Summary and Conclusion

The large urban  lakes of Bangalore has been subjected in the last few years to a drastic rate of sewage pollution due to the high loads of discharges leading to a prominent changes in physico-chemical conditions and phytoplankton community. The study of some physico-chemical parameters and their impacts on the standing crop of phytoplankton and primary production indicated that the maximum number of phytoplankton species counted was belonging to class Chlorophyceae (Chlorella blooms) in case of Urban lakes as Varthur and Bellandur which is an indicator of Eutrophication . In the otherhand T.G.Halli the Bacillariopyceae taxa dominated owing to a healthy trophic status. Chlorophyll a content is more or less similar to the pattern of phytoplankton counts. The stations nearby the inflow regions at Varthur receiving sewage from drains recorded the lowest content of chlorophyll a. However the T.G.Halli reservoir had the highest Chlorophyll a levels attributed by benthic chloroplast levels showing higher light penetration and photosynthetic productivity. The Day net photosynthesis was found to be higher in case of lake T.G.Halli compared to the urban nutrient stressed lakes. This varied from site to site depending on the characteristics of water and its microclimate. Physicochemical conditions affected the Net productivity with different patterns. Transparency exhibited significant positive relation with the total count of phytoplankton. Chlorophyll a, phosphates, nitrates and dissolved oxygen showed a negative relationship with the day net photosynthetic productivity. The relation of total alkalinity with the total count of phytoplankton and chlorophyll a, was positive. From the data obtained, T.G.Halli is considered as a pristine water body with a healthy trophies status which is least stressed. The urban lakes Varthur and Bellandur and undergoing a high nutrient stress resulting in anaerobic conditions with the lakes becoming increasingly eutrophied.