Maintaining sufficient water levels and safe water quality is crucial for sustaining ecosystem services provided by the lake.
Credit: Special Arrangement
The Government of Karnataka has allocated Rs 35 crore to BBMP to maintain 174 lakes across Bengaluru.
The majority of funds received by BBMP are earmarked for fencing and maintaining lighting and beautification around the lake.
While these efforts are appreciated, it is crucial to recognise that water is the most critical component of the lake ecosystem, and maintaining water quality is vital to sustaining the ecosystem services provided by the lakes.
Lakes offer various direct and indirect services, including groundwater recharge, biodiversity enhancement, recreational space, and storage for rainwater and excess treated wastewater from apartment complexes.
Over the past two decades, lake ecosystems have suffered significant degradation due to rapid urbanisation, migration, and population growth.
Although the city has seen rapid growth in water supply infrastructure, the wastewater infrastructure has lagged, resulting in wastewater being diverted to stormwater drains that eventually reach lakes. Failure to manage wastewater due to a paucity of funds has created several issues, including foaming of the lakes, fish-kill events, and bird deaths, significantly affecting the biodiversity services provided by the lakes.
Additionally, water from lakes used by farmers for irrigation has resulted in the accumulation of toxic heavy metals in vegetables, posing risks to human and animal health.
Maintaining sufficient water levels and safe water quality is crucial for sustaining ecosystem services provided by the lake.
To address wastewater inflows and water quality issues, lake trusts were formed to co-manage lake ecosystems with the BBMP.
The restoration of degraded lakes, prioritised for restoration, involves constructing lakeside sewage treatment plants, diversion channels, constructed wetlands, or sedimentation ponds to treat stormwater overflows, stabilise bunds, and develop parks and green spaces around the lake.
Restoration plans involving the integration of grey, green, and blue infrastructure such as sewage treatment plants, constructed wetlands, floating islands, and sedimentation ponds help improve the water quality and biodiversity and provide recreational space for the public.
However, after restoration, some lakes either dried up or experienced hyper-eutrophication, leading to massive fish kill events and bird deaths. Overdesigned diversion channels prevented stormwater from entering, causing lakes to dry. Sewage treatment plants, designed to remove organic matter, released nutrients like nitrogen and phosphorus into the lake. Poor operation and maintenance of interventions, such as constructed wetlands and sedimentation ponds, led to high nutrient levels in the lake, causing hyper-eutrophication and fish kill events.
Cyanobacteria, also known as chlorophyll a or blue-green algae, cause hypereutrophication when lakes receive inflows with very high levels of phosphorus. The recommended phosphorus levels to prevent eutrophication are less than 0.1 mg/l, but data from restored lakes in Bengaluru show phosphorus levels up to 3.5 mg/l.
Recent research has reported cyanobacterial toxicity and cyanotoxin accumulation in various aquatic organisms, edible plants, and drinking water supplies. The major routes of human exposure to cyanotoxins include chronic and accidental ingestion of contaminated drinking water, inhalation or contact with the nasal mucous membrane, and dermal contact with toxins during recreational activities such as swimming, consumption of contaminated vegetables and fruits irrigated with water containing cyanotoxins, and consumption of aquatic organisms (fish, shellfish, etc.) from contaminated waters.
Preventing human and animal exposure to cyanotoxins should be a crucial outcome of lake restoration projects, given that lakes in Bengaluru are used for fisheries and downstream farmers use water for irrigation. Reducing exposure to cyanotoxins by preventing hypereutrophic conditions is essential for making lakes safe for recreation, fisheries, and irrigation. Instead of focusing on fencing and artificial structures, funds should prioritise preventing nutrient inputs into the lakes.
India is a developing economy, and investing funds to treat the city’s wastewater to tertiary levels for nutrient removal is not economically feasible. Setting time-bound water quality targets to prevent eutrophication is also not economically feasible. Therefore, adopting an environmental management approach that aims for continuous improvement rather than a time-bound threshold is more realistic. This allows the community to set achievable goals in a phased manner over many years, which will be realistic.
Funds allocated for operation and maintenance can help achieve the goal of continuous improvement in a phased manner. Rather than allocating resources for fencing, the goal should be to maintain, improve, and upgrade existing interventions to address excess nutrient inputs into the lake. This can be achieved by involving experts with knowledge of lake ecosystems and interventions for nutrient removal.
(The writer is a Senior Fellow, Centre for Environment and Development, ATREE)