A Study of River Water Quality using Macroinvertebrates as Bio Indicator: A Case Study

Background: Benthic macro invertebrates have a sedentary and long life span, sensitive community response to organic loading, thermal impacts, substrate alteration and toxic pollution. They are regarded as the most informative bio indicators of water pollution. Macro invertebrates and water quality are interrelated to each other, as macro invertebrates are a potential indicator of water quality and therefore have been most frequently used in biomonitoring studies. Methods: The study area is the tailrace of Dikhow River, a 65 km. a southern tributary of the mighty river Brahmaputra. The stretch was demarcated into five sectors longitudinally. The study was done for a period of two years during which sampling collection was done using sampling methods. Appropriate sized net was used to sample macroinvertebrates. Identification was done using standard identification keys. Pollution tolerance of the species was measured using standard protocols. Using tolerance values, family biotic Indices were measured by Hilsenhoff standard protocols. Result: Number of pollution sensitive macroinvertebrates were found to be minimum in almost all stations indicating the level of pollution in the stations. Macroinvertebrates with higher tolerance levels were recorded in maximum numbercompared with the standard values to assess the water quality. A total of thirteen (13) species (Rhynchobdellasp, Physellasp, Soletelinasp, Gammarussp, Fenneropeneussp, Isotomussp, Caeniussp, Gomphussp, Lethocerussp, Hydrophylussp, Chaobarussp, Chironomussp) have been recorded during the study period. Among them the species with high pollution tolerance values were recorded in higher number during the study. While compared the family biotic indices as recorded from the stations with the standard data, then station I and station III have been found to be significant organic pollution and other three stations were found to be Fairly significant organic pollution.