Seasonal Variations in Abundance and Distribution of Pollution Indicator Bacteria of an Eastern Himalayan Lake of India

Mirik Lake” of Darjeeling Himalaya is an artificial reservoir of Mirik, the famous hill resort in the Kurseang subdivision of Darjeeling District, West Bengal, India at an altitude of 1767 meters above mean sea level. The Mirik Lake which was constructed in 1979 primarily for the facilitation of commercial tourism in Darjeeling is fed by both perennial streams and rain water. The Lake is used extensively for different recreational activities as well as supplies drinking water to local people of the Mirik Town. To investigate the seasonal variation of fecal coliform, total coliform and heterotrophic bacterial density of the Mirik Lake, surface water samples from seven sampling points of the Lake were collected on a monthly basis for two years. Seasonally, the highest MPN values of fecal coliform (29000/100 mL), total coliform (88667/100 mL) and heterotrophic bacteria (116667/mL) were recorded from Site 1 during monsoon season of the second year of the study period and the lowest values were recorded during winter season. The fecal coliform density of Site 1 and Site 2 were always higher than other sites might be due to the fecal contamination in these two sites where drains from houses and hotels directly discharge waste water into the lake. Both the total coliform and heterotrophic bacterial density exhibited positive and significant correlation with fecal coliform at all the sites. It was observed that fecal coliform, total coliform and heterotrophic bacteria were substantially high and much beyond the permissible limit of ISI and WHO. Result suggests that sampling station S-1, S-2 and S-6 found to be more disturbed than the others and special attention is needed to avoid health hazards. For the improvement of the quality of Lake water, the sewage must be treated before disposal into the lake.