| Fengjiashan reservoir is a comprehensive large-scale water conservancy project,which serves as a major surface water source for Baoji area and the western Guanzhong area.With the development of Qianyang county,great changes have taken place in the environment around the Qianhe river.For the effective utilization of water and soil resources,it is important to research the present situation of the soil pollution in Qianhe river basin of Qianyang county.In this paper,the soil around the Qianhe river basin of Qianyang county is taken as the main research area.It includes the determination of the physical and chemical properties of soil,the content and occurrence forms of heavy metal elements,the drawing of spatial distribution map,the analysis of the pollution degree and potential harm level of heavy metals in soil by much pollution assessment methods,and the analysis of the sources of heavy metals.Conclusions can be made as follow:(1)The p H value of the soil in the study area is 7.92～8.42,which belongs to alkaline soil.The electrical conductivity of the soil is between 146.4～311.7μs/cm.The proportion of particle size distribution in soil is mainly coarse silt and the soil texture is medium loam.The content of soil organic matter,total nitrogen,total phosphorus and total potassium is10.026～30.031g/kg,523～1410mg/kg,453～1420mg/kg and 1.49～2.3% respectively.The overall content was within the level range and can basically meet the needs of plant growth and crop cultivation.(2)Eight heavy metals in the soil content value are lower than the value at risk of soil environmental quality standards.The average proportion of the occurrence forms of heavy metal elements in sequence are Residual > Oxidizable > Reducible > Weak acid soluble >Water soluble.The soil activity of Cd is the strongest and the potential environmental risk is high.The other heavy metal elements have strong stability and are difficult to be directly used and transferred under natural conditions.(3)As,Cu,Pb,Zn and Ni have similar spatial distribution characteristics.The heavy metals content in the downstream of the study area is relatively higher than that in the upstream,concentrated in the north of qianhe River basin,which is related to geomorphic features and the migration and deposition brought by river.There is a significant correlationbetween heavy metal content and particle size,which is an important factor in the accumulation of heavy metal content in soil.(4)The results of single factor contaminant index and Nemerow comprehensive pollution assessment indicate that the soil in the study area is at a safe level.The evaluation results in Geo-accumulation index showed that As,Cd,and Hg had different degrees of accumulation,and the pollution degree was As > Cd > Hg > Cu > Ni > Pb > Zn > Cr.The evaluation results of potential ecological risk indexing showed that Cd element part of the region reached a strong and moderate risk level,while Hg showed the degree of medium risk.The rest of the element potential ecological risk index of slight ecological risk level,arrange according to the degree of potential hazard for Hg > Cd > As > Cu > Ni > Pb > Cr > Zn.Comprehensive factor potential ecological risk indexes evaluation parts to belongs to medium level of risk,mainly related to the accumulation of Cd and Hg elements,and the rest are at the level of slight ecological risk.(5)Based on the results of Multivariate statistical analyses,the results of soil heavy metal source analyses can be divided into three categories: The first type is As,Cu,Ni,Cr,Zn and Pb elements,which are mainly affected by the parent material of soil formation;The second type is Hg,which is mainly affected by the combination of coal-fired waste gas and dust,crop fertilization and sewage irrigation;The third is the Cd element,which is mainly affected by crop fertilization and sewage irrigation. |
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