Graduation Year

2024

Document Type

Dissertation

Degree

Ph.D.

Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Marine Science

Major Professor

Robert H. Byrne, Ph.D.

Committee Member

Mark Luther, Ph.D.

Committee Member

Teresa Greely, Ph.D.

Committee Member

Brad Seibel, Ph.D.

Committee Member

Kimberly Yates, Ph.D.

Committee Member

Vonzell Agosto, Ph.D.

Keywords

coastal ocean acidification, Deaf Community, organic alkalinity, organizational autoethnography, potentiometric pH, spectrophotometric electrode calibration

Abstract

One major goal of this dissertation addresses the need for improved laboratory procedures to measure chemical changes in seawater caused by the uptake of atmospheric CO2, especially in coastal environments. Due to the proximity of anthropogenic stressors in the coastal zone, the biogeochemical complexity of the CO2 system is more dynamic than the open ocean. My principal research objectives were addressed by developing methods for (1) improving the accuracy of pH measurements over a wide range of salinities and (2) investigating the acid-base properties of natural organics in the coastal ocean.

The accuracy of pH electrode calibrations is affected when seawater samples have different salinities (S). Using the spectrophotometric electrode calibration techniques developed by Easley & Byrne (2012), I developed a method to calibrate pH electrodes over various salinities, including the coastal zone (Martell-Bonet & Byrne, 2020). Consistent with theoretical expectations, my investigation affirms that electrode slopes depend on temperature but not salinity. However, calibration intercepts are more complex. Electrode intercept potentials change linearly with salinity for S > 5 but are substantially nonlinear for S < 5, a salinity range that includes the coastal environment. This experimental observation is novel; if not considered, misestimates of potentiometric pH on the order of 0.24 can result in low salinity waters.

Building on this improvement in potentiometric pH measurements, I developed novel methods for measuring organic alkalinity (Org-Alk) contributions to total alkalinity. Potentiometric titrations were used to characterize the exchange of hydrogen ions between organic bases and organic acids (i.e., determinations of the dissociation constants (pKs) of natural environmental organic matter). Quantitative assessments of Org-Alk contributions to CO2 system buffering are essential for rigorous characterizations of pH-dependent equilibria in the coastal environment. My results showed three types of titratable organics. The dominant organic, with a concentration of 200 μmol∙kg−1, had a well-defined pKOrg2 of 6.33 ± 0.01 and did not vary with temperature. One of the other two organic species had a moderately well-defined range of pK: 8.56 ≤ pKOrg3 ≤ 9.32, and the other was poorly defined: 4.1 ≤ pKOrg1 ≤ 6.1. In addition, this work brings attention to measurement reproducibility for better-estimated pK values and their uncertainties, thus improving CO2 system calculations in organic-rich coastal waters.

As a second major goal, my dissertation examined public literacy on ocean acidification among members of the Deaf Community, which included an autoethnography of my research experience. This mixed-method study involved both quantitative and qualitative data. An online questionnaire was offered to evaluate participants' knowledge of basic chemistry, ocean chemistry, and the causes and consequences of ocean acidification. Data for the organizational autoethnography included self-observations, self-reflective data, and a chronological account of significant events. This chapter contributes to the science education field by providing insights into a community not often assessed in science. It also highlights research challenges involving human subjects and the disconnect between the Deaf and hearing worlds.

My dissertation incorporates interdisciplinary approaches in STEM fields to address concerns of both science and society. The impacts of changes in ocean chemistry are complex, with components embedded in science, education, and society. As such, this dissertation is designed to provide helpful information for marine chemists and science educators.

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