| With the rapid development of industry,economy and technology,the natural environment,on which human-beings live,is constantly being transformed and polluted,endangering the ecological environment and human health.Cities have a variety of functions,but the effects of different human activities on heavy metals in urban soil are different.At present,the research on heavy metals in soil is mainly focused on a single aspect,but lack of research on the vertical and spatial distribution affected by different land use types.Therefore,taking Shanghai as an example,based on the opportunity of land redevelopment and utilization,this paper studies the heavy metals in soil of agricultural land,industrial land,residential land and other land.In study areas of different land use types,the distribution characteristics of heavy metals were revealed in the surface,middle and deep soil;the pollution characteristics and ecological risks were evaluated;the sources of heavy metals were analyzed.The purpose of this study is to provide reference for the protection and improvement of soil environmental quality in rapid urbanization areas.The main conclusions of the study are as follows:(1)Through data collection and supplementary sampling,six heavy metals(As,Cd,Cu,Pb,Hg and Ni)of soil with three layers of depth in 103 plots were analyzed and determined in the study area.The results showed that the soil was accumulated with heavy metals in different degrees,and the content of the surface soil was significantly higher than that in the middle and deep soil.The maximum value of Hg in the surface soil is 12 times higher than the background value,and the average values of Cd,Cu,Pb,Hg and Ni are all higher than the background values of Shanghai.Due to the difference of land use,Cd,Cu and Pb in the surface soil of industrial land are higher and have great variability.Hg is higher in residential land.As and Ni are higher in other land.And heavy metals in agricultural land are relatively less.(2)The pollution index,geo-accumulation index and potential ecological risk index were used to evaluate the risk of the whole soil and soil of different land use types.The results showed that the study area were polluted by those heavy metals.The Nemerow pollution index was 1.42,which belonged to light pollution level.The pollution degree from serious to light was residential land>industrial land>other land>agricultural land.The geo-cumulative index indicated that Cd,Cu and Hg some plots reached the level of slight and moderate degree.Hg had medium and strong polluted plots.Pollution in industrial land was the most serious;the study area has medium polluted level of potential ecological risk index.The potential ecological risks of Cd and Hg are more serious,and the risks of different land types showed the trend of industrial land>residential land>other land>total>agricultural land.According to the spatial distribution,heavy metal is more likely to accumulate in the densely populated areas.(3)The source analysis was analyzed according to correlation analysis,factor analysis and cluster analysis.The results showed that Ni mainly came from natural sources,and the sources of other heavy metals were affected by different human activities.Agricultural land was mainly affected by agricultural activities,coal-fired,surrounding industrial activities and traffic sources.Nearly 70%contribution of heavy metals of industrial land came from industrial activities and transportation.Residential land was affected by coal-fired,air settlement generated by traffic,domestic garbage,construction waste and other sources.The sources of other land mainly include transportation,daily life production and other anthropogenic sources. |
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