Executive Summary
Wetlands (lakes, ponds, tanks,areas of marsh, fen, peat land, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water) in urban landscape aid in (i) moderating microclimate, (ii) recharge groundwater resources, (iii) remediation – kidneys of the landscape remove contaminants, (iv) sustaining food (fish, fodder etc.), (iv) recreation and habitat for array of diverse organism, (vi) infiltration and mitigate floods and loss to human life and properties, (vii) enhance the aesthetics of the landscape and support many significant recreational, social, and cultural activities, aside from being a part of region’s cultural heritage. Despite these significant services, wetlands are being encroached, polluted and constantly abused by senseless and irresponsible urban decision makers of 21st century. Recurring episodes of fish mortality, algal bloom, profuse growth of invasive exotic weeds, introduction and rearing of exotic species of fish highlights mismanagement of fragile and ecologically vital wetlands.
Recent episodes of large-scale fish mortality in Ulsoor and Devarabisanahalli lakes of Bangalore city, Karnataka has necessitated field investigations to understand the causal factors. Analysis of water samples and fish samples reveal that the fish-kill in Ulsoor Lake and Devarabisanahalli lake were due to asphyxiation with a sudden and considerable fall in dissolved oxygen (DO) levels in some locations caused by the sustained inflow of untreated sewage. Sudden increase in temperature (>34 °C) has enhanced biochemical activities of the micro biota (algae, bacteria) as well as plant respiratory rate leading to depletion of dissolved oxygen. Higher temperature in sewage fed aquatic ecosystem increases the level of ammonia, BOD, etc.
Major agents of deteriorating lake ecology and biodiversity in any water body are due to the irresponsible act of
Causal Factors |
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Fish Mortality |
Asphyxiation due to depletion of dissolved oxygen |
Low dissolved oxygen |
The sustained inflow of untreated sewage and the quantum beyond the remediation capability of the lake. Higher organic content and increase in temperature (> 34 °C in April) has enhanced the biological activities leading to higher ammonia, BOD and COD |
Enhanced biological activities |
Bacteria and algae population have increased with higher temperature and favourable conditions (organic content) Bacteria and algal demand for oxygen (during day and night respectively) has lowered dissolved oxygen |
Viral attack |
With higher temperature and favourable organic content in the Lake, susceptible fish have died. Red spots on dead fish specimen indicate the possibility of Epizootic ulcerative syndrome (EUS), also known as red spot disease (RSD), which requires further analysis [Details at: http://www.thefishsite.com/diseaseinfo/21/epizootic-ulcerative-syndrome-red-spot-disease]. |
Solution |
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Sewage treatment |
Adopt integrated treatment system (constructed wetland and algae pond along with the conventional STP) to remove nutrients (N & P) similar to the functional model at Jakkur Lake. |
Silt removal |
Removal of accumulated contaminated sediments, through wet dredging with the help of MEG |
Maintaining buffer zone |
Maintain at least 30 m buffer with riparian vegetation (to enhance hydrologic regime and remediation) and recreation facilities |
Stop senseless developmental activities |
Plan to have floating restaurant (irrational plan of tourism department) should be abandoned as this will affect the ecological integrity and ultimately leads to the death of the lake (Ulsoor Lake) |
Ban on exotic fish species introduction and culture |
Exotic species eliminates native biota and affects local biodiversity |
Regular water quality monitoring |
Involving local educational institutions in regular water quality (physical, chemical and biological parameters) would help in capacity building and environmental awareness. |
Constitution of functional lake protection and management committee |
Lake protection and management committee involving all active local stakeholders, who regularly take part in monitoring while ensuring timely maintenance and management. |
Eco-approach in the management of Lakes |
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Control: prevent its access to get its oxygen (since it is an air-breathing fish) from the atmosphere by spreading a net of different mesh size, below 4”-6” from surface water area of any water body. This process prevents the fish to come to the surface to breath and gets chocked.
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The rapid urbanisation trend consequent to unplanned developmental activities with burgeoning population has posed serious challenges in the regional planning and management involving plethora of issues like wetland conservation, infrastructure development, traffic congestion, basic amenities, etc. The rapid urbanization has led to increased anthropogenic pressure on most of the water bodies in Bangalore. Irresponsible act of dumping of solid wastes and sustained discharge of untreated sewage has deteriorated the quality of lakes/wetlands, evident from algal bloom, profuse growth and spread of invasive exotic species of macrophytes, recurring episodes of fish mortality, etc. Untreated sewage enters directly the Ulsoor Lake which has altered the chemical integrity of the ecosystem affecting biological constituents. The physico-chemical characteristics of Ulsoor Lake reveals depletion of oxygen, high turbidity and organic contents, high biochemical oxygen demand (BOD) and ammonia toxicity. Fish usually require a minimum of 5 milligrams per liter (mg/l) of dissolved oxygen (DO) for optimum health and the maximum admissible ammonia concentration for fish is 0.05 mg/l. Fish in an aquatic ecosystem also helps in detecting the toxicity of different chemicals including heavy metals in an aquatic environment. Microbial communities present in the sewage water causes infectious diseases that infect aquatic life as well as terrestrial life through drinking water. Analysis of water samples and fish samples reveal that the fish-kill in Ulsoor Lake and Devarabisanahalli lake were due to asphyxiation with a sudden and considerable fall in dissolved oxygen (DO) levels in some locations caused by the sustained inflow of untreated sewage. Sudden increase in temperature (>34 °C) has enhanced biochemical activities of the micro biota (algae, bacteria) as well as plant respiratory rate leading to depletion of dissolved oxygen. Higher temperature in sewage fed aquatic ecosystem increases the level of ammonia, BOD, etc. Ammonia is toxic to fish at elevated pH and temperature. Fish become more susceptible to viral or bacterial infections during a low DO period and thermal stress. Red spots on dead fish specimen indicate the possibility of Epizootic Ulcerative Syndrome (EUS), also known as red spot disease (RSD), which however requires further investigations.
Keywords: Fish Mortality, Dissolved Oxygen (DO), untreated sewage, ammonia, Biochemical Oxygen Demand (BOD), Mismanagement
| * Corresponding Author : | |||
| Dr. T.V. Ramachandra Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, India. Tel : +91-80-2293 3099/2293 3503 [extn - 107], Fax : 91-80-23601428 / 23600085 / 23600683 [CES-TVR] E-mail : cestvr@ces.iisc.ernet.in, energy@ces.iisc.ernet.in, Web : http://wgbis.ces.iisc.ernet.in/energy, http://ces.iisc.ernet.in/grass |
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| Contact Address : | |||
| Dr. T.V. Ramachandra Energy & Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560 012, INDIA. Tel : +91-80-2293 3099/2293 3503 - extn 107 Fax : 91-80-23601428 / 23600085 / 23600683 [CES-TVR] E-mail : cestvr@ces.iisc.ernet.in, energy@ces.iisc.ernet.in, Web : http://wgbis.ces.iisc.ernet.in/energy |
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