| Wetlands affected by human activities,the ecological destruction increasingly serious,environmental pollution,especially heavy metal pollution has become one of the important problem that affect wetland ecological environment.The project of returning farmland to wetland is a strategic measure for wetland ecological restoration in current,and hope to restore wetland function in gradually.wetland soil become a medium that as a high stability of ecological system in wetland.So grain for the situation of wetland soil heavy metal could contributes to an understanding of wetland ecological environment change.Soil from wetland under returning farmland to lake with different periods,analysis of the distribution characteristics of heavy metals in soil and their biological effectiveness,in order to understand the environment behavior and risk assessment of heavy metals in soil in farmland wetland.Samples were collected around the in the wetland from returning farmland within various periods in Caizi lake,Anhui province.Measure and analyze the contents and available contents of Cu,Mn,Pb,N i,Zn in different returning farmland wetland soil.Combined with the soil physical and chemical properties in the study area,analysis heavy metal sources and influencing factors in the wetland.Based on the total amount and available contents of heavy metals,evaluation was carried out the heavy metal pollution on the wetland soil.The main conclusions are obtained as follows:(1)The content range of C u,N i,Mn,Pb,Zn in study area soil were 14.96-39.29,12.33-27.84,179.66-678.30,5.14-34.63,17.22-260.58mg?kg-1,and the average contents of Cu,N i,Mn,Pb and Zn are 25.39,20.46,408.53,22.96,89.12 mg?kg-1.Cu,Ni and Zn more than soil background value,but Mn and Pb is slightly lower than soil background value.The over standard rate in five kinds of heavy metals,C u(69.23%)and N i(56.52%)and Mn(42.39%)and Pb(38.04%)and Zn(35.71%).This suggests that the study area had a certain degree of accumulation of C u and N i in soil.The most of heavy metals in study area were lower than the national secondary standard soil.This suggests that the pollution degree of heavy metals in study area were low.(2)The content of heavy metals were different in soil under returning farmland within various periods.In terms of surface,the content of C u,Mn,N i and Znhad growth trend in returning farmland within 3,7,11,21 years.In the second surface soil,the content of Mn,N i and Zn were increased in returning farmland within 3,7,11 years,the content of Pb and Cu were decreased in the returning farmland within 11,21 years.Compared with soil background values in Anqing.The content of N i,Pb,Mn,Zn in returning farmland within 3 and 7 years were lower than the soil background value,and the same trend for the content of C u,N i,Mn,Zn in returning farmland within 11 and 21 years.The content of heavy metals except for Pb have higher than the soil background value in returning farmland within 21 years.In general,the content of C u,N i,Mn and Zn have accumulation in returning farmland within 11 and 21 years,but the content of heavy metals have lower accumulation in the oilseed field.(3)The available content of C u,N i,Mn,Pb and Zn were evaluated by toxicity characteristic leaching procedure(TCLP),and the average available content of C u,N i,Mn,Pb and Zn were 0.32?0.65?97.11?0.22?6.37 mg·kg-1.The average ratio of available content account for the total of Cu,N i,Mn,Pb and Zn were 1.31%?3.05%?23.29%?1.04%?9.80%.The percentage of extraction available content of C u,N i and Zn have decline in returning farmland within periods for 3 to 11 years.It is not significant change that the percentage of extraction available content of C u in second surface soil,but decline of Pb,the percentage of extraction available content of N i and Mn had change trend is "N " type.The percentage of extraction available content of Zn was decline and then increased in gradually.The percentage of extraction available content of Zn,N i and Pb were the highest in the returning farmland within periods for 21 and 3 years,the value were 4.90%,16.53%,2.15%.(4)Using the method of principal component and correlation analysis between the heavy metals.The result showed that C u,Mn,N i,Pb and Zn were significant or extremely significant correlation,so these heavy metals have the same source in the study area.According to the situation of the study area,agricultural activity is the main source of soil heavy metals in the study area.Poultry feed additive,livestock waste,pesticide and fertilizer activities were a major source of farmland soil.(5)Nemerow index method evaluate the conversion of heavy metal total quantity risk assessment in wetland soil.The result showed that therisk index of C u,Pb,Zn was increase couple with the increasing returning periods,and the risk ratings are beyond?grade level.The risk index of N i was increase in the returning farmland within periods for 3,7,11 year,the risk ratings is II grade level;and decline in 21 year.Overall,the risk ratings of single heavy metal was I or II grade level,the pollution degree was low in generally.The pollution index of heavy metals was increase with the returning farmland within periods.The pollution index of heavy metals was increase in the returning farmland within periods for 3,11 year,but was decline in the re turning farmland within periods for 11,21 year.The pollution index of heavy metals in the oilseed field was higher than the returning farmland within periods for 3 year,but lower than in other sample plots.The pollution index of heavy metals was highest in the oilseed field.O verall,the pollution index of heavy metals was low,the risk ratings of single heavy metal was II grade level,it belong to low degree of pollution,but it is worth attention.(6)Risk assessment code(RAC)was applied to investigate risk assessment form the content of available heavy metal.The risk index of available C u was decline in the returning farmland within 3,7 and 11 years,the risk ratings were lower risk.The risk index of available Mn was increase in the returning farmla nd within 3,7 years,and decline in 7 and 11 years,but increase in 21 year.The risk index of available N i was decline in the returning farmland within 3,7 and 11 years,and increase in the 21 years.The risk index of available Pb decline with increase in the returning farmland withinperiods.The risk index of Zn was the highest in the returning farmland within 3 year,and decline in the 7 and 11 years,and the lowest in the 21 year,the risk rating was middle risk level in the returning farmland within 7 year. |
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