The Occupation Of Wetlands By Urban Expansion

Wetland is named "the kidney of the earth", it takes an unneglectable part in regulating climate and river runoff, recharging groundwater, storing and preventing disasters, purifying water, controlling pollution and so on. But wetlands across the world are in danger. Wetlands and wetland organisms are under great pressure of being blindly reclaimed, abused and polluted because of the social public’s, government’s and other wetland reclaiming institution’s unawareness of the function and value of wetlands, especially in dense population areas. One of the most important cause of wetlands degradation is urban expansion. According to the urban statistical yearbook of China, this paper takes28major cities of Jilin Province as research areas, extracting urban and wetland information from total64RS images using object-oriented feature extraction function in ENVI5.0. Using the result of urban w\extraction, this paper analyzes area, pattern and spatial distribution of28cities’ expansion from1980-2010. The correlation analysis between urban expansion and population, GDP and social fixed assets investment is also done to clarify the driving force of urban expansion. Using the result of wetland extraction, change of wetland area and occupied area by urban expansion are calculated. Six landscape index like NP, PLAND, SHDI and so on are calculated using Fragstats3.0and excel to analyze the change of wetland landscape. In the last part, this paper has analyzed the correlation between urban expansion and change of wetland landscape.Results show that:total area of urban expansion from1980to2010is60417.87ha, and most expansion took place in the middle area taking Changchun as a center. Most urban expansion of28cities expands as outward expansion pattern, and some other cities are expanding linearly, which is called axial expansion. There are high correlation between urban expansion from1980to2010with the social fixed assets investment, population and GDP; the correlation coefficients are0.84,0.85, and0.85respectively. Wetland area has decreased from2240829.7ha in1980to1633046.1ha in2010, which has decreased by27.13%. In which, the forest/shrub wetland has decreased by16658.2ha, reservoir/pond wetland64826.37ha, lake/river259809.1ha, herb wetland29496.6ha, and the paddy land has decreased167326.63ha. The occupied area of wetland by urban expansion is3496.95ha,48%of which is lake/river,46%is paddy land,9%is herb wetland and the remaining1%is reservoir/pond. Wetland Landscape has changed a lot from1980to2010according to the landscape index like NP, PLAND, and FN and so on. The correlation between urban expansion and change of wetland landscape is above0.8, which is highly correlated, suggesting that urban expansion has significant effects on the change of wetland landscape.