Theses and Dissertations from UMD
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Item A DETAILED OPTICAL ANALYSIS OF CHROMOPHORIC DISSOLVED ORGANIC MATTER AND C18 EXTRACTED ORGANIC MATTER IN THE CHESAPEAKE BAY(2023) McDonnell, Shannon Marie; Blough, Neil V; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chromophoric dissolved organic matter (CDOM) is a large portion of the open ocean dissolved matter pool which contributes largely to ocean color. The composition and distribution of CDOM is essentially controlled by in-situ biological production, terrestrial inputs, photochemical degradation, and microbial consumption. Estuarine environments contain particularly diverse CDOM composition due to their large variety of inputs and shoreline land usage in addition to the mixing of freshwater and salt water. Developing a further understanding of CDOM variation and composition will help develop and improve satellite remote sensing algorithms, help us understand CDOM’s role in the global carbon, nitrogen, and oxygen cycles, and may help to prioritize in-situ sampling for water quality monitoring in areas of concern. The use of inherent optical properties combined with pH titration and chemical reduction with sodium borohydride (NaBH4), helps to probe the molecular composition of CDOM and its spatial variability. Detailed studies of CDOM from the Chesapeake Bay are limited with many studies only investigating the main channel of the Bay and neglecting the various tributaries. Also, there is a lack of studies which specifically probe the molecular composition of the CDOM samples. To address this, an in-depth analysis of the optical properties of CDOM and C18 extracted organic matter (C18-OM) from the Chesapeake Bay, focusing on various inputs, was performed. Chemical reduction with NaBH4 and pH titration were employed to probe the presence of specific functional groups and their contribution to overall optical properties, and how they vary between locations. Spectral slope (S300-700), E2:E3 absorption ratio, fluorescence intensity, and apparent quantum yield of fluorescence (AQY) were used to analyze 170 samples from various tributaries in the Chesapeake Bay. Overall, this study suggested 1) there may be multiple inputs of CDOM within the Chesapeake Bay 2) the Top of the Bay and central channel of the Bay are impacted by the heavy terrestrial input from the Susquehanna River 3) A lack of correlation between phytoplankton fluorescence and CDOM absorption suggest phytoplankton are not an immediate source of CDOM within the Chesapeake Bay and 4) removal of protein and phytoplankton fluorescence after sample filtration indicates these species must exist in aggregates >0.2 µm. Optical analysis combined with pH titration and NaBH4 reduction investigated the variation between 9 C18-OM extracts from various regions in the Chesapeake Bay and a humic material standard Suwannee River Fulvic Acid (SRFA). Additionally, this study investigated the validity of the Charge-Transfer (CT) model using the optical properties of model compounds. This study suggested 1) certain absorbing and emitting species are lost during C18 extraction but extracts are still representative of their CDOM 2) nearly identical optical responses to pH titration and NaBH4 reduction suggest similar chromophore content throughout the Chesapeake and 3) CT interactions leading to long wavelength absorption are more prevalent in Suwannee River Fulvic Acid (SRFA) than they are in the Chesapeake. To compare the molecular and optical properties of the Chesapeake Bay to other locales, these extracts were compared to extracts from the Delaware Bay (DEL), Equatorial Atlantic Ocean (EAO) and North Pacific Ocean (NPO) in addition to reference materials Suwannee River Fulvic Acid (SRFA), Pony Lake Fulvic Acid (PLFA), and Elliott Soil Humic Acid (ESHA). This study showed 1) composition of deprotonatable and reducible chromophores within the Chesapeake and Delaware Bays is nearly identical but different from the oceans 2) despite being estuaries and containing a mixture of fresh and ocean water, CDOM within both Bays looks terrestrially dominated 3) deep ocean extracts from the Atlantic and Pacific exhibit similar optical response to pH titration, NaBH4 reduction, and NaBH4 reduction combined with pH titration suggesting the similarity of deep ocean waters from both ocean basins.Item Optical Properties of Marine and Picocyanobacteria-derived Dissolved Organic Matter in the Atlantic, Pacific and during Long-term Incubation Experiments(2022) Lahm, Madeline Amelia; Gonsior, Michael; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Marine dissolved organic matter (DOM) is a large, dynamic, and complex pool of carbon, comparable in size to the carbon dioxide pool in the atmosphere, yet it is arguably the least understood component of the global carbon cycle. DOM deriving from picocyanobacterial cells via situationally unique mechanisms, such as viral lysis and metazoan grazing, complicate the picture as the resident pool present reflects sequestration processes that occur at time scales ranging from days to hundreds of thousands of years. Recently virus induced cell lysis released from the globally distributed picocyanobacteria, such as Synechococcus and Prochlorococcus, have been shown to release optically active DOM known as Chromophoric DOM (CDOM) that closely matches the “humic-like” appearance of marine CDOM raising questions about our understanding of this carbon pool given the reliance on spectral measures to assess its composition. Hence, this thesis is seeking to understand CDOM released by lysed picocyanobacteria and to investigate the molecular chemical composition of picocyanobacteria-derived DOM in general. A special focus will be to confirm the refractory nature of chromophores released by lysed picocyanobacteria (Synechococcus) given the reliance on optical properties of recalcitrant DOM being used in the investigation of timescales of carbon storage and biological processing of carbon. As we consider the outcomes of the current global carbon inventory with a sizable error in flux, linking products of microbial processes to chromophore structures and spectrometry is a capstone in understanding the global carbon cycle for decades of research. This study offers a direct comparison of fluorescence signatures from the Bermuda Atlantic Time-Series (BATS) and the Hawai'i Ocean Time-series (HOT), observes optical and nutrient profiles