| Through the ages, city has been built near the wetland(river,lake,etc.),hing for wetlands, and shall be liable on wetlands development.Urban wetlands have been the lifeline of most cities. They are preserved and looked after by the people as their main source of water supply for drinking and irrigation, a comfortable envronment and entertainment site.They provide natural flood control, and support a diverse variety of fish, wildlife, and plants.The growth of urban and suburban areas has been a dominant demographic characteristic of the20th century, the trend is intensified by the rapid development of the urban economy. Such changes, especially in built-up areas, have led to a decreasement in wetland area,wetland water quality degradation, and significant changes in the spatial distribution pattern of wetland. Urban wetland functional degradation has led to a number of problems in urban areas such as flooding, water scarcity,and water logging,which seriously affect the livability of the urban environment, hinder the sustainable development of city. Therefore, urban wetland planning and utilization, protection and construction have the urgent need to study the following questions:(1)what is the path of wetland loss in temporal-spatial scale?(2)what is the characteristic of wetland landscape pattern?(3) what’s the natural and social driving forces of urban wetland change in context of rapid urbanization?This study, integrating landscape pattern analysis and system dynamics, aims to investigate wetland landscape pattern change and its driving mechanism in the process of urbanization. It concerns the point of view of the qualitative and quantitative analysis and it was implemented with GIS and RS technology platform.The following method series were used:(1)Stock-Flow dynamic equilibrium model.(2) Dynamic-Static spatial variation mode.(3)mathematical Statistics-spatial statistical combining method.(4) the principal component analysis-gray correlation coupling models.These statistics were performed using Microsoft Excel (2003),ArcGIS Desktop software in conjunction with the Statistical Analyst extension and Geoda. Landscape metrics were calculated using specific software packages FRAGSTATS3.3.The following conclusions have been drawn:(1)At the size level,the urban wetland pattern change was significantly affected by the wetland size, The larger the size of wetlands was, the higher the proportion of retention was, the lower the proportion of filled or newly-constructed wetland was,The smaller the size of the wetlands was, the more vulnerable the landfill was.The small size wetland was easy to be more filled than the larger size wetland. The average number and area proportion with the size of0.2-8hm2wetland was91.1%、60.7%,which covered the majority in the total area.(2)In terms of temporal scale, according to the four kinds of wetland by the characteristic of elements, the wetland area increased firstly and then decreased, i.e, total areas of urban patch wetlands in Changsha increased from1955to1990, but then decreased from1990to2007.The area of ponds and ditches increased significantly from1955to1990, however, substantially decreased froml990to2007. The area of lake and reservoir fluctuated, it decreased ceaselessly from1955to1972, and increased from1972to1990, then decreased from1990to2007.The change of the area of river was small and stable.According to four kinds of wetland change status, the changing trend of stock wetland and gain wetland in the status of dynamic space increased prior to1990and decreased after1990. while the area of filled and reserving wetland continued to increase in1955-2007.The changing trend of stock wetland, newly-constructed and reserving wetland in the status of static space continued to decrease in build-up district. Consequently, the newly-constructed wetland in build-up was zero and stock wetland was near to disappear from1955-2007. The wetland density in the first ring sprawl in central city declined from0.46hm2/km2in1955to0.01hm2/km2in2007,which was near to zero and indicated that an urgen measurement should be conducted there. The density of stock, newly-constructed wetland showed a different trend after1990.(3)From the dynamic change of space, In terms of dynamic space, the wetland in suburban was most likely to be affected druing the urbanization. The ratio of filled wetland in build-up area varied in opposite directions in suburban region. The highest ratio of wetland landfill and reservation was located in peri-urban. Moreover, the stock wetland had the most amount in the district. In either dynamic or static space, the boundaries between downtown area and suburbs were key area of changes in urban patch wetlands.In terms of dynamic space, the highest area change of stock,filled, newly-constructed and reserving wetland extended from build-up district to rural district, which displayed a gradient change. The peak range of area chage of four kinds of wetland appeared in outskirts or sub-outskirt, the larger the distance to the center of city was, the more stock newly-constructed and reserving wetland was.(4)From the perspective of wetland distribution, all wetlands ring distributed around the city of Changsha from1955to2007. In the four period, according to Moran’s I index, Moran scattered point diagram, a clustered distribution was displayed in ponds, a dispersed distribution in river and a random distribution in the lakes and canals. And in1972,1990and2007, the distribution of the ponds was high value formed by the aggregation of spatial autocorrelation. Furthermore, the distribution of a lot of ponds presented positive local spatial autocorrelation in each period.(5) From the evulation of wetland centroid chang,the results indicated that the centroid of wetland land in Changsha city during1955-2007shifted various distance with a different directions, which displayed all kinds of paths for different kinds of regions.The whole wetland centroid shift was different from those of various types of wetland in Changsha city:the whole wetland centroid was at the vicinity of Xiangjiang River and the offset was not obvious, the centroid of river was near to Xiangjiang River, the wetland centroids of ditches, ponds and reservoir were distant from Xiangjiang River, wetland centroids of pond and ditch deviated remotely and those of lakes and rivers change nearly. In addition, the dynamic paradigm of wetland centroid was various, the whole city wetland centroid change of Changsha performed as the" cluster-type", centroid movement of pond emerged as "pendulum-type", centroid path of lake displayed"ring-type", wetland centroid trend of river showed as the" zigzag-type",centroid track of ditch developed as the" plotline-type". (6) From the point of wetland landscape metrics change,wetland landscape metrics were very evident, it depended on the sorts of wetlands, the pattern number and density of fragmentation index increased before the1990, which was opposed to that of change trend after the1990. Of the entire shape index, the landscape shape index change was greater than that of pattern shape index and fraction index. The monotonous drop of wetland landscape dominance showed that "accumulation and dissipation" principal was functioning in wetland planning.From the time point of view, the change of all various types landscape indices fluctuated at the demarcation point of1990, in terms of perspective of different types of wetlands, LPI index of rivers overall declined, which indicated that functions diversity of urban wetland increased.(7) From the mechanism of wetland landscape metric change,the results showed that the overall wetland landscape pattern change was different from that of specific wetland pattern aspect.The order of impact ranged from maximum to minimum:the overall wetland pattern followed the sequence of urbanization rate>rainfall> GDP>temperature> built-up area> population> evaporation; the impact order of wetland area change was as follow:GDP> evaporation> total population> built-up area> urbanization rate> rainfall> temperature; the order of impacting on wetland landscape fragmentation was presented as follow:GDP> rainfall> urbanization rate> temperature> evaporation> total population> built-up area;the rank of the landscape aggregation affecting factors was listed as follows:total population> GDP> built-up area> urbanization rate> rainfall> temperature> evaporation.The main impact of the research is its contribution to the assessment of temporal and spatial changes from urbanization through the creation and application of stock-flow and dynamic-static model(SF-DS). The SF-DS model could be extended to be used in wetland waterbody amount assessments or other natural resource change estimation. The inclusion of landscape related area and other pattern metrics could help to guide appropriate plans of urban development, help to gauge the vulnerability of wetlands to future urbanization, guide wetland risk management, and inform urban adaptation strategies. The application of principal component analysis and grey correlation analysis (PCA-GA) to estimate wetland landscape pattern changes from urbanization is a relatively new and developing area of research. The research highlights how PCA-GA analysis could be used to provide estimates of wetland landscape pattern change under future urbanization, which are more systemic, and useful for assessing driving forces of future wetland change and urbanization.Consequently, there are many gains to be seen from the continued development and application of this research methodology for wetland temporal-spatial change. |
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