Cycling of Silver, Lead and Copper in Coastal Marine Sediments Book uri icon

abstract

  • The role coastal sediments play in the biogeochemical cycles of many trace metals is poorly understood. For metals such as silver, copper and lead, this is especially important, as elevated concentrations are often found in coastal sediments due to anthropogenic activities. The sediments are potentially large sources of these metals and complex mechanisms lead to either remobilization or burial. In order to understand the diagenetic cycling and fate of these metals, porewater profiles of silver, lead and copper at two coastal sites in Massachusetts have been determined. Seasonal profiles have been collected from two contrasting sites. The first is a heavily contaminated site in Boston Harbor which received high inputs of contaminants from a nearby sewage outfall until 2000. The second site, in Massachusetts Bay, is a less impacted, offshore site that has lower organic carbon and solid phase trace metal concentrations. The three metals exhibit differing behavior in the upper 2cm of sediment but below this they all have coincident subsurface remobilization peaks. Copper and lead often show a peak at the sediment water interface, while there is no gradient in silver concentrations in the upper sediments. The highest porewater concentrations of these metals occur in subsurface peaks. These peaks are sometimes co-incident with the release of iron to the porewaters but at other times the metals are released to porewaters as iron is removed at depth. This indicates a complex cycling of metals with iron oxide carrier phases and also, most likely with sulfide species. The importance of sulfide species to the cycling of these metals is shown by the contrasting behavior of the metals at depth at each site. In Massachusetts Bay, where sulfide concentrations are less than 1$\mu$M, the metal concentrations in porewater are very low and constant with depth. In Boston Harbor, which has sulfide concentrations greater than 200$\mu$M, the metal concentrations are higher and increase with depth, most likely due to complexation with reduced sulfur species that enhances the metal solubility.

publication date

  • January 2001