Ecological Risk Assessment And Management Countermeasures For Cultivated Land Under Multiple Spatial Scales

China has a large amount of cultivated land resources,but the per capita share is less than one third of the world average.In addition,the continuous urbanization and industrialization development in recent years not only occupy many highly productive farmland,but also virtually exert many stresses on the production and ecological functions of cultivated land ecosystem,which resulting in the decline of its environmental value and the sharp increase of ecological risk level.This has seriously hindered the smooth realization of China’s agricultural sustainable development goal.In view of the scarcity of cultivated land resources and the realistic demand of "ecological civilization construction",how to ensure the continuous provision of the environmental value of cultivated land resources and reduce the potential ecological risks faced by the cultivated land ecosystem without damaging the food supply capacity has became the core problem to be solved by the land management departments at all levels in China.However,the study of cultivated land ecological risk has the characteristics of significant spatial heterogeneity and scale difference,and the management decision-making objectives and tasks of governments at different levels are also different.Therefore,a deep understanding of the scale effect and spatial heterogeneity of cultivated land ecological risk can promote the optimal allocation of management resources,improve the accuracy of risk control measures,and meet the development direction and practical needs of the current "multi compliance" and "land spatial planning".Starting from the analysis of the definition and basic characteristics of cultivated land ecosystem,taking the whole process analysis of cultivated land ecological risk as the starting point.This paper comprehensively analyzes the risk sources,exposure response approaches and evaluation end points,and constructs the research framework of cultivated land ecological risk in combination with the main and practical needs of China’s current land management.The main objectives and contents of cultivated land ecological risk research under different management scales are clarified.Based on the sustainable land use theory,risk management theory,human earth relationship theory and ecosystem service function theory,a series of methods and models such as quantitative remote sensing,econometric analysis,GIS technology,relative risk assessment model and scenario analysis were applied from the national assess the actual or potential impact on cultivated land ecosystem at provincial and regional scales,and identified the spatial heterogeneity characteristics of risk sources under different management scales.So as to provide theoretical and methodological support for alleviating the contradiction between ecological protection and economic development and building a multi-level and refined cultivated land ecological risk management and control system.The specific research contents,methods and results are as follows:(1)The farmland ecosystem is an artificial-natural complex ecosystem with multiple social,economic and ecological functions and dual attributes of nature and society shaped by human participation.Usually,farmland ecosystem has the characteristics of purpose,variablility,difference,openness and vulnerability.And consisting of four parts: agricultural input,ecological process,product output and path feedback.Farmland ecological risk can be triggered by two pathways.On the one hand,The direct agricultural input from human beings to farmland ecosystem will have a stressing effect on the biotic and abiotic factors.On the other hand,external intervention or spatial remodeling of other sub-ecosystems in the region will indirectly break the balance of energy flow and material circulation between systems,resulting in potential ecological risks.In addition,the research on farmland ecological risk has the characteristic of interdisciplinary,spatial heterogeneity and scale difference.(2)The main purpose of national scale land management is to accurately identify the possible problems in the past land use process of different natural geographical divisions or provincial administrative units,and put forward guiding,controlling and differential management objectives,so as to maximize the comprehensive benefits of land use.Taking the total primary productivity(GPP)of cultivated land ecosystem as the functional characteristic parameter,based on the conceptual model of vulnerability,this chapter applies quantitative remote sensing and GIS spatial analysis technology to identify the spatial pattern characteristics of cultivated land ecosystem vulnerability in China.Agricultural input is a direct way for human activities to affect the healthy operation of cultivated land ecosystem.Therefore,based on the spatial pattern of cultivated land ecosystem vulnerability,this study analyzed the spatio-temporal differences of input intensity of different agricultural factors in China,and combined with socio-economic development and population variables,applied multiple linear regression model to explore the main driving factors affecting cultivated land ecosystem vulnerability in seven natural geographical regions of China.The results show that from 2001 to 2018,36.11% of China’s cultivated land ecosystems were at the level of severe vulnerability and extreme vulnerability,mainly distributed in the hilly and gully areas of the Loess Plateau and the northwest of Sichuan Basin,while the slightly vulnerable and slightly vulnerable cultivated land accounted for about 44.64% of the total area of China’s cultivated land ecosystem,mainly distributed in the three major plains of Northeast China and the central plain.Although socio-economic development and changes in natural conditions are the main factors driving the changes in the vulnerability level of