Date of Award

Summer 1978

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Oceanography

Committee Director

Dennis A. Darby

Committee Member

William J. Hanna

Committee Member

Peter Fleischer

Committee Member

Joseph H. Rule

Committee Member

Donald D. Adams

Call Number for Print

Special Collections LD4331.O35N47

Abstract

In order to examine the mechanisms by which Fe, Mn, Ca, Zn, Cu, Ni and Pb are bound in sediments, a sequential selective extraction procedure was employed on sediment samples collected at an experimental dredge disposal marsh and a neighboring natural marsh located near Windmill Point, James River, Va. The metal concentrations were determined in six phases, interstitial water, exchangeable, easily reducible (oxides of Mn), organic, moderately, reducible (oxides of Fe), and residual fractions. In addition, the cation exchange capacity (CEC) of the sediments was determined as well as the actual role of organics and colloidal iron coatings as they affect the CEC.

The bulk of the Zn, Cu, Ni and Pb (ca. 40 to 90%) was present in a non-labile form associated with detrital crystalline minerals. Zinc was also detected in the more readily available phases. Iron resided primarily in the residual and moderately reducible phases, manganese resided chiefly in the easily reducible phase and calcium was found predominantly on exchange sites. Even though these three metals were found in large amounts in reactive locations they are not biologically hazardous at the levels detected in the two marshes.

Resu1ts from correlation analysis indicate that the easily reducible phase may be the dominant factor controlling the Fe, Mn, Zn, and Ca concentrations in the interstitial water. Furthermore, relationships between the easily and moderately reducible phases suggest that Fe was responsible for the actual incorporation of Cu, Ni, Zn and Pb in hydrous metallic oxides while Mn may be responsible for the initial sorption of at least Cu, Ni and Zn from solution. Variations within and between the two marshes for metal concentrations in the various phases as revealed by analysis of variance can be explained by differences in sediment composition and texture and differences in the formation, age and physical setting of the two marshes.

The organic portion of sediments contributed at least half of the exchange capacity to these sediments while the effect of colloidal iron coatings on CEC was much less important and sporadic. Furthermore, the CEC of these sediments was affected by many factors and the in situ exchange capacity was not conclusively determined from the standard procedures followed. The exchange complex was probably dominated by H+ because exchangeable Ca2+, Mg2+, K+, Na+, Fe2+, Mn2+, Zn2+ and NH4+ accounted for only 28 percent of the CEC.

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DOI

10.25777/n355-1213

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