Structure of Benthic Macroinvertebrate Communities in the Rivers of Western Himalaya, Nepal

According to River Continuum Concept (RCC), channel morphology, including sediment loads and channel width, river habitat, flow regimes and water quality, differs from the tributary to the downstream river's mainstem, allowing shifts in faunal composition from dominance of shredders to collectors downstream, respectively. Tributaries are responsible for contributing organic carbons, nutrients and water. However, such knowledge is still limited in the monsoon-dominated river systems of the Himalaya. The study was conducted in the river's mainstem and tributaries of the Karnali River Basin, which are glacier and spring-fed river systems, respectively, in the western Himalaya, Nepal. A total of 38 river stretches in the river's mainstem and tributaries were sampled during post-monsoon and pre-monsoon seasons in the years 2018 and 2019. Water quality parameters, such as pH, temperature, electrical conductivity, total dissolved solids, dissolved oxygen, alkalinity and hardness, and the benthic macroinvertebrates were studied. Ten subsamples of benthic macroinvertebrates were collected following the multi-habitat sampling approach at each site. High taxa richness was recorded in tributaries compared to the river's mainstem while abundance was similar between river types. Non-metric multidimensional scaling (NMDS) formed two distinct groups, reflecting high similarities in benthic macroinvertebrate composition within the tributaries and river's mainstem rather than between river types. Redundancy analysis (RDA) indicated water temperature and pH as major environmental predictors for benthic macroinvertebrate variability between river types. Therefore, river type-based conservation efforts that account for upstream-downstream linkages of aquatic biota and resources in freshwater ecosystems can ensure the ecological integrity of the whole river basin.