68-Upgradation and management of Rabindra Sorobar lake in Kolkata

Abstract

The inland freshwater ecosystems contribute a considerable fraction towards the available water resource which is now being increasingly subjected to greater stress from various human activities. Degradation of wetlands is very common due to discharges of liquid effluents, disposal of solid waste and localized human population in the surrounding and their activities. Almost seventy five years ago, the marshy jungle in southern part of Kolkata city - the breeding ground of mosquitoes—was converted to a major environmental reserve, known as `Rabindra Sorobar', without compromising the basic natural character of the land, The importance of the lake (Rabindra Sorobar) for ecological balancing was felt by the South Kolkata citizens who always stressed on the need for safeguarding the lake from any deterioration. But slowly the lake was found to be a victim of unplanned and uncared development of Kolkata, including unconcerned behavior of certain people residing in the surroundings of the lake. The lake water quality deteriorated due to discharge of sewage and sullage, disposal of solid waste, uncontrolled bathing and washings etc. resulting in severe eutrophication of the lake. In order to save Rabindra Sarobar Lake from ecological damage, the squatters I slum dwellers were shifted from the surrounding locality and also all point sources of pollution were diverted to the municipal sewerage system. All water hyacinths were removed from the lake. Water quality monitoring results during January and April 2007 revealed dissolved oxygen level between 6.0 and 8.0 mg/I and average ammonia-nitrogen in the lake was found to be at lower side (0.16 mg/I). The faecal coliform in the lake was found in the range between 24 and 2800 per 100mI.The Rabindra Sorobar Lake was classified as class 'D' as per water quality status. Heavy metals (zinc, cadmium, copper, lead and chromium) depositions due to disposal of solid waste, immersion of idols etc. were detected in sedimentary deposits of the lake. Environment Management Plan for the lake was suggested which included solid waste management, banning of plastic, manual removal of water hyacinths, drainage improvement etc. People participation for the maintenance of the lake was also suggested.