21
2 Eutrophication: Global Scenario and Local Threat to Dynamics of Aquatic Ecosystems
and Paspalum paspaloides occupied larger area on its northern and southern margins (Plate 1). But their density reduced
in the harvested areas on southern side. T. angustata and P.
paspaloides are harvested at small scale by local farmers and
used for making mats and cattle feed.
June 2003 The size of water body reduced in area. The
water depth varied from 25 cm to a little over 60 cm. The
duckweeds and water hyacinth disappeared. The patches of
Typha angustata expended from moist eastern coast to the
centre of pond. The water depth reduced to 12–15 cm on
northern coast. The density of T. angustata further reduced
owing to intensive harvesting. The T. angustata on eastern
side was in drying phase but relatively green on south western side. The water receded and left eastern and northern
sides as exposed moist sediments. About 20–30 m of southern coastal side of water body further dried and turned to be
a marshy area.
July 2003 The pond was recharged owing to downpour in its
catchment. The water level increased up to 90–110 cm with
lesser density of duckweeds. The Spirodela polyrrhiza was
more abundant ( + + + ) than Lemna minor ( + ). The Typha
angustata started sprouting again. The dried margins along
all its sides, recorded in preceding month became marshy
again. The water body swelled by the end of July 2003. The
water-filled area and depth of the pond increased. The duckweeds covered the water surface within and between the
patches of Typha angustata in the centre, eastern, northern
and south western sides of the pond.
August 2003 Most of the water surface was covered with
duckweeds ( Lemna minor and Spirodelapolyrrhiza). The
density of duckweeds increased in this month as compared
to July 2003. The water level increased up to 90–150 cm.
The density of Lemna minor ( + + + ) and Spirodela polyrrhiza ( + + + + ) increased as compared to the last month. The
water-filled area of the pond was almost one and a half times
larger than in the July 2003. The density of the T. angustata on eastern and southern coasts increased. The central
part of the pond was free from any floating, submerged or
rooted submerged plants. In this month, some diatoms and
blue-green algae (details not covered in this study) were also
noted to be present on coastal sides.
September 2003 Water level and area of the water body
continued to be very high. The water depth was 100–150 cm
on southern and eastern coast of the pond. The density of
Lemna minor and Spirodela polyrrhiza decreased as compared to the density recorded in August. For the first time,
some small patches of Wolffiaarrhiza were also noted on the
shallow coastal sides of the pond. The blue-green algae and
diatoms were present.
October 2003 The water level at some places receded. The
area of water body reduced. The water depth receded up to
30–50 cm on eastern southern and western coasts. The total
area and volume of the water body reduced as compared to
September. The density of Lemna minor and Spirodela polyrrhiza reduced substantially and disappeared from a large
portion of the water body. The duckweeds were limited in
4 m × 6 m size patches in open water area and between the
patches of Typha angustata on the eastern and south western sides. Some small patches of Wolffia arrhiza were also
present.
November 2003 Both the selected duckweeds ( Lemna
minor and Spirodela polyrrhiza) rebloomed on the margins
of open water body. The central part of the water body was
almost devoid of duckweeds. Sparse populations of Wolffia
arrhiza in small patches of approximately 25 × 30 cm to
50 × 50 cm sizes were found on the shallow and marshy
margins of pond. The presence of algae and diatoms caused
greenish appearance of water on the north western and western coasts of the pond.
December 2003 The duckweeds disappeared leaving the
water surface open. The Typha angustata bloomed on north
eastern, eastern and south western sides of the pond. Paspalum paspaloides grew predominantly on southern side.
The water in this month was more turbid and dirty owing
to the decaying duckweeds. The area of water body reduced
slightly.
January 2004 The duckweeds started reappearing with
abundant Spirodela polyrrhiza ( + + ) and sparse population
of Lemna minor. Dense patches of Paspalum paspaloides
were recorded. The water body size reduced further than in
the month of November and December. The north western
side of the pond turned marshy and at places, patches of sediments were exposed. The main water body was limited to
central and western side of pond. Rare occurrence of Eichhornia crassipes was seen on the eastern and north eastern
margins. The water was more turbid than in the preceding
month.
February 2004 The population of duckweeds was dense
owing to gregarious blooming. The water level and area
reduced further. The water was turbid. The density of water
hyacinth was relatively higher than in the month of January.
March 2004 The major part of the water body was covered
with densely populated duckweeds ( Lemna minor and Spirodela polyrrhiza). A dense semi-lunar stripe of water hyacinth
was formed and floated along northern, eastern and southern coasts. The water hyacinths were in the stage of drying.
