The composition of a community and the environmental conditions in which they exist fundamentally influence productivity and responses of systems to change. In the Northern Gulf of Mexico (NGoM), the relationships between nutrients, salinity, and phytoplankton populations are complex and have been changing over time.
This work focuses on describing and analyzing: 1) a case study of diversity and recommendations for change within an academic institution; 2) spatial and temporal trends in surface dissolved inorganic nitrogen (DIN) and phosphorus (DIP) in the NGoM over 35 years; 3) nutrient addition experiments (NAEs) to determine prevailing NGoM surface slope region nutrient limitation; and 4) NGoM surface continental slope phytoplankton community composition and dynamics. Over time, academic institutions have not made progress toward increasing diversity, equity, and inclusion (DEI) in the geosciences.
The first chapter of this work serves as a roadmap for other institutions to make progress toward ingraining DEI frameworks into the foundations of our institutional systems. Toward explaining trends in nutrients from 1985 to 2019, I compiled the largest data set of NGoM surface dissolved nutrient concentrations to date and analyzed it to delineate spatiotemporal trends and identify potential drivers of nutrient change. DIP concentrations in both the Mississippi-Atchafalaya River system (MAR) and in the NGoM increased over time, but the increase of NGoM DIP exceeded the DIP loads coming from only the MAR, suggesting additional sources of P to the NGoM.
To determine nutrient controls on surface slope NGoM phytoplankton growth and populations, we calculated growth rates and pigment composition using redundancy analyses and a variety of nutrient limitation criteria for each nutrient amendment over 48 hours. Nutrient limitation criteria concluded predominant NP limitation in the NGoM, though single N and P limitation and nutrient replete conditions were also present. In individual NAEs with N and NP amendments, phytoplankton pigment changes were driven by the growth of diatoms and Synechococcus (Syn).
Though release from nutrient limitation stimulated responses in some phytoplankton groups, nutrient limitation of phytoplankton growth could not fully be predicted by the criteria and response thresholds evaluated in this study. Additionally, an analysis of environmental variables and phytoplankton pigments was conducted for the surface slope region of the NGoM to determine how phytoplankton community composition varies spatially with the influence of the MAR plume using group-specific chlorophyll a (Chl-a) calculations, bivariate linear regression, multivariate redundancy analysis, and cluster analysis.
The largest proportion of Chl-a occurred in the nano/microphytoplankton group, followed by Syn, with both peaking at the high and low ends of the salinity gradient. Redundancy and cluster analyses showed that nutrients and salinity alone cannot predict or subdivide phytoplankton community composition; however, with the addition of pigments, we can characterize specific regions based on shared environmental variables (i.e., low salinity, high biomass) and pigment abundance. In sum, this work produced a straightforward and reproducible guide to leading a DEI task force, the largest NGoM surface nutrient data set to date, and characterizations of NGoM continental slope nutrient limitation and pigment composition and their relation to environmental variables.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/w310-sb64 |
| Date | January 2024 |
| Creators | Acosta, Kailani |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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