The Evolution Characteristics And Driving Mechanism Of Coastal Wetlands Landscape Along The Bohai Rim In The Past 40 Years

As an important natural resource,coastal wetlands play a key role in maintaining coastal biodiversity,providing a staging area and habitat for migratory birds,preventing coastal erosion and increasing blue carbon sequestration.Since the reform and opening up of China,the population has continued to gather in coastal areas and the high intensity of human interference,especially reclamation activities,has led to the shrinking of coastal wetlands,fragmentation of the landscape and the decline of ecological functions.Therefore,it is of great theoretical and practical significance to analyse the landscape evolution characteristics of coastal wetlands for ecological protection and restoration.This paper takes the coastal wetlands of the Bohai Rim as the research object,based on remote sensing data,field measured GPS data points,digital elevation data and socio-economic statistics of the study area in nine time phases from 1980 to 2020,1980,1985,1990,2000,2005,2010,2015 and 2020,using DSAS terminal rate method,fractal dimension,utilization index,Bay morphology index and Centre of gravity change model to reveal the evolution pattern of the Bohai Sea bay and coastline.Secondly,the evolution characteristics of the landscape pattern of coastal wetlands around the Bohai Sea are explored from the perspectives of landscape type structural changes,landscape type conversion patterns and landscape pattern characteristics,and the ecological risk index,minimum cumulative cost distance model and network analysis methods are used to construct an adaptive ecological network scheme for the Yellow River Delta and explore the positive effects of constructing potential ecological corridors on the ecological restoration of coastal wetlands.Finally,the dynamic evolution pattern and driving mechanism of coastal wetland landscape in the Bohai Rim are explored in conjunction with the evolution characteristics of shorelines and bays.The results as fellow.(1)In the past 40 years,the shoreline around the Bohai Sea has been solidifying significantly,with a zigzagging change in shape.In the last 40 years the coastline around the Bohai Sea has continued to expand in the direction of the sea by 1159.9 km,with a period of slow growth from 1980-2000 and a period of rapid shoreline growth from 2005-2015.in 2020 the artificial shoreline accounts for 93.4%of the total shoreline,with the remaining part of the natural shoreline accounting for only 20%of the original natural shoreline length.Shoreline changes are influenced by both natural and man-made factors;for example,the new estuary in the Yellow River Delta region is affected by the deposition of Yellow River water and sediment and undergoes rocking siltation,resulting in large changes to the shoreline and bay morphology.In areas of severe anthropogenic disturbance,changes in the Bohai coastline are mainly influenced by reclamation activities.Reclamation activities in the southwest Bohai Sea are on a much larger scale and the area of the bay continues to decrease,resulting in a shift in the position of the centre of gravity of the bay from southwest to northeast.The mudflats in Bohai Bay,Laizhou Bay and Liaodong Bay are large,with low reclamation costs,and are mainly used for aquaculture and salt production.In contrast,in areas where sandy and rocky shores are widespread,reclaimed land is mainly used to meet the demand for construction land arising from urban expansion,such as along the coast of Pulandian Bay.(2)The evolution of the coastal wetland landscape in the Bohai Rim in the past 40 years shows the changing characteristics of artificialization and fragmentation.In the past 40 years,the area of natural wetlands in the Bohai Rim has been decreasing,while the area of artificial wetlands has been increasing,and a large number of natural wetlands have been artificialized.In terms of spatial changes,in 1980,the natural wetlands in the Bohai Rim region were mainly distributed in the mouth of the Yellow River,the mouth of the Liao River,the mouth of the Luan River,the south coast of the Laizhou Bay and the Pulandian Bay in the southwest of the Liaodong Bay.By 2019,the area of natural wetlands was greatly reduced,mainly in the Yellow River and the Liao River estuaries.Retention rates are higher in salt and drylands(83.9%and 53.5%),and conversion of wetland types is more frequent than in non-wetlands.The transfer of natural wetlands to artificial wetlands is high,and non-wetland patches are relatively intact and rarely transferred to artificial and natural wetlands.1980-2020 coastal wetland landscape pattern around the Bohai Sea shows a continuous fragmentation,the connectivity of artificial landscape types is good,but the connectivity of artificial landscape breaks the original connectivity state between natural patches,natural wetland landscape types show a fragmentation trend,artificial wetland,non-wetland landscape The fragmentation degree is reduced,and human interference is an important factor affecting the fragmentation degree of the landscape.1995 and 2015 are the key points of change in coastal wetlands,coastal wetlands in the early protection work is not enough attention,with the social and economic development,human activity intensity is increasing,greatly occupy the natural wetlands,fragmentation of natural landscape,and after 2015 by a series of ecological protection policy influence,and to a certain extent,the problem of wetland degradation has been alleviated.(3)Socio-economic factors are important factors driving the evolution of the landscape and changes in natural wetlands in the Bohai Rim.The correlation between the evolution of coastal wetlands in the Bohai Rim and regional GDP,port cargo throughput,raw salt production and other indicators are relatively high.This indicates that socio-economic factors are the key internal factors leading to the evolution of coastal wetlands,and are important influencing factors in promoting reclamation development and accelerating wetland degradation.Indicators such as regional GDP,port cargo throughput and total aquatic production are more strongly correlated with reclamation activities,suggesting that economic interests are endogenous to the economic use of land types by reclamation,and that the scarcity of land resources(total population and land prices at the end of the year)is an important reason for the continuous expansion of urban land use.Human activities such as aquaculture,salt industry,industrialization and urbanization are the main forces influencing landscape change in coastal areas.(4)Construction of an adaptive ecological network of important deltaic wetlands around the Bohai Sea.After identifying natural landscape patches in the Yellow River Delta as habitat sources through the ecological risk index and landscape connectivity,the results show that natural wetlands and water systems are the main landscape types for the construction of ecological networks.In view of the current ecological situation of the Yellow River Delta,a better solution for constructing ecological corridors is to increase the area of natural wetlands in rivers,enhance the connectivity of water systems,and establish an ecological network in the Yellow River Delta by focusing on the Yellow River Delta Nature Reserve,adding artificial habitat islands in the southwest,and connecting broken patches of wetlands through water system channels.