| Ecosystem provides a series of important services and functions for human survival and development.However,the structure,function,stability and sustainability of ecosystem are under great risk stress under the dual impact of external human activities and internal unstable factors.In the face of this reality,the Party pointed out in its 20th National Congress report that we firmly establish and practice.Managing pressure and avoiding risks is a key part of building a beautiful China.Ecological risk assessment has attracted great attention from the academic community,the government and even the whole society,and can provide scientific basis for regional ecological management.Ecosystem provides a series of important services and functions for human survival and development.However,the structure,function,stability and sustainability of ecosystem are under great risk stress under the dual impact of external human activities and internal unstable factors.In the face of this reality,the Party pointed out in its20th National Congress report that we firmly establish and practice the concept that lucid waters and lush mountains are invaluable assets,and plan development from the height of harmonious coexistence between man and nature.Managing pressure and avoiding risks is a key part of building a beautiful China.Ecological risk assessment has attracted great attention from the academic community,the government and even the whole society,and can provide scientific basis for regional ecological management.At present,scholars have done a lot of effective studies on ecological risk from the aspects of research content,region and method.Literature analysis shows that there are some limitations in the above aspects.In terms of research content,most of the research focuses on ecological processes and risk stressors,but ignores the evaluation end point,which limits the indicative significance of ecological risk assessment.Ecosystem service is an effective means to link ecosystem process and human welfare.As the end point of ecological risk assessment,it can greatly improve the practicability and efficiency of ecological risk assessment.The research areas are mainly concentrated in developed areas,while there are few studies on the changes of ecological risks in the typical areas with complex and fragile ecological types in Northwest China.In terms of research methods,firstly,existing ecological risk analysis models mostly describe the static mode of regional ecological risk,rather than the dynamic process of risk formation,that is,the use of single-phase ecological indicators(such as land use type,landscape fragmentation,etc.)to evaluate the risk.Scientific decisions on ecological risk management are based on an understanding of the changing state of ecosystems.Secondly,traditional methods of spatial and temporal analysis of ecological risks can only find the overall change of spatial distribution of ecological risks in time series,and do not fully take into account the spatial and temporal correlation of risk data.In conclusion,this paper takes Gansu Province,an important ecological barrier and an underdeveloped area in northwest China,as the research object,and makes the following exploration:(1)Based on land use data,the characteristics of land use change in the study area are analyzed from three aspects:land use structure characteristics,dynamic change characteristics,and spatio-temporal transfer characteristics.(2)Make comprehensive use of land use,meteorological,and various socioeconomic statistical data to assess regional ecosystem services,and explore their temporal and spatial change characteristics.(3)Construct an ecological risk assessment model based on ecosystem service changes,calculate the ecological risk index of each county,and explore the spatio-temporal evolution characteristics of ecological risks in multiple dimensions with Bayes space-time model.(4)Construct the index system affecting the spatial heterogeneity of ecological risk in Gansu Province,and use the spatio-temporal geographical weighted regression model to evaluate the difference of the effect degree and spatial impact of each factor on the ecological risk index.The following conclusions are drawn:(1)From 1980 to 2020,the overall layout of land use types in Gansu Province was basically stable.The comprehensive dynamic attitude of all types of land use was 15.45%.The dynamic intensity of single land use type was as follows:construction land>water body>unused land>forest land>cultivated land>grassland.The expansion of construction land was the most dramatic,with a net transfer area of 2094.24 km~2,forming a decentralized agglomeration transformation center in the urban core areas of Longzhong and other places.The net transferred area of forest land and grassland is 590.68 km~2 and 390.35 km~2.The transfer area was mainly distributed in the vicinity of several inland river basins such as Shiyang River and Heihe River basin in western Gansu Province.In addition,the ecological type land such as grassland and forestland showed a tendency of degradation to unused land,which should be attached great importance to by relevant departments.(2)From 1980 to 2018,the total amount of ESV in Gansu Province decreased first and then increased,and the growth rate was the fastest from 2000 to 2010.The ESV proportion of each land use type was in the order of grassland>forest land>cultivated land>water body>unused land>construction land.The ESV is higher in the south of Longnan,Gannan and some parts of southwest China,while the ESV group is low in the urban core area and the northwest.The proportion of value of the four ecosystem service types from high to low is the adjustment service,the support service,the supply service and the cultural service.During the study period,ESV per unit area of 55%counties showed an increasing trend,and ESV per unit area of some cities in southwest Gansu increased significantly.Some areas of Jiuquan and Zhangye city increased slightly.The ESV per unit area of the urban belt with Lanzhou as the center showed signs of degradation.In addition,some counties in Longnan,Tianshui and Gannan were affected by geological disasters such as landslides and debris threatened by grassland degradation,which resulted in significant degradation of ecosystem services.(3)From 1980 to 2020,the overall time trend characteristics of ERI in Gansu Province were consistent with ESV,and the increase rate of ERI gradually slowed down after 2010.The study area was mainly dominated by very low risk and medium risk,which accounted for more than 45%of the whole province.During the past 40 years,the area of medium and low risk areas increased gradually,while the area of decreased significantly.ERI showed significant spatial differences among counties and districts,and 99%of counties and districts were affected by risks.ERI aggregation centers in each study stage showed a change rule of"focusing on the southwest after global multi-point outbreak and then moving to the Hexi Corridor and further gathering in the southeast",which was related to the change of spatial development strategy in Gansu Province in the past 40 years.The spatial pattern of ERI presents the characteristics of"high in the south and low in the north,with intermediate transition".ERI high value areas are mainly distributed in Longnan,Longdong and Gannan.Low-value ERI areas are mainly distributed in Hexi Corridor and a small part of them are concentrated in southern Gansu Province.As a whole,the local variation trend of ERI increases from Jiayuguan and Lanzhou to the surrounding areas,and the change in the south of Longdong and other areas is stronger than that in Hexi.(4)From the point of view of the effect intensity of each influencing factor,the effect intensity of each influencing factor on the ecological risk in Gansu Province is successively the density of traffic network,NPP and per capita GDP.As a whole,the effect of natural factors on ecological risk is stronger than that of socio-economic factors.The effect degree of average annual precipitation and average annual temperature on ecological risk showed a gradually decreasing pattern of"high in the south and low in the north".There was a negative correlation between NPP and ecological risk index,showing a differentiation characteristic of"high in the middle and low at the ends".Industrial and ecological risks are positively correlated.Per capita GDP has a positive correlation effect on ecological risk in more than 80%of counties and districts,showing a"low-high-low-high"differentiation from west to east. |
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