| The ocean is rich in resources,which provides indispensable conditions for human development and life.As the intersection of ocean and land,the coastal zone is also one of the most important parts for the ocean.Tidal flat is a typical geomorphic type in the coastal zone.Its area mainly refers to the zone from the average spring tide low tide line to the average spring tide high tide line.The characteristics of coastal zone can be expressed by various characteristics of tidal flat to a certain extent.Therefore,understanding its distribution range and characteristics is the prerequisite for scientific development of tidal flat resources and comprehensive analysis of regional ecological changes in coastal zone.The Nanhui tidal flat of the Yangtze River estuary is located in the southern edge of the Yangtze River Delta.The deposition and erosion of the beach will be affected by many external factors,and the deposition and erosion of the beach will alternate frequently.In different time periods and regions,due to the different effects of various human social activities and natural evolution,and the transformation trend and degree of change between the beach and other land types are also different.Therefore,the comprehensive analysis and evaluation of the change trend and beach status of Nanhui tidal flat in the Yangtze Estuary is of great significance to the scientific development and ecological environment protection of Nanhui tidal flat in the Yangtze Estuary.Under the joint action of human social activities and natural conditions,the landscape pattern of Nanhui tidal flat has changed significantly.At the same time of rapid economic development,we should not neglect the impact on the ecological environment,and timely protect various ecological resources in the tidal flat,so that the ecology,society and economy can develop in a balanced mode.In this study,sff-w model is used to extract the water edges of spring and neap tides in GF-1 satellite remote sensing images of Nanhui tidal flat in 2013,2015,2017 and 2019.The extracted waterside lines are superimposed to obtain the distribution map of Nanhui tidal flat in the Yangtze River Estuary in each period.Combined with the land use data of other ecological landscape types of Nanhui tidal flat,the temporal and spatial evolution of landscape ecology in the tidal flat area is analyzed.Based on socio-economic factors and natural environmental factors,the evolution trend of tidal flat regional landscape pattern is comprehensively analyzed from the perspectives of society and natural environment according to MCE multi evaluation criteria.The CA-Morkov model is used to analyze the Nanhui tidal flat area,and the changes of the regional landscape pattern of the tidal flat in 2021 and 2023 are predicted.The following conclusions are drawn:(1)An improved SFF-W model for tidal flat boundary extraction is proposed.The model combines the advantages of sffcm algorithm and water edge method,which can effectively make up for the deficiency of clustering algorithm in determining the upper boundary of tidal flat,and solve the problem that it is difficult to distinguish river channel and tidal flat gully when extracting the lower boundary of tidal flat by water edge method.The overall accuracy and mapping accuracy of SFF-W model are 2.39%and 10.79%higher than that of water edge method respectively.The model can accurately extract the tidal flat boundary under semi supervision.Through the verification of tidal flat extraction results in 2019,the overall accuracy and mapping accuracy of SFF-W model are the highest.(2)From 2013 to 2019,the main landscape changes in the study area are reflected in the decrease of seawater area year by year,the increase of construction land area year by year,the overall increase of tidal flat area,and the trend of cultivated land and forest land area increasing first and then decreasing.In 2013,the area of cultivated land in the study area was 60.85 km~2,which will be reduced to 47.10 km~2 by 2019;The area of tidal flat increased rapidly,from 17.18 km~2 in 2013 to 108.70 km~2 in 2019.From2013 to 2019,the average value of overall habitat quality in the study area decreased by0.102 from 0.794 in 2013 to 0.692 in 2019.The area of low habitat area increases slowly,the area of medium habitat quality area increases significantly,and the area of high habitat area decreases year by year.(3)The area change of main landscape types from 2019 to 2023 is basically the same as that from 2013 to 2019,and the area of forest land,cultivated land and sea water continues to decrease;Among them,the forest land has the largest change rate of-39.56%among all landscape types,and the area of construction land has increased rapidly,reaching 43.19km~2 by 2023,with a change rate of 29.74%;The tidal flat area has increased to a certain extent,and the change rate from 2019 to 2023 is 9.93%.From2019 to 2023,the transfer out rate of Nanhui tidal flat natural landscape is large,and the transfer in rate of construction land is large.From 2019 to 2023,the overall decline trend of habitat quality in the study area slowed down,and the area of low habitat quality areas increased slowly.The average value of overall habitat quality in the study area decreased from 0.692 to 0.668,with an overall decrease of 0.024.The area of low habitat landscape types kept increasing,the area of medium habitat landscape types fluctuated slightly,and the area of high habitat landscape decreased gradually. |
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