Assessment of Habitat Quality in Quarried Reach of Alluvial River

Abstract

Fluvial ecosystem function and biological communities entirely depended on habitat quality; however, increasing anthropogenic intervention damages the habitat quality day by day. Hence, this study has attempted to assess the impact of anthropogenic intervention mainly sand mining on three-tier habitats, that is, river bed, riparian and bank in Kangsabati River, West Bengal, India. Channel geometric, geomorphic responses, sediment facies and their deposition, riverine land use, microhabitat zone, water quality, species diversity were considered as components for habitat quality assessment (HQA). Quality score is estimated from the relative weightage of HQA indicators in selected habitat sites. Result demonstrated that maximum mining and pit sites in three-tier habitat systems fall under marginal (2–4) and poor category (<2), while sandbar sites in habitat system reach optimal (>4) and suboptimal (3–4) category, respectively. Mining affected channel width drastically reduces but channel depth sharply increases through the generation of turbulence flow, pool-riffle alteration, thalweg shifting, which are causes of loose coarser deposition (LCD) in bed, sand clay deposition (SCD) in riparian, and medium finer deposition (MFD) in a bank. Moreover, the mixing of pebbles with MFD disrupted the herbs and rubiaceas grass colony in the bank due to pit generation, while interruptions of SCD damage the grasses colony in riparian sites to enhance the harmful land use practice. Contrastingly, physicochemical properties continuously deteriorated in mining and pit sites; thus, species diversity and richness relatively declined but species evenness abruptly increased. Therefore, habitat quality has gradually degraded from bed to bank sites of mined rivers.