| The community structure and secondary production of the benthic macroinvertebrates in a second order river-Tanqigou Stream of Qingjiang River Basin was investigated from April, 2006 to March, 2007. Major work dealt with exploitation of the species composition and functional feeding group of the macrozoobenthos community, the biodiversity of the macrozoobenthos, evaluation of the water quality with the biological index, measurement of annual variations of standing stocks of the dominant species, calculation of secondary production of major taxa. The main results were as follows:1) Altogether 80 species of benthic macroinvertebrates were sampled in Tanqigou Stream, among which 3 species were annelida, 4 species were mollusca, 69 species were insecta, 4 species were malacostraca. Functional feeding groups were 5 species of shredders, 53 species of collectors, 10 species of scrapers and 12 species of predators.2) Biodiversities of the benthic macroinvertebrates were calculated. The annual dynamics of Simpson indexes fluctuated intensely in Site 5 and Site 6 (ranging 2.23 to 7.33 and 2.01 to 6.99,respectively) , while kept much stable in Site 1 and Site 2 (ranging 3.56 to 10.62, and 3.56 to 10.35, respectively) . Both Margalef indexes and Shannon-Wiener indexes varied slightly.3) The community structures in various microhabitats were compared each other, and the Sφrensen indexes of the microhabitats were calculated. In general, the common species were the dominant ones in various microhabitats. More than 60% of the collected species could inhabit at six different microhabitats.The similarity of Site 1 and Site3 was 84.03%, that of Site 3 and Site 4 was 81.48%, and that between Site 3 and Site 6 was 81.08%.4) According to the bioassessment methods, the water quality of Tanqigou river was evaluated by biological indexes, and the water quality was slightly polluted due to the drainage of inhabitats and agriculture.5) Annual variations of standing stocks of dominant species and the community were measured. The annual mean density (ind/m~2) and biomass (g/m~2 wet wt) of Caenis sp., Leptophlebia sp., Cloeon dipterum, Ecdyrus sp., Krenopsection sp., Trissopelopia sp., Cylindraceus sp., Hydropsyche spp. and Neureclipsis sp. were 80.75/0.052, 169.58/0.089, 524.08/0.229, 225.75/0.688, 52.3/0.011, 171.92/0.071, 66.08/0.011, 190.42/2.953, 50.5/0.058, respectively. The annual mean density and the biomass of the community were 2280.25 ind/m~2 and 52.167 g/m~2.6) Secondary production of major groups of macrozoobenthos in Tanqigou Stream was calculated. Production (g.m(-2) wet wt) and P/B ratios were:(1) Ephemeroptera. Caenis sp., 0.60～10.78(average 4.22) , 5.4～8.1(average 6.4) ; Leptophlebia sp., 4.18～17.48(average 8.08) , 5.8～8.1(mean 7.1) ; Cloeon dipterum, 6.78～99.69(average 44.01) , 13～19.5(average17.0) ; Ecdyrus sp., 37.94～194.56 (average 93.35) , 9.2～14.9(average 11.5) ;(2) Chironomidae. Krenopsection sp., 3.30, 6.4; Trissopelopia sp., 17.44, 3.4; Cylindraceus sp., 1.66, 2.3;(3) Trichoptera. Hydropsyche spp., 1541.70, 20.7; Neureclipsis sp., 65.74, 15.8.
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