Mechanisms of Metal Release from Contaminated Coastal Sediments

Linda Kalnejais, Ph.D., 2005
William Martin, Advisor

The fate of trace metals in contaminated coastal sediments is poorly understood, yet critical for effective coastal management. This thesis investigates the mechanisms that release silver, lead and copper from sediments. Two sites were investigated, a contaminated site in Boston Harbor and a site in Massachusetts Bay. Porewater and solid phase samples were collected to determine the diagenetic metal cycles. Trace metals are scavenged by iron oxyhydroxides and released to the porewaters when the oxides are reduced. At the strongly reducing Boston Harbor site, trace metals are transferred from oxides in winter, to sulfides in summer. At the Massachusetts Bay site, due to the lack of sulfide, the metals are focused into the surface oxide layer. There is a diffusive flux of copper, silver and reduced sulfur compounds to the water column, but not a flux of lead. Sediment resuspension, studied with an erosion chamber, was found to enhance the release of dissolved metals and to erode metal-enriched particles at the onset of erosion. The total benthic release of dissolved metals is 60% and 10% of the riverine flux for copper and lead, respectively. The release of metals from sediments is important in the metal budget of Boston Harbor.