Date of Award

Summer 2023

Document Type

Open Access Dissertation


Chemistry and Biochemistry

First Advisor

Timothy Shaw


The delivery of biodetritus to the sediment water interface supports a complex series of biogeochemical reactions collectively referred to as early diagenesis. From the abyssal ocean to littoral freshwater ecosystems, this work explores the dynamics of these reactions in deep ocean detrital aggregates and lacustrine benthic algal mats. In the ocean, periods of increased export flux to abyssal depths increase the organic carbon export as aggregates to the seafloor while in littoral freshwater, proliferations of benthic algae such as Microseira wollei have grown to fill much of the shallow water column they inhabit.

Data collected at Station M (Sta. M) by Smith et al (2018) shows episodic pulse events of high export of organic aggregates to abyssal depths. During these pulse events, the aggregates accumulate and cover much of the seafloor in the study area. In Chapter 2, modeling results through these accumulations of detrital aggregates show that, in accordance with measured results, much of the detrital material that reaches the seafloor is not mineralized with bottom water oxygen and thus a large fraction of the detrital material is buried in the abyssal sediments as organic carbon. As the frequency and duration of pulse events increase at Sta. M during the study period, more organic carbon is sequestered to the seafloor and removed from the oceanic carbon cycle. Thus, providing evidence that the sediment carbon distribution is more dynamic than previously thought.

In freshwater systems such as Lake Wateree, SC, the benthic filamentous cyanobacteria Microseira wollei continues to thrive around the littoral zone despite insufficient surface water nutrient supply. In Chapter 3, the nutrient availability for the algal mat community is examined for dissolved and particulate phosphorous and iron through vertical profile sampling. Using the oxygen and iron concentrations at each sampling point, and comparing them to the phosphorous trends, the biogenic and authigenic sources of phosphorous are also examined. The oxygen profiles additionally provide information on the redox conditions within the algal mat community that can mediate the release of particulate nutrient stores from authigenic reservoir phases. The trends found through the algal mat throughout the year show dynamic reservoirs of biogenic and authigenic phosphorous and that the conditions within the algal mat do become favorable for the release of both authigenic and biogenic sources.

The diagenetic model defined in Chapter 2 has been adapted to the lacustrine environment by expanding chemical factors to include iron and phosphorous dynamics in the benthic algal mat community. Using these species, phosphorous cycling with both biogenic and authigenic phosphorous phases has been modeled in the algal mat. The model shows good agreement with the sampled profiles. While collected data is not available for comparison, additional analytes, manganese and nitrogen, are also modeled and show reasonable results based on expected interactions and trends. These parameters provide additional insights into nutrient dynamics in the algal mats and may be further useful in exploring the nutrient availability through other benthic algal species that cannot fix nitrogen.


© 2023, Corrianna R. Boucher

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