CONTENTS-
Abstract
Introduction
Description of the Tank
Materials and Methods
Result and Discussion
Conclusion
References

The paper describes the physico-chemical characteristics of water, diversity and periodicity of phytoplankton.  Surface water samples were collected at an interval of 30 days for a period of one year using plastic cans of three litre capacity.   Standard procedures were followed during collection, preservation and analysis of water samples for various physico-chemical and biological parameters.   The physico-chemical parameters studied were within   the permissible limits.   The phytoplanktonic community is represented   by five classes and seventy two species.   Density of the different groups of phytoplankton is more in the summer season than during rainy and winter seasons.   Based on the results of Nygaard's and Palmer's algal indices it has been deduced that, the tank is eutrophic.   It is high time   to formulate some   strategies for the conservation of the tank and to restore the   water quality.

The utilisation of lentic water bodies for domestic purposes and fish culture has   assumed   importance in developing countries.   The disposal of agricultural waste and untreated sewage into water bodies adversely affect the plant and animal life.   Sukumaran (2002) is of the opinion that the constant discharge of sewage into the aquatic system enriches the organic content, leading to eutrophication and deterioration of the quality of water.   In India, inland water bodies attracted the attention of various workers leading to the studies on water quality and distribution of phytoplankton from time to time, (Zafar, 1967, Munawar   1974).   Although considerable work has been done on the limnological studies on some tanks and ponds of   Karnataka, the Gubbi tank, Tumkur selected for the present study remains scientifically unexplored.

In the present investigation, data on morphometric features, water quality   parameters, density and diversity of phytoplankton communities have been gathered.   Based on this data an attempt has been made to asses the quality of water and to evaluate the trophic status of the lake.

Gubbi   tank, Tumkur is a fresh water body situated towards the west, 15 kms from Tumkur city.   It lies at 13 ° 18 ¢ north latitude and 76 ° 57 ¢   east longitude.   It is a medium sized tank with an water spread area of 370 hectares.   The average depth   of the tank is 2.5 to 3 meters along the bund.   The tank   is rain fed during monsoon period.   The tank is also fed by Hemavati canal water. The water of the tank is used to cultivate paddy crops   and is also used for domestic purposes.   Washing activity is commonly seen.   Aquatic weeds like Ipomea aquatica, Nelumbo, Cyperus sp, Eichhornia are seen in the tank.  

The total catchment area of the tank is 821.77 sq.km with an average annual rainfall of 787 mm.   The tank is irregular in shape and water in the tank is held by a raised north-south earthern bund, which is 5.10 meters in height, 700 meters in length.   The soil in the catchment   area is black clay and gravel   .

Surface water samples were collected from identified stations of the lake at a depth of one feet using polythene cans   of two litre capacity for a period of one year ( April 2000 – Mar 2001) at monthly intervals.   pH was measured on the spot using pH paper and later confirmed in the laboratory using digital pH meter.     The chemical analysis was carried out following the methods suggested by Trivedy and Goel (1986) and standard methods   of APHA (1995).

For the enumeration of phytoplankton, two litres of sample was fixed simultaneously with 20 ml of 1% lugol solution for sedimentation. This sedimented sample was observed under microscope for algal composition and the diagrams were drawn with the help of camera lucid    technique.   The identification of phytoplankton up to the level of species was made with the help of literature cited   [ Philipose M.T(1967),   Deshikachary (1959), Gandhi (1955)]. Trophic status of the lake was assessed using Nygaard's   indices.

Phytoplankton population   in the Gubbi   tank, Tumkur   is composed of five major groups   namely Cyanophyceae, Chlorococcales, Bacillariophyceae , Euglenophyceae and Desmidiaceae.   The density of phytoplankton shows that Bacillariophyceae dominated and constituted (36.36%) of total phytoplankton population followed by Chlorococcales (25%), Cyanophyceae (25%) and Desmidiaceae ( 6.82%) and Euglenophyceae (6.82%).   In the present study the maximum density of phytoplankton was recorded in May - 72760 Organisms/ Litre   and minimum in September - 60099 Org / Litre.

The density of Chlorococcales ranged between 12226 in September to 13996 Org / L in July (Table-2).   The average density of Chlorococcales was low in winter season 13159 Org / L and was fairly high during summer -13447 Org / L (Table-3). The density of Bacillariophyceae ranged between 2869 in August to 6946 Org/L in March (Table-2).   The average density of Bacillariophyceae was low in rainy season 3400 Org/L   and was recorded high during summer 6223 Org/L (Table-3). The density of   Desmids   varied between 7 in September and November to 18 Org/L in July (Table-2).   The average density of Desmids was low in winter season 10 Org/L and was high during summer 13 Org/L (Table-3).   The density of Euglenoids ranged between 28571 in September to 32413 Org/L   in June (Table-2).   The average density of Euglenoids was low during winter 29972 Org/L and recorded high during rainy   season 30316 Org /L (Table-3). The density of Blue-green algae ranged between 15614 in October to 23196   Org / Liter in May (Table-2). The average density of Blue-greens was low in winter season 17989 and was high during summer 22374 Org/Liter.

