Date of Award

2017

Document Type

Open Access Dissertation

Department

Marine Science

Sub-Department

College of Arts and Sciences

First Advisor

Tammi L. Richardson

Second Advisor

Claudia R. Benitez-Nelson

Abstract

The supply of phosphorus (P) directly impacts the growth and speciation of marine microbes (i.e., phytoplankton, bacteria, Archaea). In turn, microbial communities shape the magnitude and rate of marine biogeochemical cycles, ultimately affecting global climate and food production. This dynamic reflects the continuum of temporal and spatial scales at which the marine P cycle operates. However, linking multiple scales of cycling remains a consistent challenge. The primary objective of my dissertation was to gain insight into marine P biogeochemistry, by means of analytical chemistry, at the molecular and environmental scales of cycling. The first component of my research was to examine the composition of dissolved organic P (DOP) using coupled electrodialysisreverse osmosis (ED/RO) and solution 31P-NMR. My results demonstrated the capability of ED/RO isolation to recover more than 80% of the DOP pool with minimal isolation biases or impact to its molecular integrity. Following ED/RO isolation, I applied solution 31P-NMR to estuarine samples collected at high and low tide over a full seasonal cycle from North Inlet, South Carolina. This coupled approach revealed six components of the DOP pool, including the first direct estimates of the major diester class, while also demonstrating the molecular complexity within each defined bond class. This dataset suggests marine DOP composition is in a dynamic equilibrium regardless of environmental regimes (i.e., open ocean, coastal ocean, tidal-estuary). The second component of my research examined the relative cycling of P, with respect to carbon (C) and nitrogen (N) within the North Inlet estuary. This was assessed through C:N:P stoichiometry, which was then compared and applied to models for tidal exchange and microbial community nutrient status. In North Inlet tidal creeks, persistent N limitation was observed to drive a net import of N, while temporary P surplus drove seasonal P export. These observations were linked with the biological availability of dissolved organic nutrients, such as DOP. Similar to its molecular composition, DOP appeared to be in a dynamic equilibrium: neither exported nor imported over each tidal cycle. Overall, my research provides significant insight into the molecular mechanisms of DOP, which may help describe the broader dynamics of marine P biogeochemistry.

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