Identification of Aquatic Macro-invertebrates and Determination of E. coli and Heavy Metals in Rawal Lake, Pakistan

Water is an important constituent of life’s support system. However, industrial growth, urbanization and anthropogenic activities have affected the quality of water bodies mostly in the world. The aim of the study was to assess the water quality of Rawal Lake, Pakistan, which is source of drinking water for the residents of Islamabad and Rawalpindi, using macro-invertebrates as pollution indicators, and through microbial and heavy metal analysis. For this purpose, macro-invertebrates and water samples were collected from Rawal Lake (Korang Nala Entrance), Rawal Lake (Centre) and from Rawal Lake (Spillway) points. The collected samples were preserved and transported to the Kinnaird College laboratory, where macro-invertebrates like caddisfly, water boatman, water bugs, gilled snails, mayflies etc. were identified with the help of identification guides and keys, while the presence of E. coli and heavy metals: Cadmium, Copper, Chromium, Cobalt, Nickel, Manganese and Zinc in the water samples was assessed. The results showed that pollution sensitive macro-invertebrates were mostly found in Rawal Lake (Centre), indicating that the water undergoes a self-cleaning process, whereas, water samples of Rawal Lake (Korang Nala Entrance), Rawal Lake (Spillway) had mostly pollution tolerant species, which signified that the water of these areas was moderately polluted. Simpsons’ Index of Diversity for Rawal Lake indicated a high level of diversity in the area (0.85). Microbial analysis indicated the presence of E. coli in all the three sampling points of the lake. The levels of Cadmium (Korang Nala 0.007 ppm, Spillway 0.014 ppm) were found toexceed the World Health Organization permissible limits (0.005 ppm), in the water samples, however, the concentration values of other metals were within the permissible limits. Thus, it was concluded that the water of Rawal Lake was considered fit for drinking and other purposes in residential and commercial areas after being processed through a treatment plant.