In the present study, the compound quotient value obtained is 0.7 indicating that, the lake is eutrophic.   The Myxophycean index value obtained is 1.2, Chlorophycean index value obtained is 1.5 and Euglenophycean index value obtained is 0.64, which also confirms the eutrophic status of the lake.   Sankaran Unni ( 1982) was of the opinion that, the occurrence of Microcystis and Anabaena is the characteristic feature of eutrophic water.   The same is true to the present investigation.

Data on water quality parameters having direct bearing upon the distribution and ecology of different phytoplankton communities in the Agrahara wet land are detailed in Table – 1.

The water temperature plays an important role in controlling the occurrence and abundance of phytoplankton (Nazneen, 1980).   The enhanced growth of the algal flora noticed in the present study during the pre-monsoon period could be attributed to increased temperature and light during this season as suggested by Kopoczynska (1980) (Table-1).

Verma and Mohanty (1995) have reported a direct relation ship between pH and phytoplankton.   Robert et.al., (1974) suggested that pH 5 to 8.5 is ideal for phytoplankton growth and this was found to be true in the present investigation.

Zafar in 1967 was of the opinion that,   calcium is one of the important elements influencing the distribution of Bacillariophyceae.   In the present investigation calcium ranges between 39 to 78 mg /L favouring the dominance of Bacillariophyceae (22 species).   This is in agreement with the findings of Zafar.

Presence of Microcystis and Anabaena, high alkalinity and hardness indicates the trend of the water body towards eutrophication   (Sankaran Unni,1982).   In the present investigation alkalinity ranges between 14 to 23 mg/L and the total hardness ranges between 114 to 399 mg/Liter.   Microcystis and Anabaena were recorded in all the months of the study period.   This is in agreement with the findings of Unni.

Munawar (1974) study shows a   direct relationship between concentration of silicates and the density of diatoms. .   In the present investigation, the Silica content was low and ranged between 0.09 to 0.2 mg/L, yet the water body harboured considerable number of diatoms.   This indicates that, the concentration of silica is not the only parameter that regulates the diatoms population in the water body.  

Some of the phytoplankton indicating the eutrophic status of the tank encountered during the study   is listed below. Euglena, Oscillatoria, Scenedesmus, Nitzschia,   Navicula, Synedra, Ankistrodesnus, Phacus, Phormidium, Melosira, Gomphonema, Cyclotella and Anabaena

Based on the compound quotient value and values of the Nygaard's algal indices it has been deduced that, the tank is eutrophic.   It is hightime for the conservation of the tank in order to restore the quality of water.

•  APHA, AWWA 1985. Standard. Methods for the examination of water & waste water. Washington DC 18th Edition.

•  Kopoczynska   E.E. 1980. Seasonal variation in phytoplankton in the grand river mouth area of lake Michigan. Pol.Arch. Hydrobiol. 27(1):95-123.

•  Munawar M. 1974. Limnological studies on fresh   water ponds of Hyderabad, India.   Biocenase Ibid, 45, 1-32.

•  Nazneen S. 1980. Influence of hydrological factors   on seasonal abundance of phytoplankton in Kinjhar lake, Pakistan.Int. Revu.Ges. Hydrabiol. 65(2): 269-282.

•  Philipose M.T. 1960. Fresh water phytoplankton of inland fisheries.   Proc. Symp. Algol. ICAR, New Delhi. 272 – 291.

•  Robert D.S., Robert W.H and Evereff L.G.1974. Phytoplankton distribution and water quality indices of lake head ( colorodo river). Phycol, 10: 232 – 333.

•  Sankaran Unni K. 1982. Limnological studies on Sampna Reservoir, Betul, M.P. Proc. Nat. Acad. Sci. India, 52(B), IV. 365-372.

•  Sukumaran P.K. 2002. Aquatic microflora in a perennial tank in Bangalore. Envt. and Ecol. 20(1) : 8-12.

•    Trivedy R.K and Goel P.K. 1986. Chemical and Biological methods for water pollution studies.

•    Verma J and Mohanty R.C. 1995 phytoplankton and its correlation with certain    physico-chemical parameters of Danmukundpur pond. Poll.Res. 14(2): 233-242.

•    Zafar A.R 1967. On   ecology of algae in certain fish ponds of Hyderabad, India-III.   The periodicity. Hydrobiol. 30, 96-112.

Department of PG Studies and Research in Environmental Science,
Kuvempu University,
Jnanasahyadri – 577451,
Shimoga, Karnataka, India.

* Karnataka State Pollution Control Board,
Bangalore. Karnataka, India.