Stream power as a predictor of aquatic macroinvertebrate assemblages in the Yarlung Tsangpo River Basin (Tibetan Plateau)

Assemblage structures and distribution patterns of aquatic macroinvertebrates are influenced by riverine environmental variables. The relationship between environmental variables and macroinvertebrate assemblages, however, has rarely been examined quantitatively for rivers with high stream power at high altitude. In this study, stream power was analyzed in relation to macroinvertebrate distributions in the Yarlung Tsangpo River Basin on the Tibetan Plateau. Field investigations were carried out at 22 sites in April, 2014 and 2015. Stream power, substrate size and evenness, discharge, bedload transport, and organic detritus availability varied greatly among these sites. In total, 125 taxa of macroinvertebrates belonging to 48 families and 104 genera were identified. The macroinvertebrate density was negatively and significantly correlated with the stream power (D = 3.30, P < 0.001). Both the assemblage indices (taxa richness, density, biomass, and the Improved Shannon–Wiener Index) and the environmental variables (elevation, substrate size, and discharge) differed among the sites with different levels of stream power. An adaptability analysis showed contrasting adaptive strengths of typical taxa. Orthocladius, Baetis, and Simulium adapted to wide ranges of stream power and their most optimal stream powers were relatively high, while Bethbilbeckia and Natarsia were only well-adapted to fairly narrow ranges in stream power. Some macroinvertebrates have evolved specific strategies to adapt to high stream power: Baetidae and Heptageniidae have developed specialized body shapes, and Epoicocladius has altered its host preference. The stream power has been shown to be significantly correlated with and could be used to predict macroinvertebrate density in the Yarlung Tsangpo River Basin.