| Tidal flat is a unique ecosystem generated by the interaction of land and ocean.Its formation and change are influenced by natural and human factors.As the boundary between land and sea,the tidal flat area of Liaohe Estuary wetland directly determines the formation and evolution of Liaohe Estuary wetland,which is of great significance for maintaining the stability of wetland ecosystem and regional biodiversity.This study analyzed the landscape pattern evolution characteristics of Liaohe Estuary wetland tidal flat area under the influence of natural conditions such as runoff,sediment transport and artificial activities such as reclamation,port construction and aquaculture,in order to provide scientific basis for protecting the stability and ecological security of Liaohe Estuary wetland.Based on Arc GIS technology,this paper studies the landscape pattern evolution of Liaohe Estuary tidal flat area in recent 30 years,using artificial visual interpretation combined with field investigation,spatial analysis,land use transfer matrix,landscape pattern analysis,DSAS coastline analysis system,deposition erosion rate,principal component analysis and other methods,using Landsat remote sensing images of Liaohe Estuary tidal flat area from 1985 to 2017 as the main data source.The driving forces of landscape pattern change in Liaohe Estuary tidal flat area are analyzed based on natural,social and economic driving factors.The main results are as follows:(1)From 1985 to 2017,the total area of Liaohe Estuary tidal flats increased by 11299.87 hm2,the area of tidal flats and river waters decreased,and the area of aquaculture,towns,reservoirs,oil wells,wetlands,fields and roads showed an increasing trend.Among them,the area of aquaculture area increased fastest,with an area of 7975.42 hm2,accounting for 11.37%.In 1994,two new land use types,farmland and reservoir,emerged in Liaohe Estuary tidal flat area,which were transformed from tidal flat and wetland.Due to the interference of human factors,tidal flats are transformed into aquaculture,towns,oil wells,roads and so on.From 1985 to 2017,the number of patches(NP)increased,the proportion of the largest patches(LPI)decreased,the edge density(ED)decreased,the patch density(PD)increased,and the landscape of Liaohe estuary tidal flat area tended to be fragmented.The proportion of wetland landscape patches to landscape area(PLAND)gradually decreased,the proportion of farmland patches to landscape area(PLAND)gradually increased,and the dominant position of wetland landscape in Liaohe estuary tidal flat area gradually declined in the study area,and was gradually replaced by farmland.The area-weighted average patch fractal dimension index(AWMPFD)of artificial landscape gradually decreases,and the disturbance of human activities on wetland landscape in Liaohe Estuary becomes stronger.(2)From 1985 to 2017,the tidal flat area of Liaohe Estuary showed a trend of siltation.The coastline of the tidal flat area migrated to the sea as a whole,and the coastline type of the tidal flat area changed from natural tidal flat to artificial tidal flat.The length of the shoreline in the tidal flat decreases by 5.09 km,and the winding shape of the shoreline in the tidal flat has no obvious change.Human activities are the main factors of coastline migration and transformation in tidal flat areas.From 1985 to 2017,the tidal flat area of Liaohe Estuary wetland was in the erosion stage in 1988,1990-1992,1996,1999,2001-2002,2004,2008,2010 and 2014,and the other years were in the deposition stage.(3)From 1985 to 2017,the driving forces of coastline changes in the tidal flat area of Liaohe Estuary in the study area mainly come from two aspects: human factors and natural factors.Among them,the influence of human factors on the change of shoreline in Liaohe estuary tidal flat area is greater than that of natural factors.The driving forces of landscape pattern change in Liaohe Estuary tidal flat area are mainly natural factors and socio-economic factors.Natural factors have greater impact on landscape pattern change in Liaohe Estuary tidal flat area than social and economic factors.The main factors affecting wetland landscape pattern change are annual sediment discharge and average annual discharge,and population factor is the main cause of land use area change and landscape fragmentation in tidal flat area of Liaohe estuary. |
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