Study On Land Use Change And Landscape Ecological Risk Assessment In Yongchuan District Of Chongqing Province

Land is a vital bridge and link between human and ecological environment,the change of its utilization mode affects the stability and balance of natural ecosystem in different degrees,and also affects the stability of the regional ecosystem.As a new method to quantitatively evaluate the ecological effects caused by land use change,ecological risk assessment can provide some references and theoretical basis for regional risk control and ecological management.As the new urban development area of Chongqing province,the urbanization and industrialization process of Yongchuan District has been continuously promoted.Therefore,the land use structure in this region has changed greatly,which has caused a range of environmental problems such as soil erosion and ecological deterioration.This is not conducive to the sustainable and stable development of its land resources.Taking Yongchuan District as study area,supported by some software such as ENVI,Arc GIS and Fragstats and multiple mathematical models,this paper determined the appropriate spatial analysis granularity based on the granularity effect analysis of multiple time nodes,and studied the change of landscape pattern in Yongchuan District by using remote sensing interpretation data from 2005,2010,2015 and 2018.Furthermore,the landscape pattern index was cooperated to develop an ecological risk index.Using landscape index to construct ecological risk index to study the characteristics of temporal and spatial distribution of the ecological risk and the spatial clustering with the help of spatial autocorrelation.And introducing terrain factors to study the temporal and spatial distribution of ecological risks in the terrain dimension.The research conclusions are as follows:(1)Through the particle size domain analysis method and area information loss evaluation,the suitable spatial grain of Yongchuan District is 60 m.Based on this analysis of the change of landscape pattern in Yongchuan District,it is found that:(1)At the patch type level,the multiple landscape indices of cultivated land and woodland are always the largest,and they have always been the dominant landscape types in the region.Cultivated land and waters are affected by human disturbance,and the overall development is toward fragmentation,discretization,and complex patch shapes;The patch area of woodland is increasing,and the degree of fragmentation is decreasing,but the dispersion of distribution has increased;The degree of fragmentation of construction land has weakened,the degree of landscape advantage has been strengthened,and the whole trend is towards regularization and agglomeration;The area of grassland and unused land is significantly reduced,and the degree of fragmentation and separation are gradually reduced.(2)At the landscape level,the landscape pattern of Yongchuan District is toward diversification and irregularity.The degree of fragmentation decreased in the early stage,and increased in the later stage,but the overall has improved in the study period.(2)The mean value of ecological risk in Yongchuan District decreased,the ecological security has changed for better from 2005 to 2018.From its spatial distribution law,it can be seen that the area presents the characteristics of high distribution in the northwest,southwest and northeast and the middle low value extending in a belt shape.From the results of time series changes,it can be seen that the region is always dominated by the medium risk areas from 2005 to 2010.The risk level were reduced from 2010 to 2015.The region dominated by low-risk areas from2015-2018.On the whole,from 2005 to 2018,the area of low-level risk areas increased,and extended to the southwest and southeast on the basis of the original scope;The area of medium risk areas increased first and then decreased with time,which was mainly transferred from the high risk areas;The area of high risk areas reduced,and the distribution range shrank inward on the original basis,but the area of higher risk has rebounded from 2015 to 2018,the ecological environment is still under great pressure.(3)From the results of spatial autocorrelation of ecological risks,during the study period,the ecological risks in Yongchuan District presented spatial agglomeration,and the degree of agglomeration increased first and then gradually decreased over time.Local area always showed high-high aggregation and low-low aggregation.The low-low aggregation as cold spots were distributed in a belt at the junction of mountains and extended to the middle and southeast.The high-high aggregation defined as the hot spots were distributed in the form of clusters in the northwest,southwest and south of Yongchuan District and have expanded in the period of the study.(4)From the topographic dimension,the ecological risk in Yongchuan District mainly presents the following spatial distribution characteristics.The low risk areas were mainly distributed in the middle and high terrain niche gradient.The lower risk areas were concentrated in the lower terrain niche gradient.The medium risk areas,higher risk areas and high risk areas were concentrated in the low and medium terrain niche gradient.From the change trend of the distribution curve,we can see that the distribution curve of low risk areas decrease first and then increase with the elevation of terrain niche gradient,the distribution curve of lower risk areas keep decreasing with the increase of terrain niche gradient,and the distribution curves of medium risk areas,higher risk areas and high risk areas all increased firstly and then descended with the increase of terrain niche gradient.From the change trend of the dominant terrain niche distribution index,it can be seen that the distribution index of low and lower risk areas decreased,the distribution index of middle risk areas increased as a whole,higher and high risk areas decreased in varying degrees and the general trend was shifting to low terrain niche.Comprehensively considering the terrain and the distribution characteristics of risk grade areas in Yongchuan District,it can be divided into five topographic risk areas: the north low mountain and hilly risk area,the north shallow hill and wide valley risk areas,the central hill and valley risk areas,the central shallow hill and wide valley risk areas,and the south shallow hill and flat dam risk areas.