Bacteriological quality of Mirik lake waters, Darjeeling district, West Bengal

Abstract

A study was conducted on Mirik Lake to assess the bacteriological quality of the lake water during the period of March 2009 through February 2010. Water samples were collected from five different sites of the lake and analysed for bacteriological study to enumerate the seasonal distribution of total bacterial count, total coliform, faecal coliform bacteria and faecal streptococci. Total heterotrophic bacterial count per 100 ml (cfu/100 ml) was found to be 0.2x106-0.3x106 in monsoon, 1.0 x 106-6.7 x106 in summer and 4.75 x 106 - 10 x 106 in winter. The range of total coliform was observed to be 1100 - 1750 / 100 ml, 1100 - 2400/ 100 ml and 1750 - 2400 /100 ml in winter, summer and monsoon seasons, respectively. Faecal coliform was recorded to be 49 - 1245 / 100 ml in winter, 1320 - 2400 /100 in summer and 780 - 2400 / 100 ml in monsoon. The range of faecal streptococci was found to be 43-125 /100 ml in winter, 87-1100/100 ml in summer and 87 - 1340 /100 ml in monsoon. The study indicated that the lake water was polluted by faecal contaminants of human origin to the extent that water was unsafe to be used for domestic as well as recreational purposes, also the total bacterial load exceeded the standard prescribed level (WHO, 1983) and both parameters showed variation according to the sampling sites and season.