ENVIS Technical Report: 25

ECOLOGICAL ASSESSMENT OF LENTIC WATER BODIES OF BANGALORE

CONCLUSIONS

The detailed investigations of the parameters, which are well within the tolerance limits, indicate that the Chamarajasagar reservoir is fairly unpolluted, except for the pH values, which indicate greater alkalinity. This may be attributed to the natural causes and the agricultural runoff from the catchment. On the contrary, the limnology of Madiwala Lake is greatly influenced by the inflow of sewage that contributes significantly to the dissolved solids, total hardness, alkalinity and a low DO of the lake water.

As a major element in aquatic biota, the algal community often exhibits dramatic changes in response to changes in physico – chemical properties of the aquatic environment. The differences in the dominant phytoplankton assemblage of the lakes reflect their trophic levels. It is reported that eutrophic lakes were found to be dominated by Myxophycean forms (Prescot ¹⁰⁰. 1939). The eutrophic lakes had mainly Cyanophycean element dominated by Microcystis. In the present study, although, the two study areas, differ in age, physiography, chemistry and type of inflows, yet they maintain phytoplankton overwhelmingly dominated by Cyanophyceae members, specifically Microcystis aeruginosa. Madiwala Lake phytoplankton also show a high density of Chlorophyceae members dominated by Scenedesmus sp.,  Pediastrum sp., and Euglenophyceaewhich is an indication of organic pollution. These findings are in agreement with those of Chaturvedi ¹⁰¹ et al. (1999). The bulk of the domestic sewage, which enters the Madiwala Lake, has a major influence on the chemistry and in turn on the biological aspects of the lake. The sewage treatment though treats the sewage and helps in lowering the BOD and COD, the N, P, K values remain high, which explains the high density of phytoplankton, and the reduced transparency, high hardness, dissolved solids and alkalinity values.

The results also reveal that due to anthropogenic activities (encroachments, construction activities, waste dumping, sewage disposal, etc.) in the Madiwala Lake catchment area, the drainage connectivity between wetlands have been lost and heavily altered, resulting in reduced water storage capacity and shrinkage in the wetland area which has also contributed to depletion in the groundwater table. While HSR Layout, a residential area in the vicinity was being formed, the drain connecting Agaram lake and Madiwala lake should have been widened. Instead, water was simply diverted to an area where slums have mushroomed. Today the drains are not enough to carry the water and the area was flooded during the recent downpour in Bangalore city.

Remarkably little attention is given to the alarming loss of wetlands in the city. Hence, there is a need to create awareness in public about the loss and to conserve and restore these natural resources. This necessitates the need for restoration and formulation of conservation strategies for sustainable management of wetlands. Further research is required towards understanding:

• the role of individual indicator species in an aquatic system
• linkages between aquatic ecosystem quality and food chain
• interrelationship with other abiotic factors involved
• life history, prey predator relationship, inter and intra – specific competition of indicator species
• the effect of pollution on them