Substratum Texture as a Key Determinant of Macrozoobenthic Community Structure Along the Longitudinal Gradient of River Jhelum, Kashmir Himalaya

Abstract

Substrate characteristics are among the most important physical factors governing the distribution,
abundance, and diversity of benthic macroinvertebrates in lotic ecosystems. The present study
investigated the influence of substratum texture on the spatial distribution and community
composition of macrozoobenthos along the longitudinal gradient of River Jhelum, Kashmir
Himalaya. Sampling was conducted at twelve sites representing the upper, middle, and lower
stretches of the river during December 2020 to April 2021. Macrozoobenthic organisms were
collected using a Surber sampler in coarse substrata and an Ekman's dredge in fine sediments,
while substrate composition was determined using the Wolman pebble count method. A total of
42 taxa belonging to the phyla Arthropoda, Annelida, and Mollusca were recorded. Coarse
substrata dominated by boulders, cobbles, and gravel in the upper reaches supported the highest
taxonomic diversity and were characterized by pollution-sensitive Ephemeroptera, Plecoptera, and
Trichoptera (EPT) taxa, accounting for nearly 65% of the arthropod assemblage. In contrast, the
middle and lower stretches, dominated by sandy, silty, and clayey sediments, exhibited greater
abundance of pollution-tolerant oligochaetes and dipteran larvae, particularly Chironomus spp.
Functional feeding group analysis revealed collector-gatherers as the dominant group in
downstream reaches, whereas scrapers and shredders were largely confined to the upper stretch.
The observed changes in macrozoobenthic assemblages closely reflected longitudinal variations in
substrate texture, habitat complexity, and increasing anthropogenic disturbances. The findings
demonstrate that substrate composition strongly regulates benthic community structure and
highlight the usefulness of macrozoobenthos as reliable bioindicators for ecological assessment
and conservation of Himalayan river ecosystems