Date of Award

Summer 2025

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Claudia Benitez-Nelson

Second Advisor

Timothy Shaw

Abstract

Dissolved organic matter (DOM) has important roles in many biogeochemical cycles. DOM is primarily composed of dissolved organic carbon (DOC), nitrogen, and phosphorus, and the processing of DOM is important for nutrient regulation and carbon cycling. In the coastal plains of the southeastern United States, there are many rivers and streams known as “blackwaters” with exceptionally high concentrations of chromophoric dissolved organic matter (CDOM) leached from terrestrial soils, coinciding with a region experiencing some of the nation’s highest rates of development. As changes in land use and climate continue to occur, DOM composition from natural to anthropogenically impacted systems can shift from more refractory to more bioavailable forms. This results in increased microbial remineralization, with consequences such as dissolved oxygen (DO) deficits, eutrophication, harmful algal blooms, and increased atmospheric carbon dioxide. The goal of this work was to establish baseline DOM concentrations and composition to decipher impacts on water quality due to naturally occurring versus anthropogenic activities by examining DOM composition in pristine, rural, and developed aquatic systems. Furthermore, assessing seasonal impacts and DOM degradation patterns is significant for predicting how blackwaters may respond to increased temperatures, more frequent and intense rainfall, and other future changes in climate and land use.

This thesis examines variability in DOM concentration and composition using a range of tools, including bulk carbon and nutrient concentrations, elemental ratios, absorbance spectroscopy, excitation-emission matrix (EEM) fluorescence spectroscopy paired with parallel factor (PARAFAC) analysis, and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). The first chapter of this work establishes significant variability in DOM concentrations and composition across forested to developed blackwater systems in coastal South Carolina, U.S. The second chapter further assesses seasonal and interannual impacts on DOM composition, and the third chapter examines DOM degradation patterns with landcover. These results suggest that larger-scale changes in urbanization and environmental conditions drive DOM composition and sources to coastal waters, with implications for water quality and climate.

Rights

© 2025, Gwendolyn Marcelette Hopper

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