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ENVIS Technical Report: 104,  March 2016

DEVARABISANAHALLI LAKE: PATH TOWARDS ECOLOGICAL RESTORATION
Ramachandra T.V.           Vinay .S           Sincy .V           Asulabha .K.S           Sudarshan .P. Bhat           Bharath H. Aithal
Energy and Wetlands Research Group, Centre for Ecological Sciences, Indian Institute of Science, Bangalore – 560012, India.
*Corresponding author: cestvr@ces.iisc.ernet.in
Citation: Ramachandra T V, Vinay S, Sincy V, Asulabha K S, Sudarshan Bhat and Bharath H.Aithal, 2016.Devarabisanahalli Lake: Path towards Ecological restoration, ENVIS Technical Report 104, Energy & Wetlands Research Group, CES, IISc, Bangalore, India
RECOMMENDATIONS

      1. Desilting: To remove the sediments deposited in the lake, de-silting is required. Today, technological improvements helps in wet dredging. Value of the sediment ranges from 5.3 to 13 crores. Sludge at inlets (with nutrients has C: 23.77% & N: 2.38%) could be used as manure for floriculture/horticulture/agriculture. Silt accumulated in other parts of the lake with treatment could be used sand.
      2. No-Diversion of sewage to downstream regions (everyone are residents of India), and upstream dwellers should not pollute the downstream resources through irresponsible action of diversion of untreated sewage. Treated sewage into the lake will ensure water availability all 12 months which would also help in sustaining biota.
      3. Nutrient removal through integrated wetland ecosystem (Jakkur Lake model): Integrated wetlands system consists of sewage treatment plant, constructed wetlands (with location specific macrophytes), algal pond integrated with a lake.

Constructed Wetlands - Reed bed (Typha, etc.) with Algal pond as wastewater treatment systems:  Wetlands aid in water purification (nutrient, heavy metal and xenobiotics removal) and flood control through physical, chemical, and biological processes. When sewage is released into an environment containing macrophytes and algae a series of actions takes place. Through contact with biofilms, plant roots and rhizomes processes like nitrification, ammonification and plant uptake will decrease the nutrient level (nitrate and phosphates) in wastewater.  Algae based lagoons treat wastewater by natural oxidative processes. Various zones in lagoons function equivalent to cascaded anaerobic lagoon, facultative aerated lagoons followed by maturation ponds. Microbes aid in the removal of nutrients and are influenced by wind, sunlight and other factors (Source: Ramachandra T.V., Durga Madhab Mahapatra, Sudarshan P. Bhat, Asulabha K.S., Sincy Varghese, Bharath H. Aithal, 2014. Integrated Wetlands Ecosystem: Sustainable Model to Mitigate Water Crisis in Bangalore, ENVIS Technical Report 76, Environmental Information System, CES, Indian Institute of Science, Bangalore 560012).

 

Space available in between M/s Honeywell and lake could be used for creating wetlands.
This model is working satisfactorily at Jakkur. The sewage treatment plant removes contaminants  (evident from lower COD  and BOD) and mineralises organic nutrients (NO3-N,  PO43—P  to inorganic constituents. Integration of the conventional treatment system with wetlands [consisting of reed bed (with typha etc.) and algal pond] would help in the complete removal of nutrients in the cost effective way. Four to five days of residence time helps in the removal of pathogen apart from nutrients. However, this requires regular maintenance through harvesting macrophytes and algae (from algal ponds). Harvested algae would have energy value, which could be used for biofuel production. The combined activity of algae and macrophytes helps in the removal of  ~45% COD, ~66 % BOD, ~33 % NO3-N and ~40 % PO43-P.  Jakkur lake acts as the final level of treatment that removes ~32 % COD, ~23% BOD, ~ 0.3 %  NO3-N and ~34 % PO43-P.  The lake water with a nominal effort of sunlight exposure and filtration would provide potable water. Replication of this model in Bangalore would help in meeting the water demand and also helps in recharging of groundwater sources without any contamination.

      1. Maintain shoreline topography – slope (1 in 10) and shoreline riparian vegetation (which aid in treating surface runoff, roosting and breeding sites for birds, habitat for butterflies, etc. - Lake shall maintain ecological integrity
      2. Remove all encroachments (irrespective of economic status). Land encroached by sharks be converted to children’s and elders recreation park
      3. Install water fountains (music fountains) which enhances the aesthetic value of the lake and also aid as recreation facility to IT professionals (working in IT sector in this locality) and elderly people. This also helps in enhancing oxygen levels through aeration.
      4. Introduce ducks (which helps in aeration)
      5. Introduces fish (surface, column and benthic dwellers) which helps in maintaining food chain in the aquatic ecosystem. This has to be done in consultation with fish experts.
      6. No exotic fish species introduction avoid commercial fish culturing (commercial fishery)
      7. Constitution of Lake Conservation committee involving all lake stakeholders including agencies supported lake restoration.
      8. Post maintenance of the lake: The committee shall come up with appropriate financial mechanism to manage the lake regularly (which includes regular maintenance of wetlands,  watch guards – either volunteers or appointed and monitoring of lake water quality).
      9. Monitoring of lake water quality: This shall be done by involving education institutions (schools and colleges – students and teachers). Field experiments helps the youngsters in understanding the environmental problems   and also help in evolving appropriate management strategies.
      10. Immediate eviction of Tea shop on the lake bed (creates nuisance with dumping of solid waste and smoking)
      11. Implement polluter pays principle – penalize encroachers and polluters