Landscape Pattern Change And Main Driving Factors Of Coastal Wetland In Laizhou Bay In Recent 30 Years

Coastal wetlands are the buffer zone of global environmental change and the area where human activities are most frequent and varied,which located at the intersection of land and sea.Laizhou Bay coastal area is an important port-side logistics industry,manufacturing area,aquaculture area and salt-making base of China,where human activities and reclamation activities are frequent,development methods are diverse,leading to the degradation of coastal wetland ecosystem services.Therefore,the study on the landscape pattern and fragmentation process,the analysis of the temporal and spatial changes of the reclamation,and the analysis of the landscape pattern change and the driving factors of the reclamation change of the coastal wetland in Laizhou Bay,which can not only provide reference for the protection and management of coastal wetland resources,but also Conducive to promoting the harmonious and sustainable development of coastal wetland landscape and economy of the Laizhou Bay.This paper takes Laizhou Bay coastal wetland as the research area,using Landsat remote sensing image,according to the characteristics of coastal wetland in Laizhou Bay combined with field observations,revealing the change characteristics of coastal wetland landscape pattern in Laizhou Bay from 1990 to 2018,and analyzing the heterogeneity of coastal wetland in Laizhou Bay by landscape index,and analyzing the intensity of the reclamation change through the changed of coastline.The results show that:(1)The area of natural coastal wetlands in Laizhou Bay decreased by 154.1 km~2,while the area of artificial coastal wetlands increased by 322.2 km~2.The total area of wetlands increased at an average annual rate of 6 km~2 from 1990 to 2018.By 2018,the natural coastal wetland area of Laizhou Bay is about 811 km~2,and the artificial coastal wetland area is about 1143 km~2,accounting for 42% and 58% respectively.The waters and wetland vegetation are the main types in natural wetlands and the salt fields are the main types in the artificial wetlands.By 2018,the salt field is 848.7 km~2,accounting for 74.2% of the artificial wetland area and 43% of the coastal wetland area.(2)From the perspective of land use type transfer,the natural wetland type is gradually transformed into constructed wetland and non-wetland type,while the constructed wetland is gradually transformed into non-wetland type.Among them,from 1990 to 2000,the conversion of tidal flats to farmland and bare land was the largest,reaching about 34 km~2 and 29 km~2 respectively.From 2000 to 2009,the tidal flats were the most converted to the culture ponds,and the conversion areas reached about 47 km~2 and 37 km~2 respectively.The conversion from farmland to construction land was the largest,with an area of about 602 km~2.From 2009 to 2018,there is a significant trend of transformation of coastal wetlands into construction land,among which the transformation of aquaculture pond and salt fields into construction land is about 12 km~2 and 98km~2 respectively,and the transformation of farmland into construction land is about 226 km~2.The investigation results of soil factors showed that the content of nitrogen and organic matter in the coastal wetland of laizhou bay was relatively deficient,the content of available phosphorus is moderate,the content of available potassium is relatively rich,and the content of soil nutrients in the vegetation-covered area is relatively high.(3)The number of patches of construction land is much higher than other landscape types,indicating that the landscape of construction land is highly fragmented.The area occupied by salt fields and farmland is large and the number of patches is not many,indicating that there are a large number of dominant spots.SHDI and SHEI in the study area showed an increasing trend,indicating that the landscape diversity of the study area is rich,the complexity and the heterogeneity increased and the distribution of different landscape types tended to be uniform.(4)In the past 28 years,the coastline of Laizhou Bay has advanced 65482.8 hm~2 with a forward speed of 2338.7 hm~2/a,retreated 1030.2 hm~2 with a backward speed of 36.79 hm~2/a.Among them,Weifang City has the most advancing area,with 36554 hm~2 forward area,while the retreating part is basically located in Kenli County.(5)The driving mechanism of landscape pattern change between different coastal sections of Laizhou Bay coastal wetland is not completely the same.The natural factors that aggravate the degree of fragmentation of Laizhou Bay coastal wetland are estuary erosion and deposition,precipitation change,etc.The artificial driving forces are mainly for construction of cities,ports and wharves,intensive Marine areas,aquaculture and salt industry development and utilization.