Lake Michigan 1994-1996 surficial sediment mercury

Between 1994 and 1996, sediment samples were collected from 118 stations in Lake Michigan. Samples were collected using both a box corer and a PONAR grab sampler. Samples were collected for the purpose of describing the current spatial variation of mercury in surficial sediment and for comparing current concentrations and fluxes to historic data. This work includes the first description of the spatial variation of mercury fluxes to the lake's sediment. It also provides a more recent description of the spatial distribution of mercury concentrations within the lake's sediments. For the 118 sites sampled and analyzed, the surficial sediment mercury concentration averaged 78 ng/g and ranged between 2 and 260 ng/g. Concentrations were highest in depositional basins and exhibited a distribution that conformed to the lake's bathymetry. The spatial distribution of mercury fluxes did not conform to the bathymetry. Instead maximum fluxes were shifted toward the southeastern shore. Fluxes to and concentrations in surficial sediment of each depositional basin were not significantly different from one another. Fluxes averaged 7.2 ng/cm(2)/y and ranged between 0.85 and 32 ng/cm(2)/y. Regional atmospheric fluxes account for roughly 50 percent of the total mercury flux to surficial sediments.