Semester of Graduation

Spring 2019

Degree

Master of Science (MS)

Department

Oceanography and Coastal Sciences (DOCS)

Document Type

Thesis

Abstract

Dissolved silica (DSi), plays an important role in regulating primary productivity of silicifying organisms, such as diatoms which precipitate hard parts composed of biogenic silica (bSi) in coastal and shelf ecosystems fed by major rivers. In the Northern Gulf of Mexico (NGOM), loading of nitrogen and phosphorous have increased compared to a decline in DSi in the Mississippi River. Continued decreasing in DSi loading could lead to limited diatom growth and production or shifts in community composition, therefore, it is important understand the role of benthic fluxes in providing silica to the overlying water column as there are few regional studies reporting previous benthic DSi flux estimates. The benthic flux of DSi from shelf sediments can thus represent an important source of Si to be utilized by diatoms as well as an important factor of the regional Si budget. Sediment core incubations and benthic chamber deployments were conducted at 10 sites in the Mississippi river plume with varying salinities during periods of high river discharge (May 2017), low river discharge (August 2016, October 2017, January 2018), and peak hypoxia with intermediate river discharge (July 2017). In addition, reactive silica fractions from sediment samples and silica production rates from the water column, as well as ancillary water column data were quantified. Large spatial and temporal variability in benthic silica fluxes ranging between -3.85 to 15.17 mmol Si m-2d-1 shows a clear difference in methods, with in situ exceeding ex situ by factors ranging from 1.5-5.5. Regional calculations made in the study area indicate that benthic DSi could possibly sustain 16% and 46% of water-column-integrated silica production in the region for ex situ and in situ methods, respectively.

Date

4-1-2019

Committee Chair

Maiti, Kanchan

DOI

10.31390/gradschool_theses.4883

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