cultivated land ecosystem in China,the stress of agricultural investment also affects the vulnerability level of cultivated land ecosystem in China to a certain extent,and there are significant spatial heterogeneity in the ecological effects of different agricultural factors on cultivated land resources.Specifically,increasing the input intensity of chemical fertilizer can significantly reduce the vulnerability level of cultivated land ecosystem in Central China,South China,southwest and East China,while the excessive input of labor resources may lead to more vulnerability of cultivated land ecosystem in northwest,central China,southwest and South China.In addition,large-scale agricultural machinery investment has an adverse impact on the cultivated land ecosystem in Northeast and North China,but can significantly reduce the vulnerability level of cultivated land ecosystem in Northwest and East China.(3)Under the control and constraints of national-scale research,this chapter takes Jiangsu Province as a typical case area and first applies an improved relative risk model to evaluate the ecological risks and food supply risks faced by the existing farmland ecosystems in the county-level administrative units of each district.Secondly,this chapter uses quantitative remote sensing and spatial analysis methods to identify the quantity,grade and spatial distribution of reserve cultivated land resources.Finally,this chapter points out the optimal plan for the ecological risk management and control zoning of cultivated land and land management decision-making in Jiangsu Province under different scenarios by constructing a trade-off framework.The results show that the ecological risk level of cultivated land in Jiangsu Province is generally increasing from north to south,and the existing cultivated land ecosystems in 36 district and county administrative units are facing extreme or severe ecological risks."Habitat damage" and "soil quality degradation" are the two evaluation endpoints that withstand the highest intensity of external stress,while "road construction" is the source of the strongest stress.The level of food supply risk on cultivated land in Jiangsu Province generally shows a trend of increasing "from north to south" and "from east to west".Among them,18 district and county-level administrative units are facing extreme or severe food supply risks.The soil quality of cultivated land is more susceptible to the effects of external stressors than the area of cultivated land,and road construction is still the main source of pressure that causes food supply risks at the provincial scale.There are currently 97,074 hectares of unused land in Jiangsu Province that can be considered as potential reserve cultivated land resources,which are mainly distributed in the central,southern and eastern coastal areas of Jiangsu Province.In the future,19 district and countylevel administrative units may regard the reclamation of a total of 16,578 hectares of reserve cultivated land resources as their primary land use target.In addition,in the context of“ecological protection priority” and “food production priority”,49 and 27 district and countylevel administrative units respectively should take the improvement of the non-productive service functions and environmental value of the existing cultivated land ecosystem as future land management tasks.The 8 and 28 administrative units should be classified as areas for improving grain production capacity.(4)Heavy metal pollution has become a major obstacle to the healthy operation of my country’s farmland ecosystem.This chapter starts from the pertinence and accuracy characteristics of my country’s regional-scale land management work.Under the guidance and constraints of Chapter 5,provincial-scale risk management and control divisions,the core area of economic development in Jiangsu Province---Southern Jiangsu is a typical case area.Taking the field as the basic evaluation unit,based on the Hakanson index method and geostatistics method,the potential ecological risks and spatial patterns of different crop soils due to the accumulation of heavy metal elements(Pb,Cr,Cd,As,Hg)are discussed.And try to apply principal component analysis(PCA)and Pearson correlation analysis to identify the main sources of risk.Land use/cover change(LUCC)is a process by which humans reshape the structure and spatial pattern of regional land use according to their own needs,and it is a direct expression of humans’ behavior in transforming ecosystems.Therefore,we also evaluated the the effects of human activites on farmland ecological risk using ordinary least squares(OLS)and geographically weighted regression models(GWR)based on the selection of explanatory variables.The results show that the average PLI in Nanjing is 1.774,exhibiting overall slight pollution.Meanwhile,the polluted indices of the five major heavy metals exhibited significantly spatial heterogeneity and decreased as the order as Hg(6.73)>Cd(2.57)> Pb(1.55)> As(1.019)> Cr(0.96).The potential ecological risk in Nanjing ranged from 68.46 to 5661.73,with the average value of 366.08.The five major heavy metals had the risk values decreased as the order: Hg(269.01)> Cd(77.21)> As(10.19)> Pb(7.75)>Cr(1.92).In general,there were four factors determining the soil ecological risk in Nanjing,and Cd and Hg played vital roles.Our spatially statistical analysis showed that the responses of potential ecological risk to agricultural input intensity,spatial configuration and structure played spatial differences.For instance,higher input intensity had resulted in more severe ecological risk in western regions,and the distances of agricultural plots from major roads and settlements were the key factors to affect ecological risk.Based on above results,we formulated countermeasures to control ecological risk through identifying targeted pollutants,calculating polluted areas as well as making some adjustments on human behaviours on farmland ecosystem.