TAMU-CC Theses, Dissertations, and Other Projects
Permanent URI for this communityhttps://hdl.handle.net/1969.6/1
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"
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Item Determining Nitrogen sources and processing along the Texas Coast and potential impacts due to sea-level variations(2023-08) Taylor, Erin; Felix, Joseph; Murgulet, Dorina; Wetz, MichaelThe Gulf Coast of Texas has had increased incidents of eutrophication and high concentrations of fecal bacteria since 2009, which are indicators of poor water quality. Nitrogen loading in the form of both dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) sources can contribute to water quality decline. To determine the sources and processes contributing to nitrogen loading on Texas sandy barrier islands, ground-, pore- and surface waters from Galveston to Matagorda counties were analyzed for DON and DIN concentrations and isotopic composition. Additionally, groundwater elevations were monitored to determine if water table fluctuations were associated with increases/decreases in N loading. Average nitrate (NO3-), ammonium (NH4+), and dissolved organic nitrogen (DON) in surface and porewater samples were reminiscent of ocean processing. Surface water isotopic evidence indicated assimilation and competing subsurface denitrification, while porewater isotopic evidence suggested competing DNRA/denitrification coupled with nitrification processes. In contrast, NO3- was elevated at three groundwater sites, while most wells showed elevated NH4+ concentrations. Isotopic and nutrient concentration evidence indicated a septic signature with coupled denitrification/anammox and nitrification processes, along with possible saltwater intrusion. Regarding monitoring wells, depth to water (DTW) values had a positive correlation with NO3- concentrations and a negative correlation with NH4+ concentrations, indicating direct contamination from a NH4+ source at low DTW and NH4+ source processing to NO3- at high DTW. A Bayesian-type isotope mixing model estimated NO3- source contributions to Gulf surface water as septic/sewage (35.9 ± 20.5%), dog waste/gull guano (22.9 ± 17.5%), soil (22.9 ± 15.5%), and wet deposition (18.3 ± 7.8%). Nitrate source contributions to porewater were septic/sewage (35.3 ± 21.3%), soil (26.8 ± 18.7%), dog waste/gull guano (25.2 ± 19.0%), and wet deposition (12.7 ± 6.7%). Source contributions to groundwater were septic/sewage (62.6 ± 24.1%), dog waste/gull guano (15.8 ± 21.7%), wet deposition (12.8 ± 7.7%), and soil (8.8 ± 6.3%). Results indicate that there is substantial septic/sewage contamination throughout the study area and possible contamination from animal waste, with evidence of saltwater intrusion in wells. This is the first study to attempt to characterize nitrogen processing, loading, and source contributions to the area. A history of failing septic/sewage systems, along with sea level rise and the increase of more severe climatic events, is estimated to cause more saltwater intrusion and septic/sewage malfunctions to an already vulnerable coastal area. Stakeholders and decision makers can use this data as a starting point for contamination and saltwater intrusion mitigation strategies.