长沙城市斑块湿地资源的时空演变

Abstract

Wetland is one of the important ecosystems providing various ecological goods and services to human well-being.However,in urban areas,owing to rapid economic development and urban expansion,wetlands are encountering a threaten to be converting to other land uses,including resident houses,transportation facilities,and industrial buildings.Understanding the spatial-temporal changing patterns of urban wetland and their driving forces could provide valuable information for wetland conservation and urban planning toward sustainable development. Characterized by typical hilly area and subtropical monsoon climate,Changsha has abundant wetland resources.The changes in wetland area in Changsha city represent the common phenomena in south-central cities of China.In this study,the urban wetland data in Changsha were derived from topographical maps in 1955,1972 and 1990,and remote sensing image in 2007 by using the GIS tool.Then,we selected the most representative patch wetlands as our study objectives.From the viewpoints of the time and space,dynamics and static,we investigated and analyzed the dynamics and variations of elements and spatial characteristics in urban patch wetlands ecosystem during last five decades. The result indicated that total areas of urban patch wetlands in Changsha has been increased from 1955 thorough 1972 to 1990,but then decreased from 1990 to 2007.The general tendency during the last five decades exhibited an increased process.The variation amplitude of urban patch wetland area in Changsha continued to be increased and the change rate gradually speeded up.In terms of wetland size,the area of patch wetland smaller than 32ha has increased while the area of wetland larger than 32 ha showed a reversed tendency.Whether in the downtown or the suburb area,the density of urban patch wetland has been increased.The number of the reconstructed patch wetland and the remained patch wetland per land area has been increased in both the downtown and the suburb area.The ratio of reconstructed to remained patch wetland showed reversed change tendency in the downtown and the suburb area.The number of patch wetland per land area decreased in the downtown area.Our results suggested that no matter how differences in temporal scales,spatial attribute and spatial state,urban patch wetland often appear to be different and even opposite change patterns along with city expansion.In either dynamic or static space,the boundaries between downtown area and suburbs were key area of changes in urban patch wetlands. Overall,we found three key factors that mainly determined the changes in urban patch wetlands in Changsha.The first one was the size of patch wetland,with area smaller than 8 ha constituting more than 60% the total patch wetland;The second was the land use policy and urban construction,which resulted in the decline in patch wetland in the last decade;The third was location or area in the city,with increase of wetland in suburb area and decline of wetland in downtown.However,the direct relationships among these three factors mentioned above and changes in patch wetlands,as well as the effects of other natural factors(such as climate change) are not well understood and will be the further research topics.