Mercury and methylmercury cycling in sediments of the mid‐Atlantic continental shelf and slope

Abstract

We present a detailed study of the biogeochemical factors controlling mercury (Hg) distribution, methylmercury (MeHg) production, and MeHg efflux in sediments of the mid-Atlantic continental shelf and slope. The mildly reduced surface sediments of the shelf and slope provide ideal conditions for MeHg production. They are sufficiently reduced to support microbial sulfate reduction, but contain very low dissolved sulfide concentrations. The redox zonation of sediments determined the depth distribution of MeHg production, whereas the bioavailability of inorganic Hg for methylation appeared to be the dominant driver of spatial patterns across the shelf and slope. Sediment total Hg concentrations were well predicted by sediment organic matter (SOM) content, with the highest concentrations of Hg and MeHg in the fine-grained organic clays of the slope. However, SOM-normalized Hg concentrations decreased with distance from shore. The changing character of organic matter with distance from shore appeared to affect Hg partitioning and bioavailability for methylation. The percentage of Hg in sediments as MeHg was well predicted by measured methylation rates, but not by demethylation rates. On the basis of measured concentrations in bottom waters and surficial pore waters, the average diffusive efflux of Hg(II) and MeHg from sediments to coastal waters was estimated to be 26 and 0.8 pmol m 22 d 21 , respectively. Extrapolated globally, the diffusive input of MeHg from shelf and slope sediments is estimated to be 0.01 Mmol per year. As the actual fluxes can be substantially higher than diffusive fluxes, we suggest that shelf and upper slope sediments are a major source of MeHg to the coastal ocean.

Detailed Assessment of the Kinetics of Hg-Cell Association, Hg Methylation, and Methylmercury Degradation in Several Desulfovibrio Species

“…Possible explanations for the low affinity of MeHg for the cell surface include selectivity of cell surface receptors and transporters for specific Hg(II) i -ligand complexes compared to MeHg-ligand complexes and/or inertness of MeHg complexes with regard to ligand exchange reactions at the cell surface. MeHg generally has lower particle affinity in the environment than Hg(II) i (32,35).…”

Freshwater discharges drive high levels of methylmercury in Arctic marine biota

“…5). Prior work suggests advective fluxes of MeHg are generally 5-10 times higher than diffusive fluxes (34). Extrapolating the diffusive flux to the planned reservoir regions for Muskrat Falls (41 km 2 ) (SI Appendix, Fig.…”

Seasonal Variations in the Use of Profundal Habitat among Freshwater Fishes in Lake Norsjø, Southern Norway, and Subsequent Effects on Fish Mercury Concentrations

“…Methylated Hg is an environmental pollutant of concern in aquatic environments [1][2][3][4], as it is accumulated in biota, and concentrations rise in accordance with trophic position [5][6][7][8][9][10]. Fish and fish-eating wildlife often have toxic concentrations of total Hg (Tot-Hg) as a result [7].…”