Assessing assemblage pattern, health status and environmental drivers of macrobenthic invertebrate community structure for sustainable management in a tropical tributary of River Ganga, India

The assemblage pattern of macrobenthic invertebrates concerning environmental variables on a spatiotemporal scale from river Tamas, a tributary of river Ganga was studied during the period 2017–2019. Altogether 27 genera of Gastropoda (10), Bivalvia (7), Insecta (7), and Annelida (3) belonging to 15 families, and 9 orders were recorded across six sites. Species richness at Itahara (S1), Madhavgarh (S2), Bakia upstream (S3), Bakia downstream (S4), Chakghat (S5), and Panasaghat (S6) was found to be 12, 13, 14, 22, 14 and, 10 respectively. Gastropods (44%) were the most dominant class, followed by Bivalvia (33%), Insecta (16%), and Clitellata (7%). Analysis of Variance (ANOVA) showed that physicochemical parameters (depth, water velocity, total alkalinity, dissolved oxygen, sp. conductivity, total dissolved solids, total hardness, calcium, and phosphate) and sediment quality parameters (available nitrogen, available phosphorus, and specific conductivity) differed significantly across sites (S1–S6) (p < 0.05). The Shannon–Wiener index (H’) varied from 1.23 (S6, monsoon) to 2.75 (S4, post-monsoon), while the evenness index ranged between 0.76 (S2, monsoon) and 0.91 (S6, post-monsoon). The H’ index was found to be 2.84, and the evenness index was 0.63 for the studied river stretch. The variation in the altitudinal level, availability of food items, suitable substrate habitat, and the water and sediment quality parameters mainly governs the assemblage pattern of macrobenthic invertebrates. Based on the Welch pattern, the studied river stretch falls under the river health category as moderate status, i.e., 1 < H′ < 3. Our result underlines the current status of the macrobenthic invertebrate community structure and infers for improving the health of river Tamas for sustainable management.