Theses
Permanent URI for this collectionhttps://hdl.handle.net/1969.6/1140
Browse
Browsing Theses by Author "Abdulla, Hussain"
Now showing 1 - 12 of 12
- Results Per Page
- Sort Options
Item Assessing the influence of genotypic diversity on sulfur dynamics in the seagrass halodule wrightii using stable isotope analysis(2022-07-19) Girard, Allyson; Larkin, Patrick; Abdulla, Hussain; Felix, JosephCoastal development and other mounting anthropogenic pressures are threatening valuable seagrass habitats. The greatest risks posed to seagrasses are the effects of coastal eutrophication, which stimulates primary productivity and ultimately supplies abundant organic matter to marine sediments. The decomposition of this material is initially facilitated by aerobic microorganisms, depleting dissolved oxygen and generating anoxic conditions. Under these conditions, anaerobic microorganisms such as sulfate-reducing bacteria begin to dominate the degradation process, which reduce sulfate (SO42-) to sulfide (H2S) for energy production. The accumulation of H2S in marine sediments is problematic for seagrasses, as this molecule can be highly toxic. Yet, seagrasses can withstand relatively high concentrations of H2S in their environments. Stable isotope analyses have been used to investigate sulfide intrusion in seagrass meadows, as the unique isotopic signature of sediment-derived sulfur can be used to trace the uptake of H2S and its distribution throughout the plant. This technique has allowed the study of factors that may influence sulfide production and intrusion, such as reduced light availability, organic matter enrichment, and high temperatures. However, few studies have examined the biological or biochemical features that enable seagrasses to withstand relatively high sedimentary sulfide levels. One biological feature that may help confer resistance is population genetic diversity, which has been identified as an important trait in the survival and performance of seagrass meadows under environmental stress. In general, genetic diversity is thought to play an important role in population resistance to environmental disturbance, as a wider assortment of functional traits encoded at the molecular level results in a variety of phenotypes likely to possess morphological and physiological differences that are complementary. This genotypic complementarity may extend to biochemical strategies associated with tolerance to, or detoxification of, H2S. The purpose of this study was to determine whether sulfide intrusion differs between genotypes of the seagrass Halodule wrightii, a prominent species in the Gulf of Mexico. Further, as the sulfur isotopic composition of marine sediments and seagrass vegetation is known to exhibit high spatial variability, this study also sought to assess sulfide intrusion between populations from distinct sites along the Texas Gulf Coast. Stable isotope data was used to infer the proportion of sulfur in H. wrightii tissues that was derived from sedimentary sulfide, while total sulfur (TS) data was also considered to understand the extent of sulfur accumulation within the plant. H. wrightii genotypes were determined by screening each sample at a series of microsatellite loci previously identified for this species. Although no difference in sulfide intrusion was observed between genotypes, sulfide uptake and distribution was significantly different between the three study sites. The results offer important insight to the effect of local conditions on sulfide intrusion in seagrass meadows and may guide future investigations concerned with the influence of genotypic diversity on H2S metabolism in seagrasses.Item Comprehensive approach for dissolved organic matter chemical characterization using orbitrap fusion tribrid mass spectrometer coupled with ion and liquid chromatography techniques(2021-12) Bergmann, Daniela; Bergmann, Daniela; Abdulla, Hussain; Abdulla, Hussain; Coffin, Richard; Murgulet, Dorina; Coffin, Richard; Murgulet, DorinaDissolved organic matter (DOM) contains the largest active organic carbon in the global carbon cycle. Though it has been extensively studied, only <10% of DOM has been chemically characterized into individual dissolved compounds. DOM is one of the most complex mixtures in nature; it consists of thousands of compounds with various molecular compositions, functional groups, and physicochemical characteristics. This study introduced a more comprehensive DOM characterization method by coupling both Ion Chromatography and Liquid Chromatography with high accuracy mass and resolution mass spectrometer. Estuarine DOM samples were and analyzed by Orbitrap Fusion Tribrid mass spectrometer (OT-FT-MS) coupled to both Ion Chromatography (IC) in negative mode and Liquid Chromatography (LC) in positive mode. This combination allows us to cover various DOM compounds ranging from highly cationic to highly anionic molecules. On-the-fly mass calibration of the Orbitrap at every scan by utilizing the “lock mass” function in the OT-FT-MS assures high mass accuracy throughout the whole sample run by a post-column introduction of internal labeled standards. A pooled