Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item MICROBIAL COMMUNITIES IN COASTAL ECOSYSTEMS(2024) Kim, Carol; Malkin, Sairah Y; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Firstly, I examined microbial community succession along a chronosequence of constructed salt marshes using the Poplar Island restoration project site as a case study. By comparing 16S rRNA gene amplicon sequences across 6 constructed low marshes spanning a chronosequence of 1-16 years at Poplar Island (Chesapeake Bay) and a nearby natural reference marsh, I found strong evidence that the development of soil microbial communities is on a trajectory towards natural marsh conditions following marsh restoration with successional rates within timescales expected for soil development. Results from this study showed the value of microbial communities to serve as effective bioindicators for monitoring the recovery of microbially mediated biogeochemical processes in restored or newly constructed salt marshes, as well as potentially for assessing the marsh inundation period and by extension marsh health and resiliency. Secondly, I conducted a manipulation experiment to explore microbial communities associated with cable bacteria using RNA stable isotope probing (RNA-SIP). I traced the uptake of isotopically labeled bicarbonate and acetate in sediments with baseline and with stimulated cable bacteria activity, to test the hypothesis that cable bacteria activity can stimulate chemoautotrophic bacteria in anaerobic sediments. I used 16S rRNA sequencing to identify the active “incorporators” of bicarbonate (as a tracer of chemoautotrophy) and acetate (as a tracer of heterotrophy). I found that estuarine cable bacteria activity stimulated the chemoautotrophic activity of Gammaproteobacteria (Nitrosomonas, Thioalkalispira-Sulfurivermis) and Campylobacterota (Sulfurovum, Sulfurimonas) at anaerobic depths. This result is not explainable with conventional understanding of chemoautotrophic activity. Rather, this study contributes to the emerging concept that cable bacteria activity stimulates metabolic activities at suboxic sediment depths, potentially by serving as an electron sink for other microbes. Furthermore, I found that heterotrophic activity, measured as 13C-acetate assimilation into RNA, was stimulated amongst known chemoautotrophic sulfur oxidizers at depth, highlighting that metabolic flexibility, and specifically mixotrophy, may be widespread in complex natural sediment environments. Lastly, I characterized the composition and metabolic potential of microbial communities in estuarine sediment enriched with cable bacteria. By using metagenomic and 16S rRNA sequencing, I constructed 23 medium- to high-quality metagenome-assembled genomes (MAGs) that span across 9 phyla. I retrieved MAGs exhibiting mixotrophy and a range of capabilities for extracellular electron transport. This study revealed a diverse range of metabolically flexible communities of microbes that contribute to the biogeochemical cycling of carbon, nitrogen, and sulfur.Item EXPLORING THE TEMPERATURE AND HYDROLOGIC RESPONSE OF TROPICAL OCEANS TO VOLCANIC ERUPTIONS OVER THE LAST 400 YEARS USING CORAL GEOCHEMISTRY(2020) Perez Delgado, Zoraida Paola; Kilbourne, Kelly H.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Volcanic eruptions perturb the Earth’s climate system. Open questions remain about the response of the hydrologic cycle and internal variability. Coral skeletal strontium to calcium ratios (Sr/Ca) and oxygen isotopic ratios (δ18O) record temperature and seawater oxygen isotopic signatures in the oceans, thus climatic perturbations from eruptions maybe recorded in the coral skeletal chemistry. I quantify the temperature and hydrologic response of the tropical climate system to eruptions since 1640 CE based on coral geochemical records. Data from all basins except the central and eastern Pacific show cooling and increases in seawater δ18O within the first three years of an eruption. Statistical significance of identified signals was tested by comparing against non-eruption sections from the records. Analyses with paired Sr/Ca and δ18O illustrate that the number of observations still limits detection of small signals provided by the eruptions.