75
Many of the valleys are gradually fi lled with
water to generate the landscape of today. All
these lakes are almost of same age.
Studies ( Pearsall 1930 ) refl ected that the differences between the lakes were associated with
the shapes and fertility of the valleys they lie in.
It was found that c 5 % of the catchment area is
suitable for cultivation and c 73 % of the lakeshore is rocky.
The lake district has many small lakes, called
‘tarns’, in addition to the 11 big lakes. These also,
perhaps, owe their existence to the action of
Pleistocene ice. However, many of these lakes are
quite shallow and rich in macrophytes.
Windermere Lake
It is the largest lake in English Lake District. It is
under the infl uence of north temperate maritime
climate. Thus, the lake freezes only in exceptional years and has only period of complete
mixing and one stratifi cation period per year. It
could be because, further south, the seasonality
becomes increasingly muted, although midcontinental climates are more extreme than those
of the continental margins. The dimensions of the
lake basin and its catchment area disguise the fact
that the long narrow lake actually lies in two
basins which are separated by a stretch of relatively shallow water (<5 m) and many islands
where the lake is at its narrowest. Studies conducted during 1931 revealed water temperature
to be 7 °C in the middle of the North Basin from
the surface down to 60 m. It had fallen to 5.5 °C
by April 1932. After that, the temperature at the
surface began to rise quite rapidly. By the beginning of July, it had reached 18 °C. However, the
water at the hypolimnion was still 7 °C.
Stratifi cation had lasted from end of June to end
of September. The thermocline was established
between 10 and 20 m.
Windermere is one of the most productive lakes
in England. The nutrients (nitrates, phosphates,
etc.) are not very rich but follow a regular seasonal
pattern. The nutrients support a rich growth of the
diatoms, Asterionella formosa. Growth of these
diatoms, mainly during spring, results in the
absorption of silica. The phytoplankton succession
is paralleled by seasonal changes in the dominant
zooplankton. The latter are also infl uenced by food
supply and predators.
In Windermere, fi sh eggs hatch during end of
May. The juveniles start eating rotifers, cladocerans, etc.
The Norfolk Broads
These are shallow open water surrounded by
marshland situated in the easternmost part of
England. They lie along the lower reaches of
many rivers, namely, Yare, Bure, Ant and
Waveney. These lakes originate from peat digging which ceased in the fourteenth and seventeenth centuries. The peats might lead down
during the period of high water levels and the
whole area became a mosaic of reed swamp.
The local people harvest reeds for thatching.
They also exploit fi sh and wild fowl populations. Local population was sparse and broads
continued to be remote until the end of the
nineteenth century.
Human activities had profound effects on
the ecology of the broad land area. But still,
Norfolk Broads form the largest area of seminatural ‘wetland’ in Great Britain. They are
home to some of our rarest wetland birds such
as marsh harrier and bittern. The Broads themselves are very shallow lakes which are usually
less than 4 m deep. They had their water originally and were mostly fi lled by reeds and water
lilies. A host of submerged plants also grow
across the bottom. The fi rst notable change was
a substantial increase in the submerged macrophytes. These cause hindrance in navigation. It
may be noted here that the original characteristics of the broads persisted in only one or two
of the 42 lakes.
Notwithstanding the above, the interactions
between grazing zooplankton and fi sh also affect
the balance between the plant communities.
Management of the Norfolk Broads was in
the hands of a number of different organisations.
As the evidence of change in both the aquatic
and semi-terrestrial environment mounted and
some of the causes became clearer during the
1970s, it became evident that some sort of coordinating body was needed to oversee the Broads
as a whole.
6.2 Lakes of Temperate Region
Many of the valleys are gradually fi lled with
water to generate the landscape of today. All
these lakes are almost of same age.
Studies ( Pearsall 1930 ) refl ected that the differences between the lakes were associated with
the shapes and fertility of the valleys they lie in.
It was found that c 5 % of the catchment area is
suitable for cultivation and c 73 % of the lakeshore is rocky.
The lake district has many small lakes, called
‘tarns’, in addition to the 11 big lakes. These also,
perhaps, owe their existence to the action of
Pleistocene ice. However, many of these lakes are
quite shallow and rich in macrophytes.
Windermere Lake
It is the largest lake in English Lake District. It is
under the infl uence of north temperate maritime
climate. Thus, the lake freezes only in exceptional years and has only period of complete
mixing and one stratifi cation period per year. It
could be because, further south, the seasonality
becomes increasingly muted, although midcontinental climates are more extreme than those
of the continental margins. The dimensions of the
lake basin and its catchment area disguise the fact
that the long narrow lake actually lies in two
basins which are separated by a stretch of relatively shallow water (<5 m) and many islands
where the lake is at its narrowest. Studies conducted during 1931 revealed water temperature
to be 7 °C in the middle of the North Basin from
the surface down to 60 m. It had fallen to 5.5 °C
by April 1932. After that, the temperature at the
surface began to rise quite rapidly. By the beginning of July, it had reached 18 °C. However, the
water at the hypolimnion was still 7 °C.
Stratifi cation had lasted from end of June to end
of September. The thermocline was established
between 10 and 20 m.
Windermere is one of the most productive lakes
in England. The nutrients (nitrates, phosphates,
etc.) are not very rich but follow a regular seasonal
pattern. The nutrients support a rich growth of the
diatoms, Asterionella formosa. Growth of these
diatoms, mainly during spring, results in the
absorption of silica. The phytoplankton succession
is paralleled by seasonal changes in the dominant
zooplankton. The latter are also infl uenced by food
supply and predators.
In Windermere, fi sh eggs hatch during end of
May. The juveniles start eating rotifers, cladocerans, etc.
The Norfolk Broads
These are shallow open water surrounded by
marshland situated in the easternmost part of
England. They lie along the lower reaches of
many rivers, namely, Yare, Bure, Ant and
Waveney. These lakes originate from peat digging which ceased in the fourteenth and seventeenth centuries. The peats might lead down
during the period of high water levels and the
whole area became a mosaic of reed swamp.
The local people harvest reeds for thatching.
They also exploit fi sh and wild fowl populations. Local population was sparse and broads
continued to be remote until the end of the
nineteenth century.
Human activities had profound effects on
the ecology of the broad land area. But still,
Norfolk Broads form the largest area of seminatural ‘wetland’ in Great Britain. They are
home to some of our rarest wetland birds such
as marsh harrier and bittern. The Broads themselves are very shallow lakes which are usually
less than 4 m deep. They had their water originally and were mostly fi lled by reeds and water
lilies. A host of submerged plants also grow
across the bottom. The fi rst notable change was
a substantial increase in the submerged macrophytes. These cause hindrance in navigation. It
may be noted here that the original characteristics of the broads persisted in only one or two
of the 42 lakes.
Notwithstanding the above, the interactions
between grazing zooplankton and fi sh also affect
the balance between the plant communities.
Management of the Norfolk Broads was in
the hands of a number of different organisations.
As the evidence of change in both the aquatic
and semi-terrestrial environment mounted and
some of the causes became clearer during the
1970s, it became evident that some sort of coordinating body was needed to oversee the Broads
as a whole.
6.2 Lakes of Temperate Region