Remote Sensing Monitoring Of Ecological Degradation Of The Zoigê Plateau Wetland And Quantitative Analysis Of Its Driving Force

Zoigê plateau wetland is the largest plateau swamp in China,and the largest peat swamp in the world.It plays an extremely important role in supplying and maintaining the ecological balance of water conservation of Yellow River upstream.In addition,it has very close ties with the global climate change and the environment change.Climate change and unsustainable human consumption have led to a reduction in wetland area,destruction of ecosystem structure,and decline,or even loss of ecological functions;hence,wetlands are facing significant ecological challenges.The researches of Zoigê plateau wetland are taken more and more seriously.This study focused on the Zoigê plateau wetland in China,and automatically extracted wetland data from 2000 to 2015 in the target area using an object-oriented method based on Landsat data.Based on changes in three aspects of wetlands(area,structure,and function),a comprehensive index of wetland degradation was obtained using an analytic hierarchy process encompassing five indices: area change rate,landscape fractal dimensions,landscape fragmentation,vegetation aboveground biomass,and vegetation coverage.Wetland degradation status and trends from 2000 to 2015 were analyzed and assessed at three different levels: whole area,county,and 18 key townships and villages.In addition,the main driving factors underlying wetland degradation were analyzed based on principal component analysis(PCA)and grey relational analysis(GRA).The main conclusions of this study were as follows:(1)Using the object-oriented classification method,30 and 60 were the optimal segmentation and combination scales,respectively,in this study.Classification precision using support vector machine was higher compared to that using K-nearest neighbor,with an overall precision of 93.1% and the Kappa coefficient 88.9%.Grassland was the largest land use type in the study area,followed by woodland and wetland,the average floor area ratio was 70%,respectively,16.8%,9%.(2)In the aspect of area change,compared with the 1990 S wetland area,wetland area in 2000-2015 were reduced;negative value frequency of wetland area change rate in four stages of the four counties reached 87.5%,and 18 towns 85% respectively.Wetland loss phenomenon in 2010 was most serious,with the average change rate of-35.8%;wetland spatial scale,county area change rate of Hongyuan was average minimum for-37.8%.(3)In order to avoid the heterogeneity of landscape pattern index on regional scale,we studied 18 landscape pattern indexes of levels in 2000,2005,2010 and 2015 using principal component analysis(PCA).The PCA results indicated that landscape fractal dimension(FRAC)and landscape fragmentation(LFI)were suitable for analyzing.Time changes,the FRAC of different levels had the same change trend.In 2000,the FRAC was small,and that was basically the same in the year of 2005 and in the year of 2010,the FRAC was increased,the degree of interference was alleviated,and the low value was produced in the year of 2015.The FRAC results of Ruoergai County and Hongyuan County were less than that of Maqu County and Aba County in the same period.Overall,FRAC was at a low level,which was subject to the interference of human activities in different degrees.The change trend of LFI and FRAC was approximation.From the level of structural changes,the Zoigê plateau wetland in 2000-2015 was subject to varying degrees of human interference.(4)From the spatial distribution,the total yield of wet grass in the northeast of the study area was usually higher than that of the southern region,and the high yield area mainly concentrated in Ruoergai County and Maqu County.It showed a low value in 2000.And that was essentially flat in 2005 and 2010,but better than in the year of 2000.In the year of 2015,the vegetation condition was worse.The wetland vegetation coverage in the study area was stable,and there was no deterioration of the special year.From the level of function change,the change of wetland degradation in Zoigê plateau wetland was not obvious.(5)From the whole study area,the grade of wetland degradation in the period of 2000-2015 were mild degradation,moderate degradation,mild degradation,mild degradation,and the degradation of wetland was the most serious in the year of 2005.The wetland degradation in four counties showed different trends.The wetland degradation in Ruoergai County was "obvious reversal",and the wetland degradation in Maqu County was "serious development".Wetland degradation in Hongyuan County was "serious development" to "reversal",and Aba County was "serious development" to "obvious reversal",which changed significantly and inflection point was 2010.According to the 18 key towns,the change process of Zoigê plateau wetland degradation occurred from northeast to southwest in 2000-2015.(6)Increased population and livestock were the major social drivers of wetland degradation.Of natural factors,wind speed variation and annual precipitation were the natural drivers to wetland degradation.