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During the period of April 2006 to March 2007,secondary production and its dynamics of the dominant species of mayfly community in a second order river(Hujiaxi Stream) of Qingjiang River,Yangtze River Basin were investigated.From the upper to the lower reach of the stream,we sampled at six sites of different habitats quantitatively.The life cycles of the four dominant mayflies,namely Leptophlebia sp.,Electrogena sp.,Indobaetis sp.,and Caenis sp.,were analyzed by the monthly size-class frequency distribution,the cohort and annual production were estimated by size frequency method,and the production dynamics were examined by the method sensu Benke and Wallace(1997).The results show that Leptophlebia sp.,Electrogena sp.,and Indobaetis sp.appear to develop three generations per year,while Caenis sp.completed two generation a year.Their average annual standing stocks were: for Leptophlebia sp.,407 ind./m2,1.00 g/m2;for Electrogena sp.,150 ind./m2,0.37 g/m2;for Indobaetis sp.,232 ind./m2,0.30 g/m2;and for Caenis sp.,91 ind./m2,0.17 g/m2,respectively.The annual production(g/m2(WW)) and the annual P/B ratio of four mayflies were: for Leptophlebia sp.,441.42 g/m2(WW),14.3;for Electrogena sp.,434.88 g/m2(WW),7.6;for Indobaetis sp.,747.21 g/m2(WW),15.0;and for Caenis sp.,40.52 g/m2(WW),7.2.Temporal overlap of secondary production dynamics of the four species,which measured with the proportional similarity index as 0.55,indicates that they utilize similar or same food resources along time dimension.

Community structure of macrozoobenthos and the bioassessment on water quality in a second order river—Hujiaxi Stream of Qingjiang River basin were investigated from April 2006 to March 2007. The results showed that, among collected altogether 87 species of macroinvertebrates, there were 3 species of Annelida, 3 species of Mollusca, 76 species of aquatic insects, and 5 species of Malacostraca. The community structure exhibited obvious spatial and temporal variations. The species number reached its peak in June, and descended to the lowest in December. There was the largest species number in Site 5, and more species macroinvertebrates were presented in June than those in other months. Over 75% of the collected species could inhabit in all six types of microhabitats. The density of the community reached its peak in April at 3293 each/m2, while biomass attained its peak in December at 163 g/m2. The water quality was bio-assessed with Shannon-Weaner diversity, Biotic Index (BI) and Family Biotic Index (FBI), and results showed that the river water was fairly clean during the sampling period. Considering the coincidence with physical-chemical parameters, BI and FBI bio-assessment methods were much fit to apply in rivers of China.