| A large amount of pollutant particles carry trace elements(or called trace metal)generated in the process of the natural resources extraction.The dispersal of these trace elelments in water,soil,and air has a effect on the habitat ecosystem balance,species distribution and biodiversity,and also poses a threat to human health.These ecological risk are correlated with pollutant types,the bioaccumulations factors of metals,climatic conditions and topography feature,as well as vegetation characteristics.Understanding the source of trace elements,the transport rules of trace metals and eveluate the protential eclogical risk,then proposing targetd remediation strategies,are of great significance to understanding global energy development and its environmental effects,as well as correspongding management strategies.On the basis of this,this research is mainly divided into the following sections,(1)Investigation the source of soil and water pollution caused by small-scale mining in an abandoned sphalerite mine of the Yanshan Mountains.Pearson correlation matrix and principal component analysis(PCA)indicate that Zn,Cu,Cd,and Pb in the soil are derived from mining activities.The content of trace metal elements in soil and water decreased with increasing distance from the mining area,and the pollution caused by Zn,Cd and Pb was relatively more serious in the villages adjacent to the tailings.Pollution index and enrichment factor indicate that the pollution degree of trace metals in farmland soils is reduced in the order of Cd>Zn>Cu>Pb>Hg?Cr.The potential ecological risk of cultivated land in three villages adjacent to the mine is A(Liujiazhuang)>B(Xidadi)>C(Gaobanhe).Here,the ecological risk caused by Cd is the most serious.The results of human health risk assessment indicated that the carcinogenic risk of trace metal elements in the three villages is 7.90 ×10-8(A),8.92×10-8(B),and 8.16×10-8(C).No obviously cancer risk has been observed.However,various exposure routes of trace elements in the mining area pose a significant non-carcinogenic risk to local children,and are most affected by lead(Pb).(2)Based on the MIKE21 model platform,the distribution characteristics of various trace elements in the water body are analyzed.The map of water body is coming from the high-resolution(resolution:500×500 m)spatial geographic information images collected by the UAV(UAV).The migration rates of 6 typical metal elements(Zn,Pb,Cd,Cu,Hg and Cr)are simulated.During the high water period,the concentrations of Pb,Zn,Cd;and Hg can quickly reach a stable state after the mine drainage and running water converged,and their concentrations can reach 0.096 mg L-1,0.76 mg L-1,0.011 mg L-1,0.107 mg L-1.The concentrations of Pb,Zn,Cd,and Hg are above the national drinking water quality standards,while Cu and Cr are 0.041 and 0.052 mg L-1.During the dry season,the concentration of Pb,Zn,Cd,and Hg decreased by 19.8%,15.8%,20.56%and 22%,respectively.The concentrations of Cu and Cr was basically the same as the high-water period.This result shows that mine drainage has a stressful effect on the surrounding ecosystem via the effect on the local water environment,then threatening the mining ecosystem balance(3)A optimaized ecological risk assessment framework(FEM-ENA)is proposed for landscape-scale ecological risk assessment of multiple land use types.The model framework is based on traditional environmental network analysis(Network Enviornmental Analysis,NEA),The research area is divided into digital grids according to the type of local land use.Then,the risk transmission path and risk occurrence probability of a single grid(subsystem)are calculated.The framework uses GIS/RS technology in combination with Control Assignment(C A)to solve the problem of geographical compatibility analysis.Then,and the spatial ecological risk distribution of each component is derived,which optimizes the single risk transmission path(using nodes and lines).This method can effectively improves the accuracy of the model.The case analysis indicated that the contaminated soil poses a risk to the surrounding ecological environment,which would affecting vegetation and microorganisms directly.Then threatens herbivores and predators through the food chain and food network.The probability of risk triggering in the study area is as follows:village>farmland>bare land>woodland.Sensitivity analysis showed that when the input energy(T1)of the ecosystem increased by 50%,the control distribution(CA)from herbivores to soil microorganisms increased by 1.00%,and the CA from herbivores to predators decreased by 0.71%.The results showed the robustness of the FEM-ENA model.(4)A interval multi-criteria decision analysis(IMCDA)framework has been proposed to explore the effect of the spatial pattern of plants on the phytoremediation efficiency under the Soil-Plant-Atmosphere Continuum(SPAC).Based on the solute adsorption curve and the migration rule of trace elements under the SPAC system,evaluation indexes and evaluation systems of different plant combination remediation strategies were constructed.Nine planting patterns(single crop,double crop,and triple crop)of three native plants(Setaria viridis(L.),Echinochloa crus-galli(L.),and Phragmites australis(Cav.)Trin ex Steud)are arranged to explain the appicable of the model.The optimal migration rate of different planting partterns and the phytoremediation efficiency are determined under conditions under different scenarios.The results showed that the highest concentrations of Zn,Cd and Pb in the polluted area were 7320.02,14.30.1650.51 mg kg.During the 180 day simulation period,the highest RMSE of trace metals in soil was 3.02(Zn),2.67(Pb),2.89(Cd).The results of IMCDA showed that the optimal model a9(269 mg kg-1 year-1)of Setaria viridis,Echinochloa crus-gali and Phragmites australis mixed pattern had the highest absorption rate of heavy metals,followed by a7(235 mg kg-1 year-1)and a2(240 mg kg-1 year-1).After a 20-year remediation period,the concentration of soil residual pollutants concentration under the optimal scheme(a9)is far below the national standard,and its root toxicity coefficient is 0.12(EC<EC20).This resulting remediation strategies provides agricultural practices guidance for the selection of phytoremeidayion strategies in polluted mining areas in other contaminated areas. |
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