Effect of Bioirrigation on Sediment−Water Exchange of Methylmercury in Boston Harbor, MassachusettsEnvironmental Science and Technology (2009)
Coastal marine sediments are important sites of methylmercury (MMHg) production, and dissolved efflux provides an important source of MMHg to near-shore, and possibly off-shore, water columns and food webs. We measured the flux of MMHg across the sediment−water interface at four stations in Boston Harbor that span a range of infaunal population densities and bioirrigation intensities. At each station we carried out total MMHg flux measurements using core incubations and collected near-surface pore waters to establish MMHg gradients for diffusive flux calculations. The flux cores were also imaged by CT scanning to determine the distribution of infaunal burrows, and pore−water sulfide and 222Rn profiles were measured. Total MMHg fluxes, measured using core incubations, ranged from −4 to 191 pmol m−2 d−1, and total MMHg fluxes were strongly correlated with burrow densities at the stations. Estimated diffusive fluxes, calculated based on MMHg concentration gradients below the sediment−water interface, were much lower than total fluxes at three of the stations, ranging from 2−19 pmol m−2 d−1. These results indicate that MMHg exchange may be significantly enhanced over molecular diffusion in bioturbated sediments. Furthermore, burrow density provides a strong predictor of total MMHg flux. Pore−water exchange of both dissolved MMHg and 222Rn, a naturally occurring pore-water tracer, increased across the range of observed burrow densities, suggesting that the presence of burrows enhances both MMHg production and flux.
- Boston Harbor,
- bioturbated sediments
Citation InformationDavid H. Shull, Janina M. Benoit, Rebecca M. Harvey and Sanuel A. Beal. "Effect of Bioirrigation on Sediment−Water Exchange of Methylmercury in Boston Harbor, Massachusetts" Environmental Science and Technology Vol. 43 Iss. 10 (2009)
Available at: http://works.bepress.com/david_shull/7/