| Eucalyptus is strategic short-rotation timber species in south China,with large-scale planting in recent years,the high strength of predatory operation on the local biodiversity,water environment and ecological environment had an impact,such as soil fertility,then can bring the environmental pollution of the soil is more and more attention,it is considered as a way to reduce negative effects and ecological afforestation.In this paper,the effects of heavy metal pollution on soil environmental quality and potential ecological risks were studied by evaluating the impact of heavy metal pollution on the fourth generation eucalyptus plantation planted in state-owned dagui mountain forest farm in guangxi.Eucalyptus plantation was set up for mountain burning and free mountain burning.Three groups of sample plots were set with evergreen broad-leaved forest as the control,and three standard plots were set for each group.Samples were collected before treatment,one month after treatment and three times a year to determine 8 heavy metals in soil,2 physical properties and 6 chemical properties,a total of 16 indicators.Two-factor analysis of variance,correlation analysis,typical correlation analysis,single-factor,multi-factor pollution index method and potential ecological hazard index method were used to evaluate heavy metal pollution.The main research results are as follows:(1)In the test ground,Hg,Ni,Zn and Cr were distributed unevenly,and the natural background value of Cd exceeded the standard.Before the treatment of eucalyptus plantation,the coefficient of variation of Hg and Ni was large,and the content of Cd exceeded the standard.One month after treatment,the variation coefficients of Hg,Ni,Zn and Cr were large,and the contents of Cu and Cd exceeded the standard.One year after treatment,the coefficient of variation of Hg element was large,and the content of Cd exceeded the standard.In the evergreen broad-leaved forest control group,the variation coefficient of Hg and Zn was large,and the content of Cd exceeded the standard.(2)In addition to heavy metal Cd,different treatment types produced significant differences for the other 7 elements,while except for Hg,As,Cd and Pb,different treatment times produced significant differences for the other 4 heavy metals.Hg,As,Pb elements may be introduced into the soil through management measures such As artificial forest fertilization and pesticide,while the natural background value of Cd exceeds the standard.Among the 8 indexes,except for Hg and As,the content of the other 6 indexes was the highest in the soil one month after the experimental treatment,while the content of Ni,Zn,Cd and Pb in the soil before the experimental treatment was the least,and the content of Cr and Cu in the soil of evergreen broad-leaved forest was the least.Moreover,one year after the treatment,the Cr content in the soil decreased by 50%and 22%respectively.The Ni content in the soil decreased by 64%and 32%respectively.The content of Cu in the soil decreased by 46%and 39%respectively.In the soil,the content of Zn in mountain-burning treatment decreased by 49%,and that in mountain-burning treatment decreased by 17%,while the content of Hg,As,Cd and Pb were the same.(3)According to the correlation of heavy metal contents in different types of soil under the same environment,the main sources of heavy metals Cu,Hg,As and Zn in no-smelting mountain area may be caused by the input of herbicides and pesticides in plantation management.Cu and Cr are the most influential environmental factors after mountain burning treatment,which are significantly correlated with soil mass water content and pH in physical and chemical properties.The key environmental factors were Cr,Ni,Cu,Zn and As,which were significantly correlated with soil mass water content,organic matter,total nitrogen and available potassium.The correlation between heavy metals in soil was more significant in the no-burning mountain than in the no-burning mountain.In the no-burning area,except for Hg,there was a significant correlation between the other 7 elements,while there was no significant correlation between the heavy metal contents except for the highly significant positive correlation between the contents of Ni and Cr and between the contents of Cd and Pb.(4)The different treatment methods in the test site changed the soil chemical and biological properties,and finally resulted in different adsorption and accumulation effects of heavy metals.The overall soil environmental quality in the no-burning area was better than that in the no-burning area after one month and one year of treatment.Based on the evaluation of multi-factor index,it is concluded that the grade Ⅲ of no-burning mountain exceeds the standard,and the grade Ⅳ of burning mountain is Ⅳ.Compared with one month after treatment,the grade of no-burning mountain does not change in one year after treatment,and the percentage of points exceeding the standard is reduced.The proportion of no-burning mountain that exceeded the standard was reduced from 25%to 12.5%,and that of no shan shan was reduced from 75%to 37.5%.According to the cumulative evaluation of multi-factor index,the cumulative grade of both the no-burning mountain and the no-burning mountain area is level Ⅱ.Compared with one month after the treatment,and one year after the treatment of the test site,the cumulative grade does not change.A fter the treatment of the no-burning mountain,the proportion of the cumulative point level significantly decreases from 87.5%to 75%.After one year of treatment,the proportion of As and Zn in the soil in the no-smelting area was 100%in class Ⅰ,and the proportions of Hg,Cr,Ni,Cu and Pb5 were 66.7%,88.9%,33.3%,100%and 77.8%in class Ⅱ,respectively.Only the proportion of Cd was 88.9%in class Ⅳ.In the soil of the mountain burning area,except for the proportion of As and Zn,which belongs to class Ⅰ,44.4%,100%and 44.4%of Hg,Cr and Ni belong to class Ⅱ,and 11.1%,88.9%and 11.1%of Cu,Cd and Pb belong to class Ⅳ.(5)The potential ecological risks in the test site were mainly caused by Hg and Cd,and the potential ecological risks of the other six heavy metals were all at a slight level,which could not pose an ecological threat to the soil of eucalyptus plantation.And after one year of treatment,the total ecological risk and harm degree of the no-burning area was better than that of the no-burning area.Hg pollution may be caused by mercury compounds from fertilization and weeding entering the soil environment or due to their strong geochemical activity.Therefore,large geochemical variation is likely to occur in the surface soil environment.The reason for the risk of ecological damage to Cd is mainly due to the high natural background value. |
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