The Geochemical And Heavy Metal Accumulation Characteristics Of Black Soil In The Northwest Of Songnen Black Soil Region Were Studied

Black soil is the main carrier of agricultural production in northeast China,and the environmental quality of black soil directly affects the quality of crops.In recent years,the accumulation of heavy metals has been found in some areas in the south and northeast of the black soil area of Songnen Plain.Heavy metals are characterized by high pollution concealability,long residual time,and cannot be degraded by heat and biodegradation,which seriously threaten food production and human health.Therefore,it is particularly important to identify the accumulation,distribution,risk and source of heavy metals in the black soil.In this thesis,the surface black soil of Wuniu River Basin and Yinhe River Basin in the northwest of Songnen black soil area is selected As the research object.40 profile samples and 203 surface soil samples are taken.On the basis of determining the development degree of soil,the concentrations of 8 heavy metal elements,A_S,Cd,Cr,Cu,Hg,Ni,Pb and Zn,are analyzed.Correlation analysis,principal component analysis and positive definite matrix factor source analysis were used to investigate the sources of heavy metals in two basins.The single factor index method,Nemerow comprehensive pollution index method,potential risk analysis method and ecological risk early warning index method were used to evaluate the heavy metals in the black soil.The main conclusions are as follows:(1)The mean organic matter values of surface black soil in Wuniu River Basin and Yinhe River Basin were 4.17%and 6.15%,respectively,and the p H values were 5.77 and 5.8,respectively.The CIA index of the profile was between 72-79,which combined with other coefficients comprehensively indicated that the black soil was developed from the mother material of siltation and slopediluvium in a warm and humid environment.(2)Except Hg,the other 7 elements in the two basins exceeded the Inner Mongolia background value,indicating the accumulation of heavy metals.The Wuniu River Basin has strong variation in Hg,weak variation in Pb and Zn,and moderate variation in others.The Yinhe River Basin has strong variation in Ni and As,weak variation in Cd and Zn,and moderate variation in others.(3)Parent material source,agricultural source,traffic source,domestic combustion source and industrial source were identified by the two heavy metal source analysis methods.The difference is that principal component analysis can identify multiple mixed sources,while positive definite matrix factor analysis is a single source.The comparison of the two methods eliminates the limitation of single method and improves the reliability of source analysis results.(4)The results of four evaluation methods showed that Cd and Cr in Wuniu River Basin were moderately polluted,the rest were mildly polluted,and the comprehensive pollution was moderate when Inner Mongolia soil background value was used as the standard.In Yinhe River basin,Cd and Cr are moderately polluted,Zn is the warning line,the rest are mildly polluted and the comprehensive pollution is moderate.The single factor index method and environmental risk warning index of Wuniu River Basin and Yinhe River basin indicated low risk of individual points of Cr,Ni and Cu,while the Nemero composite index method and potential risk index method of the two river basins showed no risk.