| As one of the three major wetlands in China,Zoige grassland wetland contains the largest alpine peat marsh in China.As an important ecological barrier,Zoige grassland wetland has great significance in water conservation,regional climate regulation and soil and water conservation in the upper reaches of the Yellow River and the Yangtze River,and has important ecological strategic significance.In recent years,with the changes in global climate and the disturbance of human activities,Zoige grassland wetland has been greatly reduced,showing a very obvious trend of degradation,and the ecological function has been seriously damaged.Scientifically recognizing the space-time process of the Zoige grassland wetland and quantitatively analyzing its change-driven mechanism is of great significance for the protection and restoration of the Zoige wetland.At present,although some scholars have carried out some research and exploration on the degradation and driving mechanism of the Zoige grassland wetland,the research on the driving mechanism is more inclined to qualitative analysis.Quantitative research is relatively inadequate,especially the quantitative identification of driving mechanism under the combined influence of natural factors and human activities.Therefore,this paper relies on the National Natural Science Foundation of China,“Spatial and Environmental Impacts of Glassland and Pastoral Areas,Space-Time Process Analysis and Early Warning-Taking the Source Region of the River in the Northwest of Sichuan Province as an Example(41401659)" and the Key Basic Research Fund Project of the Sichuan Provincial Department of Education,“Analysis and Early Warning of Eco-Geological Environment Safety Process of Animal Husbandry Development in River Source Area of Northwest Sichuan(13ZA0059)",takes the wetland in Zoige grassland as the research object,takes the "3S" technology as the foundation to extract the spatio-temporal distribution data of various wetlands in the study area from 1995 to 2015,and analyze its spatio-temporal distribution and dynamic change characteristics.Therefore,the law of degradation of wetlands in the study area is clarified.On this basis,comprehensively use the meteorological data of the Zoige grassland and surrounding areas,the socio-economic statistics of the counties and other survey data to quantitatively analyze the driving mechanism of the Zoige grassland wetland change,so as to fully understand the driving mechanism of natural factors and human activities on the degradation of the Zoige grassland wetland,and provide practical basis for the rational use,protection and restoration of the wetland in the study area.The main conclusions of this study are as follows:(1)The support vector machine(SVM)classification method was used to establish remote sensing interpretation marks of various wetlands in the Zoige grassland using Landsat TM/OLI multi-spectral remote sensing images to extract the information of Zoige grassland wetland in 1995,2000,2005,2010 and 2015.From the perspective of wetland types,the type of Zoige grassland wetland are mainly marsh wetlands,river wetlands and lake wetlands,and the marsh wetlands are the main wetland types,accounting for more than 85%.According to the spatial distribution characteristics,Zoige grassland wetland are mainly concentrated in the central and southern regions.In the study area,the proportion of wetland area in each county from high to low is:Zoige County,Maqu County,Hongyuan County,Aba County,Jiuzhi County,Luqu County,Songpan County.Specifically,for all kinds of wetlands,swamp wetlands distribute most in Zoige County,accounting for about 44%,River Wetlands distribute most in Maqu County,accounting for about 42%,and lake wetlands distribute most in Zoige County,accounting for more than 30%.From the perspective of area change,by 2015,the wetland area in the Zoige grassland area totaled 6364.5 km2.During the period from 1995 to 2015,the wetland area showed a degraded trend overall,with a total reduction of 168.03 km2 and a degradation rate of 2.57%.Among the counties,the county with the largest reduction in wetland area is Zoige County,with a total reduction of 72.36 km2,and the county with the highest degradation rate is Hongyuan County(3%).Specific to all types of wetlands,marsh wetlands and river wetlands are also degraded.In 20 years,the area is reduced by 176.55 km2 and 5.26 km2 respectively,and the degradation rates are 3.01%and 0.85%,respectively,while the area of lake wetlands has recovered(13.78 km2).(2)From the perspective of dynamic transformation characteristics,during the period from 1995 to 2015,the dynamic transformation process of wetlands in the Zoige grassland area was mainly from wetland to non-wetland,with a total conversion area of 192.92 km2,and the main conversion type is grassland.The conversion from non-wetlands to wetlands and between wetland types is less,with conversion areas of 24.88 km2 and 14.4 km2,respectively.Degradation is still the main trend of change in wetlands,but the area of wetland restoration is increasing year by year,and wetland restoration is beginning to bear fruit.From the perspective of landscape pattern change,during the period of 1995-2015,the degree of fragmentation of wetland landscape in the Zoige grassland area increased continuously,and the landscape complexity increased first and then decreased before and after 2010,and the degree of human interference decreases and then increases before and after 2010.From the distribution and change of wetland spatial centroid,during 1995-2015,the centroid of wetland and marsh wetland in Zoige grassland area was located in the southwest corner of Zoige County,while that the centroid of river wetland and lake wetland was located in the southeast part of Maqu County.The centroid of wetland moved 158.22m to the northeast,while the centroid of marsh wetland moved 62.21m to the southeast,the centroid of river wetland moved 631m to the southwest,the centroid of lake wetland moved 13440.94m to the northeast.In terms of stability,marsh wetland>wetland overall>river wetland>lake wetland.(3)Using statistical methods,ANUSPLIN,Kriging interpolation model and geographic detector model,the driving factors of wetland change in Zoige grassland were quantitatively analyzed in terms of natural factors,human activities factors and interactions among them.It was found that during the period 1995-2015,the degradation of Zoige grassland wetland is promoted by all kinds of driving factors of natural and human activities,and the mechanism of degradation is becoming more and more complex.During the period from 1995 to 2015,the increase of average temperature was the most important driving factor affecting the degradation of marsh wetland in the Zoige grassland,its contribution rate is over 15%,but the degree of influence showed a decreasing trend with time,while human activities have aggravated the degradation process of marsh wetlands in the region,and the degree of influence has gradually increased.The mechanism of human activities affecting the degradation of marsh wetlands in the study area has changed before and after 2005.Before 2005,the main human factors driving the degradation of marsh wetlands in the study area were animal husbandry and agriculture.After 2005,animal husbandry still affects the degradation of marsh wetlands in the region to a large extent,but the increase of population pressure has become the most important human activity factor for the degradation of local marsh wetlands. |
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