dc.description.abstract |
The objective of the study was to find the seasonal and spatial
variations of different hydrographical factors of the Vcmbanad Lake
around Panangad region and compare the situation with that of the other
parts of the lake. Salinity, temperature, current velocity and direction,
dissolved oxygen, primary production and nutrients like phosphate,
nitrite and nitrate were the parameters studied. For this monthly
observations of these factors were made from nine stations located in
and around Panangad region of Vembanad Lake. Beside this tidal cycle
observations were carried out from two stations to study the tidal
variation of the factors. S.T.D. meter was used to measure salinity, and
temperature and a current meter for the current measurements. Water
samples from surface and sub surfaces were collected with a clean
bucket and a Van Dorn bottle. The estimation of dissolved oxygen,
primary production and nutrients were done by standard methods.
Marked seasonal fluctuation was noticed in the temperature of different
stations. Annual variation showed two maxima. The temperature was
minimum during southwest monsoon and maximum during pre monsoon
months. In general, the vertical thermal stratification was small. The
salinity exhibited marked seasonal fluctuation and generally the
monsoon months recorded very low salinity values. After that there was
an increase, reaching the maximum in pre monsoon months. Some
vertical stratification was noticed during certain months. The Dissolved
oxygen values were low during pre monsoon months and the content
was more at surface than at the bottom layers.
There was high seasonal fluctuation In the phosphate
concentration. It showed high concentration during pre monsoon period.
Generally bottom layers showed higher phosphate concentration than the
surface layers. In the case of nitrite high values were observed durin
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the monsoon and low values during dry season. Nitrate concentration
also showed seasonal variation and high values were observed during
the monsoon and low values during pre monsoon. The nutrient
concentration was more in the inner smaller arms of the study area, in
general. These inner arms were vertically homogenous also possibly
due to higher mixing generated by the friction of the sides.
In the tidal cycle observations it is found that salinity showed an
increase during flood tide and decrease during ebb tide. At both stations
considerable reduction in flood current speed was observed during post
monsoon, compared to pre monsoon. During pre-rnonsoon a
comparatively well mixed condition was prevailed. Post monsoon
observations indicated very clear salinity stratification. This was due to
the effect of freshwater discharge, which continued during this season
though at reduced rate compared to monsoon season. It is found that the
tidal effect on temperature was not well marked.
It can be seen that different hydrographic factors of Panangad
region of the Vembanad Lake exhibited much seasonal and spatial
variations and the trend was in general, same to that shown by other
parts of the lake. |
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