67
region. H. verticillata was associated with Najas
falciculata in four lakes, with Potamogeton
malayanus in three lakes and with P. pectinatus
and with Ceratophyllum demersum in two lakes.
The most extensive submerged aquatic macrophytes (AM) is said to occur in Lake Toba , which
is the largest lake in this Indonesian Islands. In
Lake Toba, angiosperms had been recorded
monthly up to a depth of 5 m. At this depth, AM
like H. verticillata and P. malayanus were
recorded in Lake Toba. The marginal vegetation
is very diverse. On fl at sandy shores, it was found
to consist of sparse Panicum repens with
Nymphoides cristata.
Lake Singkarak is another quite large lake in
Central Sumatra. In this lake, H. verticillata was
found to occur up to a depth of 8 m. P. malayanus
grew in less deep water. In quite shallow areas,
from 0.5 to 1.0 m depth, this species was less
abundant. This was, perhaps, clearly infl uenced
by mechanical disturbance. Marginally, in quiet
bays, Nymphoides indicum were found to form
beautiful patches with large fl oating leaves and
white fl owers. Locally, there is a marginal swamp
vegetation of Cyperus sp., Polygonum barbatum
growing up to 40 cm and Eleocharis dulcis growing up to 70 cm of water. Ipomoea aquatica was
found to sprawl over the water surface, while
Saccharum spontaneum , etc., were found along
the margins of the lake.
Danau di Atas is a small lake in the same
region. It was found to have quite dilute water
though an alkaline pH. This lake was found to
have P. polygonifolius as the submerged AM.
Shoots of Hydrilla were found fl oating at the
surface.
Lake Ranau is another Sumatran lake. This lake
had an association of P. pectinatus and H. verticillata which was found to be well developed at a
depth of 1–7 m of water. Isolated specimens of
the Hibiscus tiliaceus , etc. , were found to grow in
places where waves may break over the bases of
the tree trunks and branches.
Lake Ranu Lamongan , in East Java, had H. verticillata and C. demersum to a depth of 5 m with
Eichhornia crassipes , Spirodela polyrhiza and
Azolla pinnata , and with Colocasia esculenta
here and there. Further, Ipomoea aquatica was
found to grow out over the water twining amongst
the most superfi cial plants of Hydrilla. The marginal vegetation had also included Typha domingensis , the grass Eriochloa subglabra , Polygonum
barbatum and Jussiaea repens . The trees like
Barringtonia racemosa generally grow along the
lake margins.
6.1.7 Lakes in the Philippines
6.1.7.1 Lake Lanao
Lake Lanao , situated in the Philippines (8° N;
124° E, altitude 702 m MSL, area 375 km
2 , max.
depth 122 m), is one of the few lakes in SE Asia
which had been largely unaffected by human
activities until the 1970s. It lies in a sparsely
populated area and has steeply sloping shores.
It has a mean depth of 60.3 m. It is stratifi ed with
40–60-m deep epilimnion, which is sometimes
disturbed by strong winds. Mixing usually occurs
once in a year. Sometimes, secondary stratifi -
cation occurs within the epilimnion. Abrupt
increases in the nutrients within the euphotic
zone initiates a new succession sequence in the
phytoplankton.
The total content of phytoplankton (PP) and
zooplankton (ZP) in the lake decreases during
seasonal mixing. The ZP includes 7 spp. of
rotifers, 4 spp. of cladocerans and 2 spp. of
copepods.
6.1.8 Floodplain Lakes
of the Chang Jiang (China)
River fl oodplains are those areas where many
lakes occur together. Here, they are found along
the course of one river and its tributaries rather
than a number of different valleys. However, it is
said that the real natural large fl oodplains now occur
in some parts of Africa and South America. They
are highly regulated by man elsewhere. In many
cases, number of lakes, which would occur naturally, is much reduced. Asia, in general, and the
Indian subcontinent, in particular, is blessed with
many natural lentic waterbodies. In this vast region,
there are a large number of lentic waterbodies of
6.1 Lakes of Tropical Latitudes
region. H. verticillata was associated with Najas
falciculata in four lakes, with Potamogeton
malayanus in three lakes and with P. pectinatus
and with Ceratophyllum demersum in two lakes.
