Abstract: The structure and distribution of macrobenthos community are important indicators for evaluating the ecological health of rivers.Based on the surveys in wet and dry seasons of typical hydrological years,we analyzed the spatial distribution of benthic community structure,feeding groups and their responses to hydraulic factors in the middle and lower reaches of the Lijiang River Basin.The results demonstrate that:1) Gastropods are predominant in the community structure of a typical river section,and Cipangopaludina cathayensis and Semisulcospira sp.are dominant species;the density of benthic animals is 829 ind/m² in wet periods and 264 ind/m² in dry periods.2) Scrapers are dominant in the feeding groups,and their relative abundance in dry season is lower than that in wet season,while the relative abundances of collector-filterers,collector-gatherers,and predators in dry season are higher than those in wet season.The relative abundances of feeding groups in the middle reach are greater than those in the lower reach.3) The biodiversity of typical river sections is spatially heterogeneous,significantly lower in the middle reach than in the lower reach.4) Velocity,bottom shearing force and geological particle size are major factors affecting the distribution of benthic organisms in the Lijiang River during dry season;water depth and laminar layer thickness are major factors in wet season.The sorting coefficient and the thickness of laminar layer are the most important factors that affect the benthic biodiversity.

Key words: macrobenthos, spatial distribution, hydrodynamic factors, biodiversity, Lijiang River