Bacterial community response to petroleum contamination in brackish tidal marsh sediments in the Yangtze River Estuary, China

The brackish tidal marsh in the Baimaosha area of the Yangtze River Estuary was severely contaminated by 400 tons of heavy crude petroleum from a tanker that sank in December 2012.The spill accident led to severe environmental damage owing to its high toxicity,persistence and wide distribution.Microbial communities play vital roles in petroleum degradation in marsh sediments.Therefore,taxonomic analysis,high-throughput sequencing and 16 S rRNA functional prediction were used to analyze the structure and function of microbial communities among uncontaminated(CK),lightly polluted(LP),heavily polluted(HP),and treated(TD)sediments.The bacterial communities responded with increased richness and decreased diversity when exposed to petroleum contamination.The dominant class changed from Deltaproteobacteria to Gammaproteobacteria after petroleum contamination.The phylum Firmicutes increased dramatically in oil-enriched sediment by 75.78%,346.19%and 267.26%in LP,HP and TD,respectively.One of the suspected oil-degrading genera,Dechloromonas,increased the most in oil-contaminated sediment,by 540.54%,711.27%and 656.78%in LP,HP and TD,respectively.Spore protease,quinate dehydrogenase(quinone)and glutathione-independent formaldehyde dehydrogenase,three types of identified enzymes,increased enormously with the increasing petroleum concentration.In conclusion,petroleum contamination altered the community composition and microorganism structure,and promoted some bacteria to produce the corresponding degrading enzymes.Additionally,the suspected petroleum-degrading genera should be considered when restoring oil-contaminated sediment.

Dynamics of arsenic in salt marsh sediments from Dongtan wetland of the Yangtze River estuary,China

The mobility and transformation of arsenic （As） in salt marsh sediments were investigated in Dongtan wetland of the Yangtze River estuary, China. As in surface water, pore water and the rhizosphere sediments were quantified. The microcosm incubation experiments were conducted during the flooding of the sediments to examine As dynamics that occurred during changing redox conditions. The concentrations of dissolved As in pore water （0.04--0.95 ixmol/L） were significantly greater than that in surface water （0.03-0.06 lunol/L）. Under anoxic conditions, the reactive As could be initially mobilized by the reductive dissolution of Fe（III） （hydr）oxides. Subsequently, most of the dissolved As was likely to be associated with secondary iron （hydr）oxide phases and remained in solid phases. The seasonal variability of acid volatile sulfide concentrations suggest the anoxic conditions are enhanced during summer by Spartina alterniflora compared to Phragmites australis and Scirpus mariqueter, causing a notable increase in As mobility. Generally, there was a typical variation in redox conditions with season in salt marsh sediments of Dongtan wetland, in which the dynamics of As mobility and transformation possibly were controlled by iron, and all of this could be significantly influenced by the rapid spread of S. alterniflora.