The most extensive submerged aquatic macrophytes (AM) is said to occur in Lake Toba , which
is the largest lake in this Indonesian Islands. In
Lake Toba, angiosperms had been recorded
monthly up to a depth of 5 m. At this depth, AM
like H. verticillata and P. malayanus were
recorded in Lake Toba. The marginal vegetation
is very diverse. On fl at sandy shores, it was found
to consist of sparse Panicum repens with
Nymphoides cristata.
Lake Singkarak is another quite large lake in
Central Sumatra. In this lake, H. verticillata was
found to occur up to a depth of 8 m. P. malayanus
grew in less deep water. In quite shallow areas,
from 0.5 to 1.0 m depth, this species was less
abundant. This was, perhaps, clearly infl uenced
by mechanical disturbance. Marginally, in quiet
bays, Nymphoides indicum were found to form
beautiful patches with large fl oating leaves and
white fl owers. Locally, there is a marginal swamp
vegetation of Cyperus sp., Polygonum barbatum
growing up to 40 cm and Eleocharis dulcis growing up to 70 cm of water. Ipomoea aquatica was
found to sprawl over the water surface, while
Saccharum spontaneum , etc., were found along
the margins of the lake.
Danau di Atas is a small lake in the same
region. It was found to have quite dilute water
though an alkaline pH. This lake was found to
have P. polygonifolius as the submerged AM.
Shoots of Hydrilla were found fl oating at the
surface.
Lake Ranau is another Sumatran lake. This lake
had an association of P. pectinatus and H. verticillata which was found to be well developed at a
depth of 1–7 m of water. Isolated specimens of
the Hibiscus tiliaceus , etc. , were found to grow in
places where waves may break over the bases of
the tree trunks and branches.
Lake Ranu Lamongan , in East Java, had H. verticillata and C. demersum to a depth of 5 m with
Eichhornia crassipes , Spirodela polyrhiza and
Azolla pinnata , and with Colocasia esculenta
here and there. Further, Ipomoea aquatica was
found to grow out over the water twining amongst
the most superfi cial plants of Hydrilla. The marginal vegetation had also included Typha domingensis , the grass Eriochloa subglabra , Polygonum
barbatum and Jussiaea repens . The trees like
Barringtonia racemosa generally grow along the
lake margins.
6.1.7 Lakes in the Philippines
6.1.7.1 Lake Lanao
Lake Lanao , situated in the Philippines (8° N;
124° E, altitude 702 m MSL, area 375 km
2 , max.
depth 122 m), is one of the few lakes in SE Asia
which had been largely unaffected by human
activities until the 1970s. It lies in a sparsely
populated area and has steeply sloping shores.
It has a mean depth of 60.3 m. It is stratifi ed with
40–60-m deep epilimnion, which is sometimes
disturbed by strong winds. Mixing usually occurs
once in a year. Sometimes, secondary stratifi -
cation occurs within the epilimnion. Abrupt
increases in the nutrients within the euphotic
zone initiates a new succession sequence in the
phytoplankton.
The total content of phytoplankton (PP) and
zooplankton (ZP) in the lake decreases during
seasonal mixing. The ZP includes 7 spp. of
rotifers, 4 spp. of cladocerans and 2 spp. of
copepods.
6.1.8 Floodplain Lakes
of the Chang Jiang (China)
River fl oodplains are those areas where many
lakes occur together. Here, they are found along
the course of one river and its tributaries rather
than a number of different valleys. However, it is
said that the real natural large fl oodplains now occur
in some parts of Africa and South America. They
are highly regulated by man elsewhere. In many
cases, number of lakes, which would occur naturally, is much reduced. Asia, in general, and the
Indian subcontinent, in particular, is blessed with
many natural lentic waterbodies. In this vast region,
there are a large number of lentic waterbodies of
6.1 Lakes of Tropical Latitudes