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 Ecosystem dynamics in tidal marshes constructed with fine grained, nutrient rich dredged material(2015) Staver, Lorie Winchell; Stevenson, J. Court; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An ecological study was undertaken of the tidal marshes at Poplar Island, a restoration project utilizing fine grained dredged material from the shipping channels in upper Chesapeake Bay. The goals of the study were to examine the effect of a nutrient rich substrate on vegetation development, elevation change, and nutrient cycling in the constructed tidal marshes. Specifically, I examined macrophyte production, nitrogen (N), carbon (C) and silicon (Si) budgets, as well as the success of a silica amendment in enriching plant tissue concentrations. Establishment of Spartina alterniflora and S. patens on fine grained dredged material was rapid, and growth peaked in the second year. Thereafter S. alterniflora dieback occurred sporadically during the growing season, but the causes remain unclear. Elevation change averaged 7.9 ±0.8 mm y-1 in the dredged material marshes (low marsh only), compared to 7.4 ±1.4 mm y-1 in a low nutrient onsite reference marsh. Elevation change was significantly correlated with biomass production suggesting that inputs of organic matter from high rates of aboveground biomass production on nutrient rich dredged material offset the reduced contribution of belowground biomass to vertical accretion. However, dieback may have a detrimental effect on vertical accretion, which is essential for keeping up with apparent sea level rise (13.6 and 11.0 mm y-1 at Baltimore and Solomon’s tide gauges, respectively) since elevation monitoring began at Poplar Island. The tidal flux study revealed that the marsh exports ~665 kg of N y-1, including 100 kg NH4+-N y-1, and 67,874 kg y-1 TSS, and imports 35 kg NO3-N y-1. Silicon is also exported on both a seasonal and annual basis, including 4,337 kg dissolved Si y-1 and 3,924 kg biogenic Si y-1, with highest exports in July, an overlooked benefit of dredged material restoration projects. Soil Si amendments increased plant tissue concentrations significantly, but this study did not show increased resistance to N related stress effects on the vegetation. Overall, this study suggests that when considering trajectories of vegetation development, nutrient exchanges and elevation change in constructed marshes, it is essential to consider the initial nitrogen content of the substrate.Item Monitoring levels of dissolved methane and metals in Maryland streams overlying the Marcellus Shale prior to hydraulic fracturing(2015) Coulter, Caroline; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In western Maryland above the Marcellus Shale, 25 streams were monitored for baseline concentrations of dissolved CH4, Sr2+, and Ba2+, constituents that may be affected by fracking activity. Migrated shale CH4 may intrude streams, and Sr2+ and Ba2+ may be introduced by fracking fluid leakages or spills. Stream constituents were also measured in Maryland’s coastal plain for reference. In western Maryland, CH4 concentrations are significantly variable yet in agreement with concentrations reported for other North American pristine rivers. Measurements of δ13C-CH4 suggest CH4 is primarily biogenic. Dissolved Sr2+ and Ba2+ are spatially and temporally variable, although Sr/Ba ratios are relatively stable at most sites, indicating these may be useful fracking fluid tracers. Major ions Na+, K+, Mg2+, Ca2+, Cl−, SO42-, and HCO3– were measured. These were elevated relative to Sr2+ and Ba2+ and are not suitable fracking fluid tracers. Major ions were highly variable, indicative of variable bedrock geology in western MD.Item Late Medieval Climate Changes in the Tropical Atlantic and Interannual Variability Documented in Northeastern Caribbean Corals(2014) Xu, Yuanyuan; Kilbourne, Kelly H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 CE) but little data exist from the tropical oceans for this time period. I collected multiple Diploria strigosa coral colonies from Anegada, British Virgin Islands (18.73°N, 63.33°W) in order to reconstruct climate in the northeastern Caribbean and tropical North Atlantic during the MCA. My Sr/Ca-temperature calibration results derived from three modern Diploria strigosa corals suggest that the temperature sensitivity for Diploria strigosa is -0.048 (±0.001) mmol/mol°C-1. My reconstruction of MCA climate suggests cooler and wetter conditions in the northeastern Caribbean during the late MCA, indicating that a Pacific La Niña-type climate pattern may have influenced local conditions. Additional analysis indicates that the North Atlantic Oscillation (NAO) was the principal driver of interannual climate variability during the late MCA.