ENVIS Technical Report: 25

Bangalore district is located in the heart of South Deccan of Peninsular India. It is situated in the southeastern corner of Karnataka state (12^o 39’ – 13^o 18‘ N latitude and 77^o 22’ – 77^o 52’ E longitude) with a geographical area of about 2,191 sq. km and an average elevation of 900 m above the mean sea level. The climate of the district enjoys an agreeable temperature range from the highest mean maximum of 36.2^o C in April to lowest mean maximum of 11.4^o C in January. It has two rainy seasons from June to September and from October to November coming one after the other but with opposite wind regime, corresponding to south-west and north-east monsoons.

Bangalore city once sported a large number of lakes, ponds and marshy wetlands, which ensured a high level of groundwater table and a pleasant climate. It is a great pity that many lakes and ponds have already disappeared due to various anthropogenic activities and pressures due to unplanned urbanisation and expansion. Surviving lakes are reduced to cesspools due to direct discharge of industrial effluents and unregulated dumping of solid wastes.

Large-scale episodic mortality among the freshwater fishes of certain lakes of Bangalore City, Karnataka State, India occurred in June 1995. Benjamin Ranjeev⁹³ et al (1995) conducted an intensive study of the Sankey Lake, which is situated in Sadashiva Nagar of Bangalore city where fish mortality occurred on quite a large scale during June - July 1995. These studies revealed that the fish-kill in Sankey Lake was due to a sudden and considerable fall in dissolved oxygen (DO) levels in some locations caused by sewage let into the lake resulting in asphyxiation. It was not due to any kind of infection because none of the fishes appeared to show any symptom of disease.

Ramachandra T.V⁹⁴ et al, discussed aspects and strategies for monitoring, which include physical, chemical and biological aspects. Commonly monitored parameters have been discussed in detail, which include the detailed methodology for analysing various physico-chemical and biological (plankton, fish, avifauna, macroinvertebrates) parameters. The methods adapted for characterisation of wetlands are illustrated with case studies, which can help in evolving overall strategies for characterisation of wetlands.

Wetlands in Bangalore are threatened owing to the pressures of unplanned urbanisation and land use pattern. In order to accommodate the burgeoning populace, many of the city’s wetlands have paved way to residential layouts, industrial complexes, etc. This has also contributed to the deteriorating water quality.

Ramachandra T.V., and Ahalya N⁹⁵ (2001) discussed restoration, post-restoration and management strategies through a holistic approach based on the findings of pilot studies in Bangalore city, Karnataka State, India. The pilot studies cover spatio-temporal analysis, restoration plans, socio-economic evaluation, community’s perception of lake restoration program and the role of the various agencies and departments.

The exploratory survey and physico-chemical and biological characterisation of lakes located all over the city show that lakes are polluted mainly due to sewage from domestic and industrial sectors. Detailed quantitative investigations of seven waterbodies (selected based on location and the type of input source) involving physical and chemical parameters and statistical analysis of selected parameters reveal that Kamakshipalya, Yediur, Hebbal and Ulsoor lakes have higher degree of pollution compared to the Sankey and Bannergatta tanks which have no major source of pollution.

The preliminary socio-economic survey carried out in the region surrounding Hebbal lake through Contingency Valuation Method showed high level of dependency on wetlands for groundwater, food, fodder, fish, fuel, etc. The high level of dependency on wetlands and its poor quality calls for immediate restoration of degraded lakes and appropriate measures for conservation and management in order to maintain ecological balance in the region.

Ranjani⁹⁶ and Ramachandra T.V (1999) studied the Hebbal lake, situated on NH-7, Bangalore, which is now a restored lake. Sewage and industrial effluents were let into the lake and the excessive sewage inflow led to the eutrophication of the lake. A preliminary socio-economic survey was carried out in the surrounding regions of the lake, which showed a high level of dependency on wetlands for groundwater, food, fodder, fuel, etc.

Rajinikanth⁹⁷ and Ramachandra T.V (2000) carried out a study of Amruthahalli lake, situated in Bangalore north taluk. It was found that the lake had attained eutrophic conditions owing to the excessive inputs of nutrients and organic matter, the sources being, sewage, storm water, and industrial effluents. The lake exhibited severe pollution with high values of alkalinity, hardness, phosphates, TSS, odour and a low level of dissolved oxygen.

Rachenahalli lake, situated in Bangalore North and South taluks was studied by Rajinikanth³¹ and Ramachandra T.V (2000). The lake was polluted due to discharges of wastewaters form the dumping of organic wastes from the surrounding areas, mainly poultry wastes. The quality of the water was affected which manifested in the values of parameters analysed, such as nutrients, alkalinity, hardness, etc.

Priyadarshini⁹⁸ and Ramachandra T.V (1998) studied the water quality of Ulsoor lake, which has very broad and deep feeder channels through which sewage and sullage flow in. It was observed by the authors that the water quality of the lake was greatly influenced by the runoff and discharges from Commercial Street, automobile workshops, aeronautical industries and a cinema hall located in the vicinity. High TSS, fishy odour, high alkalinity, hardness and phosphates, coliform population, and predominance of Microsystis were also observed which indicated high pollution in the lake.

Madiwala lake, a perennial tank located in south eastern part of Bangalore city has been reduced from 114 ha to around 100 ha due to encroachment by the BDA for a road and illegal development of private layouts. Ayesha⁹⁹, Parveen and Ramachandra T.V (1998) did a study of the lake and observed that the direct discharge of sewage from parts of Jayanagar and J.P. Nagar has increased the pollution of the lake. This was seen in low DO, high alkalinity, hardness, coliform bacteria and the predominance of the pollution indicating the algae Microsystis.