| Municipal sludge as agricultural resourceis one of the most important ways of sludge disposal in the world.However,because of heavy metals and other toxic substances in the sludge,the use of sludge as fertilizer in agricultural land is very limited.Compared with the agricultural sludge,because of the advantages of the forest land away from the human food chain,the forest land has gradually become a new way of ecological disposal of sludge.However,the sludge forest may bring the risk of heavy metal pollution,therefore,to proven migration characteristics of heavy metals in soil,environmental risk and its influenceunder the sludge application conditionhas important theoretical and practical significance for the realization of reasonable forest sludge.This research uses three plantations in Southern C hina areawhich is representative of Eucalyptus(Eucalyptus urophylla),Schima superba(Schima superba)and Pinus elliottii(Pinus elliottii)forest soil as the sludge application object,through the forest field test,choose the same locale to set up six plots in each forest stand,which were randomly selected three districts as fertilization area,in the application of sludge,each district applys sludge 9 kg,the other three areas as a blank control.After 1a,2a and 3a was applied to the sludge respectively soil samples were analyzed,effects of sewage sludge on the heavy metal(C u,Zn,Pb,Cd,N i)content and physicochemical properties of soil in the soil surface of three kinds of forest,vertical migration characteristics of heavy metals,interannual variabilityof migration characteristics of heavy metals and effects of soil physicochemical properties on the heavy metal content were researched.The main results are as follow:1.Compared with the untreated sludge,after the 3a was applied to the sludge,contents of five kinds of heavy metals in soilsurface(0~10cm)of three plantations(Eucalyptus urophylla,Schima superba,Pinus elliottii)were increased,amongthem,content of heavy metals Cu and Cd had significant increase;the content of organic matter in the surface soil of Schima superba forest was significantly higher than that of sludgeuntreatment.2.After the 3a was applied to the sludge,the heavy metals in the 3 plantations were mainly concentrated in the 0~10cm soil,only a minimal fraction migrates into the 40~50cm and 80~90cm layers.The migration velocity of sludge heavy metal Cd insoil of Eucalyptus urophylla forest is relatively large;the migration velocity of sludge heavy metal Cd,N i insoil of schimasuperba forest is relatively large;the migration velocity of sludge heavy metal Cd,Cuin soil of Pinus elliottii is relatively large.3.The results of correlation and regression analysis ofheavy metal content and physicochemical properties in soilshow that oil organic matter content and pH are the main factors affecting the content of heavy metal and the migration,and the content of soil organic matter is more related to the content of heavy metals and their migra tion.4.After the 3a was applied to the sludge,the content of heavy metals in soil all increased significantly,but the restriction standard Determination of heavy metals did not exceed the provisions of the state of "soil environmental quality standard" G B15618-1995 three value of sludge soil;after using 3athree comprehensive pollution index of soil in artificial forest mero evaluation results show that based on the the comprehensive index of three plantations,0~10 40~50 and 80~90cm I were lower than the soil comprehensive pollution index of 0.7,as the level of cleanliness.From the result of this research,most of the sludge in the migration of heavy metals in the soil is relatively small,causing no pollution to the soil,so the sludge in forestland use is feasible and can improve soil fertility,also consume large amount of sludge,sludge disposal is an important direction of city resources and utilization.As long as the proportion of sludge is controlled in a certain range,and the time of sludge application is controlled,the effect of the sludge can be maximally utilized,and the pollution risk can be reduced. |
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