was intensively studied during the
International Biological Programme (IBP) of
1966–1972. Loch Leven is of international signifi cance because it is a habitat for wild fowl
and has the largest concentration of breeding
ducks in Britain.
This loch is a privately owned natural
reserve with a rich trout fi shery since long.
However, it is still not immune from the effects
of twentieth century changes in the catchment
area. Agriculture run-off and urban sewage
have markedly increased the nutrient input into
the loch. As such, blooms of BGA have
increased in frequency since 1960. Concomitantly,
the number of AM species plus the area under
AM growth has correspondingly declined. The
nature of the zooplankton has also changed
over the same period, from dominance by
Daphnia hyalina to dominance by the copepod, Cyclops strenuous . This change was
reversed in 1970. At the same time, the phytoplankton changed from being dominated by
small species to predominantly larger species.
This might have affected the AM which have
begun to spread again.
The insecticide dieldrin was used as a moth
proofer by a woollen mill on one of the infl owing
rivers. This poisonous chemical had brought
about changes in the loch ecosystem, particularly
Daphnia , which is perhaps susceptible to it. The
factory has since stopped using these pesticides.
It is known that a rich diversity of birds and
other animals have been happily supported by a
varied and diversifi ed habitat. A lake with extensive areas of swamp, swamp fringes and fl oating
and submerged macrophytes and a variety of substrates on the bottom and varied depths of water
will support the greatest number of species. Still
more are associated with the interface between
the lake water and the land. In addition, terrestrial
species such as swallows and martins are frequently seen feeding on insects emerging from
the lake water.
A study of aquatic birds in the British lakes
revealed that the mean number of piscivorous
species declined with increasing altitude. It also
assumed that lakes at low altitude tend to be more
productive. Species related to only gulls, terns
and waders seem to be more associated with
unproductive lakes. In Britain, birds associated
with lakes of all types changed markedly between
the seasons.
Lakes like Loch Leven, thus, play a dual role
as habitat for birds. It offers facilities for nesting and feeding in summer as well as feeding
and roosting for over-wintering birds like the
geese. Certain ducks and swans like Anas platyrhynchos and A. penelope nest in Loch Leven
regularly and some are perennial residents of
the loch. A total of 30 species of waterfowls
were recorded at Loch Leven between 1966 and
1972, plus 23 waders (of which 6 bred), 11 species of gulls and terns (3 bred) and 16 other
species of water birds.
6 Lakes of the World
However, Pearsall ( 1921 ), on the basis of his
works on English Lakes, had suggested that the
main factor(s) which may determine the differences in vegetation within the broad limits of
depth and fl ux is the physico-chemical nature of
the sediment. Further, Misra ( 1938 ) had worked
on the substrata required by various submerged
plants in the English Lakes in detail. He had concluded that the mud usually required for P. perfoliatus is a mixture of organic material and silt,
with a minimum C–N ratio, a high capacity to
produce NH 3 , and a low redox potential. This
suggests much bacterial activity and a high
content of exchangeable cations. Mishra, further,
following Pearsall, opined that the more highly
organic mass are formed by too rapid sedimentation to permit growth of the plant that seemingly
might not be able to raise itself in the mud as the
latter accumulates.
Loch Leven
It is situated north of Edinburgh in Scotland in
the UK. The lake has an area of 13.3 km
2 with
many large islands providing ideal national
grounds for ducks. It has a maximum and mean
depth of 23 m and 3.9 m, respectively. However
much of its area is very shallow. There are
productive farmlands around the lake. From
these farmlands, run-off-loaded fertilisers have
increased the nutrient supply to the lake. In
winter, the fi elds also provide grazing for
geese. One of the farms is now a bird reserve.
The lake was intensively studied during the
International Biological Programme (IBP) of
1966–1972. Loch Leven is of international signifi cance because it is a habitat for wild fowl
and has the largest concentration of breeding
ducks in Britain.
This loch is a privately owned natural
reserve with a rich trout fi shery since long.
However, it is still not immune from the effects
of twentieth century changes in the catchment
area. Agriculture run-off and urban sewage
have markedly increased the nutrient input into
the loch. As such, blooms of BGA have
increased in frequency since 1960. Concomitantly,
the number of AM species plus the area under
AM growth has correspondingly declined. The
nature of the zooplankton has also changed
over the same period, from dominance by
Daphnia hyalina to dominance by the copepod, Cyclops strenuous . This change was
reversed in 1970. At the same time, the phytoplankton changed from being dominated by
small species to predominantly larger species.
This might have affected the AM which have
begun to spread again.
The insecticide dieldrin was used as a moth
proofer by a woollen mill on one of the infl owing
rivers. This poisonous chemical had brought
about changes in the loch ecosystem, particularly
Daphnia , which is perhaps susceptible to it. The
factory has since stopped using these pesticides.
It is known that a rich diversity of birds and
other animals have been happily supported by a
varied and diversifi ed habitat. A lake with extensive areas of swamp, swamp fringes and fl oating
and submerged macrophytes and a variety of substrates on the bottom and varied depths of water
will support the greatest number of species. Still
more are associated with the interface between
the lake water and the land. In addition, terrestrial
species such as swallows and martins are frequently seen feeding on insects emerging from
the lake water.
A study of aquatic birds in the British lakes
revealed that the mean number of piscivorous
species declined with increasing altitude. It also
assumed that lakes at low altitude tend to be more
productive. Species related to only gulls, terns
and waders seem to be more associated with
unproductive lakes. In Britain, birds associated
with lakes of all types changed markedly between
the seasons.
Lakes like Loch Leven, thus, play a dual role
as habitat for birds. It offers facilities for nesting and feeding in summer as well as feeding
and roosting for over-wintering birds like the
geese. Certain ducks and swans like Anas platyrhynchos and A. penelope nest in Loch Leven
regularly and some are perennial residents of
the loch. A total of 30 species of waterfowls
were recorded at Loch Leven between 1966 and
1972, plus 23 waders (of which 6 bred), 11 species of gulls and terns (3 bred) and 16 other
species of water birds.
6 Lakes of the World