Date of Award

Winter 2004

Document Type


Degree Name

Doctor of Philosophy (PhD)


Ocean/Earth/Atmos Sciences

Committee Director

Elizabeth C. Minor

Committee Member

Fred C. Dobbs

Committee Member

H. Rodger Harvey

Committee Member

Margaret R. Mulholland


Aureococcus anophagefferens, the pelagophyte responsible for brown tide blooms, was identified in Chincoteague Bay in 1997 and has “bloomed” there since at least 1998. Aureococcus anophagefferens is capable of using dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) substrates to support growth, and this utilization is hypothesized to give the organism a competitive advantage relative to other phytoplankton when inorganic nutrient concentrations are low or depleted. Because previous studies suggest dissolved organic matter (DOM) is important in initiating and sustaining brown tide blooms, a field study of the variations in DOC concentration and DOM composition was performed at two sites in Chincoteague Bay, one where brown tide blooms had been reported and another where no A. anophagefferens blooms had been reported before. DOM collected before, during, and after brown tide events in 2002 and 2003 was characterized in terms of bulk DOC concentration and ultraviolet/visible light absorption. Stable isotope signatures and direct temperature-resolved mass spectrometry were performed on high-molecular-weight-DOM (HMW-DOM) isolated by ultrafiltration. Results from 2002 suggest that during the brown tide bloom, N-enriched HMW-DOM was released into the surface water and that this material was optically active and more aromatic. Comparison of results from 2002, a drought year, and 2003, a wet year, show that spring DOM pools differed between the two years in DOC concentration and DOM composition; however, brown tide blooms developed in early summer of both years. During all the brown tide blooms monitored, the DOM pool shifted in composition, probably due to input of DOM by Aureococcus anophagefferens. In an attempt to expand the portion of DOM that can be molecularly characterized, the combination of ultrafiltration and C18 disk solid-phase extraction (SPE) for the isolation of DOM was also investigated. Using C18 SPE on LMW-DOM samples (ultrafiltration filtrate) increased the recovery of DOC from the total sample to about 70%, compared to the approximately 50% isolated within the ultrafiltration retentate alone.