Macrobenthos in Jinping reach of Yalongjiang River and its main tributaries

In this paper, an investigation was made on the macrobenthos at 25 sites in the Jinping reach of Yalongjiang River and its main tributaries in May and November 2004, aimed to study the relationships between macrobenthos distribution and environmental factors. The results showed that the dominant species of macrobenthos was Baetis sp. (Baetidae, Ephemeroptera), with a relative abundance being 14.9% and 27.0% in May and November, respectively. Based on the species composition and their relative abundance, and by using two-way indictor species analysis (TWINS-PAN) and detrended correspondence analysis (DCA), the macrobentbods was divided into four groups, according to the habitat types of the sites. Canonical correspondence analysis (CCA) on the relationships between macrobenthods community structure and environmental factors indicated that in May, elevation and water hardness and NH4+ -N content were the main environmental factors affecting macrobenthods distribution, while in November, elevation, water hardness, NH4+ -N and SiO2 contents were the main ones.