by S. Subramanya, Entomologist, Ornithologist and Wetland Expert
Our lakes can be visualized as shallow basins with several concentric zones of varying water depths, with the deepest zone lying close to the bund. This zonation of water promotes the growth of four different types of aquatic vegetation (submerged, anchored floating, emergent and floating), each of which show a preference to a particular range of water depths. This zonation of water and vegetation creates a habitat which is highly heterogeneous. Different bird species utilize the lake by occupying different zones within the lake based on the depth of water and vegetation types. Thus, it is of great importance that this basic structure is maintained while developing lakes. Our lakes by their very nature, used to have a definite seasonal cycle, in that, they would get inundated during monsoon and invariably go dry before the middle of summer. Such zonation of water-vegetation and seasonality made our lakes highly heterogeneous and dynamic and supported high species diversity. Birds are good indicators of the health of lakes. Of the 90 odd bird species that have been recorded in and around Bangalore lakes over the past decades, over 70 percent of the species inhabit the shallows and the associated aquatic vegetation covered areas.
Unfortunately, the present- day BBMP/BDA lake development model of desilting the lake to a uniform depth like, a soup-bowl, is a civil engineering model which is aimed at maximum billing. It is not biodiversity friendly and has no respect for the structure and ecology of our lakes. Further, creation of elevated and ringed jogging track is like putting a noose around the lake, which effectively prevents any inflow of clean surface run-off from the surrounding catchment area. Islands were never part of our lakes in the past. Creation of unnecessary islands, coupled with a bad choice of trees for planting has not helped our birds in any way. Besides, much of the catchment area around most of our lakes has been developed and there is hardly any clean water flowing into the lake. In addition, continuous inflow of sewage has made our lakes perennial and altered the lake ecology.
People hardly realize the importance of the shallows in our lakes. It is thus important that we make efforts to retain sloping shorelines and shallow water zones with clean water in our lakes.
*Editor’s note – Puttenahalli lake does have walking tracks and slopes, but has retained its undulating lake bed, pre-existing islands and still remains tree and bird friendly.