| Based on the data of macro-invertebrate communities and environmental variables collected from Xitiaoxi catchment, Zhejiang Province in May of 2004 and 2005, several researches were carried out: (1) the community structures and functions of EPT(Ephemeroptera, Plecoptera and Trichoptera) were studied, (2) the spatial distribution patterns and functional feeding groups of EPT with relation to the environmental variables were analyzed; and (3) the benthic index of biotic integrity (B-IBI) for Xitiaoxi catchment were established.1. The relationship between 102 species of EPT (Ephemeroptera, Plecoptera and Trichoptera) and environmental factors from 43 sampling sites in Xitiaoxi catchment was studied by Canonical Correspondence Analysis. The result showed that the altitude, total nitrogen, conductivity were major environmental factors correlated with EPT community. All sampling sites were plotted out 3 groups by CCA. Sites from the group I located in the upstream of Xitiaoxi catchment had significant positive correlation with altitude and negative correlation with total nitrogen. Shredders in the group I shared the all collected shredders of 68.5%, which indicated that the water quality was clean in this group. Sites of the group II although located in upstream too, their width were wider than those in group I and positively correlated with conductivity. Shredders were only inferior to the group I(18.6%) . Sites of the group III located in middle reaches had significant positive correlation with total nitrogen and the average value of total nitrogen and total phosphorus were 3.53 mg/L and 0.16 mg/L respectively. The filterers of the group III shared the all collected filterers of 85.01%. CCA ordination well demonstrated the EPT community distribution and its relationships of the environmental factors. The EPT community structure and function were rather complicated; they were affected by many factors. It was unilateralism to evaluate stream water quality by only use EPT abundance. Based on the canonical correspondence analysis, the physic-chemical factors of stream could fall together organically, and make up for the shortage of the biology data.2. Stream macro-invertebrate assemblages were collected from 64 stream sites in Xitiaoxi catchment, Anji County, Zhejiang Province, China. Thirty-six candidate metrics were evaluated stepwise by distributing range analysis, discriminatory power analysis, and Pearson's correlation analysis. The B-IBI was composed of seven metrics: total taxa, EPT taxa, Coleoptera%, three dominant taxa, Hydropsychidae (Trichoptera) %, filterers%, and Biotic Index (BI) . The ratio scoring method was used to transform the value of each metric into a uniform score. A variability coefficient method and an entropy method were used to calculate the weight value of each metric of the B-IBI. All of the three objective weight method had highest discriminatory power (IQ=3) and were significantly correlated ( r>0.89). The measurement accuracy of the health criteria for the B-IBI derived from all sample data was better than that from only reference data. The entropy method had a higher accuracy (92.9%) than the sum total score method (85.7%) and the variability coefficient method (78.5%) in discriminating stressed and reference sites. The B-IBI health criteria for Xitiaoxi catchment were: B-IBI > 0.69 = healthy, 0.52 - 0.68 = sub-healthy, 0.35 - 0.51 = good-fair, 0.18 - 0.34 = fair, B-IBI < 0.17 = poor. The Pearson's correlation analysis between B-IBI and chemical-physical variables showed that the B-IBI strongly corresponded with the habitat quality index (r = 0.62, p< 0.01) , water temperature (r = -0.64,p < 0.01) , and altitude (r = 0.64,p < 0.01) . Our results suggest that the B-IBI is a good indicator in stream health assessment and should be used in water resource management in China.
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