Effects of environmental factors on release amount of heavy metal and structure of microbial community in sediments

In this study, the effects of environmental factors including overlying water flow rate and solution pH on heavy metal release and microbial community structure were investigated. Five sediments were collected from the Xiangjiang River to measure heavy metal concentrations and evaluate the contamination status. The average concentrations of As and Cd in the sediments were higher than the standard value, and the contamination status of the sediments stood at a very high ecological hazards level. A pollutant release device was used to study the effects of overlying water flow rate and solution pH on heavy metal release. Results revealed that the heavy metal release amount increased with the increase of flow rate and decrease of solution pH values, while the process of heavy metal release from sediment to water is long and slow, and the maximum amount of Mn was only 7.50 μg/(g·d). Moreover, high-throughput sequencing technology was used in this study to investigate the microbial community diversity of collected sediments and experimental samples. Proteobacteria, Firmicutes, Actinobacteria, Chloroflexi, Bacteroidetes, Acidobacteria and Nitrospirae were the main species for all samples. With the increasing of the flow rates, relative abundances of Proteobacteria and Bacteroidetes gradually increased, while it formed uniformly negative associations with other microbial communities. When the solution pH increased from 6.0 to 9.0, it had a negative effect on the diversity of Proteobacteria and positive effect on other microorganisms. This research provides theoretical basis and microbiological data for in situ remediation of heavy metal-contaminated sediments in the future.