| This article takes the Kezi River Basin as the research area,and obtains the land use/cover data of the Kezi River Basin in 1990,2000,2010,and 2018 through interpretation of remote sensing images and field verification to analyze the temporal and spatial changes of the natural vegetation in the basin.feature.At the same time,according to the natural vegetation area in different periods and the vegetation quantity characteristic data of the field survey,the natural vegetation ecological water demand change characteristics and the current situation of satisfaction degree are calculated and analyzed.Finally,the ecological risk assessment model is used to analyze the ecological risk change characteristics and current situation of the Kezi River Basin.,And get the following relevant conclusions:(1)The area of natural vegetation in the Kezi River Basin has been reduced by 1612.48 km2 in 28years,a reduction of 18.99%;the vegetation coverage has been reduced by 22.26%accordingly.The main transfer objects of natural vegetation are cultivated land and unused land.Natural forests and grasses have transferred out areas of 272.59 km2and 1409.20 km2 to cultivated land,and 14.94 km2and 398.39 km2 to unused land.The main transfer objects are unused land.The area transferred to natural forests and grasses was 11.61 km2 and 296.09 km2 respectively;it can be seen that the area of natural vegetation transferred was significantly larger than the transferred area,and the qualitative and quantitative analysis of the social and economic factors of the watershed showed that the main reason for this trend of change was population growth.(2)The water demand of the natural vegetation in the Kezi River Basin in the four periods is7.69×108 m3,7.49×108 m3,6.65×108 m3 and 5.84×108 m3;however,the inflow of water in the four periods in the basin cannot be fully satisfied.Natural vegetation ecological water demand,and the water shortage in the four periods was 6.65×108 m3,7.49×108 m3,6.11×108 m3 and 5.84×108 m3,which shows that the water shortage of natural vegetation in the basin has been very serious.As far as the current situation is concerned,to restore the average buried depth of groundwater to the evaporation limit of natural vegetation in the entire basin,the water volume needs to be restored to9.73×108m3·a-1.(3)During 28 years,the severely fragile ecological areas in the Kezi River Basin showed an obvious increasing trend,with an increase of 303.39%;the mildly fragile areas decreased by 45.50%.Its spatial distribution presents a state of higher midstream,second downstream,and lowest upstream;its ecosystem service function value decreased by 50.98%during 28 years,and the ecological service function value of natural vegetation as the main contributor also showed a significant decline,A total reduction of 55.39%;the spatial distribution of ecological service function value presents a decreasing distribution trend from upstream to downstream.This distribution combined with the distribution of ecological fragility can effectively reduce the ecological risk of the region.(4)The overall spatial distribution of ecological risks in the Kezi River Basin,from high to low,is the middle reaches,the lower reaches and the upper reaches.The high-risk areas in the basin increased by 188.09%during 28 years.The range of changes in the medium-risk area and the low-risk area were 205.35%and-39.52%respectively,which shows that the ecological environment of the river basin has been seriously damaged.Therefore,in order to ensure the gradual restoration of the ecological environment of the Kezi River Basin and the restoration work is effective,the ecological restoration project of the Kezi River Basin must be carried out. |
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