Assemblages of Benthic Macroinvertebrate Communities Downstream of a Dam on River Alaknanda in Garhwal Himalaya, Uttarakhand, India

The assemblages of benthic macroinvertebrate communities along with the physicochemical variables in River Alaknanda  (Garhwal Himalayan region of Uttarakhand) downstream of a dam of 330 MW power project, were recorded from three sampling sites during January 2019 to March 2019. The water temperature and pH remained low throughout the study, while the nutrient concentration, turbidity and conductivity were high at the downstream site. Among the benthic macroinvertebrates, a total of 37 genera, belonging to 22 families of 7 orders including molluscs were recorded. The maximum density of benthic fauna was recorded from the site nearest to the dam. Dipterans (Chironomidae) were the predominant order at all the three sampling sites, whereas Molluscs had the least density during the study. The canonical correspondence analysis (CCA) reveals that high nutrient, dissolved oxygen and moderate water velocity governs the occurrence of benthic fauna downstream of the dam. The present study reveals that the chironomidae being the most pollution tolerant taxa and occurring in  high density suggest the organic pollution at sites downstream of the dam.