| During the past 20 years,with the rapid development of Remote Sensing technology,this study uses the data recorded in the literature since 1950 and the Landsat image from 1973 to 2017 to analyze the lakes range change in the western section of the Wu-shen Canal.The fusion of Landsat optical image and ALOS PALSAR radar image improves the resolution and definition of the Remote Sensing image,which enhances the texture information and helps reveal the driving factors behind the water area transition.The historical books reveal that the Shijiu Lake,Gucheng Lake,Danyang Lake and Nanyi Lake in the western section of Wu-shen Canal belong to the Ancient Danyang Lake that are large to 4000 km2.In order to explore the area of the ancient Danyang Lake in the Neolithic Age,this study uses the ancient relics of the study area from the Neolithic Age to the founding of New China to analyze the lake range,and combines the DEM elevation data to establish a digital terrain model which helps to reconstruct the water boundary of the ancient Danyang Lake.In addition,this study analyzes the driving factors of the water range change.The following are the results.(1)The waters area has generally fluctuated during the period from 1950 to 1979.The total lake area in the early days of the founding of New China was 720 km2.Then it was reduced to 576.5 km2 in 1973,but this is the highest water area after 1973.The annual water area has a large reduction from 1973 to 1979,and the fluctuation range is between 600 and 300 km2.The fusion image of Landsat and ALOS PALSAR shows that there are a lot of small water area in the cultivated area of the study area.According to the human activity and meteorological data in the study area,it is inferred that the change of water area before the 1980s is subject to large-scale uncontrolled farmland construction in the past years.The water range changes greatly.The farmland caused frequent floods and droughts.In the process of human beings'request for nature,Danyang Lake was completely disappeared.The southwestern area of Shiju Lake has gradually shrinks into farmland.The vast area in the western part of Gucheng Lake was reclaimed.The Nanyi Lake is located in the moutainous area of southern Anhui province,and the reclaimed surrounding area is relatively small.In conclusion,the changed water area under the activity of human beings is larger than the naturally driven water change.(2)From 1980 to 1990,the water area fluctuated from 500 to 300 km2.The floods and droughts caused by the construction of manmade farmland are more frequent and more serious.After 1980,the relevant departments gradually adopted a series of measures to control floods,and the human activities have gradually shrunk.The peaks of the water range between the 1980s and 1990s appeared in 1984 and 1988,which were in the midst of a strong El Nino event.Therefore,the water area from 1980 to 1990 is the result of the combination of natural factors and human factors.With the decrease of human activities,the role of climatic conditions is more prominent.(3)The water range changes steadily.The peak of water range after the 1990 appeared in 1991,1994,1997,1998,2002,2004,2006,2007,2009,2015,which are the occurrence of the strong El Nino event.The fluctuation of temperature and precipitation after 1990 determines the breadth of water boundary in the study area,and the change of water area is relatively small.The fluctuation of water area in the western section of the Wu-shen Canal is basically consistent with the change of monsoon precipitation.(4)The data of the relics in the study area indicate that there are few human activities in the lake from the formation of the ancient Danyang Lake to the Wei and Jin Dynasties.The lake area changes are basically consistent with the temperature and precipitation data reconstructed by the climate indicators of environmental archaeology,so they are mainly subject to natural factors.From the Wei and Jin Dynasties to the Song Dynasty,the manmade farmlands were gradually emerging.The change of lakes area was the result of natural causes and the construction of farmland.The Song Dynasty was the peak period of the construction of the farmland.The water changes from Song Dynasty to 1949 were mainly controlled by human activities.(5)The results show that the 8m elevation area is basically consistent with the undistributed area of the ancient remains of the study area.This area is calculated to be about 4000 km2,which is consistent with the water range recorded in the ancient books.In order to further explore the rationality of the digital terrain model's results,this study uses the humidity level map,the historical data of the different dynasty's man-made farmland,and the geological data to verify the range of the ancient Danyang Lake.The study found that since the formation of the ancient Danyang Lake,the Shuiyang River,Qingyi River as well as other rivers originating from the mountainous area of southern Anhui Province carried a large amount of sediment to deposite here.As a result,the water area gradually shrinks.The geological data of the area reveals that the ancient Danyang Lake has the Pleistocene and Quaternary rivers and lakes alluvial deposits.The soil moisture map proves that the reconstructed ancient water area have high humidity.Besides,the reconstructed water shape basically corresponds to the boundaries of the man-made farmland.Through the cross-integration research of Remote Sensing and Environmental Archaeology,this study deepens the understanding of the water changes in the western section of the Wu-shen Canal,and analyzes its impact factors in detail,which is helpful to further explore the relationship between the people and land,clarify the relationship between the waters change and the climatic environment in the period of no written records and recorded historical periods,reveal the law of the human-land relations,and provide important data support for the coordinated development of human-land relations in the future. |
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