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.Item Sorption of Yttrium and the Rare Earth Elements on the Marine Macroalga Ulva lactuca(2011) Zoll, Alison M.; Schijf, Johan; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Trace metal interactions with organic matter are relatively poorly understood, though organic matter is ubiquitous in aquatic environments and likely instrumental in controlling metal geochemistry. To better understand the mechanisms underlying metal interactions with organic substrates, sorption of Yttrium and the Rare Earth Elements (YREEs) on Ulva lactuca, a marine macroalga, was studied in batch laboratory experiments at different ionic strengths over a large pH range (2.7 - 8.5). At all ionic strengths and experimental pH values, colloid-bound YREEs make up a substantial portion of sorbed metals as described by a two-site Langmuir model, which has implications for bioremediation and metal sorption studies. YREE sorption on U. lactuca can be modeled as a function of pH with a three-site non-electrostatic surface complexation model, and patterns of conditional YREE complexation constants were used to determine possible identities of metal-complexing functional groups.Item Intact bacterial hopanoids as specific tracers of bacterial carbon in marine and estuarine environments(2009) Taylor, Karen Ann; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Intact bacteriohopanepolyols (BHPs) and their degrative products were investigated in surface sediments and particulate organic matter from the Bering Sea, Western Arctic Ocean and Chesapeake Bay to trace the inputs of bacterial carbon sources and the dominant microbial processes operative during organic matter recycling. Despite cold temperatures and the dominance of diatoms, cyanobacteria are ubiquitous and inhabit the deeper layers of the euphotic zone in the Bering Sea, where their contributions to sediments were directly traced. As a small but important contribution to the total system chlorophyll, cyanobacteria represent a previously undocumented fraction of the organic carbon pool in this region. In the Western Arctic, soil derived bacterial sources were abundant and include a fraction that likely degraded on land prior to being transported into the Arctic Ocean. Bacterial signatures in Chesapeake Bay transition along the salinity gradient with intact hopanoids reflecting a diverse range of potential bacterial sources.Item A Molecular and Isotopic Approach to Examine the Role of Terrestrial Organic Matter in the Carbon Cycle of the Arctic Ocean(2008) Belicka, Laura Lee; Harvey, H. Rodger; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The organic carbon cycle in the Arctic Ocean is complicated by the delivery and redistribution of terrigenous material through rivers, sea-ice, and erosion. This dissertation combines an isotopic and molecular biomarker approach to assess the role that terrestrial organic carbon plays in the Arctic organic carbon cycle, with a focus on a comparison of geochemical proxies for the quantification of organic matter, an analysis of the sources and transformation of organic carbon to particulate organic matter (POM) and sediments, and an experimental investigation on the kinetics of recycling. Estimates for preserved terrestrial organic components varied considerably for identical sediment samples, suggesting that proxies account for different sources of terrestrial material (i.e., soil versus vascular plants). In spite of the variability, an estimated 12-43% of the organic carbon preserved in surface sediments was terrestrial in origin. This contrasted sharply with surface and halocline POM, in which marine inputs dominated despite spatial variability. With depth, POC composition reflected the increasing significance of inputs from secondary production and microbial degradation, as well as continental material. Acid-volatile sulfide (AVS) and redox-sensitive elements coupled with δ13C and lipid biomarkers demonstrated a transition from intense metabolism of labile marine organic matter in shelf sediments to slower sedimentary metabolism from occasional delivery of labile organic matter in the basin. Experimental determinations of the kinetics of microbial recycling revealed striking contrasts in marine and terrestrial organic carbon lability. Marine organic matter was recycled on very short timescales compared to terrestrial organic matter, corresponding to results of sedimentary and particle analyses. A simplified box model of organic carbon cycling in the Chukchi/Alaskan Beaufort Sea region reveals that 0.9 Mt and 0.7 Mt of marine and terrestrial organic matter, respectively, are buried in shelf sediments, while an additional 0.2 Mt marine and 0.1 Mt of terrestrial organic carbon are buried in basin sediments annually, confirming that land-derived organic matter plays a large role in carbon dynamics in Arctic systems, even on non-river dominated margins.