The Evolution And Driving Factors Of Lake Wetlands In The Dongting Lake Region In The Past 100 Years

Lake wetlands are important natural resources.They not only support the survival and reproduction of animals and plants,but are also an important carrier for interacting with human activities.Therefore,the rational development and utilization of lake wetland resources is a necessary means to protect the natural environment,creating a harmonious ecology and taking the road of sustainable development.Dongting Lake Region is located in the northern part of Hunan Province,the south bank of the Jingjiang River in the middle reaches of the Yangtze River,with the “four waters” inflowing from the south and the “three mouths” inflowing from the north.Dongting Lake is an important regulator of the Yangtze River.It has extremely rich lake wetland resources.Wetlands are rich in types,fertile land,and abundant in resources.Dongting Lake also suffered from a long history of human social civilization.The evolution of lake wetlands in Dongting Lake region for thousands of years has a very close relationship with the production activities of local people and has a profound impact on each other.Since the 1930 s,with the increasing needs of social development,the lake wetlands in the Dongting Lake region have undergone large-scale wetlands reclamation,dykes and embankments construction,and large-scale water conservancy projects construction in the early period of reform and opening up.The area of lake wetland in Donting Lake region has been greatly reduced,with wetland function being degraded rapidly,the balance of species diversity being disrupted,and the regulation and storage function of the Yangtze River declining.Investigation of the changes in the area and spatial distribution of lake wetlands in the Dongting Lake area in the past 100 years and associated drving forces are of great significance for the sustainable development of lake wetland resources.The data in this study mainly include historical topographic maps and remote sensing images.According to data characteristics and research needs,the lake wetlands information in the 1930 s,1970s,1980 s,1990s,2000 s,2010s and 2020 s were extracted through Arc GIS software and Google Earth Engine platform.The spatial distribution data of lake wetlands in the Dongting Lake region,through temporal and spatial analysis and collection of relevant historical data,summarizes the temporal and spatial variation laws and main driving factors of the Dongting Lake region in the past 100 years.The main research contents and results are as follows:(1)Taking the area of lake wetlands larger than 10 km~2 in the Dongting Lake area in the 1930 s as the largest mask area,the total area of lake wetlands in the 1930 s was5645.1 km~2,3794.5 km~2 in the 1970 s,3305.3 km~2 in the 1980 s,and 3396.8 km~2 in the1990 s.3494.8km~2 in the 2000 s,3434.4km~2 in the 2010 s,and 3279.0km~2 in 2020,respectively.The lake wetlands area generally showed a downward trend,of which the downward trend is the most significant from the 1930 s to the 1980 s,and it tends to be stable after the 1980 s,and fluctuates around 100km~2 in 2020.(2)In the past 100 years,the number of lakes and wetlands with an area of more than 10 km~2 in the Dongting Lake region continued to decay and degrade,and the number of lakes and wetlands continued to decline,and stabilized after the 1980s: 45 in the 1930 s.sublake are counted separately),30 in the 1970 s,26 in the 1980 s and1990s,28 in the 2000 s,27 in the 2010 s,and 28 in 2020.(3)The temporal and spatial changes of lake wetlands in the Dongting Lake area were analyzed through the overlay analysis and land use transfer tools in Arc GIS and the calculation of the MSPA model,and the following conclusions were drawn:(I)From the 1930 s to 2020,the extinct wetlands in the Dongting Lake area were about 2439.1 km~2(the largest decline was close to 1/3 from the 1930 s to the 1970s),and the Eel Lake Group and the Chongtian Lake Group in the West Dongting Lake almost completely disappeared;,the lake wetland between the two lakes has been degraded on a large scale,the west coastline of the East Dongting has moved eastward,the northern coastline of the South Dongting has been reclaimed in a large area,and the South Dongting has moved southward as a whole.The newly added lake wetland is about 377.7km~2,which are distributed on the southwest side of South Dongting and on both sides of Yuanjiang Hongdao.(II)From 1930 s to 2020,about 1,156.37 km~2 of lake wetlands were converted into cultivated land,accounting for 91.9% of the total extinction of lake wetlands(about32.8% of wetlands converted into cultivated land from 1930 s to 1970 s accounted for the highest proportion).It is reflected in the northwest coastline of East Dongting and the distance from Datong Lake;the north bank of South Dongting and Datong Lake facing each other,Baitang Lake,Helong Lake and the surrounding tidal flats of Lanni Lake Group;West Dongting Lake Eel Lake Group,Chongtian Lake,Tidal flats around Weidi Lake;Shishou Baini Lake,silt ridges,the main water body of Xiangjia Lake and surrounding tidal flats of other smaller lakes.The increase of wetlands is mainly manifested in the return of farmland to Weidi Lake and Yuanjiang Hongdao from the1970 s to the 1980 s,and the plan of returning farmland to lakes after the 1980 s.(III)Based on the classification of wetland types based on the MSPA model,the landscape pattern of wetlands in the Dongting Lake area can be divided into three periods: the first stage,from the 1930 s to the 1970 s,the total area of wetlands decreased significantly,all types of wetlands decreased,and the connectivity of wetlands decrease,overall decrease.In the second stage,from the 1970 s to the 2000 s,the marginal wetlands declined,the connecting bridges and branch lines rose,the core wetlands rose more and more integrally,the landscape connectivity increased,and the material exchange between wetlands was frequent,which was conducive to maintaining the stability of the wetland ecosystem and biodiversity.sexual development.In the third stage,from 2000 to 2020,the core wetland declined,the edge area rose sharply,the isolated islands and pores declined sharply and tended to be stable,and the change trend of connecting bridges,roundabouts,and branch lines was V-shaped,indicating that the core wetlands in this stage experienced a certain degree of The fragmentation of wetlands,the more complex edges,and finally the rise of connected wetlands and the decline of isolated islands also reflect the stabilization of the wetland landscape pattern and the restoration of landscape connectivity.(4)The changes of lakes and wetlands in the Dongting Lake area in the past century have been influenced by natural factors and human activities.Natural factors mainly include precipitation in the basin,sediment entering the lake,and lake erosion and silting.Human activities are mainly reflected in the reclamation of lakes,returning farmland to lakes and building water conservancy.In contrast,human activities are more than natural factors in the time window of nearly a hundred years.The performance is more direct and important.