Date Awarded

2022

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

Iris C. Anderson

Committee Member

Kimberly S. Reece

Committee Member

Bongkeun Song

Abstract

Benthic-pelagic coupling is defined as the deposition of organic matter from the water column to the sediments, and the subsequent remineralization of this organic matter and release of inorganic nutrients back to the water column. This process plays an important role in determining the magnitude of benthic net community production (NCP), a metric that reflects the balance between gross primary production and respiration. Environmental factors, such as the presence or absence of intense phytoplankton blooms can influence the direction and magnitude of benthic-pelagic coupling and determine if benthic NCP is net autotrophic or heterotrophic. The objective this thesis was to quantify the feedbacks among intense phytoplankton blooms, benthic NCP, net nutrient fluxes, and nitrogen cycling in the York River Estuary (YRE). Sediment cores were collected from shoal and channel stations across the YRE in January June, July, August, and October 2020 and April 2021 to characterize spatiotemporal variability in benthic NCP, net fluxes, and nitrogen cycling rates. To characterize these parameters in the context of intense phytoplankton blooms, sediment cores were also collected in the lower YRE (LYRE) in July and September 2020 before and after the occurrence of a bloom. The cores were incubated at ambient temperatures in both the light and dark to determine fluxes of dissolved oxygen and organic and inorganic carbon and nitrogen. Rates of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were determined via the isotope pairing technique. Results indicated that the benthos was net heterotrophic, with increased heterotrophy observed after the bloom. Dissolved organic carbon uptake increased post bloom, fueling benthic respiration and net heterotrophy. There was primarily net uptake of nitrate and both uptake and release of ammonium. Rates of DNRA were higher than denitrification, especially after the occurrence of the bloom. Overall, results indicated that the presence of intense phytoplankton blooms have the potential to dramatically alter benthic NCP and nutrient cycling, with increased heterotrophy and rates of DNRA having the potential to recycle inorganic nutrients that can further promote blooms.

DOI

https://dx.doi.org/10.25773/v5-am46-8e75

Rights

© The Author

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