| The Three Gorges fluctuating backwater area is rich in fish resources and is one of the important areas for fish habitat protection.The characteristics and diversity of various fish habitats in the Three Gorges fluctuating backwater area to be studied because of the complex river topography and variable flow conditions.Although there have been many studies on river habitat classification and fish habitat suitability analysis,there are fewer studies on the classification of fish habitats and their landscape pattern analysis in the Three Gorges fluctuating backwater,which can help to clarify the internal linkage and spatial structure of the habitats.Therefore,in this paper,the classification of river habitats is carried out at the mesoscopic scale,and habitat types are classified according to the hydrodynamic and geomorphic heterogeneity of the river and the fish habitat conditions.Using the principles of landscape ecology,the landscape pattern of river habitats is studied according to the classified habitat types,and the spatial composition and functions of various river landscapes are analyzed from the perspective of landscape ecology to provide a theoretical basis for habitat restoration.The main findings of this paper are as follows:(1)The topography and hydrodynamic heterogeneity of the river during the fish breeding period are obvious,and the flow velocity and Froude number during the fish breeding period of the whole river are much larger than those during the water storage period.The habitat types in the river section from Chaotianmen to Guoxikou were classified as follows: flow velocity,water depth and topography as habitat classification factors,six types of river habitats were classified according to flow velocity and water depth,including side shoals,deep pools,main flow velocity zones,shallow water areas,slow flow areas and high flow velocity areas;characteristic topography dams,cranes,gorges and beams were extracted.(2)Landscape pattern of river channel: Considering the size of patch area,shape index,fractal dimension and river landscape structure in the landscape,it is considered that the borderland habitat and the main flow velocity zone in the study river section are both the substrate and the corridor in the landscape.From the results of landscape diversity,landscape uniformity and dominance analysis,the overall landscape has good diversity and more habitat types,and the distribution and number of each habitat type in the area is relatively uniform.Combined with the local analysis,the river section where the topographic tors appear has the best habitat diversity and is evenly distributed,followed by the bend river section and the branching type river section,and the worst habitat diversity is the DC river section.The landscape in the study area is poorly connected and highly separated,and the connection between different areas is not close enough;the overall fragmentation of the landscape is minimal,and the degree of spatial fragmentation is low,and the ecological integrity of the natural landscape is good.(3)Landscape pattern of fish habitat: from the analysis results of patch density and porosity,it was found that the fragmentation degree of the main fish habitat spaces(shallow water habitat,slow flow area and high flow area)in this landscape was relatively higher,and there were stability hazards;and the habitat separation degree was the highest,reflecting the high degree of landscape dispersion and low accessibility of the fish habitat.The fragmentation of shallow-water habitats is higher than the overall level,and the spatial structure and complexity of patches in slow-flowing areas are the lowest and the regularity is relatively higher.The shallow water habitat and high velocity zone are the "stepping stones" for the fish passage function,and the slow flow zone provides good habitat for fish.In addition to the core fish habitat,the protection of the stepping stone habitat should be enhanced to prevent further separation from the class habitat. |
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