The Impact Of The Expansion Of The Hangzhou Bay Town On The Wetland Landscape

Wetland is a transitional zone between water and land,which belongs to a kind of fragile zone of ecological environment.But the wetland has rich biological diversity,it plays an important role in regulating the local climate and river runoff,preventing and controlling floods,purifying water.Wetland brings great environmental benefits to humankind,it becomes one of the important living environment of mankind.China's wetland area accounts for about 10% of the global wetland.In recent years,the rapid development of urbanization and a large increase in urban population has brought great pressure to the local.Large numbers of land is needed to promote the expansion of urban.The government introduced the "red line" policy to protected arable land to a certain extent.However,the public,the government and wetland development departments have not recognized the importance of wetlands.Blind reclamation and abuse of wetlands are failed to monitor effectively.The phenomenon of abusing water resources and indiscriminating discharge sewage is allowed,and all these behavior lead to wetland ecosystems suffering great damage.Thus,urban expansion has become one of the important factors in the destruction of wetland landscapes.In this paper,we selected 14 districts around the Hangzhou Bay as study area,it includes part of Shanghai in the northern bank and part of Zhejiang in the southern.Using a total of 28 remote sensing images covering the study area during 1985-2015 and basing on the auxiliary non-remote sensing data,such as digital elevation data,this paper extracted the data of the study area from 1985 to 2015 through unsupervised classification and artificial visual interpretation.These data include land use and cover data,built-up area data and wetland data.The land use change of Hangzhou Bay area from 1985 to 2015 was analyzed based on the land use and cover data.According to the results of the built-up area data,the area,pattern and spatial distribution of the urban expansion in Hangzhou Bay from 1985 to 2015 were analyzed.On the basis of the results of wetland extraction,the change of wetland area and the occupation of wetland in Hangzhou Bay during the study period were analyzed.At the same time,the landscape pattern index,such as the maximum plaque index,the weighted average fractal dimension of patch area,and the patch land index and so on were chosen to analyze the landscape pattern of Hangzhou Bay area.Finally,the influence of urban expansion on wetland landscape was determined by correlation analysis.The results show that the total area of the 14 districts in Hangzhou Bay is estimated to be 60014.44 ha from 1985 to 2015,and the expansion of Cixi and Shaoxing in the south bank of Hangzhou Bay is 330.06 ha and 236.28 ha,respectively.Xiaoshan District also has a large expansion,the average annual increase is 250.72 ha.While the expansion of Pinghu City and Haiyan are not obvious,with an average annual increase of 21.72 ha,35.62 ha,respectively.There was no significant change in the area of the river in Hangzhou Bay from 1985 to 2015.The area of paddy field and coastal water decreased significantly,and the reductions were 264632 ha and 70792 ha,respectively.While the area of reservoirs and lakes increased by 46.1% and 33.4% respectively.From the landscape index in patch level and the landscape level from 1985 to 2015,Hangzhou Bay area wetland landscape has undergone great changes.There was a significant positive correlation between the area expansion of urban built-up area and plaque diversity index at the landscape level,and the correlation coefficients were 0.953 and 0.912,respectively.