Wetlands constitute the ecological barometers of the health of a region. They regulate the micro climate apart from being highly productive, support exceptionally large biological diversity, and provide a wide range of ecosystem services such as food, fibre, and waste assimilation, water purification, flood mitigation, erosion control, groundwater recharge, etc. They also enhance the aesthetics of the landscape and support many significant recreational, social, and cultural activities, aside from being a part of our cultural heritage. Unplanned urbanization has telling influences on the natural resources such as decline in green spaces (vegetation) including wetlands and/or depleting groundwater table. Sustained inflow on untreated sewage to wetlands has altered the integrity of fragile wetlands disturbing the complex interactions and self purification capacity of aquatic ecosystems. Sustained inflow of untreated or partially treated sewage enriches the wetlands due to the availability of higher nutrient concentrations resulting in the prolific growth and spread of invasive exotic species such as water hyacinth (Eichhornia crassipes). This hinders aerobic functioning of the lake by restricting sunlight penetration and also affecting algal photosynthesis. This results in anoxic environment due to blockage of air-water interface, influencing oxygen diffusivity. Reduction in DO (0 mg/l) impacts the viability of aquatic biota and result in the disappearance of biodiversity. This is evident in the recent episodes of fish mortality in Jakkur lake with asphyxiation in some locations due to the considerable fall in dissolved oxygen (DO) levels caused by sustained inflow of large quantum of sewage let into the lake (through illegal diversions by local civil contractors). It is not due to any kind of infection because none of the fishes showed any signs of disease symptoms.

Enrichment of nutrients due to the sustained inflow of untreated sewage has led to  algal blooms and profuse growth of macrophytes. Decomposition of algae  or/and dense cover of macrophytes reduces dissolved oxygen leading to anaerobic conditions, which asphyxiate aquatic life including fish. The current study was carried out in response to a request from Mr.Jayaram B, DCF, Forest division, Bangalore Development Agency (BDA) subsequent to series of news reports in local dailies with large scale fish mortality in Jakkur Lake Bengaluru, Karnataka. The physico-chemical and biological composition of the lake was studied using standard protocols.  Results reveal of  higher nutrients due to the sustained unauthorized inflow of large quantum of untreated sewage along with partial treated water. This is confirmed with the profuse growth of invasive exotic weeds and also large scale algal blooms. The presence of dense cover of macrophytes hinders the light penetration leading o the decline of dissolved oxygen (DO) due to the prevailing anaerobic conditions with lowered algal communities. Apart from this, algal blooms also leads to anaerobic conditions during non-photosynthesis period (at night) with respiration. This lake is being monitored by us at Energy and Wetlands Research Group, CES, IISc since 36 months. Current investigation reveals that nutrients (N and P) in the water increased by four times since unauthorized inflow of sewage from the adjacent neighbourhood. The overall water quality has deteriorated compared to previous years due to the sustained inflow of sewage from neighbourhood.  The act of polluting waterbodies and consequent contamination of ground water is liable for penalty as per “Polluter pays principle”, water act 1974, government of India (Water (Prevention and Control of Pollution) Act – 1974, 1977; Environmental (Protection) Act – 1986).

Current investigation reveals that nutrients (N and P) in the water increased by four times since unauthorized inflow of sewage from the adjacent neighbourhood. The overall water quality has deteriorated compared to previous years due to the sustained inflow of sewage from neighbourhood.  The act of polluting waterbodies and consequent contamination of ground water is liable for penalty as per “Polluter pays principle”, water act 1974, government of India (Water (Prevention and Control of Pollution) Act – 1974, 1977; Environmental (Protection) Act – 1986).

RECOMMENDATIONS: 

• Penalize polluters as per “Polluter pays principle”
• Restrict the nutrient discharge into the lake;
• Allow only treated water into the lake;
• Maintain macrophytes through regular harvesting and restrict the region infested with weeds

To control the growth of algae dominated by spirulina spp the following fish species should be introduced into the lake

• Silver carp (Hypophthalmichthys molitrix) Exotic carp
• Sandkhol- (Thinnichthys sandkhol )  Local carp
• Bighead carp (Aristichthys nobilis) Exotic carp

Silver Carp, Bighead carp and Sandkhol Carps are introduced to fresh water systems because of their ability to decrease phytoplankton (algae) density although zooplanktons are preferred food.

Keywords: fish mortality, Jakkur Lake, wetlands, bioremediation, “polluter pays principle”