| Natural resources are constantly being consumed and the space for human activities continues to sprawl,in the meantime,the ecological environment has been polluted and damaged.Eco-environmental problems such as increased air pollution,sharp decline in biodiversity,and eutrophication of water bodies have become increasingly serious.How to protect the ecological environment has become a vital realistic problem focused on by the whole society.Fengjie County,Chongqing City is located in the heart of the Three Gorges Reservoir area of the Yangtze River and shoulders the important responsibility of the ecological barrier of the Three Gorges Reservoir.However,in the Three Gorges Reservoir area,its geology and landforms are the most complicated and disasters are the most frequent,so the study of the temporal and spatial dynamic evolution of its ecological environment has practical guiding significance.This paper takes Fengjie County,Chongqing City as the research area,selects seven remote sensing image data from 1990,1994,1998,2003,2007,2015 and2020,and extracts four indicators of greenness,humidity,heat and dryness based on ENVI5.3 software.The Remote Sensing Ecological Index(RSEI)is constructed by the principal component analysis method,and the temporal and spatial dynamic evolution of the ecological environment is analyzed from the three scales of county,town,and village.Combined with the statistical data,a comprehensive evaluation system for the ecological environment of the county and town is constructed to conduct an extension cloud evaluation.The main contents and conclusions of the study are as follows:(1)Greenness,humidity,heat and dryness values are the important indexes to measure the regional ecological environment,and greenness and humidity values increase,which has a positive effect on RSEI.The RSEI values of each period were calculated by using the weighted sum of contribution rate and integrating the information of four sub-indexes by using principal component analysis.Among them,the feature vector of greenness and humidity is positive,which has a positive effect on the ecological environment.The heat and dryness feature vectors are negative values,which have a negative effect on the ecological environment.Using 5000 random points in the study area to extract the value of each sub-index and the RSEI value for regression analysis,it is verified that the RSEI value can better express the information of each sub-index.(2)The average value of RSEI in the study area is between 0.5274 and 0.6001,showing an overall upward trend of fluctuation,with a change rate of 8.41%.The standard deviation of RSEI is between 0.2555 and 0.2715,and the difference in ecological environment among the units is relatively small.The study area is divided into 5 grades of ecologically poor,poor,general,excellent,and excellent using the equal spacing method.The ecological environment is dominated by excellent and excellent,but the proportion of poor and poor is between 22.5 and 33.54%.The task of ecological environment construction is still arduous.Based on the proportion of each level as the standard,it is divided into three dominant modes: general-comparatively superior,comparatively superior-superior and comparatively superior-general.From the perspective of each dominant level,the overall ecological environment of the study area is showing a trend of improving.(3)The RSEI level of the study area generally presents a distribution pattern of high in the south,low in the north,and depressions in the middle.Ecologically superior grades are concentrated in southern towns such as Yunwu,Taihe,Longqiao,Xinglong,and ecologically poor grades are concentrated in the middle of the study area,namely towns on both sides of the Yangtze River,and Baidi,Kangle,Gongping and Hongtu towns along the Meixi River.From 1990 to 2020,the spatial distribution of RSEI high and low values was more trivial,and the areas where high and low values are concentrated had decreased.The overall trend was that the north and south were getting worse and the middle was getting better.(4)The topographic position index and the distribution index are used to analyze the RSEI topographic gradient effect in the reaserch area,and the natural break point method is used to divide the topographic gradient area into 5 topographic gradient regions.The results show that there is a clear correlation between the ecological environment level and the terrain gradient level.As the terrain gradient level increases,areas with better ecological environment have more advantages.Areas with poor and poor ecological environment in each period mainly have advantages in low terrain gradient areas.Ecologically general areas have certain advantages in low and medium terrain gradient areas.Ecologically superior areas mainly have advantages in high terrain gradient areas,and the advantages are the most significant in grade V terrain gradient areas.With the passage of time,the advantages of lower grades of ecological environment in low terrain gradient areas have slightly declined,and the advantages of higher grades of ecological environment in high terrain gradient areas have slightly increased,and the direction of equilibrium has changed.The impact of terrain gradients on ecological environment levels has slightly decreased.(5)The average RSEI of 33 townships in the study area is between 0.1874 and0.7799,showing a distribution pattern of high in the south and north and low in the middle.From the perspective of grade division,the ecological environment of each township is mainly of general grade,there are 20 in total,accounting for 60.61%.There were 19 townships with an increase in RSEI value,accounting for 57.58%,and 14 towns and townships with a decrease in RSEI value,accounting for 42.42%.The RSEI average showed that high-value townships became lower and low-value townships became higher,and shifted from the poles to the middle,and the spatial distribution tended to be balanced.(6)The number of ecologically poor grade units in the 446 villages in the research area has decreased slightly,and the number of poorer grade units is greatly reduced,the number of general grade units has not change much,the number of better grade units has increased significantly,the number of units with higher grade has increased slightly,and the ecological environment grades of most villages have risen.In each period,the grade unit generally showed a trend from two grades to a relatively middle grade,and from a relatively middle grade to the other two grades.Moreover,the two fluctuate continuously or alternately,and the spatial pattern has declined from the initial stage along the Yangtze River to the north-south,and is approximately axisymmetrically distributed,evolving from the west to the east.The spatial distribution of each level is more fragmented and balanced,showing an overall trend of change for the better.(7)The distribution of RSEI values in each period of the village community unit has a positive spatial correlation,is highly clustered and has a confidence level of greater than 99%.As time changes,the total number of cold and hot spots in the village community has declined,with a decrease of 37.33% and 18.82%,respectively,and the number of insignificant areas has increased,with an increase of 191.53%.The local Moran index identifying clusters and abnormal areas showed that the number of highhigh clustering areas,low-low clustering areas,and high-low abnormal areas in the village decreased by 63.04%,53.28%,and 38.89%,respectively.The number of lowhigh anomaly areas and insignificant areas increased,and the overall trend of clustering areas and high-low anomaly areas decreased,low-high anomaly areas and insignificant areas increased,and spatial aggregation generally weakened.(8)Select 20 indicators from 7 element layers including human activities,environmental pollution,meteorology and hydrology,vegetation coverage,agricultural production,social economy and agricultural resource utilization to construct comprehensive evaluation indicators for county ecological environment.The analytic hierarchy process and entropy method are used to obtain the weight value of each indicator.The extension cloud model is constructed by coupling the normal cloud model and the matter-element extension method.The matlab platform is used for calculation,and the ecological environment level is divided into level I(poor)to level V(excellent).From 2009 to 2019,the overall ecological environment of the study area and counties developed well,and the evaluation level showed a fluctuating upward trend.Among the 20 indicators,16 index levels have increased,which has a positive effect on the overall improvement of the ecological environment,and 4 index levels have decreased,which has a negative impact on the ecological environment.(9)Fourteen indicators are selected from 4 aspects of topography,climate,surface and socio-economic factors to conduct comprehensive evaluation of the ecological environment at the town scale of the research area.The low-value areas of the ecological environment of the research area are mainly concentrated in the middle and eastern townships of the research area and along the river.The flow area expands outward and a small number of towns in the northwest.The high-value areas are mainly located in the northeastern townships,while the southern townships are generally higher.(10)Comparing the RSEI value and the statistical data evaluation results,the two are in good agreement,and the overall change of the ecological environment in the study area in different periods shows a similar upward trend of fluctuations.It has a spatial pattern of poor ecological environment in the central region along the river,better ecological environment in the south of the Yangtze River,and the ecological environment of the north of the Yangtze River is in the middle. |
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