Distribution Characteristics And Ecological Risk Assessment Of Typical Heavy Metals In Surface Soil Of Nansi Lake Catchment

With the acceleration of urbanization,heavy metal pollution in soil caused by human activities has attracted extensive attention.Heavy metals in soil can enter the water environment through surface or underground runoff,which can cause potential harm to the water ecology and water environment in the catchment.In this paper,the Nansi Lake catchment was selected as the research area,6875 surface soil samples were collected from Jining,Zaozhuang and Heze.The content and distribution characteristics of mercury?Hg?,cadmium?Cd?,arsenic?As?,lead?Pb?and zinc?Zn?in surface soil were analyzed,and the pollution assessment was carried out.Finally,the possible sources of them were analyzed.This study provided the basic basis for water environment protection and management.The main research results are as follows:?1?The statistical contents of Hg,Cd,As,Pb and Zn in the surface soil of Nansi Lake catchment were analyzed.The results showed that the average contents of Hg,Cd,As and Zn in the surface soil were higher than the background values except Pb,which were 2.3,1.9,1.1 and 1.1 times of the background values,respectively.The enrichment degree of the five elements in the surface soil decreased in the following order:Hg>Cd>As>Zn>Pb.By comparing the difference coefficient of Hg,Cd,As,Pb and Zn,the difference coefficient of Hg,Cd and As were relatively large,especially that the difference coefficient of Hg was greater than 100%,while the difference coefficient of Pb and Zn was relatively small.?2?The distribution characteristics of Hg,Cd,As,Pb and Zn in the surface soil of Nansi Lake catchment were analyzed.The results showed that the spatial distribution characteristics of Cd and As were very similar.The contents of Cd and As in the surface soil of Heze city were significantly higher than those of Jining city and Zaozhuang city.The contents of Cd and As in the surface soil of lakeside area of Weishan lake in Yutai county were at the highest level in the whole catchment.The distribution of Pb content in the surface soil is relatively uniform.The Pb content in the surface soil of Heze city is slightly lower than that of Jining city and Zaozhuang city.The contents of Pb in the surface soil of lakeside area of Weishan lake in Yutai county were at the highest level in the whole catchment,while the Pb content in other areas is generally low.The Zn content in the surface soil of Jining,Zaozhuang and Heze is similar,and the Zn content in the surface soil of Weishan lake lakeside area is the highest in the whole catchment.The distribution of Hg in surface soil is very uneven.The Hg content in surface soil of Heze city is lower than that of Jining city and Zaozhuang city.The Hg content in surface soil of Jining provincial capital city?Jining?is the highest.?3?The effects of typical metal elements Hg,Cd,As,Pb and Zn on the ecological environment of NanSi Lake catchment were evaluated.The results showed that the average I_geoeo value of Hg and Cd was both 0.3 and the pollution level was 1.The average I_geoeo value of Pb,Zn and As was all less than zero,and the pollution level was 0.Pb,As and Zn contents showed a slightly pollution level,while showed a pollution-free level in most areas of the catchment.Contents of Cd and Hg showed a slightly pollution level in most areas,while showed a moderately pollution level in a few areas of the catchment.The potential ecological risks of Pb,Zn and As to the catchment are low,while Hg and CD in the surface soil of the catchment have higher ecological risks.Hg had moderate ecological risk in 59.5%of the sampling areas and strong ecological risk in 29.2%of the sampling areas.Cd had moderate ecological risk in 49.6%of the sampling areas and strong ecological risk in 7.6%of the sampling areas.There is a strong potential ecological risk especially in the west of Jining city and lakeside area of Nanyang Lake.?4?The possible sources of Hg,Cd,As,Pb and Zn in the surface soil of NanSi Lake catchment were analyzed.The results showed that Zn was probably from the diagenetic minerals,that is,natural sources.The Pb in surface soil may be a mixed source.The high contents of Cd and As in surface soil were mainly derived from agricultural activities,and the abundance of organic matter promoted the enrichment of Cd and As in surface soil.Hg in surface soil mainly comes from anthropogenic activities in the catchment,especially the industrial and civil coal burning.The distribution of Hg in surface soil in the catchment is closely related to the economic development.