quality control sample was used to increase reproducibility by applying systematic error removal using the random forest (SERRF) technique. The on-the-fly internal calibration application was tested on standard mixes before applying to actual DOM samples. In LC, the mass accuracy for the standards was consistently below +1.0ppm, and in IC below -4.0ppm, giving the OT-FT-MS the potential of reaching the massaccuracy of the Fourier-transform ion cyclotron resonance mass spectrometer (FT-ICR-MS). Once “lock mass” was established, estuarine surface water DOMsamples were analyzed in negative and positive modes. LC coupled to the OT-FT-MS for positive mode detection resulted in 915 compounds including 53 peptides and deaminated peptides that were identified through an in-house mass list comparison. IC coupled to the OT-FT-MS for negative mode detection resulted in 1432 extra compounds and including 361 deaminated peptides. Comparing the number of compounds detected shows the importance of analyzing both detection modes and the promising results of using IC in negative mode. A random forest-based normalization termed SERRF was compared to the traditional way of data normalization constant sum technique. Although constant sum provides already meaningful PCA data, SERRF assured a tight cluster of all Quality Control (QC). In IC mode, the relative standard deviation of QC samples was as high as 34.1% and corrected to 4.4% with SERRF, and in LC, the relative standard deviation was corrected from 28.1% to 3.9%. A combination of IC, LC, “lock mass”, and SERRF with the OT-FT-MS provides reliable and comprehensive approaches for DOM molecular characterization.Item Corals in crisis: How temperature and nutrient fluctuations affect physiological responses of corals and their microbiome in K?ne‘ohe Bay, Hawai‘i(2023-05) Ruben, Zoe; Bahr, Keisha; Turner, Jeffrey; Abdulla, HussainCoral reefs are the foundation of the social, cultural, and economic life in Hawai?i; however, these reefs have not escaped the conditions that have ravaged coral reefs in other areas. Along the east coast of O?ahu lies K?ne?ohe Bay, which serves as a living laboratory with distinct differences in environmental gradients due to variations in circulation and residency times. This provides a unique opportunity to explore the impact of water quality and ongoing ocean warming on coral health, susceptibility, and tolerance. Pairs of historically bleached/non-bleached corals were collected at two sites within K?ne?ohe Bay and subjected to experimental treatments varying in temperature and nutrient levels for one month at the Hawai?i Institute of Marine Biology. Biological response variables were measured, and subsamples were taken from the coral fragments at the beginning and end of the experiment for bacterial community analysis. Results demonstrate that coral decline and bleaching susceptibility were least prevalent in the Control and Elevated Nutrient treatments but most prevalent in the Elevated Nutrient + Elevated Temperature treatment, indicating that low-level nutrients may benefit the corals. Still, the combined stressors may have a synergistic, negative effect. Microbial clustering analyses reveal a shift in relative abundances of bacteria before vs. after exposure to stress. These findings may support that coral bleaching susceptibility is manifested throughout the coral holobiont and that physiological response to interactive stressors can be better understood and potentially mitigated.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 Distribution of pesticides in groundwater and surface water flood-impacted unconnected communities in South Texas following Hurricane Hanna(2022-08) Matarrita Rodríguez, Jessie; Abdulla, Hussain; Conkle, Jeremy L.; Murgulet, DorinaPesticides are a vital farming input as they help protect crops from pests and diseases for quality yields and high productivity. However, pesticides' high production, extensive use, and persistence are a potential risk for human health and ecosystems due to their leaching or runoff into the surface water (SW) and groundwater (GW). Over the years, there has been an increasing concern regarding the water quality of SW and GW next to farming areas, specifically after spills or industrial discharges, heavy rainfall, and intense storms. In the case of hurricanes, these cause deposition of contaminants from the atmosphere, disturbance and transport of the sediments in surface water bodies, surface run-off, and penetration of floodwaters to GW. In addition, pesticide degradation in the environment due to different biotic and abiotic transformation processes produces transformation products (TPs), sometimes even more toxic than the original compound. In July 2020, Hurricane Hanna severely damaged infrastructure and agriculture in many counties across the Rio Grande Valley. This area has the largest colonias in South Texas, predominantly Hispanic low-income semirural communities near the Texas-Mexico border that mainly rely on GW as a drinking water source. As part of this study, surface water and groundwater samples were collected from colonias in South Texas