Date of Award


Document Type

Campus Access Dissertation


Marine Science

First Advisor

Tammi L Richardson


The underwater light field in blackwater environments is strongly influenced by colored dissolved organic matter (CDOM) which absorbs blue light and shifts the underwater light field to the red end of the electromagnetic spectrum. My dissertation research examined relationships between spectral irradiance (water color) and phytoplankton community composition in blackwater habitats. Spatial and temporal variability in water color and phytoplankton community composition were examined in two South Carolina estuaries: Winyah Bay and North Inlet. In Winyah Bay, the composition of the phytoplankton community in CDOM-rich upstream regions of the estuary was distinct from low-CDOM downstream communities. Cryptophytes dominated when wind-induced mixing was low, whereas diatoms were abundant when water column mixing was more pronounced. In North Inlet, phytoplankton community composition consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, and shifts in community composition were driven mainly by temperature, resulting in three temporally distinct communities.

In blackwater estuaries like Winyah Bay, exposure of phytoplankton to full spectrum irradiance occurs only when cells are mixed up to the surface, and the final chapter of my dissertation explored phytoplankton taxon-specific light absorption by modeling three different mixing scenarios. I found that cryptophytes and cyanobacteria harvested light in blackwater environments with greater efficiency than diatoms or chlorophytes. In habitats where green light prevailed, both haptophytes and cryptophytes absorbed most of the light.