| The aquatic eutrophication has been seriously induced via human activity in Beiyunhe River during these years. The study of macrofauna could absorbed the community structure and reflected water quality as a result of the fact that macrofauna is an important component in wetland ecosystem. Sampling of macrofauna was carried out at Dahuangpu Wetland Natural Conservation located on the downstream of Beiyunhe River from March to October, 2010, based on which species composition and quantitative distribution, community structure and diversity, the effect of environmental factor and bioassay of water quality were discussed in present study.Samples, including quantitative collection and qualitative collection, were taken at 5 sites set according to the conditions of water current at every month interval. 2 reduplications were done at each sampling site. Quantitative statistics and determination of biomass were carried out after classification. Density biomass analysis, biodiversity index analysis, similarity clustering analysis were performed to evaluate the time dynamics and seasonal difference of community, community diversity, and to compare the similarity among sites, respectively. Meanwhile, H, BPI and FBI were used for bioassay of water quality.Macrofauna including 65% aquatic insects, mainly tendipes, 17.5% oligochaeta distributed in 37 genus and 40 species. The results indicated that tendipes and oligochaeta were dominant in the macrofauna community with the later being most stable and in the largest percentage (63.13%). Group composition of macrofauna community was simple and stable from spring to fall. The trends of changes in density and biomass towards increasing from March to May, then decreasing till October with peak value occurring both in May was apparent. Both density and biomass showed the most quantity from sampling site at water intake.Both Index of Margaleff and Shannon-Weiner went up to peak in May (2.5964 and 3.3522, respectivly) , and down to valley in August; while Simpson index happened reversely; seasonal changes of Pielou index was not distinct. Margaleff and Shannon-Weiner showed evident seasonal changes among sampling sites: spring>summer>autumn. Similarity coefficient was 0.8557 at most, indicating high similarity between communities. Cluster analysis demonstrated that it could be divided into two groups including the reedmarshes and the group containing all other sites at 0.5 level. Similarity analysis together with cluster analysis indicated similar community struture of macrofauna among different sites.No significant correlation was observed between biodiversity and NH4+, total nitrogen, total phosphorus, DO, pH and KMnO4 as a result of the group composition containing mainly groups with high tolerance value. The results of biodiversity index analysis indicated that reedmarshes, other than vast waters, was preferentially suitable for the survival of macrofauna, where the biodiversity was higher. It could be inferred that vegetation had significant effect on the macrofauna community.The biological index showed that biological pollution index was greater than 1.0, and family biotic index was more than 6.50 in every month, indicating water pollution to varying degrees in different months. Biological pollution index and family biotic index which were both the greatest in August (4.15 and 9.64, respectively) demonstrated that pollution was the most serious in August. Value of H indicated pollution of different levels from spring to autumn with exception of results from sites at reedmarshes, border and side in spring. The analysis of level of pollution at different sites indicated that the water showed little improvement on quality when floating across the wetland, the water quality got worse at water outlet with quality improvement only at reedmarshes. Human disturbance and lacking of emergent aquatic plant, floating vegetation and microrganism community were associated with present environmental condition. The comprehensive analysis of H, BPI, FBI, physical and chemical character demonstrated that the water body had been seriously polluted, and was at high level of eutrophication.
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