Water quality in urban lakes of Bengaluru, Karnataka due to idol immersion activities

Deterioration of water quality in the urban lakes of Bengaluru, Karnataka due to anthropogenic activities, has been an alarming issue in the recent times. Immersion of idols coated with synthetic paints and dumping of organic wastes in the lakes as part of religious rituals, is adversely affecting the lake water quality. These activities contaminate the water with alkali, alkaline earth metals and heavy metals, thereby reduce the level of dissolved oxygen, increase the hardness of water and therefore, threaten aquatic ecology. In this context, periodic analysis of Yelhanka and Yediyur lake water were undertaken to investigate the effect of idol immersion activities on the water quality. In Yelhanka lake water, the maximum concentrations of calcium and magnesium were recorded to be 8.3 and 4.08 meq l-1, respectively after one month of immersion. The mean concentrations of Na and K were 96 and 63.47 ppm, respectively during the period of study. The pH of the Yediyur lake water dropped from 7.24 to 6.7 after seven days of immersion activities. The BOD and COD levels increased from 11.3 and 97.5 to 19.3 and 134.25 mgL-1 in Yediyur lake in the post immersion period reflecting, anoxic aquatic environment. The concentrations of different inorganic ions including heavy metals (Cr, Cd, Ni and Pb) in the post immersion period were also found to increase. Since, water of these lakes can potentially be used in the lean season for irrigation in the adjoining agricultural lands as well as for other purposes; their proper management is of utmost necessity.