communities after hurricane Hanna for one year. The analytical approach involved solid-phase extraction (SPE) followed by suspect and target screening of pesticides using ultrahigh-pressure liquid chromatography (UPLC) coupled to a high-resolution Orbitrap Fusion Tribrid mass spectrometer system (OT-FTMS). The advantages of the state-of-the-art high resolution mass spectrometry allowed the accurate identification and quantification of pesticides using an in-house compound database of 308 pesticides for target screening. This is one of the most extensive studies that has screened and quantified over 200 pesticides in a single sample in the United States and, to my knowledge, is one of the largest in Texas. The results of eight monitoring sampling campaigns revealed the occurrence of 21 pesticides with minimum instrumental limit of detection (LOD) of 0.05 ng/mL and limit of quantification (LOQ) of 0.10 ng/mL. Six herbicides were the most detected compounds, followed by insecticides (5), fungicides (4), TPs (3), and a plant growth regulator (1). The most frequently detected compounds were atrazine, clothianidin, cycluron, DEA, dinotefuran, and norflurazon and those with the highest concentrations were clothianidin (211 ng/L), DEET (13,885 ng/L), and norflurazon (952 ng/L). In general, more compounds were detected in GW than in SW, except for atrazine and DEA. Atrazine in SW showed higher detections frequency (67%) than GW (15%) as well as DEA (GW = 6%, SW = 8%). DEET was the compound detected at the highest frequency in GW (74%) while atrazine was detected at the highest frequency in SW (67%). The leaching of pesticides to GW is a complex process and depends on the pesticide's chemical properties, characteristics of the soil, volatilization, climatic conditions of the site, plant uptake, and pesticide management practices. Mainly, pesticides with high leaching potential are more likely to be transported in groundwater beyond application area. In this study, clothianidin and norflurazon with high leaching potential showed significant concentrations in GW. This is one of the few studies able to survey more than 200 pesticides in the United States in general and in Texas specifically, using high resolution mass spectrometry. This work provides a baseline of the water quality for those communities that rely on GW as the primary source of drinking water supply. The occurrence of pesticides in GW demonstrates the vulnerability of the area and the need to continue monitoring the water quality in this region.Item Distribution of polymer types in Matagorda Bay & biofilm presence on surface of plastic pollution: A study using attenuated total reflectance-Fourier Transform Infrared Spectroscopy and principal component analysis(2023-12) Ivy, Kiersten M; Abdulla, Hussain; Conkle, Jeremy; Olson, MarkGlobal plastic pollution presents significant environmental and economic challenges, exacerbated by mismanagement and low recycling rates. Studies have shown other pollutants like persistent organic pollutants (POPs) and heavy metals can sorb to plastic debris in aquatic ecosystems, making them more readily dispersed throughout ecosystems. This study (1) quantified the spatial and seasonal distribution of different plastic polymer types along the Matagorda Bay system, and (2) explored the nature of the biofilm form on these plastic debris and any correlation between biofilm type and polymer type throughout different seasons. This comprehensive study, the most extensive of its kind with over 3,000 samples, investigates the distribution of plastic polymers AND biofilm formation in the Matagorda and San Antonio Bays across three seasons in 2022. Attenuated total reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) along with Principal Component Analysis (PCA) was employed to identify polymer types and investigate biofilm formation on the collected samples. Polyethylene and polypropylene were the predominant polymer types observed across all sites and seasons. PCA suggested that biofilm was prevalent across all polymer types and seasons, and it is made mainly of extracellular polymer substances (EPS) that are rich in carbohydrates and proteins. Spectra integration showed a positive linear relationship between carbohydrate and protein biofilm components. This study not only provides a deeper understanding of biofilm roles in pollutant adsorption, but also introduces a novel, nondestructive approach for examining bacterial biofilms, paving the way for improved environmental management strategies.Item Metabolomic profiling of human embryo during pre-implantation in vitro fertilization non-invasive approach(2021-05) Al Shaikh, Maryam; Abdulla, Hussain; Billiot, Fereshteh; Gonzales, Xavier FonzIn vitro fertilization (IVF) is a standard protocol used to treat infertility. However, the probability of successful embryo implantation during IVF is very low. Most of the IVF clinics depend on morphological scoring by embryologists to select high-quality embryos capable of implantation. But morphological scoring has only around 30% successful pregnancy rate. In this study, I investigated the potential of a new embryo