Summary and Conclusion

Urban lakes of Bangalore have been subject to appreciable anthropogenic nutrient loads due to high rate of sewage discharge during the last 50 years, which has resulted in predominant changes in physico-chemical conditions and phytoplankton communities of the lake. The study of the physico-chemical parameters and their impacts on the standing crop of phytoplankton indicated that the maximum number of phytoplankton species counted, belonged to class chlorophyceae (Chlorella blooms), which is an indicator of eutrophication. The higher ammonia content favoured the growth of these members. It was observed that in anoxic-aerobic conditions the chlorophycean and euglenophycean members dominating the lake. However, the partial anaerobic regions (N limited) were dominated by the cyanophycean members. There was a transition of phytoplanktons with seasons where the chlorophycean members dominted in the monsoon period and the cyanophycean members during he dry periods.  Transparency/ turbidity exhibited significant positive relation with the total count of the phytoplanktons. In terms of biomass the algae were found to be the major uptaker of nutrients as N among other biotic members. The major nutrient sink among the biotic component was found to be the lake phytoplankton accumulating N upto 3.3 tN/day. From this study, we conclude that Bellandur and Varthur are undergoing a high nutrient enrichment at the same time they act as nutrient store, by accumulating nutrients mostly as bacterioplankton, phytoplankton and macrophyte biomass. Chlorella and Chlorogonium were found to be potential candidates for the lake which triumph at such anoxic conditions with optimal nutrient uptake.