tracking long-term incubation experiments of oligotrophic microbial communities amended with Synechococcus-derived DOM, and explores new techniques in DOM solid-phase extraction (SPE). This work is part of a National Science Foundation project - The Fate of Lysis Products of Picocyanobacteria Contributes to Marine Humic-like Chromophoric Dissolved Organic Matter – linking the accumulating evidence of picocyanobacterial-derived DOM to our understanding of marine organic carbon. Furthermore, we seek to understand how picocyanobacteria-derived DOM is degraded and what role changing heterotrophic microbial communities plays. This research is important to the concept of a microbial carbon pump that supplies a constrained and constant source of DOM which has important implications for the marine carbon cycle and its role in global climate.Item CHARACTERIZATION OF LEACHABLE DISSOLVED ORGANIC MATTER FROM BIOSOLIDS AND IMPLICATIONS FOR NUTRIENT RELEASES, MODELING, AND EMERGING CONTAMINANTS(2019) Fischer, Sarah Jane; Torrents, Alba; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Treated wastewater residuals are utilized as a soil amendment to recycle nutrients to agricultural soils. Due to international application, biosolids are also a significant source of anthropogenic dissolved organic matter (DOM) to the environment. The first contribution of this dissertation characterized DOM and nitrogen mineralization rates of anaerobically digested (AnD) biosolids with variable pre-treatments, such as the thermal hydrolysis pretreatment coupled to anaerobic digestion (THP-AnD). There was not strong evidence that differently pretreated-AnD material had largely different aerobic inorganic nitrogen releases when incubated in a sandy loam soil. Variable pools of DOM decayed in soil treatments over time. Biosolids-DOM was then characterized from a greater representation of full-scale stabilization processes including (i) limed stabilization (LT), (ii) aerobic digestion (AeD), and (iii) anaerobic digestion (AnD). These different final stabilization processes produced substantially different leachates characterized by organic carbon content, size-exclusion chromatography, and fluorescence spectroscopy. Traditional optical metrics previously defined for aquatic DOM did not consistently capture fluorescence maxima of the anthropogenic material. Therefore, boundary-based excitation emission matrix (EEM) analyses were re-defined based on local fluorescence maxima. Novel parallel factor analysis (PARAFAC) and spectral database comparisons confirmed that biosolids-DOM contain both common high energy stimulated components and low energy stimulated components that are unique to digested leachates. The third research contribution applied fluorescence suppression experiments to measure interactions of halogenated ECs with contrasting biosolids-DOM types. Despite digested biosolids-DOM containing different humic acid-like or fulvic acid-like signatures than limed leachates, antimicrobial triclocarban and industrial compound 2-4 dichlorophenol suppressed similar high energy fluorescent signatures in all biosolids-DOM. This suggests TCC and 2-4 DCP electronically interacts with smaller aromatic compounds, such as amino acids, and this interaction is not unique to DOM from different waste stabilizations. This study contributes to future bioavailability assays modeling complex effects of leachate quality on halogenated contaminants. This thesis also confirmed the presence of dehalogenating microbes in the anaerobic microbial community structure of a THP-AD system. These results contribute to on-going work assessing solids treatments, where halogenated emerging contaminants can be dehalogenated before land application. This work advances understanding of biosolids DOM leachates, modeling EEM data, and fate of ECs during full-scale solids treatment processes.Item Alterations to headwater stream microbial communities and carbon cycling in response to environmental change.(2015) Hosen, Jacob Daniel; Palmer, Margaret A; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Organic carbon, principally as dissolved organic matter (DOM), is a fundamental energy source that powers microbial metabolism and shapes food webs in stream ecosystems. The community structure and metabolic activity of stream microbes are significantly impacted by the quantity and quality (i.e. molecular structure) of organic matter resources. Much of the organic matter in headwater streams originates on landscapes. Thus, external inputs of terrestrial organic carbon shape microbial community structure and, subsequently, food webs of headwater streams. Despite the recognized importance of DOM, there is limited understanding of how stream organic matter resources and bacterial community structure respond to watershed urbanization. I studied DOM quantity and quality, microbial heterotrophic function, and bacterial community composition along a gradient of watershed urbanization in headwater streams of the Parkers Creek watershed (Coastal Plain, Maryland, USA). In Chapter 1, I found that watershed impervious cover was significantly related to stream water DOM composition: increasing impervious cover was associated with decreased amounts of natural humic-like DOM and enriched amounts of anthropogenic fulvic acid-like and protein-like DOM. The DOM found in urbanized streams was more bioavailable, but only during spring and summer experiments. I report in Chapter 2 that microbial heterotrophic enzyme production was not strongly related to urbanization. Instead, enzyme levels were most strongly related to temperature and natural groundwater chemical gradients. I show in Chapter 3 that bacterial community composition and co-occurrence patterns also changed significantly in response to increasing urbanization, becoming more dominated by primary producers common to eutrophic waters. I conclude from my research that watershed urbanization fundamentally alters microbial communities and carbon cycling in headwater streams. This urbanized material is more readily metabolized by microbial communities, but only during warmer months. Increased biodegradation of DOM in warm seasons was related to greater microbial enzyme activity, which generally responds positively to increasing temperature. Thus, rising temperatures with climate change and urbanization combined with altered organic matter content are predicted to result in greater CO2 evasion from urbanized streams.