scoring method based on measuring the change in culture media's metabolomic profiles. I analyzed 71 culture media samples with known pregnancy outcomes from two different culture media by ultraperformance liquid chromatography (UPLC) coupled with ultrahigh-resolution and accuracy mass spectrometer. I used a newly developed on-the-fly dynamic data acquisition technique to increase the percentage of metabolite compounds with MS2 fragmentation spectra. To identify potential metabolomic pregnancy biomarkers, we used a combination of statistical analysis techniques like principal component analysis (PCA), differential analysis (volcano plots), and trend charts. We used Molecular Formula Calculator software, ChemSpider, and mzCloud databases to assign the molecule formula and chemical structure for the detected significant biomarkers. Also, we applied in-silico fragmentation and FISh scoring to validate the chemical structures of the identified biomarkers. Using PCA, we did not find any apparent clustering for pregnant or non-pregnant samples, but we could locate a few outliers' spectra. However, with volcano plots, we were able to identify a set of up-regulated biomarkers that are associated with non-pregnancy and down-regulated biomarkers that are associated with pregnancy in both media. Utilizing the KEGG and Metabolika databases, we recognized two possible metabolomics pathways. This study can improve selecting viable embryos, which will lead to an increase in the success rate of IVF. It will also provide a better understanding of human embryos' metabolomic biochemical pathways during the preimplantation stage.Item Mobilization and transport of contaminants to groundwater in response to extreme weather events in South Texas(2022-12) Vickers, Christopher M.; Murgulet, Dorina; Murgulet, Valeriu; Kapoor, Vikram; Abdulla, HussainUnderstanding how shallow aquifers respond to tropical storms, including the possibility of groundwater contamination via floodwaters that carry pathogens and mobilize contaminants, directly affecting human and ecosystem health, is crucial. Hurricane Hanna made landfall in July 2020, impacting coastal, rural, and urban south Texas with storm surges reaching over 1.2m in Baffin Bay (BB) and floodwaters in the Rio Grande Valley (RGV) over 1m deep. The RGV borders Mexico is densely populated and comprises four counties, several cities, and dozens of towns with encircling lands used for agriculture. A sizable portion of the RGV population lives in impoverished settlements called colonias: lands originally used for agriculture, not bound by municipal regulations, and lacking infrastructure including paved roads, sewage, water connections, and access to portable water. This project aimed to determine aquifer responses to flooding resulting from Hanna via biological and geochemical evaluations over one year. This project also aimed to evaluate the nature of the risk of groundwater contamination in response to other seasonal changes (e.g., times of little to no precipitation or rain lasting weeks and months) in both inland, urban settings and rural, coastal settings. Nutrient levels in groundwater were found to fluctuate based on both hydroclimatic season and time of year. Both dissolved inorganic nitrogen (DIN) and phosphate (HPO4 2- ) were highest during the extended summer storms in 2021, lasting weeks/months, which coincides with the planting season when substantial amounts of fertilizer are used. Most of the samples collected throughout the project had varying amounts of total coliform present in both surface- and groundwater, with the highest concentration in surface water. Most of the groundwater E.coli was below detection limits regardless of the season. However, following Hanna a noticeable E.coli level was measured at one location in RGV, indicating direct contamination of the aquifer from flooding via water well conduits. Both lead (Pb+2) and zinc (Zn+2) were present in groundwater, particularly at RGV, where concentrations significantly increased during the extended wet season. While not as high, concentrations of both metals were higher following Hurricane Hanna's flooding when compared to the dry season. The quick response of the aquifer to hydroclimatic changes is also revealed by the stable isotopes of oxygen (δ18O) and hydrogen (δD). Both surface- and groundwater were most depleted in the isotopes immediately after Hurricane Hanna with significant enrichment observed beginning approximately one month after the hurricane's landfall. In addition to the evaporative effects during hot months, the isotope data also show faster infiltration rates immediately post-flooding when compared to the extended wet event when the recharge of runoff is slow through the arid soils. The results underscore the importance of proper infrastructure, such as sewage, drainage, and capping of water wells no longer in-service and/or non-compliant with current regulations, in order to protect groundwater and those who rely on this valuable resource.Item Molecular networking with network analysis(2021-12) Cross, Breeanna; Abdulla, Hussain; Guardiola, José; Felix, Joseph D.Network