93
widely distributed throughout the lake. The
increase in fi sh harvest is a signifi cant bonus for
both Egypt and Sudan.
6.7.4 The London Reservoirs
A number of cities in Britain obtain their drinking water from reservoirs in the uplands of
Wales or the Pennines. These reservoirs are
formed by damming steep-sided river valleys
and are small- scale equivalents of the large
‘dam lakes’. They gather water from largely
undeveloped catchments and contain unproductive water which needs little treatment before it
can be supplied to the human population.
However, London is too far from the upland to
be supplied from reservoirs of this type. Instead,
it has been necessary to build artifi cial lakes on
fl at, low land to the west and north of London.
These act as storage lagoons and are fi lled from
the River Thames and its tributary, the Lea.
These London reservoirs are vital to the nation’s
capital and are also of biological interest, being
the largest waterbodies in southeast England.
Zooplankton is dominated by large population
of Daphnia.
6.8
Gravel-Pit Lakes
Derelict industrial sites are often thought of as
blots on the landscape. But in the case of gravel
pits, these so-called wastelands could often be of
greater interest than the land all around or that
which they replace. In course of time, the pits
become colonised by plants and animals. Many
of them apparently fi nd the peculiar characteristics of gravel pits, perhaps, exactly what they
need. Dry-worked pits and areas of open sand are
attractive to primary colonisers of open, disturbed ground, which itself is a scarce transient
habitat. Some species may take advantage of the
exposed gravelly substrate even while excavation
is in progress. When the pits are fl ooded and
develop fi sh and invertebrate fauna, they may be
able to support larger number of animals, like
frogs, newts, water voles, mink and even otters.
The birds seem to be most benefi ted with a
clear succession over time. Even a small pit of
8 ha may support >20 species of birds. Openwater birds like the ducks are the most obvious. There are different kinds of ducks, each
with their own feeding specialisations. Thus,
they are suited to a particular part of the pit at
a specifi c time. Widgeons prefer grazing grass;
shovelers dabble for fl oating food; mallards do
upending for shallow-water plants; pochards
dive to lake bottom to feed on the benthos;
goosanders dive in pursuit of fi sh; and so on.
Many more species are generally attracted to
gravel pit lakes which have gently shelving littoral zones. They may get varied depths of
water and greater diversity of feeding opportunities. However, the bird, great crested grebe
( Podiceps cristatus ), seems to have gained the
most from the gravel-pit lakes in Britain. The
gravel pits are not just attractive in summer.
Many waterfowls, which breed in the Arctic
and the northern Russia, do not migrate south
because they may then remain in harsh, midcontinental winters.
Notwithstanding the above, the reeds also
provide shelter to insects and birds during winter, especially from the chilling effects of the
wind. In addition, enhancement of suitability of
the new habitat could be done by speeding up
the natural development of the fl ora by appropriate planting. It could also be geared up by
ensuring the greatest possible diversity of physical conditions, e.g . if various ducks like to feed
in different depths of water, it could be useful to
bulldoze waste earth into the pit to form shallows, where AM could also develop quickly.
Formation of islands would be attractive as
secured nesting sites. Promontories could
increase the length of total shoreline. Bays and
curved islands form shelter away from the wind
and waves and could make good ‘loafi ng spots’
for ducks. Concomitantly, studies have shown
that ducklings need a protein (animal)-rich diet.
But it is diffi cult to fi nd in newly established
gravel pits.
Most of the gravel-pit lakes in SE England
are <30 years old. Often they are rather small
and shallow. Gravel-pit lakes in Britain exceed
6.8 Gravel-Pit Lakes
widely distributed throughout the lake. The
increase in fi sh harvest is a signifi cant bonus for
both Egypt and Sudan.
6.7.4 The London Reservoirs
A number of cities in Britain obtain their drinking water from reservoirs in the uplands of
Wales or the Pennines. These reservoirs are
formed by damming steep-sided river valleys
and are small- scale equivalents of the large
‘dam lakes’. They gather water from largely
undeveloped catchments and contain unproductive water which needs little treatment before it
can be supplied to the human population.
However, London is too far from the upland to
be supplied from reservoirs of this type. Instead,
it has been necessary to build artifi cial lakes on
fl at, low land to the west and north of London.
These act as storage lagoons and are fi lled from
the River Thames and its tributary, the Lea.
These London reservoirs are vital to the nation’s
capital and are also of biological interest, being
the largest waterbodies in southeast England.
Zooplankton is dominated by large population
of Daphnia.
6.8
Gravel-Pit Lakes
Derelict industrial sites are often thought of as
blots on the landscape. But in the case of gravel
pits, these so-called wastelands could often be of
greater interest than the land all around or that
which they replace. In course of time, the pits
become colonised by plants and animals. Many
of them apparently fi nd the peculiar characteristics of gravel pits, perhaps, exactly what they
need. Dry-worked pits and areas of open sand are
attractive to primary colonisers of open, disturbed ground, which itself is a scarce transient
habitat. Some species may take advantage of the
exposed gravelly substrate even while excavation
is in progress. When the pits are fl ooded and
develop fi sh and invertebrate fauna, they may be
able to support larger number of animals, like
frogs, newts, water voles, mink and even otters.
The birds seem to be most benefi ted with a
clear succession over time. Even a small pit of
8 ha may support >20 species of birds. Openwater birds like the ducks are the most obvious. There are different kinds of ducks, each
with their own feeding specialisations. Thus,
they are suited to a particular part of the pit at
a specifi c time. Widgeons prefer grazing grass;
shovelers dabble for fl oating food; mallards do
upending for shallow-water plants; pochards
dive to lake bottom to feed on the benthos;
goosanders dive in pursuit of fi sh; and so on.
Many more species are generally attracted to
gravel pit lakes which have gently shelving littoral zones. They may get varied depths of
water and greater diversity of feeding opportunities. However, the bird, great crested grebe
( Podiceps cristatus ), seems to have gained the
most from the gravel-pit lakes in Britain. The
gravel pits are not just attractive in summer.
Many waterfowls, which breed in the Arctic
and the northern Russia, do not migrate south
because they may then remain in harsh, midcontinental winters.
Notwithstanding the above, the reeds also
provide shelter to insects and birds during winter, especially from the chilling effects of the
wind. In addition, enhancement of suitability of
the new habitat could be done by speeding up
the natural development of the fl ora by appropriate planting. It could also be geared up by
ensuring the greatest possible diversity of physical conditions, e.g . if various ducks like to feed
in different depths of water, it could be useful to
bulldoze waste earth into the pit to form shallows, where AM could also develop quickly.
Formation of islands would be attractive as
secured nesting sites. Promontories could
increase the length of total shoreline. Bays and
curved islands form shelter away from the wind
and waves and could make good ‘loafi ng spots’
for ducks. Concomitantly, studies have shown
that ducklings need a protein (animal)-rich diet.
But it is diffi cult to fi nd in newly established
gravel pits.
Most of the gravel-pit lakes in SE England
are <30 years old. Often they are rather small
and shallow. Gravel-pit lakes in Britain exceed
6.8 Gravel-Pit Lakes