| Aiming at the impact of rice soil of different parent materials in Changsha-Zhuzhou-Xiangtan Region on the content of five heavy metals,namely Pb,Cr,Hg,Cd,and As,this paper selects the rice soil developed from five kinds of parent materials(river sediment,purple sandshale weathered product,granite weathered product,plate shale weathered product,and quaternary red clay)in this region as the object of study,gathers the profile soil in the method of systematic classification and topsoil samples from different parent materials in the method of random sampling,to analyze the total content of heavy metals and the content in effective state,as well as the basic physicochemical indexes of the soil(pH,free ferric oxide content,organic content,and soil particle composition).Moreover,it analyzes the profile distribution rule of heavy metal content in the rice soil of different parent materials,and the impact of basic physicochemical properties of the soil on the content of heavy metals,and evaluates the pollution state of rice soil developed from different parent materials in Changsha-Zhuzhou-Xiangtan Region.(1)Seen from the profile distribution of five heavy metals in the rice soil of different parent materials,the content of effective Cr and Hg in the reddish clayey soil of different parent materials is relatively high,and heavy metals mainly gather in the plow pan,showing “?”-shaped changes.But the impact on the content of rest three heavy metals is not evident.In hemp sandy soil,the total content of Cr and content of effective Hg and Cr are the highest,characterized by evident surface enrichment.In addition,the total content of As is also the highest,and it also gathers in the plow pan,showing “?”-shaped changes;in purple sandy soil,the content of effective Cr,Pb,Cd and As presents uniform distribution in the soil profile,while the total content of Hg and Cd and content of effective Cr,Pb,Cd and As decrease with the increasing depth of profile,and the total content of heavy metals and content in effective state are relatively small.In yellow clayey soil,the content of Cr and Pb is relatively high in the soil of these parent materials,and its total content also equally distributes in different profiles,but the content in effective state displays remarkable surface enrichment.River sandy soil,the total content of Pb and Cd and content of effective Cd and As are the highest in the soil of different parent materials,and the total content of Pb and Cd distributes evenly in the profile.Moreover,the content of effective Cd and As is characterized by surface enrichment.(2)From the correlation between the content of heavy metals in the profile soil and basic physicochemical indexes of soil,the organic content of the soil is in a positive correlation with the total content of Cr,Pb,Hg and Cd in the soil,as well as the content of effective Pb,Cr,Cd and As,as a primary soil factor influencing thecontent of heavy metals.The free ferric oxide content and pH come next,also as important factors.The soil clay shows an unremarkable correlation with the content of heavy metals in this research.(3)From the total content of heavy metals and the content in effective state: the average total content of Cr and Hg in yellow clayey soil of five parent materials is the highest,93.1 mg/kg and 0.272 mg/kg respectively;the average total content of Pb in hemp sandy soil is the highest,reaching 48.0 mg/kg;the average total content of Cd in purple sandy soil is the highest,namely 0.648 mg/kg;The variable coefficient of Cd is the highest,as high as 67%.The total content of Cd and Hg would be easily impacted by external environmental factors.The average content of effective Pb,Cr,Hg and As is the highest in yellow clayey soil,about 17.34mg/kg,0.455mg/kg,0.0022mg/kg and 21.9mg/kg respectively.The average content of heavy metals(excluding As)in river sandy soil is relatively low,so is the variable coefficient.Among the five heavy metals,Hg would be slightly impacted by soil factors.The content of effective Pb,Cr,Cd and As would be greatly influenced by different environments and parent materials,while the content of effective Hg would be slightly influenced.Regarding the correlation between the total content of heavy metals and the content in effective state,the total content of Pb,Cr,Cd and As in the soil of different parent materials is in a remarkable positive correlation with the content of heavy metals in effective state,but the total content of Hg is only in a remarkable correlation with its effective in purple sandy soil,and the correlation index reaches 0.865,and correlation is not obvious in the rest four parent materials.The effective content of Cd and As is mainly influenced by its parent material,and slightly by the environmental factors.(4)Pollution assessment is carried out with the single factor index method,and the average single factor pollution index of Pb,Cr,Hg and Cd in the rice soil of five parent materials ranks as follows: Cd(1.40)> Pb(0.51)> Hg(0.47)= As(0.47)> Cr(0.29).The hemp sandy soil,yellow clayey soil and purple sandy soil are moderately polluted,while the red clayey soil and river sandy soil are slightly polluted.From the over standard rate and times of ultra standard,the Cd pollution is relatively serious in Zhuzhou;among the rice soil of five different parent materials,the Cd pollution of yellow clayey soil and purple sandy soil should be brought to the forefront.According to Nemerow's composite pollution index method,the composite pollution index of yellow clayey soil and purple sandy soil is 1.28 and 1.42 respectively,which is slightly polluted,while that of hemp sandy soil,red clayey soil and river sandy soil is 0.91,0.80 and 0.82 respectively,suggesting that it is still clean,but already approaching the warning line.Therefore,the soil environmental monitoring and concurrent monitoring of agricultural products should be reinforced. |
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