| The contents of five kinds of heavy metals(Cu,Zn,Ni,Cd,Pb) in the soil and corn from Minle, Ganzhou, Linze, Gaotai of Zhangye city in the middle reaches of Heihe River’s farmlands were studied in this paper. By using traditional statistics, geostatistics and GIS, the statistical characteristics, migration and enrichment features, spatial variable structure and spatial distribution of the contents of heavy metals in soil and corn in the study area were analyzed.The results prove that:(1)The average content of heavy metals in soil in the study area ordered in Zn> Ni> Cu> Pb> Cd, which all exceeded the average content of background values in oasis soil, indicating that the soil in the study area has been polluted by Zn, Ni, Cu, Pb, Cd in different degrees. The spatial distribution of content(Cu, Zn, Ni, Cd) in the study area shows a trend that decrease from the middle to the northwest and the southeast sides, and the content of the northwest is higher than that of the southeast in the overall. The distribution of Pb’s content in soil in the study area is not obvious, its higher content is mainly concentrated in the central region of Ganzhou. Research shows that the spatial distribution of heavy metals’ content(Cu, Zn, Ni, Cd) is influenced by both structural factors such as soil texture and pH of soil and random factors such as a large number of long-term unreasonable use of fertilizers; however, the spatial distribution of Pb’s content is mainly affected by random factors such as exhaust pollution generated by road transport.(2)The average values of the cumulative pollution index of soil(Cu, Zn, Ni, Cd, Pb) are more than1, indicating that soil pollution has appeared in the study area; The average values of the single factor pollution index of soil(Cu, Zn, Ni, Cd, Pb) are less than1, indicating that accumulation of heavy metals in the study area has not been a threat to agricultural production and human health in the overall; The average value of Nemero index of soil in the study area is0.68, the max value is0.96, which indicates that the heavy metal content in soil in the study area is still in the clean range and the quality status of the soil environment is good.(3) The average content of heavy metals in corn root in the study area ordered in Zn> Ni> Cu> Pb> Cd, while the average content of heavy metals in corn seed in the study area ordered in Zn> Cu> Ni> Pb> Cd. The spatial distribution of Cu’s content in corn root shows a trend that decrease from the northwest to the southeast; The spatial distribution of content(Zn, Ni, Cd, Pb) in corn root shows a trend that decrease from the southeast to the northwest. The spatial distributions of heavy metals’ content in corn root are different from that in soil except for Cu, indicating that the accumulation of heavy metals in corn root is affected by not only the full amount of heavy metals in soil but also other factors such as soil type, available forms of heavy metals in soil, organic matter, pH value of soil and so on. The spatial distribution of Cu’s content in corn seed shows a trend that decrease from the northwest to the southeast; The spatial distribution of content(Zn, Ni, Cd, Pb) in corn seed shows a trend that decrease from the southeast to the northwest, which means that the heavy metals’ content in corn seed is influenced by that in corn root in a great extent.(4) The average values of the single factor pollution index of corn seed(Cu, Zn, Ni, Cd, Pb) are less than1and the The average value of Nemero index of corn seed in the study area is less than0.5, which means the quality of corn in the study area is good and there is no risk of heavy metals pollution.(5)The highest enrichment coefficient in corn of absorbing heavy metals from the soil is Zn while the lowest is Pb, and the enrichment coefficient of com root is higher than that of corn seed. The average value of enrichment coefficient in corn root in the study area ordered in Zn> Ni> Cu> Cd> Pb, while those in com seed is Zn> Cu> Ni> Cd> Pb. The average value of migration coefficient in corn in the study area ordered in Zn> Cu> Pb> Cd> Ni, indicating that Zn and Cu are easier to transfer from the root to the seed as they are the essential elements for plants. |
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