Abstract: Characteristics i.e.species diversity and community structure,of the ciliate community in the Linxia Section of the Daxiahe River in low water seasons were studied by analyzing with microscopy and fixed cell staining method.16 water samples were collected in two times from that section during the period from November 2008 till March 2009.A total of 114 species(including 9 unidentified),belonging to 57 genera of 45 families of 13 orders,were identified.Colpidium colpoda and Tetrahymena pyriformis were dominant species,while Paramecium caudatum,Cyclidium citrullus,Litonotus fasciola,Glaucoma macrostoma,C.campylum,Vorticella microstoma and Cohnilembus fusiformis were sub-dominant ones.They can be cited as indicator species for domestic organic pollution of rivers.Integrated evaluation of the environmental quality of the Daxiahe River was conducted based on the characteristics of ciliate community(number of species,dominant species,biodiversity index,saprobic index,percentage of BS groups,percentage of PA groups,community similarity index) and other biodiversity index,such as fecal coliform bacteria.Results show that the water body is mainly polluted by organic pollutants of domestic sewage.The pollution can be divided into four levels,that is,slightly polluted(Os in Section 1#),moderately polluted(α-ms in Section 4#),moderately polluted(α-ms in Section 2#) and near-heavily polluted(α-ms-Ps in Section 3#).

Key words: Linxia Section of the Daxiahe River, low water season, characteristics of ciliate community, assessment of water quality