TAMU-CC Theses, Dissertations, and Other Projects
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Find theses, dissertations, and other projects completed by students of Texas A&M University-Corpus Christi. Associated files for theses, dissertations, and other projects, such as data sets and Honors Projects of Excellence, can also be found within this community.
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Browsing TAMU-CC Theses, Dissertations, and Other Projects by Department "Coastal and Marine System Science Program"
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Item Dissolved inorganic nitrogen concentrations and isotopic values of wastewater treatment plants in a semi-arid region(2023-08) Cox, Anthony; Felix, J. David; Wetz, Michael; Murgulet, Dorina; Abdulla, HussainWastewater treatment regulations evolve as detrimental ecological impacts of wastewater nitrogen loading becomes more apparent. Determining the significance of the N loading contribution of wastewater treatment plants to coastal waters in comparison to other primary N sources is necessary when creating efficient mitigation strategies. However, current research tends to be biased toward nitrate within effluent because it is often the main species of nitrogen entering the environment via the effluent. This work contributes concentration and isotopic data for all dissolved inorganic nitrogen (DIN) in both influent and effluent wastewater from three south Texas wastewater treatment plants equipped with activated sludge secondary treatment. The average (n=30) influent concentration of NH4+ was 2300±1100 µM, NO3- was 40.±35 µM, NO2- was 2.3±7.0 µM, and dissolved organic nitrogen (DON) was 140±41 µM. The average (n=33) effluent concentration of NH4+ was 190±270 µM, NO3- was 520±430 µM, NO2- was 14±8.0 µM, and dissolved organic nitrogen (DON) was 300±290 µM. Average isotopic ratios of influent ?15N-NH4+ (n=28) was 3.9±2.8‰, ?15N-NO3- (n=12) was 15±3.5‰, and ?18O-NO3- (n=12) 19±2.6‰. Average isotopic ratios of effluent ?15N-NH4+ (n=7) was 110±190‰, ?15N-NO3- (n=18) was 16±4.9‰, and ?18O-NO3- (n=18) 7.8±2.7‰. These wastewater isotope signatures local to the study’s semi-arid region were employed in Stable Isotope Analysis in R (SIAR) mixing model and compared to the use of literature signatures to convey the large variability in source apportionment that can be reported if locally characterized endmembers are not used in isotope source contribution models. The regional wastewater isotope signatures provided will help constrain isotope mixing models specific to the semi-arid Gulf Coast which in turn will help create informed nitrogen loading mitigation strategies. The treatment plants did not remove all the DIN in the influent and ~20% was subsequently returned to the environment. It was observed that activated sludge secondary treatment is capable of fully nitrifying raw sewage but is limited with respect to complete denitrification. Understanding the capabilities of activated sludge will help determine which tertiary treatment would be needed to remove excess anthropogenic nitrogen from wastewater. For the treatment plants in this study, simply increasing residence time may increase denitrification efficiency. The efficacy of this and other advanced treatment options should be explored further. Also, an argument for using enclosed aeration tanks to further reduce the release of anthropogenic nitrogen into the environment is given.Item Examining micropaleontology to gain insights into long -term oceanographic, glacial, and climatic processes in the Western Amundsen Sea, Antarctica(2023-08) Szemak, Magkena; Prothro, Lindsay; Liu, Chuntao; Zhang, LinThe West Antarctic Ice Sheet (WAIS) is undergoing rapid glacial retreat, posing a significant threat to global climate, sea level, and elemental cycles. The sector of WAIS that has exhibited the highest rates of change are the outlet glaciers draining into the Amundsen Sea Embayment (ASE). These glaciers release high volumes of glacial meltwater, disrupting the formation of dense shelf water and enabling warm Circumpolar Deep Water (CDW) to freely access the underside of ice shelves and generate basal melt. The precise timing and frequency of these events are unknown, largely due to the remote location of the ASE, heavy ice coverage, and limited satellite observations over this region. However, with concerns that a large-scale collapse of this portion of the WAIS is possible on human timescales, it is crucial we understand the specific atmosphere-ocean-ice dynamics that drive elevated melt in this region. To obtain the most complete spatiotemporal observations of this change while also avoiding the logistical challenges of working directly at the modern ice margin, we focus on the geologic record from the portions of the continental shelf that have already deglaciated. This study of ten archived sediment cores is the first-ever high-resolution diatom analysis to be conducted on the deglaciated continental shelf offshore of the eastern Getz ice shelves and the Dotson Ice Shelf, which currently see some of the most rapid volume changes of the WAIS. Diatoms are well diversified, and their composition and distribution are closely connected to ecological conditions, rendering them excellent proxies for environmental changes over time. Our analysis revealed four major paleoenvironmental units. One unit was dominated by sea-ice diatoms, one exhibited evidence of high primary production, one was characterized by a relatively high abundance of F. kerguelensis, which is commonly associated with warm CDW, and the final unit displayed elevated levels of reworked species. The distribution and relative timing of these units, as well as the overall unexpectedly low abundance of Chaetoceros and F. kerguelensis, were interpreted within the context of existing records of environmental conditions and deglacial retreat in the Amundsen Sea, shedding light on the intricate interplay between oceanic processes and glacial change over time. Most notably, diatom assemblages suggest strong similarities in water mass structure during both the present and the time of initial deglaciation following the Last Glacial Maximum; namely, these two intervals show that water column mixing, sea ice formation, and brine export are reduced due to the interference of fresh meltwater. This study also revealed discrepancies between different coring methods, highlighting the need for improved core handling in the field.Item Impact of disturbances on serpulid reef and soft-sediment macrofauna in Baffin Bay, Texas(2023-08) Gilmore, Jennifer; Pollack, Jennifer Beseres; Wetz, Michael; Lebreton, BenoitIn subtropical regions, low inflow estuaries are influenced by long residence times that promote hypersalinity and are intermittently affected by acute rainfall events; extreme cold temperatures, while uncommon, can also occur. Baffin Bay, TX, USA experienced a sustained period (~7 days) of freezing temperatures during “Winter Storm Uri” in February 2021, and experienced an acute freshwater flooding event three months later with a 20 unit drop in salinity. This study used benthic macrofauna from soft-sediment and serpulid reef habitats as indicators for understanding the impact of successive freeze and flood disturbances on this low inflow estuarine ecosystem. Traditional community analyses were supplemented by stable isotope analysis of basal food resources and resource use by an abundant benthic predator and economically important fisheries species, black drum (Pogonias cromis). Successive disturbances in 2021 had minimal effects on soft-sediment benthic macrofauna abundance, biomass, richness, and diversity, with values falling within historically measured ranges. Serpulid reef benthic macrofauna were lower in biomass and richness following Winter Storm Uri, and higher in abundance and richness after freshwater flooding, with values outside of historic records. Despite this fluctuation during 2021 disturbances, serpulid reef macrofauna remained higher in abundance, biomass, and richness and more stable in community composition than soft-sediment macrofauna. Greater prey availability and reliability on serpulid reefs may be important for higher-level consumers. Stable isotope results indicate reliance of black drum on benthic macrofauna prey resources in both Baffin Bay and the adjacent Upper Laguna Madre in 2021. Understanding the response of benthic macrofauna indicators to environmental disturbance from acute freeze and flood events can inform future resource management strategies, particularly in light of increasing climate variability and water resource development.