Remote Sensing Monitoring Of Temporal And Spatial Evolution Of Key Geographical Elements In Chang Dang Lake

With the economic development and strong interference of human activities,many lakes are polluted,the water quality is deteriorating,the lakes become eutrophic,and the lake ecosystem is destroyed.As an important element of the lake,the changes of purse seine culture and aquatic vegetation have a great impact on the lake water quality and ecosystem.Mastering the long-term changes of purse seine culture and aquatic vegetation in the lake can provide basic data and decision support for lake water environment governance and lake ecological restoration.Taking Changdang lake,a small shallow lake in the middle and lower reaches of the Yangtze River,as the study area,this paper adopts the visual interpretation method of purse seine culture area and the decision tree classification method of aquatic vegetation,Based on multi-source remote sensing image data(mainly Landsat series,supplemented by HJ-CCD),the temporal and spatial distribution characteristics of key geographical elements(aquatic vegetation and purse seine aquaculture area)of Changdang lake from 1984 to 2020 are studied,and its temporal and spatial variation rules and driving factors in recent 40 years are analyzed.The main conclusions are as follows:1.Classification by decision tree according to floating leaf vegetation sensitivity index and submerged vegetation sensitivity index,Aquatic vegetation in Changdang lake(floating leaf vegetation and submerged vegetation)are extracted and classified;the purse seine aquaculture area of Changdang lake is visually interpreted according to the spectral characteristics,shape,texture,tone,size and other interpretation signs of the purse seine aquaculture area.The classification results are cross verified by sentinel-2 images in 2016 and 2018 and measured data in 2020,and the overall score of aquatic vegetation in 2016,2018 and 2020 is calculated The class accuracy was 87.9%,87.7%and 82.5%respectively;The classification accuracy of purse seine culture area was 90.2%,89.3%and 91.3%respectively.2.Purse seine culture in Changdang lake has experienced four stages:growth period(1984-1997),peak period(1998-2003),fluctuation decline period(2004-2017)and stable period(2018-2020).From 1984 to 1997,the area of the purse seine aquaculture area of Changdang Lake increased continuously,from 0.21km2 to 63.59km2,with a total increase of 63.38km2,with a growth rate of 99%;from 1998 to 2003,the area of the purse seine aquaculture area of Changdang lake was at its peak,with an average of about 63km2,accounting for about 75.2%of the lake area;from 2004 to 2017,the fluctuation of the area of the purse seine aquaculture area of Changdang Lake decreased,from 60.88km2 to 7.9km2,a total decrease of 52.98km2,a decrease of 87%.From 2018 to 2020,the area of purse seine aquaculture area in Changdang lake was stable,about 8.75km2,accounting for about 10.5%of the lake area.3.The area of aquatic vegetation in Changdang Lake fluctuated and decreased from 71.83km2 in 1984 to 9.62km2 in 2020,a total decrease of 62.21km2,a decrease of 86.6%.The coverage area of aquatic vegetation in Changdang Lake decreased significantly,the submerged vegetation degraded seriously,and the dominant groups changed from submerged vegetation to floating leaf vegetation.From 1984 to 2020,the fluctuation of submerged vegetation area in Changdang Lake decreased,from 39.55 km2 in 1984 to 2.27 km2 in 2020,a total decrease of 37.28 km2,a decrease of 94.26%;Floating leaf vegetation decreased from 31.13km2 in 1984 to 9.62km2 in 2020,a total decrease of 21.51km2,a decrease of 69%.4.The change of purse seine culture area is greatly affected by local policies.Purse seine culture will affect the water quality.After the purse seine is removed,the area of aquatic vegetation is greatly affected by purse seine culture.Air temperature can inhibit the growth of submerged vegetation;Wind speed can promote the growth of submerged vegetation;Too much or too little rainfall will not be conducive to the growth of aquatic vegetation,and the change and proportion of land use structure will also affect the growth of aquatic vegetation.Figure[35]Table[9]Reference[104]...