| In order to deeply understanding the pollution status and vertical distribution characteristics of heavy metals in the major farmland soils of Henan province,the migration and enrichment characteristics of heavy metal elements in the vertical direction were analyzed.In this paper,12 soil profiles and 340 samples were collected from two typical tidal soils in Xinxiang Sizhuangding and Kaifeng Huafei River with high density sampling study,and 6 soil profiles were collected in each sewage irrigation area.ICP-AES was used for the determination of Co,Ni,Pb,Cd,Cr,Cu,V and Zn eight kinds of heavy metal content,The chemical forms,physical and chemical properties of heavy metal elements were also analyzed.And vertical changing characteristics of the potential ecological risk of Xinxiang Sizhuangding and Kaifeng Huafei River of the farmland soil heavy metal pollution was analyzed based on improved Hakanson potential ecological risk index method in the evaluation.Primary studies showed:(1)Different sections of heavy metal pollution conditions are different,except V xinxiang sewage irrigation area of each section on other elements have been varying degrees of pollution on the average.Co,Pb,Cd,Cr,Cu,Zn and other elements are polluted in different degrees except that Ni and V are not polluted in Kaifeng sewage irrigation area of each section.The content of Ni in the soil of Xinxiang sewage irrigation area was higher than that of Kaifeng sewage irrigation area,while the contents of heavy metals Cd,Cr and Zn were significantly higher in Kaifeng sewage irrigation area.The coefficient of variation of Cd in the cross section of sewage was the largest.(2)The overall variation characteristics of heavy metals in Xinxiang sewage irrigation area are similar,Ni down from the surface of a smaller range,Cd has obvious phenotypic phenomenon,and the content of 0 ~ 30 cm decreases rapidly,and the content of 30 cm below In the stability,the change is small.Co,Pb,Cr,V,Cu,Zn and other elements have a tendency to decrease as a whole,but the variation range is larger in each layer.(3)The heavy metal Co of the soil profile in Kaifeng Sewage Irrigation Area showed a downward trend from the surface,and the fluctuation range was larger in each section.Ni and V are not significantly changing trend,in the profile of a significant roundabout fluctuations.Pb,Cr,Cd,Cu and Zn have obvious phenolic phenomenon in each section,the content of soil in the upper layer is higher,the soil content in the middle and lower layers is lower,on the whole can be reduced within 0 ~ 30 cm,30 cm below the smaller range.(4)The enrichment and migration of heavy metals in the soil profile is not only related to the parent material,but also has a great correlation with sewage irrigation and tillage.Co is easy to accumulate in the upper layer of 0 ~ 35 cm,the migration degree is weak.Ni in Xinxiang and Kaifeng sewage irrigation areas are obviously different.The Ni in Xinxiang sewage irrigation area is obviously enriched in the upper layer,and the depth of migration is mainly concentrated in the upper section of the section,and there is no obvious migration in the whole section of Kaifeng irrigation area.The enrichment depth of Pb,Cu and Zn is consistent with the enrichment depth in the two sewage irrigation sections,and the enrichment depth is more than 40 cm,but the depth of migration is different.Cd migration and enrichment in Xinxiang.Kaifeng irrigation and sewage irrigation area,were more than 20 cm were obviously enriched,migration depth can reach 30 cm.and two Cr in the sewage irrigation area in the upper layer of soil profile were enriched,below 40 cm enrichment is not obvious.(5)The distribution of heavy metals on the profile.The whole sewage irrigation area of Xinxiang Co distribution of residual > exchangeable> iron and manganese> organic state> carbonate state,The Kaifeng sewage irrigation area of each section of Co exists mainly in exchangeable form and residual form,was significantly higher than that of Xinxiang sewage irrigation area of each section can be the proportion of exchangeable,residual in the upper soil showed lower content of each section in the upper soil bioavailability and migration capacity is higher.The Pb in each section of the two sewage irrigation areas is mainly in the form of residual state,followed by the iron and manganese oxidation state and organic state,exchangeable and carbonate state content is low.Cr in the Xinxiang sewage irrigation area and Kaifeng sewage irrigation area on the surface of the general performance of the residual state> organic state> iron and manganese oxidation> exchangeable> carbonate state.The proportion of interchangeable cases in Kaifeng sewage irrigation area was significantly higher than that in Xinxiang sewage irrigation area.Carbonate Cr in the layers of considerable content,other forms have different degrees of difference.Cd residues in the proportion of about 50%,significantly lower than other heavy metal elements.The Cd content in the upper and lower layers of Xinxiang sewage irrigation area and Kaifeng sewage irrigation area is the lowest in the upper soil,and the exchangeable Cd has the highest content in the upper soil,carbonate state,organic state,iron and manganese oxidation state Cd in two sewage irrigation areas There is no uniform law.The distribution of Zn in the soil profile of the two sewage irrigations was the same as that of the upper soil.The results showed that the distribution of Zn in the soil was the lowest in the soil.(6)Cd is the most important ecological risk factor of two sewage irrigation areas.Xinxiang sewage irrigation area in different soil layers of Cd with strong risk,other heavy metals Co,Ni,Pb,Cu,Cr,V,Zn are a slight risk.The Kaifeng sewage irrigation area Co,Cr,Ni,V,Zn are slight the risk of Cd in common.The potential ecological risk serious.Individual profiles such as QT1,PT3 in some samples Pb,Cu at moderate risk,the other is a slight risk.The potential ecological risk index of each sample point section has obvious surface aggregation phenomenon.Copying Hakanson classification standards will underestimate the potential ecological the risk index of heavy metals. |
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