analysis is the analysis of a collection of elements and their relationships based on graph theory. Graph theory has become essential for identifying and understanding the relationships between compounds in mass spectrometry (MS). A molecular network is the visual display of the chemical space in MS experiments. The advancements in coupling different chromatography techniques with high resolution and mass accuracy mass spectrometer have increased the ability to produce better quality tandem mass spectrometry (MS/MS) of individual compounds in a single run. With these advancements, compounds within complex mixtures were be analyzed and detected more thoroughly using both the targeted and untargeted approaches. Further, the structures of these compounds might be able to be identified with higher confidence. Using the generated MS/MS spectra, molecular networks were developed based on the similarities of molecular structures. However, the traditional 2-dimensional network analysis is static and could not show how these compounds change with depth, time, or distance. In this study, I have created a three-dimensional (3-D) molecular network analysis software to examine how dissolved organic matter (DOM) transforms with depth, with time, or with distance to have fully understood, for example, the accumulation and reactivity of DOM in the marine ecosystem. As a proof-of-concept example, I have used 3D molecular network analysis to understand abiotic sulfurization mechanisms in marine sediments better. The abiotic sulfurization enhances organic matter preservation and proto kerogen formation at low temperatures within marine sediments. The molecular networking method presented here supports the evidence of abiotic nucleophilic addition reactions involving bisulfide (HS−) and polysulfide (HSx−) in Santa Barbara Basin sediment porewater. This 3D-molecular Network analysis technique has a great potential to reveal different transformation and degradation pathways of dissolved organic matter by various biotic and abiotic environmental perturbations.Item PH effects on solid phase extractable dissolved organic matter: Expanding the analytical window(2023-08) Elliott, Justin Yoshida; Abdulla, Hussain; Felix, Joseph; Hu, XinpingMarine dissolved organic matter (DOM) is the largest exchangeable organic carbon pool, holding comparable amounts of carbon as CO2 in the atmosphere and exceeding all biomass. DOM constituents are made up of thousands of unique organic compounds with astounding molecular diversity, featuring a wide range of hydrophobicity, size, and acidic or basic properties. Modern high resolution, high accuracy, and fast cycle time mass spectrometers can provide deep molecular insights into complex mixtures but require compatible samples. The inorganic matrix and low DOM concentrations have required organic biogeochemists to rely on Agilent Bond Elut Priority PoLutant (PPL) Solid Phase Extraction (SPE) to isolate and concentrate DOM through hydrophobic interactions. Currently, the standard SPE method has been optimized to maximize recovery? of dissolved organic carbon (DOC) through sample acidification and methanol elution. However, there is a lack of full understanding of the effect of adjusting the sample pH on the extraction efficiency of different DOM compounds. This study investigated the effects of pH modification on the SPE recoveries and the effects of various procedures on the isolated DOM. This study collected water samples from three sites to represent different marine systems (Lavaca River, Baffin Bay and Gulf of Mexico) with unique sources and signatures of DOM. Samples were acidified to pH 2, kept at natural pH, basified to pH 10 or run sequentially where the permeate was further isolated. Various modified methanol elution solvents were tested, comparing methanol, acidic methanol, basic methanol, and combinations of both. The isolated DOM was chemically characterized in positive mode separated with reverse-phase high performance liquid chromatography (RP-HPLC) and in negative mode with Anion Exchange Ion Chromatography (AEX-IC) on an Orbitrap Fusion Tribrid mass spectrometer (OT-FTMS) using data dependent acquisition (DDA). The standard SPE procedure with acidification yielded the highest recoveries but showed bias against dissolved organic nitrogen (DON). The samples that were not acidified, including natural pH or pH 10, yielded a different fraction of enigmatic DOM with a higher nitrogen percentage than the DOM isolates using the standard procedure. We found that through isolating DOM from a water sample at natural pH and pH 2, two fractions of DOM can be isolated, including hydrophobic DOM, acidic DOM, and basic DOM. These results suggest in order to better represent DOM from marine systems, collecting both fractions and analyzing in both positive and negative modes provide a more comprehensive and representative isolate of DOM.Item Quantification and transformation of water soluble organic nitrogen in a coastal urban airshed(2021-05) Apacible, Scilyn; Apacible, Scilyn; Felix, Joseph; Felix, Joseph; Coffin, Richard; Abdulla, Hussain; Coffin, Richard; Abdulla, HussainAtmospheric