| River habitat was significant influenced by in stream physical structure, topography, geomorphology and human disturbance and was also important to river biodiversity. Macroinvertebrate and fish, which is sensitive to river habitat variation, were important component of mountain river ecosystem. In the past twenties years, numerous small diversion type hydropower stations were constructed in mountain river of China for their good economic benefit. As a consequence, a lot of environmental problem relative to river ecosystem and aquatic organisms exhibited including dysbiosis, drought of river channel, habitat fragmentation and loss of aquatic biodiversity. Therefore, maintenance of mountain river ecosystem health, biodiversity integrity was important and urgent for water energy resource exploitation in China.In view of the need of reality and present environment status of mountain river in China, we conducted research on river habitat. In this study, we classified river habitat of mountain river ranging from macro to meso and micro habitat scale, explored the relationship between macroinvertebrate and meso habitat and micro habitat, discovered both character of river habitat and pattern of macroinvertebrate and fish community diversity which were influenced by small diversion type hydropower stations.The main contents and researeh results are summarized as follows:(1) According to Bisson's river habitat classification system and basing and based on GIS technology and field survey date, we classified river habitat of Dong River ranging from macro to meso and micro habitat scale. At river system scale, we divided Dong River in to three parts, including upstream, middlestream and downstream. At river segment scale, we identified three types segment, including colluvial valleys, bedrock valleys, headwear valleys. At river reach scale, six types of river reaches presented in Dong River, including bedrock reaches, headwear reaches, cascade reaches, step-pool reaches, plane-bed reaches, pool-riffle reaches. At channel unit scale, Dong River had 14 types of habitat as followings: falls, cascade, rapids, riffle, chute, run, eddy, trench, midchannel pool, latteral pool, plunge pool, landslide dam pool, backwater and abandoned channel pool. River habitat at micro habitat scale can be classified according to substrate particle size.(2) Aquatic insect larva on stone surfaces played an important role in headwater ecosystem. In May 2007, aquatic insect larvas on small and large cobble surface in four sampling section were investigated in the headwater of Yudu stream in Chengkou County, Chongqing. The aim of present research is to discover the community characteristic and biodiversity of aquatic insect on stone surface and analyze the influence of stone size on insect larva. The result shows that there were 62 species of 30 families of 8 orders in headwater of Yundu stream. Ephemeroptera, Trichoptera and Diptera were the dominant groups. Trichoptera showed more proportions in stream reach of higher altitude. Shredder and Collector-gatherer were dominant functional feeding groups. Abundance, Shannon-Wiener Index and Margalef index of large cobble were significantly higher than that of small cobble, which may be determined by heterogeneity and stability difference of these two types of stone habitats. There were no significant differences in biodiversity index of aquatic insect larva on small cobble among four sampling sites, while abundance and Margalef Index of larva on large cobble were significant different.(3) Riffle and pool was the most common habitat unit in mountain river. In July 2011, macroinvertebrate of twenty one riffles and pools respectively in upstream of Dong River in Kaixian County of Chongqing were sampling to compare their difference in assemblage structure and composition. The result indicated that there were 31 and 24 in riffles and pools respectively. The density, wet biomass of riffles were 450.62 ind/m~2 and 2.88 g/m~2, respectively, compared to 86.24 ind/m~2 and 0.55 g/m~2 of pools. Eleven taxon, including Hydropsyche sp, Iron sp, Pseudocloeon sp, Glossosoma sp, Epeorus sp2, Notacanthurus sp, Heterocloeon sp, Serratella sp, Antocha sp, Isonychia sp and Rhithrogena sp, were indicator species of riffles, while pools only had two indicator species, Ephemera sp and Hexatoma sp. Scraper was the dominate functional feeding group in both habitat. Riffles exhibited significantly higher percentage of collector-filterer and scraper, while percentage of collector-gatherer and predator in pools were significantly higher than that of riffles. Difference of macroinvertebrate community structure among two habitats was significant. Density, biomass, species richness, Shannon-Wiener index and Improved Shannon-Wiener index of riffles were significant higher than that of pools. Habitat stability and heterogeneity affected by habitat morphology, hydraulic characteristics and erosion/deposition pattern may be the major explanation.(4) Stream habitat and fish community of Dong River in Chongqing were investigated in order to explore the impact of two small diversion type hydropower station, Baili station and Honghua station. Mechanism of their influence on fish community was analysis from stream habitat angle. One hundred and forty-nine fishes were collected in our survey, which were subordinate to seventeen species, sixteen genus, eight families and four orders. The result showed that biodiversity of fish community of the river reach influenced by small diversion type hydropower station was rather lower and the stations was an important reason to explain depressing of fish biodiversity in mountainous stream. After the construction of water dam, habitat heterogeneity and diversity of reservoir area was lost as a result of sediment deposition. Habitat area for fish in reach between dam and powerhouse was decreased and riffle-pool structure was destructed as a result of water regime alteration. Small diversion type hydropower station influenced fish community mainly by deterioration of stream habitat.(5) Macroinvertebrate in river reaches influenced by two small diversion type hydropower stations on Dong River, namely Baili and Honghua, were sampling to explore their influence. The result indicated that there were 43 species belonging to three phylum, four classes and thirty families. Mayfly and caddify were the dominated taxa. Water quality was not significant changed by small diversion type hydropower stations, while river habitat deteriorated a lot. The reach behind the dam was influenced by sediment deposition and the flow pattern here was lotic. Component of macroinvertebrate community in the reach behind the dam were not significantly different from the reach disaffected by dam, but density, biodiversity and biomass were significantly depressed. Habitat suitability of the reach downstream of the dam was declined by flux decreasing and macroinvertebrate here exhibited lower density, biodiversity and biomass.(6) An evaluation model was established originated from both stream ecosystem structure and function integrality. This model was composed by an index system including stream habitat diversity indicator, channel wet rate and habitat unit quality indicator for rapid habitat quantificational assessment. The weight of indicators was determined by means of Delphi method. The model was used to assess the stream habitat quality of the Dong River which located in the Three Gorges region and influenced by hydroelectric projects. The results show that the habitat quality of the segment behind the dam is worse than the segment both in front of the dam and behind the hydroelectric plant water outlet. Lack of river ecological basic flow should be responsible for the worse status of the segment behind the dam and sediment deposition depressed the status of stream habitat in front of dam. Results of the evaluation can more directly reflect the status of habitat in mountain streams under the influence of hydropower projects, and the reasons of their deterioration.
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