Spatial Distribution Of Heavy Metals In Soils Of The Yellow River Delta And Their Effects On Soil Microbial Communities

In recent years,a series of environmental problems emerged along with the rapid development of both agriculture and industry,among them the pollution of heavy metals in soil attracts more and more attention and has already become one of the focus in the environmental scientific research.The main sources of the heavy metals pollution consist of the stack of solid waste,sewage irrigation,the use of farming materials and atmospheric sedimentation.It is very hard to be degraded by organisms after they entered soil environment,because heavy metals are persistent,elusive and convergent poisonous pollutant with low mobility and long retention time.The balance and the function of the ecosystem will be destroyed when the concentration of heavy metals in the soil surpasses the self-purification capacity of soil ecosystem.Furthermore,the heavy metals could be accumulated into organisms through the food chain to affect the human health.As crucial components of soil,microbial communities play an important role on the structure and the stability of the soil ecosystem.The heavy metals in soil can probably affect the structure and diversity of microbial communities.The results of study on effect of heavy metals in the soil on microbial communities can provide basis for the stability of the soil ecosystem or recovery of destroyed ecosystem.Study on the effect of content and distribution characteristics of six kinds of heavy metals on soil microorganism such as bacteria,fungus and actinomycetes were conducted in the soils in the core zone,buffer zone and the experimental zone of the national reserve of the Yellow River Delta wetland..The results are as follows.1.The result of comparing between the concentrations of heavy metals in the endosexine of the Yellow River Delta wetland and the environmental background value of the soil in Shandong Province showed that the concentrations of cadmium found in all the sampling points in the core zone,buffer zone and the experimental zone surpassed the background value,the concentrations of manganese were all lower than the background value,the concentrations of copper in sampling point No.4 were higher than the background value,the concentrations of lead and zinc in sampling point No.1,2 and 3 of the buffer zone,the content of copper in sampling point No.3and the content of chromium in sampling point No.1 were all higher than the background value.The result of analysis showed that the element of cadmium was the most severe heavy metal pollution in the Yellow River Delta wetland and the pollution of zinc,lead and copper ranked after it,there were no obvious accumulations of chromium and manganese.The result of correlation analysis showed that there was a extremely significant positive correlation betweenthe concentrations of the six different heavy metals and the concentrations of organic substance,total nitrogen and total phosphorus.2.There were insignificant differences among the heavy metals pollution in the core zone,buffer zone and the experimental zone of the Yellow River Delta wet land,only with a slight differences in the correlation between different heavy metals.As for horizontal distribution in the core zone,there were extreme significant positive correlations between the concentrations of cadmium and that of copper,lead and zinc,between the concentrations of copper and that of manganese,lead and zinc,between the concentrations of manganese and that of lead,zinc and chromium,between the concentrations of lead and that of zinc and chromium,and between the concentrations of zinc and that of chromium.And there was a significant positive correlation between the concentrations of cadmium and manganese.In the buffer zone,there were extremely significant positive correlations between cadmium and lead and zine,between copper and manganese,zinc and chromium,between lead and zinc and chromium,between zinc and chromium and manganese.There were significant positive correlations between the concentrations of cadmium and that of chromium,between the concentrations of manganese and that of lead and chromium.In the experimental zone,there were positive correlations between the concentrations of cadmium and that of lead,zinc and chromium,between the concentrations of copper and that of manganese,between the concentrations of zinc and that of cadmium,manganese,lead and chromium.According to the correlation analysis,there was no obvious regularity between the change of concentrations of heavy metals and the deepening of soil about the vertical distribution.Generally speaking,the concentrations of heavy metals presented surface cumulativity showing relatively high pollution in the surface of soil.In the core zone and the experimental zone,the fluctuation of the heavy metals concentrations are mild for the depth increases.In the buffer area,the fluctuation of the heavy metals concentrations presented high frequency volatility for the depth increases.3.The results of study on the effect of heavy metals in soil on the microbiological indicators and diversity of community showed that the concentrations of the six different heavy metals in soil had significant negative correlations with the microbial biomass carbon(MBC),microbial biomass nitrogen(MBN)and the microbial quotient which indicated that the microbial biomass decreased with the increase of the concentration of the heavy metals.The combined action of multiple heavy metals had a negative correlation with the enzymatic activity of urease,catalase,phosphatase and surcrase,and there was some inhibiting effect on the enzymatic activity which indicated that MBC,MBN,microbial quotient and enzymatic activity could reflect the the influence of heavy metals in soil to a certain extent.The contaminations of heavy metals in soilhave certain effect on the microbiological indicators and diversity of communities.They had inhibiting effect on the growth of communities.For instance,copper and chromium had considerable inhibiting effect on fungi and bacteria respectively.The relationship between the concentrations of heavy metals and the indicator of microbial diversity was not evident,which indicated that the number and diversity of microbial communities could not be used to indicate the degree of soil heavy metal pollution to some extent.