The Study On Dynamic Change Of Wetland Landscape In The Middle And Lower Reaches Of Yangtze River Based On RS And GIS Technology

The research of Wetland Science evolved from limnology and telmatology, it can be traced back to the17th century.After more than300years of continuous development, wetland science evolves from the first bud into the science framework build phase, and has become a focus issue by the experts at home and abroad.The middle and lower reaches of Yangtze river is the most concentrated area of freshwater lakes in China, the lake wetland landscape has a important significance to this area. However in recent decades, the human activities and the river sediment has influced the lake region a lot. Reclaiming farmland from lakes and excessive deforestation aggravated the soil erosion. The large number of lake sediment deposition accelerated the decline of the freshwater lake region, the area of lake water narrowed dramatically, and the area of mudflats, marsh, reed beds and other landscape gradually increased, coupled with the rapid development of urbanization and the increase of artificial surface and construction land, the Lake District landscape and its function has undergone tremendous changes.In this paper, RS and GIS are used to study the dynamic changes of the middle and lower reaches of the Yangtze River wetland landscape.Firstly, extracting the based information of the wetland landscape from the Landsat TM/ETM, MODIS satellite remote-sensing images between1984and2012as well as the2009shot by ESA ENVISAT satellite remote sensing image,then by classify these mote-sensing images, collecting the basic data of each year combined with Google Earth and the land use types map of each year which is made in ArcGIS. Analysing on landscape pattern through a series of landscape indices such as: PLAND、LSI、LPI、CONHESION、SHDI、 SHEI,exploring the wetlands and land use types of dynamic variation as well as the reason on Yangtze River Poyang Lake, Dongting Lake, Taihu Lake, Concluded as follows:1、The analysis of the wetland landscape pattern index of the three freshwater lakes on the middle and lower reaches of the Yangtze River indicates that the landscape indices trend on Taihu Lake is slightly different from that on Poyang Lake and Dongting Lake due to geographical location and higher levels of socio-economic development. 2、The wetland landscape area on Poyang Lake, Dongting Lake, Taihu Lake District trend towards downward, where arable land and water decrease the most, the number of patches of arable land is decreasing, the largest patch index gradually increases and arable lands turn into large patches, which indicates that the human activities on the landscape changes play an important role.3、On the impact of human activities on the wetland landscape, this paper finds that, for the landscape of the natural wetlands (mudflats, marsh land, reed beach land), human activities, to some extent, increase the degree of landscape broken and reduce the uniformity; but on the aspect of arable land, human activities reduce the degree of fragmentation and increase the degree of uniformity of the landscape.4、Compared the well-developed Taihu Lake region with the underdeveloped Poyang Lake, Dongting Lake area, it finds that the advanced area sharply increase in building lot in the past20years, while the water-based natural wetland landscape area, including mudflats, marsh, reed beds, reduce to some varying degrees; however, in the underdeveloped Lakes region, due to the process of urbanization, the building lot is also increasing, but the increase is smaller, natural wetland landscape trends except water are contrary to the Taihu Lake District.5、To some extent, the research to the three freshwater lakes Lakes infers that the evolution of the landscape of lakes and wetlands in the entire middle and lower reaches of the Yangtze River region-water and arable land is declining; natural wetland landscape in the well-developed regions trend to downward in the past20years, while in the underdeveloped areas it was a slight increase in the trend; the construction land area trend upward due to urbanization and socio-economic development,.6、Wetland succession is the origin of the natural evolution of landscape, with a large number of sediment siltation, mudflats, marsh and reed beds will be appear successively at the water margin area, which will eventually be transformed into forested wetlands.7、Sediment deposition is one of the reasons that exacerbate the changes of the Lake District landscape, especially changes in water landscape. A large number of plants will accelerate sedimentation, sedimentation then conducive to wetland succession, the two form a vicious circle.8、Reclaiming farmland from lakes and returning farmland to the lake is main cause to the changes of the Lake District landscape. The landscape indices analysis shows that human activities have an important impact on surrounding landscape changes of the water, especially changes in arable land, water, and building lots.