CONCLUSION

The biomonitoring of the lake was done to assess the present status of Bangalore lakes - Sankey lake, Rachenahalli lake, Ulsoor lake and Tippagondanahalli lake, that were selected on the basis of the use values. The investigations included the physicochemical characterization of the lakes as well as the zooplankton diversity of these lakes. The physicochemical analysis was performed by standard methods. The zooplankton analysis was carried out by standardization of volume of water to be filtered for zooplankton analysis and the identification by using standard keys.

Water quality analysis: Among the four selected lakes, Rachenahalli and Ulsoor were found to be the most affected by anthropogenic activities. The possible entry of industrial effluents contributed to the high levels of heavy metal concentration and low levels of dissolved oxygen was due to the decomposition of organic matter from sewage entering the Ulsoor lake. The runoff from surrounding agricultural fields and concentration of chemical constituents in partially dried up aquatic environment of Rachenahalli were the cause for the deterioration of water quality in the lake. Rachenahalli lake was further disturbed by unplanned developmental activities along the shorelines of the lake, which had its influence on the water quality. Sankey lake also showed less dissolved oxygen levels, which might be due to the entry of organic matter during runoff from the surrounding urban areas. Tippagondanahalli lake is influenced by natural processes, which was the cause of the increase in pH and decreased dissolved oxygen levels. The lake water however, has to be treated properly due to faecal contamination by bird droppings.

Zooplankton analysis: The standardization of the volume of water to be filtered for zooplankton analysis as per the iterative experiment is 100L. Thus the species-volume curve had reflected that the surface water sampling for Zooplankton analysis requires a minimum of 100L of water to be filtered for sampling all the species in the area sampled. Filtering 100L of water might eventually lessen the sampling errors. The zooplankton analysis also confirmed the poor water quality of Ulsoor and Rachenahalli. The lakes had poor representation of the zooplankton community, which is vital for the survival of the higher trophic states. This had eventually let to the death of fishes in Ulsoor lake. In Rachenahalli anthropogenic activities had altered the zooplankton community structure, which would influence the entire trophic structure of the lake. The Shannon-Weiner index also showed the less diversity in these lakes. Sankey lake had higher diversity of zooplankton when compared to other lakes because of the sufficient nutrient input resulting in mesotrophic condition and lesser disturbance to the water quality. Tippagondanahalli lake was oligotrophic in nature because of lesser nutrient input and hence zooplankton community was sparse.

Thus, the results for the present study on Bangalore lakes indicates the need for comprehensive monitoring of these lakes for proper management decisions to be taken for the restoration of Ulsoor and Rachenahalli lakes, which had been threatened ecologically due to various anthropogenic activities. Concerned authorities of the Bangalore Water Supply and Sewerage Board (BWSSB) have to take appropriate action by controlling the sewage and industrial effluent let into the Ulsoor lake. Letting in treated water would maintain the water quality that will improve the aquatic biota. The Rachenahalli lake needs immediate remedial actions against shoreline degradation. Hence the Bangalore Development Authority (BDA) should stop the construction of road, which has affected the water quality and aquatic biota in the lake as revealed in this study.