Role of oxygen and salinity on biogeochemical processes controlling mercury and monomethylmercury flux from estuarine sediments
- UNCW Author/Contributor (non-UNCW co-authors, if there are any, appear on document)
- Joshua S. Vinson (Creator)
- Institution
- The University of North Carolina Wilmington (UNCW )
- Web Site: http://library.uncw.edu/
- Advisor
- Stephen Skrabal
Abstract: Estuarine sediments are complex biogeochemical microenvironments that play an
important role in the transformation and redistribution of mercury and methylmercury
(MeHg) to overlying waters. The presence of sulfate-reducing bacteria is widely accepted
to be a critical factor in mercury methylation. As freshwater contains typically low
concentrations of sulfate and seawater is sulfate-rich, salt water intrusion to freshwater
sediments by sea level rise or anthropogenic causes may significantly increase MeHg
production and release by sediments. This study used high-resolution (millimeter-scale)
pore water profiling of redox-active analytes, combined with simultaneous measurement
of benthic fluxes, to discern how biogeochemical processes affect sediment-water
exchange of dissolved mercury and MeHg in predominantly tidal freshwater and
estuarine wetlands. Sediment incubations and manipulations of oxygen and salinity
conditions were performed using sediment cores from two contrasting sites in the Cape
Fear and White Oak estuaries.
The dominance of manganese reduction in Cape Fear sediments in February and
June apparently inhibited the expected thermodynamic progression toward sulfate
reduction and subsequent MeHg fluxes. Maximum MeHg fluxes of 29-36 pmol m-2 d-1
were observed in early fall (September) under anoxic, low salinity conditions and were
coincident with of Fe2+ and Mn2+ pore water accumulation at the sediment-water
interface (SWI) and low concentrations of H2S (5-40 µM) below the SWI. Presence or
absence of Mn2+ and Fe2+ at the SWI was consistently associated with MeHg fluxes,
suggesting the reduction of metal oxyhydroxides in conjunction with sulfate reduction are
factors controlling sediment-water exchange of MeHg. Variable fluxes of MeHg (0, -6, 6 pmol m-2 d-1) during summer in White Oak sediments was observed in the presence of
sulfate reduction under low salinity, suggesting the presence of other methylationinhibiting
mechanisms. These data suggest increasing salinities of freshwater sediments
due to sea level rise or human activities promote sulfate reduction and associated MeHg
production resulting in elevated concentrations of MeHg in the Cape Fear River
sediments. In addition, Fe and Mn oxyhydroxides, which are effective barriers against the
diffusion of MeHg to overlying water, are reduced during periods of anoxia and release
MeHg to the overlying waters.
Role of oxygen and salinity on biogeochemical processes controlling mercury and monomethylmercury flux from estuarine sediments
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Created on 1/1/2008
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Additional Information
- Publication
- Thesis
- A Thesis Submitted to the University of North Carolina Wilmington in Partial Fulfillment Of the Requirements for the Degree of Master of Science
- Language: English
- Date: 2008