A quantitative relationship that remonstrates mercury methylation rates inmarine sediments are based on the community composition and activity of sulfate-reducing bacteria

A quantitative framework was developed which estimates mercury methylation rates (MMR) in sediment cores based on measured sulfate reduction rates (SR R) and the community composition sulfate-reducing bacterial consortia. MMR and SRR as well as group-specific 16S rRNA concentrations (as quantified by probe signal) associated with sulfate-reducing bacteria (SRB) were measure d in triplicate cores of saltmarsh sediments. Utilizing previously document ed conversion factors in conjunction with field observations of sulfate red uction, MMR were calculated, and the results were compared to experimentall y derived measurements of MMR. Using our novel field data collected in salt marsh sediment where sulfate reduction activity is high, calculated and ind ependently measured MMR results were consistently within an order of magnit ude and displayed similar trends with sediment depth. In an estuarine sedim ent where sulfate reduction activity was low, calculated and observed MMR d iverged by greater than an order of magnitude, but again trends with depth were similar. We have expanded the small database generated to date on merc ury methylation in sulfur-rich marine sediments. The quantitative framework we have developed further elucidates the coupling of mercury methylation t o sulfate reduction by basing calculated rates of mercury methylation on th e activity and community composition of sulfate-reducing bacteria. The quan titative framework may also provide a promising alternative to the difficul t and hazardous determination of MMR using radiolabeled mercury.