Horizontal and vertical distributions of mercury in 1983 Lake Superior sediments with estimates of storage and mass flux

Persistent elevated mercury concentrations in some species of Lake Superior fish and the general lack of information on mercury storage in and fluxes to the lake's sediments prompted the analysis of samples that were collecte d in 1983. Results of the analyses support the conclusion that Lake Superio r sediments have mercury? concentrations above background levels at all sit es sampled. For those cores which penetrated the sediment deeply enough (th e majority of the cores), background mercury concentrations ranged between 0.016 and 0.048 mg/kg. Mercury concentrations in surficial sediments ranged between 0.027 and 0.96 mg/kg. The maximum mercury concentration found in s ub-surface sediments (2 to 20 cm deep) was 6.5 mg/kg. The surficial 20 cm o f sediment contained 342 metric tons of mercury of which 51% or 174 metric tons was anthropogenic. The surface 2 cm of sediment contained 29 metric to ns of mercury of which 76% or 22 metric tons was anthropogenic. Estimated t otal mercury fluxes to surficial sediments ranged between 0.1 and 10 ng/cm( 2)/y with a mean of 3.2 ng/cm(2)/y. Baclcground total mercury fluxes to the lake ranged between 0.20 and 0.72 ng/cm2/y with a mean of 0.48 ng/cm2/y. E stimated fluxes of anthropogenic mercury to surficial sediments ranged betw een -0.42 and 10 ng/cm(2 f)/y with a mean of 2.7 ng/cm(2)/y. The fluxes rep orted here are only the second known reporting of mercury, fluxes to Lake S uperior sediments. The inventory of mercury in the sediments is the first r eported.