Migration And Distribution Of Heavy Metals In Oxidation Pond Sediment And The Effects Of Heavy Metals On Microbial Diversity And Sediment Quality

In this study,we detected the concentrations of heavy metals Cr,Pb,Cd,Hg,Cu,Zn,Ni,As from the sediment in Qiqihar oxidation pond,and examined the regional characteristics of the distribution and pollution degree of these heavy metals in the sediment.And then,the study area was divided according to the concentration of heavy metals and working functionality in each processing units of Qiqihar oxidation pond(High,middle and low block).Physicochemical properties of sediment,sediment respiration,enzyme activity,sediment microbial quantity and microbial diversity were used to investigate the impact of major heavy metals on sediment environmental quality.Scores of sediment evaluation indices are weighted according to multivariate statistical analysis which are used to comprehensive evaluate sediment quality in different blocks.Our study will provide evaluation system of the environmental pollution of heavy metals in oxidation pond in order to provide scientific basis for ecological remediation of sediment and provide a reference for environmental restoration in this region.The research results are as follows:(1)The detection results showed that the concentrations of heavy metals in all sampling points form the oxidation pond were ranked in order from Zn > Cu > Cr > Pb > Ni > Cd > As > Hg,and the concentration of Cd significantly exceeded the control standard.According to the concentration of heavy metals and working functionality in each processing units,the study area was divided into high concentration block,medium concentration block and low concentration block.Correlation analysis results showed that the heavy metals Cd,Pb,and Cr had a very significant positive correlation,indicating that Cd,Pb,and Cr may have similar pollution sources and levels.The geoaccumulation index method was used to evaluate the pollution degree of heavy metals in different blocks.The results showed that the study area was polluted by heavy metal Cd,Pb,Hg,Cr,Cu and Zn.These heavy metals may cause sediment pollution and potential ecological risks.(2)Sediment pH in different blocks is all acidic.Sediment moisture content,and electrical conductivity decreased with the concentration of heavy metal increase.There were remarkable difference between three blocks.The concentration of organic matter decreased with the concentration of heavy metal increase.There were remarkable difference between low,middle block and high block.Nutrient characteristic in sediment such as total nitrogen,available nitrogen,total phosphorus,available phosphate,and available potassium decreased with the concentration of Cd increase.Likewise,sediment respiration and enzyme activity increase with the concentration of Cd decrease and the differences are significantly(P<0.05).Under the effect of special ecological environment and complex pollutants,sediment environmental quality gets worse increase with the concentration of heavy metal.(3)The order of microbial population in high,moderate and low concentration block is bacteria > actinobacteria > fungi.The total microorganisms in sediment decrease in proportion to the increase of heavy metal concentration.The microbial population in different concentration blocks was different with two domain strains in high and moderate block(Proteobacteria and Firmicutes),and one in low block(Proteobacteria).Furthermore,in each sample site,Proteobacteria was the most dominant flora according to GenBank database.The average microbial diversity index in high,moderate and low concentration block is 3.40,3.58 and 3.63.The average evenness index in high,moderate and low concentration block was 0.994,0.993 and 0.994.(4)The ? diversity index in low concentration block is significantly greater than the data in high concentration block.In contrast,the ? diversity index index in low concentration block is significantly smaller than the data in low concentration block.In all the sediment samples,Proteobacteria,Bacteriodetes,Firmicutes and Actinobacteria were the main category.Bacteriodetes and Firmicutes can grow and proliferate well in high concentration block.At the genus level,fusobacterium,Paludibacter,Trichococcus and Petrimonas had a strong adaptability for heavy metal pollution.GAOs,dechloromonas and Proteus Hauser widely exist in low block.The biomarkers of high concentration block were Bacteriodetes,Firmicutes,Clostridiales and clostridium difficile which indicates they can grow well in high concentration block.They have the potential for repairing sediment which was polluted by heavy metals.(5)The results is L>M>H after comprehensive sequencing of indicators which indicated heavy metals have significant effects on sediment quality.The quality of sediment in high concentration block deteriorates as the concentration of heavy metals higher.