Vol. 6(1), pp. 12-24, January 2014 DOI: 10.5897/JENE2013.0371 ISSN 2006-9847 ©2014 Academic Journals http://www.academicjournals.org/JENE Journal of Ecology and the Natural Environment Full Length Research Paper Diel variations in limnological characteristics of Omkareshwar reservoir of Narmada river, India Khwaja Salahuddin 1 * Manish Visavadia 2 , Suresh Gor, 3 Chirag Gosai 2 , Virendra Kumar Soni 2 and Mohammad Dilshad Hussain 4 1 Department of Botany, Bahauddin Science College, Junagadh-362001, Gujarat, India. 2 Department of Zoology, Bahauddin Science College, Junagadh-362001, Gujarat, India. 3 Department of Botany, Government Science College, Gandhinagar-382010, Gujarat, India. 4 School of Zoology and Biotechnology, Vikram University, Ujjain- 456010, M. P, India. Accepted 18 November, 2013 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/m 3 /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. INTRODUCTION River plays a major role in assimilating or carrying Indus- trial and municipal waste water, manure discharge and run off which are responsible for river pollution (Choudhary et al., 1991; Toman, 2009). In India, it is important to study the status of pollution of the rivers in relation to various anthropogenic activities as river water has been used as drinking water, for mankind (Suther et al., 2010). River is vital and vulnerable freshwater ecosystems that are critical for the sustenance of all life. The physico- chemical properties affect the nutrient status of water body hence trophic status depends on rate of energy flow which may be assessed by estimating primary produc- tivity (Dudani et al., 1987; Zambave et al., 2004; Iqbal et al., 2004). The study of diel cycle is important for a num- ber of obvious reasons. Diurnal fluctuations in these parameters adversely affect the population of an aquatic *Corresponding author. E-mail: khwajasalahuddin@yahoo.com, salahuddin212@gmail.com. Tel: +91 8950776280. Fax: +91 2852675731.