Abstract: In May 2009, an investigation was conducted to understand the macrobenthos community structure and its relationships with water environmental factors in Erhai Lake and in three small lakes (Haixihai, Cibihu and Xihu) in Erhai watershed. In Erhai Lake, the mean density of macrobenthos was 1556 ind·m^-2, and the biomass was 8.9 g·m^-2. The macrobenthos community was dominated by Chironomus sp., Limnodrilus hoffmeisteri, and Radix sp., with the relative abundance being 43.5%, 39.5%, and 8.6% respectively. The biomass was mainly contributed by Corbicula largillierti, Radix sp., and Chironomus sp. The spatial distribution of macrobenthos community based on GIS interpolation showed that the density was the highest in the north region of Erhai Lake, the biomass was the highest in the littoral zone of the middle region, both the density and the biomass were relatively low in the south region, and the Shannon diversity index was higher in the littoral zone. In the three small lakes, the main taxa were Nematoda, Chironomidae, Tubificidae and Chaoboridae. Both the density and the biomass had the maximum values (260.8 ind·m^-2 and 1.14 g·m^-2, respectively) in Cibihu Lake. CCA analysis showed that the total phosphorous and Ca²⁺ concentrations in water body had significant effects on the macrobenthos community, with the contribution rate being 34% and 27%, respectively. The Xihu Lake nearest to Erhai had the similar macrobenthos community type as Erhai Lake, mainly because of the relatively high total nitrogen concentration in the water. Compared with historical data, the proportions of Oligochaete and Chironomid in Erhai Lake continued to increase, which implied that the organic pollution in the Lake was further intensified.

Key words: Arid climate, Bothrichloa ischaemum community, Root system, Biomass