| The ocean is a precious resource for human survival and development.The coastal zone,which is the junction of land and sea,is an important part of the ocean.Tidal flat refers to the zone between the low tide line of the average spring tide and the high tide line of the average spring tide.It is one of the typical landform types of the coastal zone.The characteristics of tidal flats can represent the main characteristics of the coastal zone where they are located.To find out their nature and distribution is of great significance for the rational development of tidal flat resources and the study of sustainable management of coastal ecosystems.The Shanghai section of the north shore of Hangzhou Bay is located on the southern edge of the Yangtze River Delta.The erosion and deposition of the tidal flat is affected by various dynamic factors.The tidal flats alternate frequently with erosion and deposition.Siltation and erosion alternate with each other in different time and space.In different sections and time periods,the impacts caused by the natural environment and human activities are not consistent,and the degree and trend of transformation between tidal flats and non-tidal flats are also different.Therefore,scientific evaluation and judgment of the current status and development trend of the tidal flats on the north shore of Hangzhou Bay,and studying the changes of tidal flats are of great significance to the ecological protection and sustainable development of the landscape pattern.Under the combined influence of human activities and the natural environment,the landscape pattern of the Shanghai section of the tidal flat on the north shore of Hangzhou Bay is undergoing significant changes.While pursuing social and economic production,we should not ignore ecological and environmental issues.We should strengthen the ecological conservation of tidal flats to promote the coordinated development of society,economy,and ecology.In this study,using GF-1 and Landsat7 satellite remote sensing images,the tidal flat distribution map of the Shanghai section on the north shore of Hangzhou Bay in2007,2013,2015,2017 and 2019 was obtained by extracting the water edge lines of high and low tide images.Based on this,an analysis of the temporal and spatial evolution of tidal flats was carried out.Furthermore,other ecological landscape types in the study area are classified,combined with natural factors and socio-economic factors,and the logistic regression model is used to explore the quantitative relationship between driving factors and tidal flat pattern changes from an ecological perspective.Then the CA-Morkov model is used to predict and analyze the changes of tidal flats in2025 and 2031.The main conclusions are as follows:(1)The tidal flats of the Shanghai section on the north shore of Hangzhou Bay are distributed in a strip along the coast due to the erosion of tidal currents,coastal reciprocating currents,and the sedimentation of incoming sand from the Yangtze River.The tidal flats of artificial banks are affected by natural erosion and siltation and human activities,and their individual areas are relatively large,and their distribution presents regular quadrilateral shapes;the tidal flats of natural banks are widely distributed,and the distribution presents irregular polygonal shapes,and the individual areas are relatively small.From 2007 to 2019,the main target for the transfer of tidal flat area in Pudong New District is water,the main target for transfer of tidal flat area in Fengxian District is arable land and water area,and the main target for transfer of tidal flat area in Jinshan District is construction Land and water areas.The main transfer objects of tidal flats are water areas.From the changing trend of tidal flats,it can be found that under the intervention of human activities,part of the tidal flats will be filled into land,and at the same time,they will continue to silt in the direction of the sea,generating new tidal flats.This shows that the degree of human intervention on tidal flats is getting stronger and stronger,and human activity factors have gradually become the dominant factor in the development and changes of tidal flats.The shoreline of the Shanghai section on the north shore of Hangzhou Bay has a trend of gradually advancing toward the sea.This is gradually formed under the combined influence of natural erosion and deposition and human activities.(2)The total tidal flat area in 2007,2013,2015,2017 and 2019 were 10.6385 km~2,8.8938 km~2,9.5928 km~2,10.7316 km~2and 9.2295 km~2,respectively.The tidal flat area first decreased by 1.7447 km~2from 2007 to 2013,and then increased year by year from2013 to 2017,and then decreased from 2017 to 2019.The area decreased by 1.4090 km~2in 12 years,and the dynamic degree in 12 years was-1.10%.From 2007 to 2013,the tidal flat changed most drastically.From 2007 to 2019,the overall tidal flat migrated0.6323 km and 2.3142 km to the southwest at 255.1°and 255.4°twice,and the tidal flat migrated 2.9466 km southwest 255.3°in 12 years.The overall spatial distribution pattern changed drastically from 2013 to 2019.From 2007 to 2019,the tidal flats in Pudong New District were generally siltated,the tidal flats in Fengxian District were slightly eroded,and the tidal flats in Jinshan District were greatly reduced.(3)In the logistic regression analysis,the main driving factors affecting the overall tidal flat transition on the north shore of Hangzhou Bay,from high to low contribution,are as follows:clay content,silt content,distance from rivers,sand content,population density,GDP,distance from grassland and distance from cultivated land.The main driving factors that are positively related to tidal flat development are:clay content,silt content,and GDP.The main driving factors negatively related to tidal flat development are:distance from rivers,sand content,population density,distance from grassland,and distance from cultivated land.(4)The tidal flats on the north shore of Hangzhou Bay in 2025 and 2031 are still in a zonal distribution.The distribution range of tidal flats is not much different from that in 2019.The predicted results are basically in line with actual development trends.From2019 to 2031,the distribution of the spatial center of gravity of the tidal flats in each region is basically on the same line.The overall tidal flats first migrated to 251.3°southwest by 1.8525 km,then to 83.6°northeast by 0.4024 km,and overall to the southwest by 247.9°1.4619 km has been migrated,and the overall spatial distribution pattern has changed drastically from 2019 to 2025.The area of the tidal flats on the north shore of Hangzhou Bay will be 9.8153 km~2in 2025 and 9.3177 km~2in 2031,respectively.From 2019 to 2031,the total tidal flat area will increase first and then decrease,increasing by 0.0882 km~2in 12 years,and the dynamic degree is+0.08%.From 2019 to 2031,the tidal flats in Pudong New District will gradually silt up;the tidal flats in Fengxian District and Jinshan District have been eroded,and the area is decreasing year by year.It shows that in the future,under the condition that the interference intensity of natural factors and socio-economic factors is stable,the shoreline of the Shanghai section on the north shore of Hangzhou Bay will gradually advance toward the sea,and the tidal flat will gradually silt up. |
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