Eco-environment Effect Of Urban Expansion In Songhua River Basin

China's urbanization has entered a period of accelerated development,population and industrial agglomeration's greater demand for urban space makes it one of the fastest urban land expanding countries in the world.The blind expansion of construction land and its disordered planning were often accompanied by irrational spatial structure and uncontrolled occupation of cultivated land and ecological land,which resulting in not only serious land-wasting problems but also growing food insecurity,a large number of land-lost peasants,deteriorate environment in cities and surrounding areas.Songhua River is one of the seven major rivers in China,whose ecological security relates not only to the revitalization of Northeast China,but also to the relationship with neighboring countries.The acceleration of urbanization along Songhua River intensified watershed exploitation,aggravating water pollution,wetland degradation,biodiversity reduction and other ecological issues.Evaluating the ecological and environmental effects of urban spatial expansion in the Songhua River basin has great significance for ecological security and sustainable development of river basin.This research,carrying out from the man land coordination perspective,integrated the achievements on two hot fields——urban spatial expansion and watershed ecological security——to explore the comprehensive effect that construction land explosion and its intensified human activities did on eco-environment.I hope it could be instructive to optimize urban land allocation,improve watershed ecological management and promoting the coordinate development.This paper focused on the following aspects:(1)Found out the basic features and evolution law of elements in the urban ecology-land system,from the aspects of economic growth,construction land development and eco-environment quality.Identified the difficulties and challenges facing the system,to pave the way for quantifying the eco-environment effect caused by the expansion of urban space.(2)Based on the construction land patches extracted from the DMSP/OLS image,this paper described the characteristics of construction land expansion in Songhua River Basin,which had also been compared with area of the whole research region and urban districts extracted from TM image.The research had also depicted urban spatial expansion pattern and external morphological evolution by calculating the landscape indexes.(3)Combining the previous research on ecological security,we tried to clarify the interactive feedback mechanism between the three subsystems,namely,spatial expansion pressure,land use status,ecological environment condition.Taking manland coordinated development as the starting point and the fundamental purpose,we established the research framework of urban spatial expansion,to evaluate the development degree of urban land ecological system,as well as describing the characteristics and evolution trend of each subsystem and finding out the internal relations between them.(4)The coordination type and the rank of each city were identified by applying the Coupling Coordination Evaluation Model.Further,the hysteretic systems and its hysteretic degree were found out through the differences of the three subsystem.Accordingly,cities in Songhua River Basin were sorted into three different categories by development path: economic priority,ecological priority and land use priority.