The Effects Of Rice Straw Biochar On The Leachability Of Heavy Metals And Indigenous Microbial Community In Sediment

Biochar is a not fully carbonized product produced by pyrolysis of biomass(such as crop residues,manure and organic waste)under oxygen-limited condition.Besides,it can promote nutrient availability and increase carbon sequestration as well as soil fertility.Thus,biochar has been universally applied in soil amendment.Besides,its utility in the remediation of heavy metal pollutions in water,soil and sediment is being increasingly considered due to its large surface area,complex porosity and variable surface composition.However,the effects of biochar on sediment microbes were still unknown.In this paper,the research included the following three parts.The first part studied the effect of rice straw biochar on physicochemical properties and heavy metals.The results showed that after incubated with biochar,the increases in pH value and organic matter content were observed.The application of biochar notably decreased the mobility of heavy metals,especially in treatment with high concentration level of biochar.After 90 days of incubation,the TCLP extractable Zn was decreased by 21%when treated with 5%biochar.Similarly,a reduction was also found in extractable fraction of Cd by 13.1%compared with that of the control.The second part studied the effect of rice straw biochar on the activity of urease,invertase and alkaline phosphatase.The results showed that the changes of the activity of urease,invertase and alkaline phosphatase were different which were related to biochar concentration.The activity of urease kept stable during the whole experimental period except day 7 when the concentration of biochar was 1%.But significant increases were found when biochar concentration was up to 5%,and the activity of urease peaked on day 90.On the contrary,the activity of invertase was decreased when treated with biochar along the whole experimental period especially in treatment with high concentration level of biochar.The activity of alkaline phosphatase keep stable after day 45 and it increased when sediments were treated with 1%biochar.However,when the concentration of biochar was up to 5%,the activity of alkaline phosphatase was decreased.There were significant negative correlation between pH and the activity of invertase.The third part investigated the changes of microbial abundances and bacterial community structure in sediment by molecular biology.The results showed that when sediments were treated with 1%biochar,the bacterial and fungal gene copies were increased compared with that of control.On the contrary,significant reductions were found in the abundances of bacteria and fungi when the concentration of biochar was increased to 5%.Changes in relative intensities were observed in main bands under different concentration level of biochar treatment.These indicated that the microbial community succession occurred and some species of bacteria responded differently compared with that of the control.The relative intensities of dominate bacterial species were decreased upon high concentration level of biochar application which was in accordance with the decrease in bacterial gene copies.The results of redundancy analysis indicated that environmental parameters(pH,organic matter,extractable fraction of Cd and Zn)could explain almost 92%of the total sediment microbial community variation and they could affect bacterial community.