| Soil has been an indispensable and crucial material basis for human beings,and soil environment is a significant factor concerning major strategic issues such as maintaining the stability of ecosystem and human food security.With the development of modern society,especially continuous urban expansion and industrialization,the soil environment has been suffering from environmental contamination challenges caused by human activities such as pollutant emissions from industrial enterprises,over inputs of fertilizers,urban waste dumping and landfilling,mines exploration and traffic emissions ect.Heavy metals in soils have the characteristics of highly toxicity,resistance of degradation,and a wide range of contamination sources.They do not only do damage to life in nature or destroy the stability of various ecosystems,but also cause inverse harm to human body health through the accumulation of food chain.Therefore heavy metals in soils has been a conundrum in the management,control and treatment of soil pollution which is urgent to be monitored and treated.“Controlling sources and cutting sinks” is a vital content in the field of soil heavy metals pollution research.Source identification and apportionment can qualitatively identify the types,determine the characteristics,and quantitatively output the contribution values of every contamination sources,which can provide effective reference for the formulation of relevant policies;the sink characteristics,which considers the existing pollution conditions,and aims to deeply excavating pollution characteristics,thus provides effective suggestions for repairing treatment of soil heavy metals.Based on such "source-sink" theory,this thesis used spatial analysis and data mining technological methods,coordinating 9 natural and economic covariates in the coastal city center and suburban areas of Zhejiang Province.Cadimium(Cd),Mercury(Hg),Arsenic(As),Lead(Pb),Chromiun(Cr),Copper(Cu),Zinc(Zn),Nickel(Ni)eight heavy metals in 947 soil and plant samples were investigated for "source-sink" contamination characteristics.The research content and conclusions mainly include:(1)A Geo-Detector branch-the Factor-Detector was used in the job of screening nine natural and economic covariate factors which may contribute to the soil heavy metals contamination in the study area,and the Interaction-Detector of Geo-Detector was applied to identify their correlation analysis.The results showed that eight factors that were significantly correlated with the soil heavy metal contamination in the study area,referring to soil parent material types,soil types,land use types,population quantity,road types,industrial enterprise types and quantity,mine types and quantity,fertilizer types and inputs individually.Meanwhile Non-linear enhancement or Two-factor enhancement were discovered within these eight factors.Based on the spatial distribution and quantity magnitude analysis,six actual contamination sources including the natural background source,urban waste source,traffic emission source,industrial enterprise emissions source,mines exploitation source,and fertilizer inputs sources were determined in the study area.(2)The Finite Mixture Distribution Model(FMDM)and the Positive Matrix Facor(PMF)receptor model were used to analyze the sources of the study area through both qualitative and quantitative perspectives.The results showed that the data distributions of eight heavy metals in soils were identified as single,double,triple,and four lognormal distributions corresponding to different forms of composite pollution characteristics,of which Cd belonged to multiple mixed composite pollution,Pb belonged to double composite pollution,Hg,As,Cr and Cu belonged to triple compound pollution,and Zn and Ni belonged to quadruple compound pollution.The six contamination sources in the study area had different contribution values to the eight soil heavy metals.Especially,industrial enterprise pollutants and fertilizer inputs sources were the major two pollution sources among six.The contributions from industrial enterprise pollutants source to Cd,Hg,As,Pb,Cr,Cu,Zn,Ni are 17.01%,74.40%,23.55%,30.27%,26.28%,26.25%,17.56%,24.18% namely,and the contributions from fertilizer inputs source to these eight heavy metals are 28.93%,14.77%,47.90%,34.98%,61.39%,43.59%,42.69%,62.36% individually.(3)Including five parts referring as the basic statistical analysis,correlation analysis,spatial distribution analysis,pollution evaluation and pollution hotspots analysis of eight heavy metals in soils,the Sink contamination characteristics analysis was carried out in this study.Particularly,spatial distribution analysis used the Ordinary Kriging to interpolate eight heavy metals across over the study area.Pollution evaluation included Nemero comprehensive pollution index and potential ecological risk index,and hotspots analysis consisted of Getis-Ord Gi* and Bivariate Local Moran's I.The results showed that the average values of the eight heavy metals all exceeded their corresponding soil background values,indicating that they were affected by anthropogenic pollution sources,and most of the heavy metals in soils showed a strong positive correlation,mostly in the form of compound pollution.Cd,Pb,and Zn were in the form of planar pollution,while Hg,As,Cr,Cu,and Ni were mainly concentrated in the central urban area.Overall,31.89% of the samples in the study area were safe and free of pollution risks;39.81% of the samples touched the pollution warning line;28.30% of the samples were affected by different degrees of pollution.The whole research area had a strong ecological pollution risk,mainly from Cd and Hg.The Getis-Ord Gi* results showed that the hotspots of eight heavy metals in soils were mainly concentrated near the central urban area,and their pollution distribution was similar to the industrial enterprises pollutant emissions distribution;the hotspots of eight heavy metals in plants were clustered in the farmlands located in the southwest part of study area.Such distribution was correlated to the status of fertilizer inputs,indicating a strong relationship.Local Moran's I analysis results showed that among Cd and Hg,the pollutants emitted by industrial enterprises had a greater influence on the contribution of Hg;Within four categories of industrial enterprises as metals,chemicals,textiles,and heavy industries,the Metal and Chemical related enterprises had a greater impact both on the contamination status of such two elements. |
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