Date of Award

Fall 2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

David J. Burdige

Committee Member

Desmond C. Cook

Committee Member

Peter N. Sedwick

Call Number for Print

Special Collections LD4331.O35 P58 2011

Abstract

Mixed redox conditions in sediments due to physical reworking may allow for enhanced remineralization of refractory organic matter due to Fe(III) redox cycling. In part this may occur because easily reducible iron oxides can be used by heterotrophic bacteria to remineralize the organic carbon. This phenomena has been observed in bioturbated sediments and in areas where physical factors (such as strong bottom currents) constantly rework the sediments. To specifically determine the effects of physical reworking and bioturbation on concentrations of easily reducible iron oxides, reactive iron concentrations were measured in surface sediments taken from two contrasting sites in the York River, a Chesapeake Bay tributary. Box core samples were collected between March 2007 and December 2007. Operationally defined iron fractions as well as total iron concentrations were measured using chemical extraction methods. Concentrations of easily reducible iron oxides and total iron at the site experiencing physical reworking were higher than those at the bioturbated site. A selection of sediments were also further analyzed using X-ray diffraction (XRD) and Mossbauer Spectroscopy (MS). Initial XRD analysis did not indicate the presence of iron oxides due to possible interference by the high concentrations of major mineral species such as quartz, or possibly due to nanophase Fe minerals. 300 K and 77 K MS analysis allowed for the determination of Fe(II) and Fe(III) fractions in the samples. Specific iron minerals were not discerned at these temperatures. The Fe(II) and Fe(III) results obtained using XRD combined with the results obtained through chemical extraction did not agree with the amount of Fe(III) obtained using MS. Total iron calculated using XRD analysis was within 1-2% (absolute percentage) of total iron obtained by ashing sediments and extracting Fe chemically for the majority of sites compared. However, XRD determined concentrations of easily reducible iron oxides were not consistent with the results obtained through chemical extraction.

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DOI

10.25777/m24q-d177

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