Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean & Earth Sciences

Program/Concentration

Ocean and Earth Sciences

Committee Director

David J. Burdige

Committee Member

Richard C. Zimmerman

Committee Member

Fred C. Dobbs

Call Number for Print

Special Collections LD4331.O35 H685 2013

Abstract

This thesis presents two studies focusing on phosphorus cycling in calcium carbonate sediments inhabited by seagrasses. Phosphorus is a major limiting nutrient for primary productivity in these sediments as well as in the overlying waters. In large part this is due to removal of phosphate from solution by adsorption and precipitation reactions.

In chapter II, the relationship between the size of the sedimentary phosphorus pool and the abundance of seagrass on the Great Bahama Bank, as well as the relationship between phosphorus content and grain size in the sediments, were examined to better understand the biogeochemistry of carbonate sediments and the associated sediment-seagrass interactions. Additionally, the depth distribution of fluoride in the pore waters was used to infer precipitation/dissolution of phosphate mineral phases that may occur during diagenesis. A strong positive relationship between the magnitude of the sedimentary phosphorus pool and seagrass density was observed. This association, along with phosphorus inventory calculations, suggests that seagrasses maintain high productivity through utilization of nutrient resources in the sediment. A likely mechanism to access these resources is seagrass-mediated metabolic carbonate dissolution. Additionally, a surface area control of phosphate is evident but not the primary factor controlling phosphate adsorption. While results provide no evidence for carbonate fluorapatite precipitation, its presence may be masked by low rates of this transformation relative to the time scales of pore water advection.

In chapter III, sediment trap and tidal current flow data were examined to explore the physical/chemical factors that may influence the distribution and density of seagrass across the Great Bahama Bank. Sediment trap data were used to quantify the flux of phosphorus from the water column to the sediments. Sedimentation rates were correlated to tidal current flow amplitudes to elucidate the source of the phosphorus associated with particle deposition and to predict spatial patterns of the phosphorus deposition that may affect seagrass distribution across the Great Bahama Bank. The observation that the highest tidal flow velocities, sediment fluxes, and seagrass densities occur at sites geographically positioned on the bank margin suggests that tidal current flow in the LSI region strongly controls nutrient delivery and deposition.

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DOI

10.25777/0f7n-3t27

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