Sand-Gravel Mining as a Threat to Macro-benthic Assemblage and Habitat Parameters: A Case Study of River Ganga, India

Abstract

The present study was conducted for assessing the impact of sand-gravel mining on the habitat parameters, diversity and abundance of macro-benthic species in the mining impacted area of the Ganga river from April 2017 to March 2018. Samples were collected from four different zones i.e. zone A as reference zone while zones B, C and D are mining impacted area of Ganga river correspondingly. During the study, habitat parameters such as substratum type, pH, dissolved oxygen, biochemical oxygen demand, turbidity and TDS showed a significant difference at selected zones throughout the study. Besides, during the survey, a total of twenty-nine macro-benthic species belonging to ten groups mainly Oligochaeta (2 species), Turbellaria (2 species), Hirudinea (3 Species), Odonata (2 species), Ephemeroptera (4 species), Trichoptera (3 species), Diptera (6 species), Gastropoda (3 species), Decapoda (1 species) and Coleoptera (3 species) were found respectively. The Diptera group was found a maximum of 30.77% throughout the study period at selected zones. Besides this, the other major groups were such as Coleoptera 12.73%, Gastropoda 10.80% and Ephemeroptera 9.65%. The result showed that the zone A contains the higher number 1205 ind./m2 while zone B, zone C, and zone D contain 899 ind./m2, 714 ind./m2 and 497 ind./m2 respectively throughout the year. The canonical correspondence analysis (CCA) analysis showed a strong relationship with habitat parameters mainly substratum structure, pH, water temperature, dissolved oxygen with the macro-benthic species. Besides this, the reason for the decline in species number in respected zones (B, C & D) is the removal of the sand and gravel material. The removal of these materials causes habitat destruction in the form of increasing depth, slope, channelization of river and water quality.