06-bioresourcesstatu.. - M. S. Swaminathan Research Foundation

the spring tides around 1 m and the tidal influence
around 10 km from Pulicat pass (Krishnamurthy,
1974).
iv. Soil
The bottom soil is mainly composed of fine quartz
sand along the eastern shore and bar mouth area.
Shallow marginal areas are oozy mud and sandy
mud along the western shore of the lake from
Edamanikuppam on the south to Arambakkam-
Puliancheri on the Northern side. Most of the Lake
bottom is composed of clay to clayey-sand with
patches of algae and weeds (Krishnan and
Sampath, 1978). The substratum could be
classified into three types: (a) Predominantly
sand, (b) Sand and Mud in equal mixture and (c)
Predominantly mud. Composition of soil is silt
2.5%, Sand 45-60% and clay 40-50%. The soil pH
varies from 7.2 to 7.6.
v. Wind and wave action
Continuous strong winds with an average speed of
9.0 to 16.4 km. ph are common from the southwest
quadrant for about seven months (March-
September) of the year. Such winds giving rise to
strong waves in the lake through out the daytime.
During October to February, the wind is from
northwest quadrant in the morning and northeast
quadrant in the evening (report of the Regional
Metrological Observatory, Chennai).
vi. Water movements and tidal action
The water movement in the lake is dependent on
the quantity of water received from the rivers and
the tidal oscillations of the sea. The river entering
the Lake receives maximum rainfall, only during
the monsoon periods (October to December). The
maximum mixing and movement of the water
occurs during this period which is felt up to 10 km
from the bar mouth. As the freshwater influx
lessens, tidal effects begin to appear in certain
parts of the Lake and the flow of fresh water into
the sea is very much reduced. When there is no
discharge of water from the river, evaporation in
the lake is considerably high and the water level
in the lake decreases and a marine isostatic head
develops near the lake. The strong southwest and
southeast winds favors the distribution of seawater
in the lake. During this period the currents in the
channel are controlled by the tides and in the lake
by the winds (Rao and Rao, 1975).
Waves in the Pulicat Lake are mostly wind
generated. The wave direction changes according
Pulicat Lake
to the wind direction. Height of the wave in the
lake seldom exceeds 0.6 m with short wave
lengths. The Bar mouth openings are generally
shorter in width and keeps away the larger waves
of the open sea and therefore the waves in the
Pulicat Lake are not rough through out the year.
The height of the wave ranges from 0.3 to 0.7
meters and the period of the wave only up to 5
seconds (Rao and Rao, 1975).
The lake is subjected to a limited tidal influence.
The tidal effect is to a larger extent masked by the
influence of wind-generated waves, which can
sufficiently account for the diurnal changes of
water level in the lake. The oceanic tide enters
the lake area and the fluctuations are of diurnal
types with amplitudes usually less than one foot.
The magnitude of salinity variations is directly
proportional to the amount of .rainfall. Plankton
biomass and phytoplankton standing crops follow
the tidal cycle. Zooplankton populations though
varied with the tide are generally more abundant
during night high tides than during other tidal
stages (Kaliyamurthy, 1976).
145
vii. Temperature, Salinity and pH
The surface waters of the lake have a temperature
range of 32.6" C to 33.8" C in the dry season and
from 23.5" C to 24.5" C in the monsoon. The western
and southern lagoon have slightly lower
temperatures (23.5"C) in the monsoon season
compared to the other parts of the lake, as large
volumes of fresh water debouch into these regions
exerting a cooling effect. During monsoon season,
the salinity of the surface waters of the lake is
minimum and at some places less than 0.5 '(00' The
dry season salinity of the lake waters is generally
high. The salinity of the channel area is 34.4 '(00'
which is more or less equal to the salinity of the
Bay of Bengal waters near the lake mouth. In this
period the main area of the lake is super saline
and the channel is almost filled with seawater.
Northern extremities of both the western and the
northeastern lagoons have highest salinity of 41.5
'(00' This is of special interest from ecological point
of view, since it determines the limits of invasion of
marine and fresh water organisms. (Rao and Rao,
1975)
The pH values of the lake range from 7.8 to 8.4.
During dry season the pH values of the lake
closely follow the salinity values. Evaporation
plays an important role during dry season in the
Pulicat Lake resulting in super saturation with