A Study On Fish Habitat Geomorphology And Hydrological Regime Features Of National Nature Reserve Of Rare And Endemic Fish In The Yangtze River Upstream Area

With vast area and many rivers, lakes, ponds, reservoirs, Yangtze River, as the cradle and gene bank of freshwater fisheries and also the richest area of rare aquatic wildlife diversity in China and the World, has a large number of high quality fish and many excellent germplasm. However, with the obvious trend of ecological degradation of Yangtze territorial waters resulted by growing human activity, the situation offish of the Yangtze River becomes more difficult. Problems such as reclaim the land, discharge mining wastewater, barrier lakes, water conservancy and agriculture non-point source pollution are the Yangtze River fish must face. Establishment of National nature reserve of rare and endemic fish in the Yangtze River upstream helps to preserve a complete and important completed life history river for rare and endemic fish of Yangtze River upstream. White sturgeon, Acipenser, mullet and other rare fish, Coreius, long LEPTOBOTIA endemic fish and other66kinds offish as well as copper fish, S. sinensis and other important economic fish all live in the waters of protected areas. Meanwhile,1.8km upstream of the protected area lays the Xiangjiaba hydropower dam, which is one of the most downstream four cascade hydropower station of Jinsha River downstream, and because of busy shipping and sever dredging quarrying behavior, the mainstream is disturbed intensely by human activities.Based on the research on section of the river hydrology, terrain data and combined with the distribution of fish spawning location and bio-information, the paper conducts a comprehensive analysis to the water environment and geomorphological features of mainstream habitat of National nature reserve of rare and endemic fish of Yangtze River upstream. Main researches and conclusions are as following:(1) According to the daily measured data of Pingshan and Zhutuo hydrological station of the protected areas, through classifying three kinds of environmental flow component, the paper has defined that from January to May and December the protected areas mainstream lies in low-flow period, from June to July and from October to November lies in high-flow period, from July to September lies in the flood pulse period. When the flow of Pingshan station is below2000m3/s, low flow process starts; above10000m3/s is flood pulse flow. When the flow of Zhutuo station is below4000m3/s, low flow process stats; above18000m3/s is flood pulse flow.(2) According the water temperature observation record of Pingshan station for many years, adopted the RVA method of ecohydrology, the paper has calculated the suitable ecological water temperature targets for each month and has made reliability test of suitable water temperature range using the spawning period of17kinds documented fish of protected areas to certify the final ecological water temperature target.(3)Based on the partial reach, geomorphic unit and section levels of the medium-scale habitat, the paper adopted13indicators to respectively describe the river planar geomorphology, longitudinal profile, cross section and geomorphic unit. In partial reach scale, choose four indicators for research which included the change rate of section area, the sinuosity, the site where the spawning field center locates and river bed gradients of the longitudinal profile. In geomorphic unit scale, choose the density of riffle and pool, the number of aits as indicators. In section scale, choose7indicators including the river width, width-depth ratio, entrenchment ratio, section inhomogeneity and the location of3spawning sites. Finally elaborate the connotation, the computational method and the ecological significance of the13indicators.(4)The paper generalized the geomorphology characterization of entire mainstream reach in the reserve. The reserve reach is in type of mountain meander river, the section in the river bend presents a "V" shape, while in the straight or transition site, it presents a "V" shape of a "U" shape,and as to the ait, it presents a "W" shape. The study river is divided into3reaches which are separately cut from YiBin to LuZhou, from LuZhou to ZhuTuo and from ZhuTuo to ChongQing. Analyze the3reaches in perspective of the partial reach scale, geomorphic unit scale and section scale. In partial reach scale, on the point of flow, only the change rate of section area varies with different discharges, and the section area becomes less with more discharge. In the reach aspect, the change rate of section area of the3reaches has little distinctions, the reach from ZhuTuo to ChongQing gets the maximum value, the reach from YiBin to LuZhou comes second and the reach from LuZhou to ZhuTuo gets the minimum value. The sinuosity value in the reach from LuZhou to ZhuTuo is the highest, the one from YiBin to LuZhou is less, the reach from ZhuTuo to ChongQing comes last. The river bed gradients are much influenced by the land topography, which get bigger from the upstream to the downstream. In the geomorphic unit scale, the density of riffle and pool also gets bigger along the reach from upstream to downstream. The number of aits in the reaches from YiBin to LuZhou, from LuZhou to ZhuTuo and from ZhuTuo to ChongQing is respectively14,14and4. In the section scale, the river width and the width-depth ratio in the reach from LuZhou to ZhuTuo gets the maximum value, the entrenchment ratio in the reach from LuZhou to ZhuTuo gets the minimum value, while the section inhomogeneity of the3reaches is much similar.(5) with the calculation and statistics of the13indicators in the reserve mainstream geomorphology index system, the paper analyzes the results according to different spawning class group. The conclusion is as follows:the fish which spawn the demersal eggs prefer the concave bank with big sinuosity and wide water surface and lay their eggs in the riffle, in the cross section, they tend to spawn in the water area which is close to the shore and far from the talweg and has the shallow depth. The fish which spawn the pelagic eggs spawn around the pool in the the concave bank with bigger sinuosity and wider water surface, in the cross section, it prefers the water area far from the shore and close to the talweg with larger depth. The above two kind of fish have little selectivity with the section inhomogeneity and river bed gradients. Based on the computational and statistic results of the width-depth ratio and entrenchment ratio,count the number and frequency of the spawning sites of the fish which spawn the pelagic eggs located in the3reaches respectively, finally put forward a suitability curve describing the width-depth ratio and entrenchment ratio of the fish spawning sites in the reserve mainstream.