Biology
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Item Impact of Plant-Derived Allelochemicals on Harmful Algal Blooms(2023) Armstrong, Christen Taylor; Place, Allen; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Harmful algal blooms (HABs) are a global concern in both freshwater and coastal systems; creating dire consequences for public health, water resources, and local economies. Thus, there is a focus among scientists and environmental managers on HAB prediction, prevention, and mitigation. Current chemical mitigation methods include algicides such as copper sulphate, chlorination, and hydrogen peroxide, which can have high financial costs and secondary pollution associated with them. The use of natural allelochemicals produced by plants and bacteria has received considerable attention as an alternative to synthetic algicides, as they can have negligible toxins, be highly selective, and easily degraded in the environment. This dissertation is a coalition of research looking into new sources of plant allelochemicals and whether natural levels of allelochemicals in the water column, can impact phytoplankton communities and the presence of toxin-producing algal species. The first objective focused on the use of the waste product: brewer’s spent grain (BSG), as a new control mechanism to inhibit the growth of toxic algae. BSG extract of doses higher than 250mg/L inhibited the growth of freshwater and marine toxin-producing cyanobacteria and dinoflagellate species (Microcystis aeruginosa and Karenia brevis), while not impacting the diatom and chlorophyte tested (Scenedesmus obliquus and Prorocentrum tricornutum). This same dosage of BSG caused cyanobacteria abundance in lake water to decline by 90% within 4 days and chlorophytes to dominate the community by day 6 during a microcosm study. However, an experiment controlling bacteria levels demonstrated that the decline of K. brevis growth was likely due to the increase in abundance or presence of certain types of bacteria growing with exposure to BSG extract rather than due to chemicals released from the BSG. The second and third objectives shifted focus to the New Jersey Pinelands and whether the chemicals released into the water from terrestrial and marine plants in these waters, like phenolic compounds, impact the phytoplankton community and toxin-producing species. The second objective focused on the spatial and temporal distribution of phycotoxins along two New Jersey estuaries using passive samplers and whether the utility of passive samplers was impacted by the excess phenolic compounds in the water. By utilizing passive samplers in New Jersey, phycotoxins not previously reported in the area were described, such as azaspiracids, goniodomin-A and yessotoxins. However, this objective also showed some of the caveats of passive samplers, especially at sites with high phenolic compounds. The third objective focused on identifying the primary environmental drivers of chlorophyll a concentration and phytoplankton community along the freshwater – marine continuum of two New Jersey Estuaries with varying levels of disturbance. This dissertation explored BSG as a novel control method of HABs, and provided new information for monitoring, managing, and modeling HABs based on phenolic content measured in the water.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 Effects of seawater Sr/Ca on coral paleothermometry in the Florida Keys and Virgin Islands revealed by multi-year continuous monitoring(2020) Hughes, Hunter Passman; Kilbourne, Kelly H; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Coral skeletal Sr/Ca is a widely applied proxy indicator for tropical sea surface temperature (SST) because the elemental ratio in coral aragonite is influenced by both SST and seawater Sr/Ca. Application of the methodology assumes that seawater Sr/Ca is a constant in coral reef environments, and the ratio can be used to solve for paleotemperatures based upon an established coral Sr/Ca – SST relationship. This study tests that assumption by documenting seawater Sr/Ca variability in the Florida Keys and in the U.S. and British Virgin Islands using continuous osmotic pumps. Samples are analyzed for Sr/Ca using a novel method via Inductively Coupled Plasma – Atomic Emission Spectrometry. While mean seawater Sr/Ca did not vary significantly between sites, all sites exhibited significant annual variability (~0.5 – 0.1 mmol/mol), with the greatest variability observed in locations most impacted by freshwater discharge. These findings correspond to large temperature offsets (>2 degrees Celsius) in standard coral Sr/Ca-based SST reconstructions.Item YEAR-ROUND DETERMINATION OF METHANE (CH4) SOURCES AND SINKS IN ARCTIC LAKES USING CONTINUOUS AND AUTONOMOUS SAMPLING(2020) McIntosh Marcek, Hadley; Lapham, Laura L; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Methane (CH4) is a potent greenhouse gas and its concentration has been increasing in the atmosphere. While