Analysis Of Spatio-Temporal Dynamics Of China's Lakes Under The Impact Of Land Use Changes Based On Remote Sensing Data

As an important part of Earth's water resources,lakes serve as important regulators of global carbon cycle and climate change,and play a critical role in the terrestrial surface system and ecological environment.Under the impacts of climate change and human activities,the lakes around the world have experienced significant changes and are suffering from various ecological problems,such as reduction of flood storage capacity,water pollution and eutrophication,and biological diversity decline.In the context of global warming,with the development of social economy and polulation growth,China is undergoing comlex changes in land use and land cover,which have significant influence on the number,area,and distribution of the nationwide lakes.However,due to the limitations of data sources and technical approach,there is no data on the long-term spatio-temporal changes of all the lakes in China.There is also a lack of research on quantitative analysis of the impact of climatic factors and human activities on the lakes in China.In this paper,long-term Landsat satellite remote sensing images,global surface water data and China's land use/cover data,combined with meteorological records and socioeconomic data,were used to investigate the spatio-temporal dynamics of China's lakes and the associated driving force.Moreover,this study put the emphasis on the impacts of land use changes on the lakes in the densely populated regions(including the middle and lower reaches of the Yangtze River Basin and the urban area).This study led to not only the establishment of China's lake area change database but also several significant findings.The main research results are as follows:1.Analysis of long-term changes of lake area in the middle and lower reaches of the Yangtze River Basin.The middle and lower reaches of the Yangtze River Basin is covered with the most intensive freshwater lake resources in China,which experienced dramatic changes under the influence of human activities.At present,there is no research on the quantitative analysis of the impact of land use changes on the lake area across the basin.Using the long-term Landsat sattelite images,the database of lake area changes over the past 40 years was established in this study.The spatio-temporal evolution of the number,area,and distribution of the lakes across the basin was systematically analyzed.From 1975 to 2015,the water surface area of the lakes across the basin experienced rapid shrinkage.The total area of the lakes reduced by 2132.3 km~2(a decrease of 13.8%),and the number of lakes decreased from 389 to363.Among the five lake zones,the Dongting Plain had the most severe loss in lake area(a decrease of 855.1 km~2),and the Yangtze River Delta had the lowest reduction in lake area(a decrease of 153.7 km~2).A land use classification method based on remote sensing information index was proposed to obtain the land use conversion types and areas from the lakes aross the basin.Combined with the meteorological data and socioeconomic data,the influence of human activities and natural factors on the lakes was also discussed.With the development of regional social economy and population growth,human activities such as lake empoldering,fence breeding and urban expansion were the main driving factors of the rapid loss of lake area in the basin,resulted in significant reduction of lake area reaching 898.3 km~2(34.6%),627.7km~2(24.2%)and 64.5km~2(2.5%),respectively.Climate change,sediment deposition and hydrological regulation had also certain impacts on the lakes,especially for the Yangtze-connected lakes(such as Dongting Lake and Poyang Lake),resulting in the exposed wetland vegetation area from the lakes reaching 976.0 km~2(37.3%).This study revealed the long-term evolution of the lake area under the influence of natural and human factors,which is of great significance for the management and protection of the lakes in the middle and lower reaches of the Yangtze River Basin.2.Analysis of the spatio-temporal landscape changes of urban lakes in China.As an important part of lake resources in China,urban lakes are suffering from multiple water environment problems such as shrinking water area and broken landscape under the process of rapid urbanization.At present,there is still a lack of research on the spatio-temporal changes of urban lake landscape on a national scale.Using China's land use data set,the built-up area and lake area in China's 32 major cities between1990 and 2015 were extracted through visual inspection and manual correction.Landscape index was used to investigate the spatio-temporal landscape patterns of the urban lakes.The lake shrinkage type index was aslo proposed to quantitatively analyze the evolution process of water surface area of urban lakes under rapid process of urbanization.From 1990 to 2015,drastic changes occurred in the water area and landscape pattern of the urban lakes in China's 32 major cities.The total area of the urban lakes reduced by 176.2 km~2(a decrease of 24.2%)and the number of th urban lake patches decreased by 30.5%.Moreover,the edge density of the urban lakes increased by 9.0%,and the landscape shape index and fractal dimension decreased by4.6%and 0.5%,respectively,which could indicate that the whole landscape fragmentation of China's urban lakes increased and the landscape shape of watershed boundary became more regular and simpler.Furthermore,the driving factors of landscape changes in China's urban lakes under the rapid process of urbanization were also investigated by extracting the types and areas of land use transformation of urban lakes.The results showed that the rapid expansion of urban area was the major influencing factor of the sharp reduction of urban lake area.The water surface area of the urban lakes was mainly converted into urban built-up area and industrial area due to urban construction activities,which accounted for 67.9%of the total loss of lake area.Additionally,the human-induced land reclamation was also an important reason for the reduction of urban lake area,with 19.9%of the total loss in urban lake area being reclaimed into agricultural land.3.Analysis of the spatio-temperal dynamics of China's lakes and driving force.To investigate the long-term spatio-temporal changes of all the lakes in China and driving factors is still a difficult task in the research field of lake water environment.Using the long-term global surface water data set,the database of China's lake changes during the past 30 years(1985~2015)was established through visual inspection and manual correction.The spatio-temporal changes in the number,area and distribution of China's all lakes were analyzed,and the changing trends of lake area in the five lake zones were compared in this study.In the past decades,the total area of lakes in China increased by 4616.7 km~2(an increase of 6.0%),and the total number of lakes decreased from 2924 to 2919,including 109 vanished lakes and 104newborn lakes.The vanished lakes were mainly in the Northeast Plain and Mountain Lake-zone(NPML,number of 50)and Inner Mongolia autonomous region(number of 49).The newborn lakes were mainly in the Xinjiang uygur autonomous region(number of 53)and the Tibetan Plateau Lake-zone(TPL,number of 49).Over the past three decades,the lake area of the NPML,Eastern Plain Lake-zone(EPL)and Yunnan-Guizhou Plateau Lake-zone(YGPL)showed significant decrease trends(0.48?R~2?0.91,p<0.05),while the lake area of the Inner Mongolia-Xinjiang Lake-zone(IMXL)and the TPL showed significant increase trends(R~2=0.66 and 0.82,p<0.05).Moreover,the land use changes in the basins of China's lakes were obtained by using the land use data set.Combined with the meteorological records and socioeconomic data,the driving factors of lake area changes in China were systematically evaluated by analyzing the correlation between natural/human factors and the lake area changes in the five lake zones.The results revealed that the rapid lake shrinkage in the EPL,NPML and Inner Mongolia autonomous region was mainly due to the influence of regional human activities,including agricultural irrigation,overgrazing,coal mining,urban expansion and water conservancy project construction.The lake area expansion in the TPL and Xinjiang uygur autonomous region was mainly attributed to the increased precipitation and the water supplies from snow/glaciers melting and permafrost degradation under climate warming.