Study On The Spatio-temporal Change Of Eco-environmental Quality And Its Driving Mechanism In Qilian Mountains

Ecosystems are critical to human survival and development,and socioeconomic sustainable development.The degradation of the ecological environment will bring adverse effects on the stability and balance of the ecosystem,thus impacting ecosystem service functions,and even further threatening the development of human society.Qilian Mountain is located in western China and plays an important role in ecological security and water conservation,which maintains the balance of the local mountain-oasis-desert ecosystems.However,the ecosystem of the Qilian Mountains is very fragile and vulnerable to climate change and human activities,which have caused frequent environmental problems in this region.Recently the government has raised more attention to the above issues.A full understanding of the eco-environmental quality in this region and its driving mechanism is imperative for protecting and managing the local ecosystems.We mainly used the Landsat surface reflectance dataset on the Google Earth Engine(GEE)platform and some auxiliary data of vegetation and soil data.A comprehensive ecological environment index(CEEI)for Qilian Mountains Area was constructed by using principal component analysis.Then,we assessed the quality of the ecological environment from 2000 to 2018 and quantitatively analyzed the temporal and spatial dynamics of eco-environmental qualities in the Qilian Mountains.Lastly,we used geographic detectors to explore the driving factors affecting its spatial distribution.In our study,the following conclusions are obtained:(1)The CEEI constructed by the principal component analysis has lower information redundancy and higher average correlation with individual index components.It can comprehensively represent the information of each index component and is suitable for monitoring the eco-environmental quality of the Qilian Mountains.Besides,the construction of CEEI introduces natural basal information,which has certain reference significance for eco-environmental quality evaluation in similar areas.(2)There are significant regional differences in eco-environmental quality in the Qilian Mountains,showing a spatial pattern of "poor in the northwest and excellent in southeast".On the whole,there is an obvious positive spatial autocorrelation in the quality of the ecological environment.From a local point of view,it has strong spatial positive correlation characteristics.Except for the two areas located in the northwestern part of the study area,the ecological environment qualities of most areas are at a medium or above level.The ecologically excellent areas are mainly distributed in the southeastern and central part of Qilian Mountain,while the ecologically fragile areas are mainly distributed in the northwestern of the study area and the east bank of Qinghai Lake.The local spatial autocorrelation patterns are roughly similar in all stages.The "high-high" type is mainly distributed in the eastern part of Qilian Mountain,which the "low-low" type is mainly distributed in the southwest of Qilian Mountain.(3)During the study period,the dynamic variation of eco-environmental quality in the Qilian Mountains was relatively stable,showing the characteristics of "overall stability,and local destruction".In terms of area ratio,the area of fluctuating degradation type accounted for 7.23%,and its distribution was relatively scattered,while the area of fluctuating improvement type accounted for 10.54%,mainly distributed in areas such as the southeast and south.Analyzed at intervals of every 5years,the areas with poor eco-environmental quality grade are relatively stable,and the changes mainly occur in other grade areas.In addition,the fluctuation range of the eco-environmental quality grade in the Qilian Mountains is mainly one grade.(4)The ranking of the factors affecting the spatial distribution of CEEI is the annual precipitation,soil factors,and human activities.The study found that the explanatory power of the annual precipitation was higher than 44% from 2000 to2018,and it was as high as 57% in some years.The annual precipitation has the highest explanatory power for the spatial distribution of CEEI in the Qilian Mountains.The explanatory power of silt content,sand content,clay content,and soil type on the spatial distribution of CEEI exceeds 39%,39%,32%,and 28%,respectively.The explanatory power of the degree of land use and the distance from the cultivated land to the spatial differentiation characteristics of CEEI exceeded 32% and 23%,respectively.In addition,the impact of human activities on the eco-environment quality in the Qilian Mountains gradually increased from 2000 to 2015,and weakened in 2018.(5)The interaction between factors is a synergistic enhancement type,which is specifically manifested as a non-linear and two-factor type.Combinations with high interaction intensity are mostly composed of main influence factors.Although some of the secondary influence factors are not very powerful in explaining the spatial differentiation characteristics of CEEI,the ability will be enhanced under the interaction with other factors.Additionally,most of the main influencing factors have no significant differences in the impact of CEEI spatial distribution.But they are all significantly different from the topography and geomorphology factors.