Date of Award

12-2010

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Environmental Sciences/Environmental, Earth & Ocean Sciences

First Advisor

Gordon T. Wallace

Second Advisor

Eugene D. Gallagher

Third Advisor

George B. Gardener

Abstract

Water samples and hydrologic data were collected during 1994-1996 in New England coastal waters near Massachusetts, USA to examine the distribution of silver and other trace metals (Cu, Pb, Cd, Zn, and Fe) in the coastal systems of Massachusetts and Cape Cod Bays. These investigations were designed to test the hypothesis that silver could serve as a tracer of dispersion of municipal wastewater in Boston Harbor into Massachusetts and Cape Cod Bays and estimate the relative contribution of wastewater discharge to the overall silver budget of the Massachusetts Bays system. Silver concentrations in both particulate and filtered (<0.4 µm) fractions averaged 103 and 117 pmol kg-1 for Boston Harbor, 34 and 10 pmol kg-1 in western Massachusetts Bay, and 11 and 7 pmol kg-1 in the central portion of Massachusetts Bay, respectively. Average Ag concentrations in southern Gulf of Maine coastal waters were 10 and 2 pmol kg-1 for filtered and particulate fractions, respectively. While nearly half of the silver existed in particulate form in Boston Harbor, nearly 80% of the silver in Massachusetts and Cape Cod Bays occurred in the filterable fraction. Coastal water surveys revealed non-conservative Ag behavior and probably the result of incomplete mixing of three or more water masses with unique Ag signatures (e.g., Merrimack River, Boston Harbor, surface and intermediate Gulf of Maine waters). Quasi-steady state mass balance approaches estimate most of the silver entering into the Massachusetts Bays system during the study period was the result of municipal wastewater discharge to Boston Harbor (84-93%).

Multivariate analyses were conducted to evaluate fundamental controls on the distribution and fate of Ag in Massachusetts coastal waters. The results of observations from water samples collected during surveys in Massachusetts Bays and the near coastal region of southwestern Gulf of Maine show that Ag is intermediate with respect to particulate reactivity when compared to the metals observed for this study and consistent with observations of Ag speciation in other coastal and open ocean systems. Exploratory factor analysis revealed behavior of Ag similar to that of Cu and Zn, and may reflect similar complexation potential with and preference for common ligand classes in the water column.

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