natural emissions from inland water bodies are known to be important, there is large uncertainty in the amount of methane released from lakes to the atmosphere, especially from Northern latitudes. Part of this is due to limited sampling in these systems during dynamic periods, such as ice-over and ice-melt. To better understand these temporal dynamics, I used autonomous, continuous samplers (OsmoSamplers) to collect lake water year-round over two years (2015-2017). Lake water was collected at a fine temporal resolution to provide time-integrated (~1 week) samples from multiple Arctic lakes within the Mackenzie Delta. The Mackenzie Delta is a lake-rich, productive environment that is expected to be a significant source of methane to the atmosphere. Lakes spanning the central delta and outer delta were sampled for methane concentration and stable carbon isotope ratio (δ13C-CH4) changes, ion concentrations, and water column characteristics were measured with continuous sensor data (temperature, water pressure, conductivity, light, and dissolved oxygen). These unique time-series datasets show lakes exhibit a close coupling of dissolved oxygen, and other electron acceptors, with the timing of methane increasing during ice-cover. The increase in methane concentrations is primarily from diffusion out of sediments and possibly water-column methanogenesis. One lake in the outer delta exhibited thermogenic gas bubble dissolution that contributed to under-ice methane concentration increases. Following ice-melt, lake depth appears to impact methane release to the atmosphere. Shallower lakes exhibit rapid fluxes followed by significant microbial methanotrophy. Deeper lakes in the central delta are connected to groundwater, though it does not appear groundwater transports methane. This is the first study of dissolved methane and gas bubble 14C-age in the Mackenzie Delta and shows that dissolved methane is produced primarily from modern carbon sources, such as macrophyte biomass and terrestrial material, but some methane transported in gas bubbles is significantly older, with seeps in the outer delta rapidly releasing radiocarbon-dead, thermogenic methane. This study demonstrates the importance of multi-lake studies particularly with fine scale temporal sampling to understand methane processes in seasonally ice-covered lakes.Item POTENTIAL IMPACT OF VARIATION IN THE SEAWATER STRONTIUM TO CALCIUM RATIO ON CORAL PALEOTHERMOMETRY IN THE FLORIDA KEYS, USA(2018) Khare, Agraj; Kilbourne, Kelly H; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Standard methods of reconstructing past sea surface temperatures with coral skeletal Sr/Ca ratios assume that the seawater Sr/Ca ratio is constant. However, data to support this assumption are sparse in coral reef environments, in part because analytical techniques capable of determining seawater Sr/Ca with sufficient accuracy and precision are time-consuming and not widely available. This work presents a new method to measure seawater Sr/Ca based on inductively coupled plasma atomic emission spectrometry that can be easily adopted by many coral paleothermometry laboratories. The work also presents a spatially gridded study of summer and winter seawater Sr/Ca from the middle Florida Keys Reef Tract. The results indicate that seawater Sr/Ca in nearshore waters influenced by the Florida Bay varies by ~0.1 mmol/mol. The observed variation could lead to errors of ~2°C in temperature reconstructions and suggests that corals growing in waters influenced by Florida Bay are less suited for paleoclimate studies.Item Sampling Errors Arising from Entrainment and Insufficient Flushing of Oceanographic Sampling Bottles(2017) Paver, Christopher Raymond; Codispoti, Louis A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Collection of representative water samples is important for accurately determining biological and chemical constituents. Modern carousel packages can permit bottle “soak times” to approach zero while increasing the impacts of entrainment due to their large size. In addition, some modern sampling bottles have relatively small openings relative to their volumes, a factor that inhibits flushing. Examination of qualitative evidence from various expeditions suggested that insufficient “soak times” can produce unrepresentative water samples. In this study, historical data are presented, but the emphasis is on field experiment data that better quantifies the errors that can arise from insufficient bottle flushing. The experiments suggest that under some conditions, soak times of more than 2 minutes may be required to collect representative water samples. The experiments also suggest the occurrence of stratification within bottles. The impact of insufficient soak times on some chemical gradients is discussed and improved sampling protocols are suggested.Item A Proteomics Approach to the Examination of Proteins in Marine Systems(2014) Faux, Jessica Felicia; Harvey, Henry