| Soil is not only an important part of the ecosystem,but alsothe essential natural resource for agricultural production-Because of unsustainable social and economical development in the last several decades,soil pollution,especially pollution of heavy metals,is becoming a serious environmental and ecological problem.High concentrations of heavy metals can cause various types of harms to plants,animals and humans.Identifying the pollution sources of heavy metals in soil and apportioning their respective contributions are critical to mitigate soil heavy metal contamination.This dissertation investigated the distribution of 4 heavy metals(Cd,Pb,Cu and Zn)and other elements(B,Ca,Sn,and Sr)in Meishan Basin,Changxing County,Zhejiang Province,China.Principal component analysis(PCA)and spatial analysis were employed to identify the potential sources of the heavy metals and elements.Bulk soil samples were collected from the profiles at the sites close to the potential sources to determine the pollutant contribution.Lead stable isotopes were used to identify the samples' lead sources.Positive Matrix Factorization(PMF)was used to further apportion the sources.The results from PMF were compared with the soil profile data to test its accuracy.The following are the key findings from this research:(1)The mean concentration of Cd in the topsoil(0-20 cm)in Meishan Basin was 0.43 mg kg-1.Cd concentrations in 30.71%of the topsoil samples exceeded the National Soil Quality Type II limit.The finite mixture distribution model(FMDM)showed that 44.8%of the samples were not polluted by Cd,and the mean Cd concentration of the unpolluted soil samples was 0.145 mg kg-1,while 55.2%the soil sampels were classified as polluted by Cd with a mean Cd concentration of 0.66 mg kg-1.The mean concentrations of Pb,Cu and Zn of the soil samples were 39.93 mg kg-1,17.25 mg kg-1 and 63.42 mg kg-1,respectively.(2)The heavy metals showed distinctive spatial distribution characteristics.Higher Cd concentrations were observed in Qianjingwan region and on the northeast side of the basin.The highest Pb concentrations were obserbed on the northeast side of the basin.High concentrations of Cu and Zn,which showed similar spatial pattern,were found in the vasinities of coal mines in the study area.High soil pH values were observed in the middle of Meishan Basin,which was consistent with the spatial distribution of Ca.PCA was applied to track the sources of the pollutants.The four prinicpal components identified by PCA were interpreted as lead-acid battery plant,construction material related activities,coal mining related activities and soil parent material sources.Most soil samples around the 3 anthropogenic sources were classifies as Cd polluted by FMDM.(3)The concentrations of Cd,Pb,Cu,Zn,Ca in the topsoil(0-20 cm)were much higher than those in the subsoils below 40 cm taken from the vicinity of the potential pollutant sources.The higest concentrations of Cd and Pb were observed around the lead-acid battery plants,and Ca around the cement plants.Concentrations of elements and heavy metals varied with soil types.Thus,anthropogenic concentration of elements in the topsoil were calculated to compare the soures' impact on the soils.The result showed that the main pollution elements from lead-acid battery plants were Cd and Pb,from cement plants were Ca and Cd,from coal mining related activities were Cd,Cu,Pb and Zn,and from lime mining related activities were Ca.This result was consistent with PCA analysis.(4)We proposed to use fractional abundance to express the Pb isotopic composition for environmental Pb source apportionment.Due to the low varaiation of fractional abundance of 204Pb in terrestrial materials,the terrestrial Pb isotope fractional abundance data(204Pb,206Pb,207Pb and 208Pb,)fell nearly in a plane,which allows to plot the Pb isotope fractional abundance on a two-dimensional diagram.This lead isotopic composition diagram was no longer ambiguous when fractional abundance was used,and the source identification and apportionment results become more accurate and reliable.The lead isotopic composition indicated that the soil parent material accounted for 22.06-38.27 mg kg-1 of Pb in the soil samples from Meishan Basin.(5)Due to the outliers in the dataset,we failed to get a reasonable result by PMF.When the 8 abnormal values in the dataset were removed,the contributions of the elements and heavy metals from soil parent material were much lower than the respective concentrations in the subsoil of the same profiles,indicating that PMF underestimated the contributions of soil parent material.The underestimation might be attributed to the variation/heterogeneity of the sources profiles in the study area.The concentrations of the elements varied largely among different soil types,and it needed at least 4 factors to fit the concentrations data well.The source profile of the anthropogenic sources also varied greatly with sampling locations in the study area. |
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