Doctor of Philosophy (PhD)


Oceanography and Coastal Sciences

Document Type



Salt marshes are dynamic, highly productive habitats and serve as nursery grounds for many commercially and economically important species. Benthic microalgae (BMA) are considered an important food source for benthos and provide the principal source of nutrition that fuels secondary production. Estuarine sediments around the world are a repository for many contaminants from anthropogenic sources. In particular, hydrocarbons and metals are ubiquitous contaminants in coastal systems. The primary goal of this study was to study the effects of diesel fuel and copper, alone and in combination, on the BMA assemblage from a coastal salt marsh. To achieve this objective, salt marsh sediments were exposed to various combinations of diesel fuel and copper during a 20-day microcosm experiment. Response of the BMA assemblage was assessed based on the analysis of photosynthetic pigments, species composition, biomass, and production of carbohydrates. Through use of a cryopreservation technique, these variables were measured in the top 2 mm of sediment at 200-µm vertical intervals. This experiment is the first attempt to measure the influence of contaminants on BMA with such high resolution. Hydrocarbons caused significant indirect effects on the BMA assemblage, such as blooms of large diatom species (Bacillaria paxillifer), and diesel combined with copper induced responses that differed from the effects of either contaminant alone (e.g., the stimulation of diatoms was reduced). Diversity of the diatom assemblage was reduced in the presence of diesel, and copper significantly reduced species richness. Contaminants significantly influenced water-extractable but not EDTA-extractable carbohydrate concentrations. The effect of sediments contaminated with phenanthrene and Cd was evaluated in relation to its influence on the feeding activity of a harpacticoid copepod, Schizopera knabeni. My results suggest that there was no interactive effect on feeding when Cd and phenanthrene are combined. When other metals were added (Pb and Hg) to that mixture, an additive influence on feeding rate was observed. Collectively, my results indicate that the BMA assemblage is significantly affected by diesel and copper. Contaminant effects influence BMA structure and distribution within the top 2 mm of sediment, which may have important implications for the biological and physical properties of marsh sediment.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Kevin R. Carman