Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
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Item THE EFFECT OF SUMMER STORM EVENTS AS A DISTURBANCE ON THE MOVEMENT BEHAVIORS OF BLACK SEA BASS IN THE SOUTHERN MID-ATLANTIC BIGHT(2019) Wiernicki, Caroline Jane; Secor, David H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Storm events are a key disturbance in the Middle Atlantic Bight (MAB), driving thermal, hydrodynamic, and acoustic perturbations on demersal fish communities. Black sea bass are a model MAB species as their sedentary behavior exposes them to storm disturbances. I coupled biotelemetry with an oceanographic model, monitoring black sea bass movement behaviors during the summer-fall of 2016-2018. Storm-driven changes in bottom temperature (associated with rapid destratification) had the greatest effects on fish movement and evacuation rates, while the cumulative effects of consecutive storms had little to no observed effect. Storms also generate substantial noise, but the hearing frequencies of black sea bass are currently unknown. I conducted a quantitative literature analysis on fish hearing based on swim bladder elaboration, successfully classifying detected sound frequency ranges among fishes, including black sea bass. Climate change will likely alter the intensity of MAB storms, prioritizing research on their impacts to fish communities.Item EFFECTS OF SEA LEVEL RISE ON TIDAL FRESHWATER, OLIGOHALINE, AND BRACKISH MARSHES: ACCRETION, NUTRIENT BURIAL, AND BIOGEOCHEMICAL PROCESSES(2019) Allen, Jenny; Baldwin, Andrew H; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Tidal wetlands provide critically important ecosystem services such as storm surge and flood attenuation, pollution retention and transformation, and carbon sequestration. The ability of tidal wetlands to maintain surface elevation under accelerated sea level rise is critical for their persistence. Saltwater intrusion can further threaten tidal freshwater marshes by decreasing primary production and organic matter accumulation as well as cause shifts in microbial pathways, leading to increases in organic matter decomposition and an overall decrease in marsh elevation. The objectives of this research were to examine accretion dynamics across the estuarine gradient of the Nanticoke River, a major tributary of the Chesapeake Bay, and determine the relative contribution of organic and inorganic matter to accretion in the marshes; determine the accumulation rates of C, N, and P across the estuarine gradient; and examine the effects of sulfate intrusion on biogeochemical transformations and marsh surface elevation in tidal freshwater marsh soil. Results of the collective studies suggest that the mechanisms controlling accretion dynamics and nutrient accumulation are complex and are likely driven by site-specific factors rather than estuary-wide factors. Accretion rates and nutrient accumulation rates were highly variable across the estuarine gradient, but were largely dependent on both organic matter accumulation and inorganic sedimentation. Only 8 out of the 15 subsites had accretion rates higher than relative sea level rise for the area, with the lowest rates of accretion found in the oligohaline marshes. Organic matter accumulation is especially important in marshes with low mineral sediment supply, particularly mid-estuarine oligohaline marshes, but may not be enough to help keep these marshes above relative sea level. The tidal marshes along the Nanticoke River removed approximately 15% and 9% of the total N and P load entering the system, but their ability to continue to remove nutrients may be compromised due to rising sea levels. Shifts in microbial pathways and increases in organic matter decomposition due to saltwater intrusion further threaten the ability of these marshes to keep pace with sea level rise, potentially resulting in the loss of an extremely valuable ecosystem.Item The long-term change of Chesapeake Bay hypoxia: impacts of eutrophication, nutrient management and climate change(2019) Ni, Wenfei; Li, Ming; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Eutrophication-induced coastal hypoxia can result in stressful habitat for marine living resources and cause great economic losses. Nutrient management strategies have been implemented in many coastal systems to improve water quality. However, the outcomes to mitigate hypoxia have been mixed and usually small when only modest nutrient load reduction was achieved. Meanwhile, there has been increasing recognition of climate change impacts on estuarine hypoxia, given estuaries are especially vulnerable to climate change with