R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The response of global carbon and nitrogen cycles to future climate change is uncertain. In order to understand the impacts that future changes to climate will have on these cycles, a more detailed understanding of them is essential. This dissertation utilizes a combined approach of molecular biomarkers and proteomic investigations to elucidate historic source material contributions and microbial protein production to contribute to a more thorough understanding of the marine carbon and nitrogen cycles. The examination of molecular organic biomarkers throughout an Arctic sediment core showed the dominant input in the area was from marine sources with lower but steady contributions from terrestrial sources during the Holocene. Attempts to recover proteins from deeper sediments to correlate with lipid biomarkers were unsuccessful but led to the optimization of an extraction protocol for an added protein standard, bovine serum albumin, from sediments. An investigation into the expressed proteome of the heterotrophic marine bacterium, Ruegeria pomeroyi, under environmentally realistic carbon supply conditions during exponential and stationary growth phases identified over 2000 proteins. The most abundant proteins identified were responsible for porins, transport, binding, translation, and protein refolding and could represent potential biomarkers of bacterial processes and/or activity. A parallel study of R. pomeroyi, in which 13C-labeled leucine was added to the culture during exponential growth phase, showed labeled incorporation ranging from 16 to 21% of the total proteins produced depending on growth phase. The widespread distribution of the label among the growth phases indicates active recycling by the bacteria. This study demonstrates a method through which bacterial protein synthesis can be tracked. A study of the marine diatom Thalassiosira pseudonana acclimated to iron replete or iron-limited conditions showed iron-limited organisms increased proteins involved in pathways associated with intracellular protein recycling, the pentose phosphate pathway, lower photosynthetic energy production, enhancement of photorespiration, and increased polysaccharide production. This application of proteomics to the examination of proteins in marine sediments, a marine diatom, and a heterotrophic marine bacterium shows the potential for these techniques to help elucidate the fate of proteins in marine environments and could be used in conjunction with well-established molecular organic marker studies.Item EFFECTS OF COMPLEXATION WITH THE SIDEROPHORE DESFERRIOXAMINE B ON TRANSITION METAL REMOVAL FROM SEAWATER(2013) Christenson, Emily Ann; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Complexation of transition metals with strong organic ligands of unknown structure and origin plays an important role in their behavior and distributions in seawater. I present here a series of stability constants for complexes of several transition metals with the trihydroxamate siderophore desferrioxamine B (DFOB), representative of a class of small organic ligands that are exceptionally selective for Fe(III) and found in open ocean surface waters at low-picomolar concentrations. Stability constants for DFOB complexes with divalent metals are similar to conditional constants that have been measured in seawater for highly metal-specific, but unidentified organic ligands. Titration data indicate that free Hg2+ forms a very stable complex with DFOB, however the more toxic methylmercury cation does not. A revised scavenging model for yttrium and the rare earth elements suggests that their removal from seawater is dominated by sorption onto Mn oxides, yet not significantly influenced by biogenic silica or calcite.Item The influence of iron and manganese oxides on the production of marine sedimentary cerium anomalies(2011) Marshall, Kathleen; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Cerium is the only metal in the yttrium and rare earth element (YREE) series that can be oxidized under natural conditions, resulting in anomalous Ce distributions relative to those of the other YREE. Marine sedimentary cerium anomaly records have thus been used to signify relative shifts in bottom water oxygenation. However, Ce anomalies form via several pathways often not considered in paleo-oceanographic interpretations. To determine the relative influence of two important marine particulate components, Fe and Mn, on Ce oxidation, YREE sorption was investigated under anaerobic conditions in 0.5 M NaCl solutions over a range of pH (4-8) on hydrous ferric, manganese(IV) and ferromanganese oxides. Non-electrostatic surface complexation models were developed that describe non-oxidative sorption mechanisms on each surface. Cerium oxidation occurred on all sorbents containing Mn, indicating that sedimentary Ce records cannot be directly related to past marine oxygen conditions, even in the presence of relatively little manganese.