Distribution Characteristics And Ecological Risk Assessment Of Heavy Metals In The Sediments And Soils Of Caohai Lake In Guizhou Province

Sediments and soils are both the acceptors of heavy metal contaminants and potential secondary sources of pollution.Heavy metals are characterized by strong bio-toxicity,refractory degradation,concealment,and long period.Heavy metal pollution in sediments and soils has become increasingly serious,which rise to a worldwide ecological environment,and has become a research hot-spot in the fields of Ecology,Soil science,Environmental science,Wetland science,and Marine science.Caohai lake in Guizhou province belongs to a national nature reserve.It is the highest altitude natural freshwater lake in Guizhou and a complete and typical plateau wetland ecosystem.Caohai lake is strongly interfered with by human activities,and the fragile nature of the wetland ecosystem is not conducive to regional ecosystem balance and social sustainable development.Therefore,the study on the distribution of heavy metal contents and potential ecological risk assessment of the sediments and soils in Caohai Lake can provide important reference for water quality monitoring,sustainable agricultural development and prevention of heavy metal pollution in the region and its downstream.This study on the current status of soil and agricultural fertilization in Caohai wetland ecosystem,and collected the sediments and soils from the marsh lands,irrigated lands,wood lands and vegetable lands of Caohai Lake,respectively.By using inductively coupled plasma emission spectrometer and dual-channel atomic fluorescence spectrometer,the heavy metal elements in lake sediments and soils were analyzed.Among them,the evaluation of the status of heavy metal pollution in the lake sediments by the cumulative index method and the enrichment factor method,while the heavy metals in the soils are applied by the single factor index method and the Nemerow comprehensive pollution index method,but the ecological risk assessment of the two by Potential ecological risk assessment.The results are mainly as follows.(1)It was found through the investigation that the soil types of wood lands,marsh lands,irrigated lands and vegetable lands are different in the Caohai Nature Reserve.The forest soils has yellow brown soils,lime soils and stony soils.The marsh soils are marsh soils and peat swamp soils.The irrigated lands and vegetable soils are gray foam soils,large soils mud and sea muds.The fertilization types have organic fertilizers and inorganic fertilizers,wherein the organic fertilizers are pig manure,chicken and other livestock manure,and the inorganic fertilizers include urea,potassium fertilizer,superphsphate.The combination of organic fertilizers and inorganic fertilizers are used as the base fertilizer,and the urea in the inorganic fertilizers are used as the main fertilizer.(2)The average content of heavy metals in surface sediments from 0 to10 cm of Caohai Lake is Fe,Zn,V,Cr,Pb,Ni,Cu,As and Cd from high to low,which is 31412.0±10163.8,219.2±134.8,59.8±19.2,56.2±18.7,54.0±25.9,33.6±10.7,20.4±5.4,15.4±4.4 and 0.8±0.6 mg/kg,respectively.Among them,the Cd content is higher than the standard limit of 0.2 mg/kg of the soil environmental quality standard(i.e.GB15618-1995).The contents of Cd,Zn and Pb were higher than the average contents of the three heavy metals in the sediments of the five provinces of Southwest China,which is 0.59,24.01 and 132.18 mg/kg,respectively.They were highly variable and the spatial distribution was discrete.The spatial distribution of the contents of Fe,Cr,V,As,Cu,Ni is relatively uniform.In the vertical from 0 to 25 cm,the contents of 9 heavy metals in lake sediments decreased with the increase of profile depth.The contents of Pb,Cu,V and Ni were mainly wave type,and the contents of Zn,Cd and As were mainly stable,but the Cr and Fe contents are enriched.According to the evaluation of the accumulation index and enrichment coefficient,the heavy metals of Zn and Pb in the sediments of the Caohai Lake are moderately polluted,while Cd is moderately polluted and mainly contributed by Cd,Zn and Pb elements by human activities.However.Cd is the main potential ecological risk contribution factor by the potential ecological risk assessment in the sediments of Caohai Lake.The potential ecological risk of heavy metals in the sediments of downstream is higher than that in the upstream and middle reaches.The heavy metals in the sediments of downstream lakes have reached the medium potential ecological risk hazard,while the heavy metals in the sediments of the middle and upper reaches to the slight ecological risk.(3)The average content of heavy metals in the surface soils from 0 to 20 cm of four land use types in Caohai lake is Zn,Cr,Ni,Pb,Cu and As from high to low.The heavy metal content of each soil is lower than the limit of Grade II standard of Soil Environmental Quality Standard(GB15618-1995),but the heavy metals in the four soils,such as Zn,As,Pb and Ni,higher than the background values of soil heavy metals in Guizhou Province.Zn,Cr and Ni in the soils of the vegetable lands were moderately distributed,and the contents obeyed the normal distribution.Cu was moderately variable,and As and Pb were highly variable,and the contents obeyed the normal distribution.According to the potential ecological risk assessment,the potential ecological risk index of marsh lands,irrigated lands and wood lands are both 35 and 40,and the vegetable lands plot is 23.97,which is less than the limit of 150 for the potential ecological risk.It can be seen that the potential ecological risk hazards of heavy metals in the four use modes of marsh lands,irrigated lands,wood lands and vegetable lands are in a slight ecological hazard.In summary,the heavy metals of Cd,Zn,Pb and the heavy metals of Zn,As,Pb and Ni in the sediments of Caohai Lake are relatively high,which is closely related to the activities of indigenous zinc smelting in this area.while the ecological risk is slightly ecologically harmful.The degree should be paid attention by the goverment,and it is intended to provide reference for the prevention and control of heavy metal pollution,ecological environmental protection work,and avoiding regional diseases caused by the heavy metal pollution in Caohai.