The patches of mature duckweeds formed thick brownish
2 Eutrophication: Global Scenario and Local Threat to Dynamics of Aquatic Ecosystems
and Paspalum paspaloides occupied larger area on its northern and southern margins (Plate 1). But their density reduced
in the harvested areas on southern side. T. angustata and P.
paspaloides are harvested at small scale by local farmers and
used for making mats and cattle feed.
June 2003 The size of water body reduced in area. The
water depth varied from 25 cm to a little over 60 cm. The
duckweeds and water hyacinth disappeared. The patches of
Typha angustata expended from moist eastern coast to the
centre of pond. The water depth reduced to 12–15 cm on
northern coast. The density of T. angustata further reduced
owing to intensive harvesting. The T. angustata on eastern
side was in drying phase but relatively green on south western side. The water receded and left eastern and northern
sides as exposed moist sediments. About 20–30 m of southern coastal side of water body further dried and turned to be
a marshy area.
July 2003 The pond was recharged owing to downpour in its
catchment. The water level increased up to 90–110 cm with
lesser density of duckweeds. The Spirodela polyrrhiza was
more abundant ( + + + ) than Lemna minor ( + ). The Typha
angustata started sprouting again. The dried margins along
all its sides, recorded in preceding month became marshy
again. The water body swelled by the end of July 2003. The
water-filled area and depth of the pond increased. The duckweeds covered the water surface within and between the
patches of Typha angustata in the centre, eastern, northern
and south western sides of the pond.
August 2003 Most of the water surface was covered with
duckweeds ( Lemna minor and Spirodelapolyrrhiza). The
density of duckweeds increased in this month as compared
to July 2003. The water level increased up to 90–150 cm.
The density of Lemna minor ( + + + ) and Spirodela polyrrhiza ( + + + + ) increased as compared to the last month. The
water-filled area of the pond was almost one and a half times
larger than in the July 2003. The density of the T. angustata on eastern and southern coasts increased. The central
part of the pond was free from any floating, submerged or
rooted submerged plants. In this month, some diatoms and
blue-green algae (details not covered in this study) were also
noted to be present on coastal sides.
September 2003 Water level and area of the water body
continued to be very high. The water depth was 100–150 cm
on southern and eastern coast of the pond. The density of
Lemna minor and Spirodela polyrrhiza decreased as compared to the density recorded in August. For the first time,
some small patches of Wolffiaarrhiza were also noted on the
shallow coastal sides of the pond. The blue-green algae and
diatoms were present.
October 2003 The water level at some places receded. The
area of water body reduced. The water depth receded up to
30–50 cm on eastern southern and western coasts. The total
area and volume of the water body reduced as compared to
September. The density of Lemna minor and Spirodela polyrrhiza reduced substantially and disappeared from a large
portion of the water body. The duckweeds were limited in
4 m × 6 m size patches in open water area and between the
patches of Typha angustata on the eastern and south western sides. Some small patches of Wolffia arrhiza were also
present.
November 2003 Both the selected duckweeds ( Lemna
minor and Spirodela polyrrhiza) rebloomed on the margins
of open water body. The central part of the water body was
almost devoid of duckweeds. Sparse populations of Wolffia
arrhiza in small patches of approximately 25 × 30 cm to
50 × 50 cm sizes were found on the shallow and marshy
margins of pond. The presence of algae and diatoms caused
greenish appearance of water on the north western and western coasts of the pond.
December 2003 The duckweeds disappeared leaving the
water surface open. The Typha angustata bloomed on north
eastern, eastern and south western sides of the pond. Paspalum paspaloides grew predominantly on southern side.
The water in this month was more turbid and dirty owing
to the decaying duckweeds. The area of water body reduced
slightly.
January 2004 The duckweeds started reappearing with
abundant Spirodela polyrrhiza ( + + ) and sparse population
of Lemna minor. Dense patches of Paspalum paspaloides
were recorded. The water body size reduced further than in
the month of November and December. The north western
side of the pond turned marshy and at places, patches of sediments were exposed. The main water body was limited to
central and western side of pond. Rare occurrence of Eichhornia crassipes was seen on the eastern and north eastern
margins. The water was more turbid than in the preceding
month.
February 2004 The population of duckweeds was dense
owing to gregarious blooming. The water level and area
reduced further. The water was turbid. The density of water
hyacinth was relatively higher than in the month of January.
March 2004 The major part of the water body was covered
with densely populated duckweeds ( Lemna minor and Spirodela polyrrhiza). A dense semi-lunar stripe of water hyacinth
was formed and floated along northern, eastern and southern coasts. The water hyacinths were in the stage of drying.
The patches of mature duckweeds formed thick brownish