Abstract: The correlations between ciliate species diversity and community structure and water quality in the Heihe River basin were studied during the period of February 2013 to January 2014. Water samples were collected each season in order to analyze the ciliate community and physicochemical parameters. The results showed that total nitrogen content, chemical and biological oxygen demand, dissolved oxygen content significantly differed from upstream to downstream, while total phosphorus content and pH value had no obvious change. The change of water environment significantly decreased diversity index, richness index, and evenness index of ciliate community in the river, but the saprobic index increased significantly. These results indicated that the composition change of ciliate community can reflect the change of water quality. The redundancy analysis results suggested that the variation of ciliate communities was significantly correlated with the changes of water environmental conditions. Water quality was evaluated as mildly to moderately polluted by biological indicators. These findings suggest that ciliate community structure is a potentially reliable indicator of water quality in the Heihe River basin.

Key words: shrub layer., secondary natural forest, functional group, Pinus tabuliformis, interspecific association