Relationship between macrobenthos and abiotic characteristics of river Alaknanda in a stretch from Chamoli to Devprayag in Garhwal Himalayan region of Uttarakhand, India

Macrobenthos is the best water quality indicator for ecosystem health assessment. The present study aimed to examine the interrelationship between macrobenthos and different water quality parameters of the river Alaknanda at Garhwal Himalaya. Four demarcated sampling zones viz. zone-A (Chamoli to Nandprayag), zone-B (Karanprayag to Rudraprayag), zone-C (Rudraprayag to Srinagar) and zone-D (Srinagar to Devprayag) were taken from its approximately 170 km long stretch during 2016-2018.  River water characteristics were analyzed for the important parameters viz. substratum, water temperature (WT), water velocity, pH, electrical conductivity (EC), total dissolved solids (TDS), calcium (Ca), and magnesium (Mg) using standard methods. The results indicated that the river water velocity was the highest 1.02 m/s at zone-C, TDS of 114.19 mgl-1 was maximum at zone-A ; and Ca and Mg were recorded highest 23.17 mgl-1 and 5.44 mgl-1 at zone-A and zone-B, respectively. All abiotic parameters (pH, EC, TDS, DO, Ca and Mg) were recorded to be below BIS/WHO limits. A total of 27 macrobenthos taxa belonging to the five orders such as Coleoptera (6 ind./m2), Diptera (5 ind./m2), Ephemeroptera (8 ind./m2), Hemiptera (4 ind./m2),  and Odonata (4 ind./m2) were recorded. Macrobenthos represented an important relationship between the water current and water temperature. The lowest number was reported at zone-C due to the river's high water velocity (1.02 m/s). The changes like biota loss, presence of some  pollution indicator species (Cloeon sp., Bateis sp., Emphemera sp.) at zone-C, in sediment structure of habitat were due to the anthropogenic activities on the riverbank of different zones. The study will help in the conservation of macrobenthos diversity of the river Alaknanda.