Studies On The Relationship Between Heavy Metals And Soil Physicochemical Properties And Wetland Soil Microbial Biomass And Bacterial Community Structure

As one of the most important ecosystems in the world,wetland plays significant roles in nutrients?carbon,nitrogen and phosphorous?retaining and cycling.However,with the increase of population,agricultural fertilizer leaching and industrial wastewater discharging,wetland ecosystem has been strongly influenced by heavy metals?HM?.The contamination of HM in wetland soil has attracted much attention due to their persistence,toxicity and non-biodegradable properties.In addition,microorganisms are recognized as indicators of disturbance in soil ecosystem since they are far more sensitive than macro-organisms to environmental stress,it can reveal the disturbance in soil environment as early as possible.EDT wetland,troubled by HM contamination was selected to study the effect of HM on wetland soil microorganisms.Soil samples were collected in March 2014 from three different areas?Caisang Lake,CS;Junshan Island,JS;LuJiao Port,LJ?.These three areas can be classified as?1?protected area?CS?;?2?area affected heavily by human?JS?and?3?area affected heavily by industries?LJ?.The main objectives of the study were:?1?investigating the HM contamination risk of soil in EDT wetland;?2?identifying the effects of HM and soil physicochemical properties on soil microorganisms and prioritize some parameters that contributed significantly to soil microbial biomass?SMB?and bacterial community structure.Geo-accumulation index(I_geo)is a geochemical criterion was used to evaluate HM pollution in soil,the I_geo showed that the areas investigated were strongly polluted by only Cd.One way analysis of variance?ANOVA?was carried out to compare the values among soil samples from different areas.The MC of soil in CS and LJ showed a significant difference?p<0.05?.There was no significant difference between the MC of JS and the other samples.SOM in JS and LJ did not show a significant difference,whereas the SOM in CS showed a significant difference?p<0.05?between the other samples.The concentration of Cd and Pb showed significant difference?p<0.05?and decreased as follows:LJ>JS>CS.Cr in soil samples from LJ was much?p<0.05?higher than that from CS and JS,the Cr in soil from CS and JS did not show significant difference.Soil texture?clay?,pH and Cu did not show significant?p<0.05?differences in the three areas.Pearson's correlation coefficients between the parameters indicted that clay,MC and soil organic matter SOM showed positive correlations between each other.There was a significant?p<0.01?positive correlation between the MC and the SOM.The correlation analysis also demonstrated a significant?p<0.01?correlation between clay and MC.Besides,Cd and Cr,Cd and Pb also showed significant?p<0.01?correlations.SMB from the three areas showed some change,ranging from the minimum 217.15mg/kg to the maximum 291.49 mg/kg.The SMB of CS was much higher?p<0.05?than that of LJ.And there was no significant difference between the SMB of JS and either of the other samples.Clay?p<0.05?,MC?p<0.01?and SOM?p<0.05?were positively correlated with SMB.SMB was negatively correlated with Cd?p<0.05?,Cr?p<0.05?and Pb?p<0.05?.There was no significant difference in number of bands in the three areas.The Shannon–Weiner diversity index?H?suggested that there was a significant difference between CS and LJ,but there was no significant difference between the H of JS and either of the other samples.The RDA showed all eight parameters explained 74.9%of the variation in the bacterial DGGE profiles.Cr,Cd,Pb and Cu together explained 43.4%of the variation in bacterial community structure,whereas Cr solely explained 19.4%?p<0.05?and Cd explained 17.5%?p<0.05?,which implied that Cr and Cd were the major factors related to the change in bacterial community structure.