Assessment of urban river pollution using the water quality index and macro-invertebrate community index

Water quality assessment is among the most important approaches for understanding the environmental status of rivers and streams. In India, the Bharalu River, a tributary of the Brahmaputra River, is listed among the most polluted rivers of the country. The river is part of the greater Basistha-Bahini-Bharalu (BBB) river network, which spreads across the rapidly urbanizing Guwahati city. The present study describes the current state of pollution in the BBB river network and its impact on the spatial distribution of benthic macro-invertebrates. Further, an attempt is made to elucidate the application of Macro-invertebrate Community Index (MCI) in determining river systems pollution status compared to the Water Quality Index (WQI) method. WQI was determined using the weighted arithmetic method. The hydrochemical analyses and the WQI revealed the severe pollution status of the rivers. Downstream stretches of the rivers were highly polluted due to the dumping of urban sewage, untreated organic and inorganic wastes from industries. MCI was developed utilizing the benthic macro-invertebrate data collected at 10 sampling sites. Ninety-one individuals of macro-invertebrates belonging to 9 orders and 17 families were identified. The MCI values for sampling location were found to be significantly correlated with hydrochemical parameters. Results revealed an inverse relationship between WQI and MCI. This implied the occurrence of pollution-sensitive macro-invertebrates in unpolluted locations and vice versa. This study illustrates the effectiveness of MCI as a tool for determining the pollution status of rivers and also depicts its potential for application within citizen-science initiatives for restoring degraded river ecosystems.