Seasonal and diurnal variation of hydrobiological characters of coastal water of Chennai (Madras), Bay of Bengal

Seasonal and diurnal variations in the hydrobiological characters of coasta l water of southern Chennai, Bay of Bengal were studied. Parameters such as current, pH, salinity, inorganic nutrients, (NH4, NO2, NO3, PO4, SiO3-SiO2 ) and heavy metals exhibited unimodal oscillation and temperature, dissolve d oxygen (DO), biological oxygen demand (BOD) and suspended solids exhibite d bimodal oscillation. Particulate organic carbon (POC) was positively corr elated with suspended solids. Chlorophyll-a (chl-a) and phytoplankton densi ty showed two maxima; one in summer and another in southwest monsoon season and minimum value during the northeast monsoon. Productivity was low in no rtheast monsoon compared with other seasons. Temperature, dissolved oxygen (DO), chlorophyll-a (chl-a) and productivity increased in the day time and vice vel-sa for inorganic nutrients. Low tide brought more nutrients and le ss saline water from the estuarine region; high tide brought more chi-a fro m the offshore water. All the parameters were highly influenced by monsoona l rain, littoral drift and land drainage in a season but diurnal variation was due to the combination of more than one factors.