Study On Habitat Suitability Assessment Of Four Family Fish In The Downstream Of The Three Gorges Project

Rivers are important freshwater resources on the earth,which can be regarded as the artery of catchment area.They maintain the water cycle and energy and material balance on the earth.With the rapid development of human society,the rapid increase of population and the rapid development of industry,human activities such as dam water conservancy projects and river canalization have changed the water environment,resulting in the destruction of river ecosystem and river biology.Habitat degradation is serious,River biological species are decreasing.River habitat is an important part of river system,which can provide material security and environmental basis for the survival of organisms.River habitat assessment is the key link of system assessment and an indispensable part of river assessment plan.At the same time,the quality of habitat reflects the degree of river health to a large extent.Effective assessment of environment is of great practical significance to river health.This paper extensively studies the relevant information,explores the connotation and temporal and spatial characteristics of river habitats,and summarizes the evaluation methods of river habitats at home and abroad.The changes of eco-hydrological conditions in the lower reaches of the Three Gorges Project before and after impoundment,the effects of impoundment of the Three Gorges Dam on the habitat conditions of the four major fish in the lower reaches,and the suitability evaluation of the micro-habitats of the four major fish were analyzed.(1)According to the hydrological conditions during the spawning period of the "Four Big Fish",the mean value,variation range,standard deviation,flood duration and daily rising rate of water level of the hydrological elements during spawning and reproduction period of the "Four Big Fish" were analyzed.The suitable range of hydrological elements during spawning period of "four big fish" was counted.The optimal interval of water temperature elements was calculated by Sturge rule.The spawning times of "four big fish" in different hydrological elements were counted and the frequency curves of hydrological elements were obtained.(2)Taking Yichang Hydrological Station downstream of the Three Gorges Reservoir as the research object,the trend of flow,sediment and water temperature before and after impoundment of the Three Gorges Reservoir and the degree of change of the situation are analyzed by using linear tendency estimation method,Mann-Kendall method and RVA analysis method.The results show that the flow situation downstream of the Three Gorges Reservoir has changed moderately and the sediment situation has changed highly after impoundment.The water temperature situation has changed moderately.The number and mileage of spawning grounds of the four major domestic fishes in the downstream of the Three Gorges Reservoir are decreasing day by day,and the spawning and reproduction time of the four major domestic fishes has been postponed.(3)Seven habitat hydrological factors were selected as the evaluation index,and based on the theory of fuzzy comprehensive evaluation,a model for evaluating the habitat suitability of river fish was established.Taking the four major fish habitats in the lower reaches of the Three Gorges as an example,the evaluation results show that the habitat quality of the four major fish habitats is at an appropriate level,but the suitability of the four fish habitats has a downward trend after the Three Gorges impoundment.The evaluation results provide a scientific basis for river management departments to formulate river protection policies,lay a foundation for the establishment of river ecological restoration evaluation system,and thus improve river life.Eco-remediation technology can improve the service value of river environmental ecosystem.