Abstract: The present study deals with the study of the seasonal changes in phytoplankton population in Tungabhadra river from Harihar, Karnataka. From the selected 3 stations of Tungabhadra river water samples were collected at monthly intervals. Qualitative and quantitative analysis of phytoplankton were carried out during the year 2003-2004. About 71 species of phytoplankton were found comprising Chlorophyceae 35.47%, Bacilleriophyceae 18.11%, Cyanophyceae 37.48% and Euglenophyceae 8.93%. The peak of the phytoplankton population was observed during summer.

INTRODUCTION

Phytoplankton constitute the very basis of nutritional cycle of an aquatic ecosystem. Phytoplanktons play a key role in a fresh water ecosystem as primary producers and constitute the major fraction of food energy transferred to the second trophic level (herbivores). It becomes quite essential to study the trends of seasonal variation in phytoplankton community.

Phytoplanktons are plants inhibiting almost all kinds of habitats. Majorities of them inhabits water bodies and are sensitive to pollution. They quickly respond to environmental changes. This aspect led several workers to use algae as biological indicators of water quality (Sreenivasan, 1963, 1964; Munawar, 1974; Hegdae, 1989; Patil, 1960; Sharma and Sharma, 1992). Phytoplanktons of fresh water rivers have been studied extensively in India Mishra and Saksena (1993), Somasekar (1988) and Trivedy and Khatavkar (1996) various phytoplankton groups prefer to exist in various kinds of water. However, no particular group there may be certain species which resist pollution while others may be very sensitive, Pearsall (1930, 1932) have attempted to pin point that water containing chlorophyceae are different from diatoms and member of myxophyceae. The density of phytoplankton has been reported to be affected by the quality of water (Bilgrami and Munshi, 1985).

The present investigation have been undertaken to study the seasonal changes in phytoplankton population in Tungabhadra river during December 2003 to November 2004 near Harihar town, Davangere District., Karnataka. For convenient three sampling stations S1-S3 from the river were selected.

MATERIALS AND METHODS

The water samples for phytoplankton analysis were collected from the river for a period of 12 months starting from December 2003 to November 2004. Quantitative determination were carried out refering the algal samples were presented by Trivedy and Goel (1984). A qualitative and quantitative study of 4 groups of algae was made, the pollution tolerant genera and species were recorded at 3 stations of river according to Palmer and Rao (1992) and APHA (1995).

RESULTS

The total number of phytoplankton and monthly average phytoplankton number per mL were shown in the Table 1. While seasonal variation and percentage composition of plankton components has been shown in Table 2 and 3. It was noted that the total number of phytoplankton at station S1 from 2513-5602 mL^-1 and at station S3 2343-5999 mL^-1 during the year 2003-2004.

Chlorophyceae: Chlorophyceae was encountered as the 2nd most significant group of phytoplankton with a contribution of 35.47% (Table 2) to the total annual population.

Table 1:	Mothly variatios in phytoplakto count mL-1 (2003-2004)

Table 2:	Percentage of phytoplankton

Table 3:	Seasoal variatios of phytoplakto groups of the river Tuga Bhadra

It exhibited maximum density during January, April and December and least in September (Fig. 1). The group includes Pediastrum dup ex sp., Spirogyra sp., U othrix sp., Cosmarium sp., Scenedesmus sp., Costerium anceo atum sp., Desmidium grevie ei sp.

Bacillariophyceae: It accounted for a contribution of 18.11% (Table 2) to the total annual phytoplankton population. Its maximum density was noticed during April, October and August and least in February (Fig. 1). This group includes Cymbea sp., Nitschia sp., Meosires sp., Pinnuaria sp., Synendra sp. and Fragiaria sp.

Cyaophyceae: It was the most significant group of phytoplankton having and contribution of 37.48% (Table 2) to the total population. It exhibited maximum density during July, March and December and least in September and April (Fig. 1). This group includes Yngbaea sp., Nostoc sp., Anabaena sp., Phormodium sp., Osci atoria sp. and Microcystis sp.

Eugleophyceae: It contributes 8.93% to the total annual phytoplankton production and was represented by Eugena spirogyra sp., Eugena minuta sp., Phagus sp. and Tracheomonas sp.

Fig. 1:	Monthly variations in the average total count of all phytoplankton population

DISCUSSION

In water body, there usually occurs seasonal qualitative and quantitative fluctuations in the planktonic population in temperate and tropical climate. The reports of some workers suggest that the maximum development of phytoplankton occur during summer and minimum in winter (Philipose, 1960; Kumar and Dutta, 1991; Anjana and Kanhera., 1980). While Kumar estimated that the density of phytoplankton is greater during summer, post monsoon and winter and is lowest in monsoon. In the present investigation also peak of the phytoplankton was observed during summer followed by winter (Table 3 and Fig. 2). Saha and Choudhary (1985) obtained the maximum density of phytoplankton during July and minimum during January.

Fig. 2:	Seasonal variation of phytoplankton

Fig. 3:	Monthwise distribution of phytoplankton

In this study, the peak of phytoplankton was observed during July, May and December while lowest peak was found in September followed February and June (Table 1 and Fig. 2). Sreenivasan (1964) have observed that the peaks of phytoplankton occurred at different period in different years. In present study, the population of green algae and blue green algae were abundant as compared to other groups of algae, cyanophyceae was dominant in summer season as compared to other seasonal. In overall, the phytoplankton of algal flora was greater in summer season as compared to the other seasons as agreed with observation of Singh (1960), Nazneen (1980) and Nandan and Patel (1984). Margalef (1968) suggested that phytoplankton population in fertile water is more diverse than those in infertile water.

The study revealed dominance of cyanophytes followed by chlorophytes, bacillariophytes and euglenophytes. Similar finding was also reported by Padhi (1995) in a polluted pond. Low phytoplankton density recorded during rainy season may possibility be due to dilution by the rainy water coupled with other unfavorable environmental conditions (Fig. 3). The percentage of chlorophyceae was observed greater as compared to 4 groups of algae (Table 2 and Fig. 3) similarly total population of green algae was greater at all 3 stations as compared to those of other groups. Uglenoids were more or less uniform in population. Its percentage was very less as compared to other groups.

CONCLUSION

It may be concluded that the density of phytoplankton is dependent on different abiotic factors either directly are indirectly.

ACKNOWLEDGEMENTS

The researchers are grateful to Management of Bapuji Educational Association (R) and Principal, Bapuji Institute of Engineering and Technology, Davangere for having given magnanimous support, encouragement and facilities.