Study On Land Use And Landscape Change In The Crisscross Region Of The Three Gorges Reservoir Area

Water-fluctuation zone is a special zone of fragile terrestrial and aquatic ecosystems that is periodically inundated and exposed by the water level of seasonal rivers or reservoirs.Water-fluctuation zones overlap both terrestrial and aquatic ecosystems.People in the reservoir area usually live along the shore,and all kinds of human activities will disturb the ecological stability of the water-level-fluctuation zone.Therefore,it is of great significance to study the water-level-fluctuation zone and its surrounding land use changes after the completion of the reservoir construction in order to protect the ecological environment and people’s safety on both sides of the river.The Three Gorges Project is one of the largest water conservancy projects in the world.It has the functions of flood storage,transportation,and power generation.Since2003 when the water reservoir initial water level 145 m,to 175 m,the highest level since2010,water storage,form the elevation difference between 30 m down.The San Xia Reservoir adopts an anti-seasonal drainage and storage method,that is,the water is stored in summer and drained in winter.In this paper,the water-level-fluctuation zone extends 150 m outward along the highest water level as the research scope,which is called the staggered area of water-level-fluctuation zone.A total of 3 phases of Landsat image data were collected in the whole reservoir area,and 2 phases of high-definition Google earth history image data were selected according to the type of the fluctuation zone.Based on 3S technology,landscape ecology theory and Fragstats4.2.1,the land use change and landscape pattern in the ecotone of water-level fluctuation zone in the reservoir area from 2000 to 2020 were analyzed.Under the condition of stable water storage.We can draw the following conclusions:(1)The water-level-fluctuation zone of the reservoir area is distributed in 20 counties,with a total area of 2474.5131km2,accounting for 4.28% of the total area of the administrative areas through the Three Gorges Reservoir Area.During the study period,the area of pure soil,pure rock and grassland decreased continuously while the city scale increased continuously,and the area of rivers in other regions increased rapidly except the area of rivers in the upper reaches.(2)In this paper,the land use types are divided into cities,roads,pure rock,pure soil,grassland,farmland,forest,shrub,pond and river.Among them,the woodland formed by forest and shrub occupies the dominant position of the staggered area.(3)From 2000 to 2015,the land use pattern in the ecotone of water-level-fluctuation zones changed significantly,and the river area increased rapidly.And the river area did not change significantly from 2015 to 2020.Pure rock and pure soil can be easily transformed into cities.Forest,shrub,farmland and grassland can also be transformed into each other.The conversion between forest and other types is more frequent.In the 20 years,the comprehensive utilization degree of the eclectic zone in the water-level-fluctuation zone increased from 193.68 to 223.74,indicating that the comprehensive utilization degree is continuously increasing.The comprehensive characteristic value of land use from upstream to downstream ranges from 1.0932 to1.1662 and then to 1.2615.The whole library is a type of very slow change,but the rate of change is increasing.(4)During the study period,the number of plaques in the upper and middle reaches decreased while the number of plaques in the lower reaches increased.The density of all patches in the upstream is decreasing,while the density of patches in the downstream part is increasing,indicating that the disturbance of human activities in the downstream to the landscape is gradually decreasing.The longer the water is stored,the lower the Shannon diversity index,and the worse the ecosystem diversity.The closer to the Three Gorges Dam,the lower the Shannon evenness index is,and the worse the landscape heterogeneity is.In the intersecting area,the values of all the landscape integration degrees except the ponds are close to 100,indicating good connectivity,but with a decreasing trend under human activities.At the beginning of impounding,the spread degree of the staggered area is relatively large,and further increase in 2020 indicates that the dominant landscape becomes stronger and the number of small patches decreases.(5)For the future management of level-fluctuation zone staggered zone,in terms of land use type and landscape pattern,the area of land directly related to human activities,such as urban and rural construction land,is increasing.Therefore,the main body of future development will still be the progress of urbanization.However,the arable land area around urban and rural construction land is constantly decreasing.In future urbanization development,attention should be paid to the basic red line of arable land to ensure the arable land area.The development of the downstream is the most environmentally friendly,and the proportion of forest area is increasing,which can be learned from the development of the upstream and middle.Considering the landscape heterogeneity and stability,attention should be paid to not developing the same type of landscape on a large scale in the water-level-fluctuation zone of the whole reservoir area to ensure the stability of the ecological environment.