Abstract:

Investigation of macrozoobenthos in the mainstream and branches of the Yarlung Zangbo River near Xiongcun,Tibet,was carried out in June 2007.Altogether 47 species belonging to 20 families and 42 genera were recorded,with the dominant group being aquatic insects (928%).Species composition of macrozoobenthos had great differences between the mainstream and its branches.Species diversity of the mainstream was lower than those of the branches.The standing crop of macrozoobenthos was much lower in the mainstream than those in the branches.The mean density and biomass (dry weight) of macrozoobenthos were 385±98 ind/m2,0010±0.003 g/m2 in the mainstream and 130.2±150 ind/m2,0055±0.040 g/m2 in branches,respectively.Three chironomids and one gastropod dominated the benthic community in the mainstream,while three mayflies and one chironomid did in the branches.In terms of functional feeding groups,collectorgatherers and scrapers dominated the mainstream community,while collectorgatherers and predators did in the branches.Analysis showed that differences of macrozoobenthos community between the mainstream and its branches were mainly due to the difference of sediment types.Comparison with other studies suggested that macrozoobenthos community in Yarlung Zangbo River was quite different from those of rivers in the south Himalayas.Also,the standing crops of riverine macrobenthos at high altitudes were much lower than those of the Yangtze lowlands.