Multi-scale Assessment Of Ecosystem Health In Dianchi Lake Basin Based On VOR Model

Dianchi Lake Basin is a special plateau basin with ecological fragility.It is also the center of social,economic,political and cultural development in Yunnan Province.It plays an important role.At present,with the continuous development of social economy and urbanization,the health risks of Dianchi Lake Basin ecosystem are serious.Therefore,carrying out multi-scale assessment of ecosystem health in Dianchi Lake Basin is conducive to providing theoretical basis for multi-scale assessment of ecosystem health in Dianchi Lake Basin and practical guidance for ecosystem health protection in Dianchi Lake Basin.Based on Landsat remote sensing images,DEM and administrative maps of Dianchi Lake Basin in 2000,2005,2010,2015 and 2018,this study uses ENVI and ArcGIS software to interpret and obtain land use maps of Dianchi Lake Basin in 2000,2005,2010,2015 and 2018.Fragstats software is used to obtain the landscape pattern index of Dianchi Lake Basin.According to the change trend of the landscape pattern index,the appropriate research granularity is selected.VOR model is established to evaluate the ecosystem health of Dianchi Lake Basin from three scales: quadrat scale,ecological scale and administrative scale.The appropriate evaluation scale is finally selected through superposition analysis.The main research results are as follows:(1)At the level of type,the granularity effect of landscape index in Dianchi Lake Basin can be divided into three categories: the first category is landscape index,which shows a downward trend with the increase of granularity,with strong granularity effect,and the gap between landscape types gradually decreases.The second kind of landscape index,this kind of index shows an upward trend with the increase of grain size,grain size effect is more obvious,and the gap between all kinds of landscape shows an upward trend.The third kind of landscape index,this kind of landscape pattern index changes gently with the increase of grain size.The inflection point is concentrated in 150 m and 330 m granularity.According to inflection point method,150 m is the most suitable granularity.(2)According to the connotation of VOR model,indicators that can effectively reflect the health status of watershed ecosystem are selected from three aspects of vitality,organizational structure and resilience.The evaluation index system is summarized as follows:(1)Criteria layer: including vitality,organizational structure and resilience,with weights of 0.2014,0.6796 and 0.1190 respectively;(2)Seven indexes of index layer: vegetation normalization index,forest land coverage rate,diversity index,evenness index,contag index,dispersion and juxtaposition index and comprehensive elasticity value,with weights of 0.2014,0.0840,0.2208,0.2244,0.0694,0.0810 and 0.1190 respectively.(3)At the quadrat scale,the results of ecosystem health assessment in Dianchi Lake Basin show:(1)The minimum value of ecological health fluctuates with the increasing quadrat,and the maximum value is relatively stable.With the increase of sample size,the loss of information is also increasing.However,the 10 km×10 km sample size shows a higher degree of detail and the integrity of the ecosystem is higher than the 5 km×5 km sample size.Therefore,the 10 km×10 km sample size is the most suitable size.(2)From 2000 to 2018,the comprehensive score of ecological health showed a trend of decreasing at first and then increasing,and the main distribution laws were approximately the same,mainly in Dianchi Lake and its nearby lakeside areas,where the health value of ecological system was relatively low.(3)The health grade of the ecosystem in Dianchi Lake Basin is mainly 1-4.With the passage of time,the areas of 3-4 and 3-4 are continuously increasing and occupying the main area.By 2018,there will be only 3-4 and 3-4.This shows that the health condition of the ecosystem in Dianchi Lake Basin is improving.The areas of 1-2 and 3-4 are smaller and showing a decreasing trend.(4)At the ecological scale,the ecosystem health assessment results of Dianchi Lake Basin show that:(1)The ecosystem health values of Dianchi Lake Basin from 2000 to 2018 are between 0.000000 and 0.80000,and the ecosystem health assessment values are relatively high in some regions in the north and south,and their distribution is relatively scattered,most of which are distributed in the central region of the basin;The low value is mainly concentrated in the urban areas in the north of Dianchi Lake.(2)The health grade of the ecosystem is mainly 2-4,which indicates that the health condition of the ecosystem in Dianchi Lake Basin is relatively good.The third grade is distributed in the northern and southern parts of the basin,mainly concentrated in the northern and central parts of the basin.The second grade is mainly concentrated in the main urban area of Kunming in the northern part of Dianchi Lake,and also distributed in a small area in the urban area of Jinning in the southern part.(3)From 2000 to 2018,the areas of 3 and 4 etc.accounted for the largest proportion,showing a trend of increasing first and then decreasing.(5)At the administrative level,the ecosystem health assessment results of Dianchi Lake Basin show that:(1)the ecosystem health value is between 0.1000 and 0.9000.The high value of ecosystem health of Dianchi Lake Basin is mainly concentrated in the south of Dianchi Lake Basin,which includes most of Dianchi Lake and the platform areas around Dianchi Lake.The lowest point is in some areas in the northwest of Dianchi Lake Basin,while the value in the western region is relatively high,while the values in the central,northern and eastern regions are relatively low.(2)The health grade of the ecosystem is mainly 2-4,with grade 3 distributed in the northern and eastern parts of the basin,mainly concentrated in the northern and central parts of the basin,and grade 2 mainly concentrated in the northern part of the Dianchi basin.(3)From 2000 to 2018,the sum of the area proportions of Grade 3 and Grade 4 is 0.818743,0.688347,0.819291,0.0.826165 and 0.996946 respectively,showing a rising trend and reaching the highest value in 2018,indicating that the health status of the ecosystem in Dianchi Lake Basin is continuously improving.(6)The superposition analysis results of the ecosystem health evaluation results of Dianchi Lake Basin on the sample scale,administrative scale and ecological scale show that the ecological scale overlaps with the evaluation results of other scales to the largest extent in 2000,2005,2010,2015 and 2018,and the integrity of the ecosystem is maintained best under the ecological scale.Finally,the ecological scale is determined as the most suitable evaluation scale of Dianchi Lake Basin.