Evaluation Of Island City's Ecological Status Based On Multiple Elements

Recently,China has vigorously implemented strategies for marine development,which set off a boom of island exploitation.Gradually,the trend of insular urbanization has become increasingly obvious.Especially,island is an ecologically fragile zone with high sensitivity,low stability,ecological vulnerability,and low self-recovery capability.The impact from human's activities for development on ecosystem tends to be irreversible.Therefore,objective and accurate evaluation on the ecological change of the island,and ecological development mode suitable for the island's characteristics,is of great significance to the construction and sustainable development of the island city.Pingtan Island,located in the eastern part of Fujian province,had been officially established as the 'Pingtan Comprehensive Experimental Zone of Fujian' since 2010.This paper took it as the research object to discuss spatio-temporal changes of ecosystem in the process of urbanization during the period from 2001 to 2015.In the beginning,with three Landsat images of 2001,2010 and 2015 and a variety of statistics from research,a multiple-element ecological remote sensing index(M-RSEI)has been proposed based on the remote sensing based ecological index(RSEI),which added two indicators(human activity intensity and slope)on the basis of four existing remote-sensing indicators(greenness,dryness,wetness and heat).They were created for monitoring and assessing regional ecological changes.Instead of a weighted addition of the six indicators,the principal component analysis(PCA)was utilized to compress the six indicators into one in order to assess the overall ecological status.The M-RSEI was then constructed using the first component(PC1).Secondly,stepwise regression method was used to establish island ecological evaluation model.In the meantime,landscape pattern metrics were used to analyze the distribution of the dynamic change.Finally,this paper put forward suggestions and measures for the ecological protection in the further development and construction of Pingtan Comprehensive Experimentation Zone.The main research contents and results are as follows:(1)The six remote-sensing indices are the normalized difference vegetation index(NDVI),soil index(SI),wetness component of the tasseled cap transformation(Wet),land surface temperature(LST),intensity of human activities on land use/cover(HAI)and slope(Slope).M-RSEI could quantitatively reveal regional ecological changes through the principal component analysis.The results showed that the mean value of M-RSEI in Pingtan Island fell from 0.477 in 2001 to 0.47 in 2010 and then to 0.462 in 2015,a 3.14%drop in the 14-study years.As a whole,the overall ecological quality of Pingtan Island was below-average.(2)The image-difference method was used to analyze the ecological condition of Pingtan Island.The results show that,from 2001 to 2015,the area of the ecological conditions remained stable,degraded and improved accounted for 38.27%,31.98%and 29.75%of the total area,respectively.The overall ecological changes showed a slight downward trend.Furthermore,combined with the analysis of landscape pattern,it is found that ecological level changes of Pingtan Island tend to expanding in spatial distribution.Specifically,during the period from 2001 to 2010,the extended form is fragmentary and unstable,while the extended form is biased in favor of groups and the stability is enhanced,during 2010 to 2015.(3)The island ecological evaluation model was constructed by using the stepwise regression analysis method.It was found that the human activity factor was the most influential factor in the multiple-element ecological evaluation model.According to the change of ecological condition classification image and the transfer matrix of land use type,it was found that the area of the worst ecological situation usually occurred in the western of the island,and the ecological situation-unchanged areas frequently distributed in the central,northeast and southwest of the island,while the ecological situation slightly elevated areas spread in the north and south of the island scatteredly.Combined with the general layout planning of Pingtan comprehensive experimentation area,it is found that the poorest ecological region is the development center of the comprehensive experimentation area.The poor ecological environment is the results of human activities,while the area of good or unchanged ecological condition belongs to the area in higher altitude and less affected by human activities.The results also proved that the increasing human activities lead to a dramatic reduction of vegetation in the island,and the increasing construction is a major factor to the decline of the ecological condition of the island in recent years.Finally,in order to protect and improve the ecological environment in the development and construction in the later stage of Pingtan Island,some suggestions about the protection forest construction,city construction,new reclamation on sea,drinking water,farmland protection and district protection were put forward through the analysis of driving factors of several typical regions ecological changes.