MEES Theses and Dissertations

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Subject: search.filters.subject.Dissolved Organic Matter

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    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.
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    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.