organic nitrogen (ON) is poorly quantified due to its complexity, measurement difficulty and historical consensus that it was less significant than inorganic nitrogen. Studies that have measured ON are not evenly spread across various environments or geographic regions further contributing to a general lack of knowledge about global atmospheric ON deposition and transformations. In this study, PM2.5 and PM10 samples were collected in an urban coastal airshed, Corpus Christi, TX, USA between November 2019, and October 2020. The organic and inorganic forms of nitrogen were analyzed and the factors controlling their concentrations were examined. The mean concentrations of water soluble organic nitrogen (WSON) in PM2.5 and PM10 were 0.081 ± 0.12 and 0.12 ± 0.11 µg m-3, respectively. The observed WSON concentrations were similar to those observed in remote and marine sites. The WSON concentrations showed significant correlation with NO3⁻ and NH4⁺ during spring season in PM10 indicating that marine source (e.g., sea salt) and biogenic emission are contributing factor for NO3⁻, while agricultural sources are contributing factor for NH4⁺. On average, ON contributed 15% and 10% to total nitrogen in PM2.5 and PM10 at the coastal urban airshed. The average annual dry deposition fluxes for PM2.5 NO3⁻, NH4⁺, and WSON were 0.217, 0.027, and 0.68 kg ha−1 y −1, respectively. The annual dry deposition fluxes for PM10 NO3⁻, NH4⁺, and WSON were 0.55, 0.031, and 2.48 kg ha−1 y −1. The EPA CASTNET network’s closet monitoring site reports annual dry N deposition flux of 3.67 kg ha−1 y −1 , but does not account for ON thus potentially overlooking ~40% of N deposition. Furthermore, the photochemical transformation of ON into IN was investigated and results from these experiments revealed alternating photoproduction and degradation of IN (NO3⁻, NH4⁺). These WSON photochemical transformation will contribute to the increase or decrease of nitrogen bioavailability after deposition in this coastal region. This study highlights the significance of the ON component of atmospheric deposition in this northern Gulf of Mexico region and the need to for ON inclusion when determining coastal N loading and N mitigation strategies.Item Seasonal ammonium benthic flux and photo-ammonification of dissolved organic nitrogen in Baffin Bay - Texas(2022-12) Ton, Quang; Abdulla, Hussain; Felix, Joseph; Seemann, FraukeEstuaries and coastal regions are hot spots of global primary production as they account for 30% of the net marine productivity, despite representing only 7% of the total marine surface area. Nutrient patchiness is the second most influential factor (after temperature) in site seasonal variability of net primary production. This guides a consensus that nitrogen (N) loading is a primary factor in eutrophication and hypoxia. Despite this recognized connection between excess N loading and ecosystem decline, the internal N cycling and transformations in coastal areas are still not well characterized. This study quantified the sediment porewater flux of ammonium (NH4 + ) and photo-ammonification from benthic dissolved organic nitrogen (DON) as well as investigated changes in porewater DOM chemical structures of Baffin Bay - Texas during different irradiation time periods using the state of art Orbitrap Fusion Tribrid Mass Spectrometer. Baffin Bay (BB) is a semi-arid inverse estuary ecosystem that has experienced prolonged and intense brown tide blooms (Aureoumbra lagunensis species) since the 1990s, and several occurrences of hypoxia conditions that caused seagrass die-off and several occasions of large fish kill over the past decades. Pore water samples were collected from six stations in the bay during six seasons (October 2020, February 2021, June 2021, October 2021, February 2022, and May 2022) for depth profile analysis. The bay showed a large spatial variability of NH4 + benthic flux, with BB1 having the lowest average NH4 + flux at 56 ± 27 µmol.m-2.day-1 and BB3 had the highest average flux at 347 ± 211 µmol.m-2.day-1. The seasonal NH4 + average benthic flux to the entire bay water column was 124 – 244 µmol.m-2.day-1 and served as a significant source of inorganic nutrients to support the primary production. In addition, the photo-ammonification rate of benthic DON (after it entered the water column) ranged from 0.038-0.361 µmol.L-1.hour-1 and served as an additional source of inorganic nutrients to primary production. Chromophoric dissolved organic matter (CDOM) absorbed sunlight radiation then degraded to lower molecular weight CDOM and released ammonia, deaminated peptides, free amino acids, and organic acids. Peptides and deaminated peptides with chromophoric amino acids such as tryptophan, tyrosine, proline, phenylalanine, and histidine degraded with solar irradiation. It was suggested that rings and conjugated double bonds were responsible for absorbing sunlight radiation and degrading CDOM structures. This study shed light on internal N cycling and transformations in Baffin Bay and the need to consider these processes in any future attempt to remediate and lower the brown tides events in the bay.