Mechanisms of metal release from contaminated coastal sediments
Citable URI
https://hdl.handle.net/1912/1715Location
Massachusetts BayBoston Harbor
DOI
10.1575/1912/1715Keyword
Marine sediments; Chemical elementsAbstract
The fate of trace metals in contaminated coastal sediments is poorly understood, yet critical
for effective coastal management. The aim of this thesis is to investigate and quantify the
mechanisms leading to the release of silver, lead and copper across the sediment-water
interface. Two contrasting sites were investigated, a heavily contaminated site in Boston
Harbor and a less impacted, offshore site in Massachusetts Bay. High-resolution porewater
and solid phase samples were collected in each season to determine the diagenetic cycles
and chemistry controlling the fate of these metals. The trace metals are scavenged by
iron oxyhydroxides and released to the porewaters when these oxides are reduced. At the
strongly reducing site in Boston Harbor, there is seasonal transfer of trace metals from
oxide phases in winter, to sulfides phase in summer. At the Massachusetts Bay site, due to
the lack of sulfide, the metals are focused into the surface oxide layer, giving a solid phase
enrichment. There is a diffusive flux of copper to the water column throughout the year,
while silver is released only in winter. Lead is strongly scavenged and is rarely released to the
overlying waters. Analysis of reduced sulfur compounds in the porewaters has shown that
there is also a significant flux of these strong ligands to the overlying waters. Polysulfide
species enhance the solubility of copper within the porewaters. Sediment resuspension
fluxes were quantified using an erosion chamber. Sediment resuspension leads to enhanced
release of dissolved metals and is especially important in redistributing contaminants as
the first particles to be eroded are enriched in trace metals. The total release of dissolved
metals from the sediments by diffusion and sediment resuspension is estimated to be 60%
and 10% of the riverine flux for copper and lead respectively. With continued pollution
control reducing the discharge of metals from other sources, the benthic release of metals
will become increasingly important terms in the metal budget of Boston Harbor.
Description
Submitted in partial fulfillment of the requirements for the degree of
Doctor of Philosophy at the Massachusetts Institute of Technology
and the Woods Hole Oceanographic Institution
September 2005
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Suggested Citation
Thesis: Kalnejais, Linda H., "Mechanisms of metal release from contaminated coastal sediments", 2005-09, DOI:10.1575/1912/1715, https://hdl.handle.net/1912/1715Related items
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