The present study was carried out to ascertain the magnitude of seasonal diel variations in physicochemical and biological variants with reference to phytoplankton, zooplankton and primary productivity at newly formed Omkareshwar reservoir on the river Narmada for the year 2012. Diel variations in physicochemical parameters such as temperatures, pH, transparency, total alkalinity, total hardness, chloride content, dissolved oxygen, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) were observed between 1100 and 0700 h. No phytoplanktonic diel variations have been observed, but zooplanktons were well known for their diel variations as they can actively swim towards most suitable environmental niche in the river. The result shows the oligotrophic nature of this reservoir. Maximum value of total phytoplankton (271.97 Org/L) was observed around 1100 h in summer but the highest value of total zooplankton (930.78 Org/L) was recorded at 2300 h in summer season. Maximum value of net primary productivity (600 g C/m3 /3 h) was noticed at 1100 h in summer season. The suitable correlation coefficients were calculated for 15 pairs of variables and correlation matrices were then established seasonally. Net primary productivity (NPP) depicted a positive correlation with dissolved oxygen and phytoplanktonic productivity (r = + 0.577 and r = + 0.459), respectively.
Key words: Biochemical oxygen demand (BOD), chemical oxygen demand (COD), diel, zooplankton, phytoplankton.
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