Date of Award

Summer 2010

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Ocean & Earth Sciences

Committee Director

David J. Burdige

Committee Director

Robert F. Dias

Committee Member

Margaret R. Mulholland

Committee Member

Paula Mazzer

Abstract

In the biogeochemical study of dissolved organic matter (DOM) in natural waters, stable isotopes are used to provide insight into both the sources of DOM and the processes affecting its alteration. Through the research presented here, oxygen isotopes are incorporated into the study of DOM through the adaptation of a pyrolysis elemental analysis isotope ratio mass spectrometer method, and sample preparation using two-stage ultrafiltration.

The application of oxygen isotopes to the study of DOM is demonstrated in two studies. First, natural abundance of δ18O in DOM is explored in the Delaware estuary. Using a two end-member mixing model, DOM oxygen isotopes are compared with carbon isotopes, DOC concentrations and elemental ratios to determine if changes are a result of two water bodies mixing. Isotope values are decoupled from concentration values and indicate that from an isotopic perspective two end member mixing is completed by mid bay. A conceptual model is presented with comparison to the observed data. However, the extension of this model to DOM δ18O values show that additional processes affect the DOM oxygen along the estuary transect.

Oxygen isotopes are also used in an enrichment study to assess the sources of DOM oxygen in the photochemical oxidation of organic matter. In a series of laboratory irradiations using York River and Dismal Swamp water amended with either 18O-enriched dissolved oxygen or water, the amount of 18O incorporated into the high molecular weight dissolved organic matter was determined. For both sites, a fraction of the oxygen in DOM was photochemically incorporated from dissolved oxygen, although a larger fraction was incorporated from water. The differences in incorporation between sites are attributable to DOM compositional differences. An oxygen budget is proposed for the observed Dismal Swamp photochemical DOM oxidation.

DOM oxygen isotopes provide an additional dimension in the investigation of DOM sources and alteration processes. As DOM δ18O values appear to be affected by processes that do not alter the δ13C values and are not correlated with the water δ18O value, it provides an additional parameter for characterizing high molecular weight DOM.

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DOI

10.25777/wqht-et83

ISBN

9781124271378

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