multiple influences from river, ocean and the atmosphere. Due to the limitation of observational studies and the lack of continuous historical data, long-term oxygen dynamics in response to the changes of external forces are still not well understood. This study utilized a numerical model to quantitatively investigate a century of change of Chesapeake Bay hypoxia in response to varying external forces in nutrient inputs and climate. With intensifying eutrophication since 1950, model results suggest an abrupt increase in volume and duration of hypoxia from 1950s-1960s to 1970s-1980s. This turning point of hypoxia might be related with Tropical Storm Agnes and consecutive wet years with relatively small summer wind speed. During 1985-2016 when the riverine nutrient inputs were modestly decreased, the simulated bottom dissolved oxygen exhibited a statistically significant declining trend of ~0.01 mgL-1yr-1 which mostly occurred in winter and spring. Warming was found to be the dominant driver of the long-term oxygen decline whereas sea level rise had a minor effect. Warming has overcome the benefit of nutrient reduction in Chesapeake Bay to diminish hypoxia over the past three decades. By the mid-21st century, the hypoxic and anoxic volumes are projected to increase by 10-30% in Chesapeake Bay if the riverine nutrient inputs are maintained at high level as in 1990s. Sea level rise and larger winter-spring runoff will generate stronger stratification and large reductions in the vertical oxygen supply to the bottom water. The future warming will lead to earlier initiation of hypoxia, accompanied by weaker summer respiration and more rapid termination of hypoxia. The findings of this study can help guide climate adaptation strategies and nutrient load abatement in Chesapeake Bay and other hypoxic estuaries.Item Seasonal Migrations of Atlantic Sturgeon and Striped Bass Through the Maryland Wind Energy Area(2019) Rothermel, Ella Rick; Secor, David; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Baseline information is needed on migrations through US Mid-Atlantic Bight shelf waters in advance of offshore wind development. Acoustically-tagged Atlantic sturgeon and striped bass were detected from 2016-2019 in an array of 20 acoustic telemetry receivers centered on the Maryland Wind Energy Area and extending 10-50 km offshore. Both species were transient (mean residency < 3 days), but migration patterns differed seasonally and were related to depth and temperature. Generalized additive models showed that Atlantic sturgeon occur at inshore sites during spring while striped bass shifted toward the outer shelf as inshore waters cooled in winter. The movement of hundreds of tagged striped bass and sturgeon, originating from shelf waters from Maine to South Carolina suggests that the Wind Energy Area is part of a multi-species Atlantic coastal flyway, particularly during spring, fall, and winter periods. Thus, summer presents a potential window for wind tower construction.Item The effect of salinity on species survival and carbon storage on the Lower Eastern Shore of Maryland due to saltwater intrusion(2019) de la Reguera, Elizabeth; Tully, Kate; Palmer, Margaret; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As sea levels continue to rise, coastal ecosystems are vulnerable to saltwater intrusion (SWI), the landward movement of sea salts. Specifically, in coastal farmlands, we expect SWI to drive changes in plant species composition and carbon (C) storage. As soils salinize, standard crops (i.e. corn, soybean, and wheat) can no longer survive and farmers must consider alternatives. Further, transitioning agricultural fields may become C sinks as SWI advances inland and farmlands begin to resemble tidal wetlands. My objectives were to determine: (1) the effect of SWI on the germination of standard and alternative crop species, and (2) the C storage potential of salt-intruded farmlands. Most standard and alternative crops were intolerant to high levels of osmotic and ionic stress at the germination stage. However, sorghum and salt-tolerant soybean showed promise in field experiments. I show that agricultural fields exposed to SWI have a high potential to store C in soils.Item HYDROLOGIC DRIVERS OF SOIL ORGANIC CARBON STORAGE AND STABILITY IN FRESHWATER MINERAL WETLANDS(2019) Kottkamp, Anna Isabel; Palmer, Margaret; Tully, Katherine; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mineral wetlands comprise most of historic wetland loss, yet few studies focus on mineral wetland soil organic carbon (SOC). We explore SOC across continuous hydrologic gradients within and among seasonally flooded mineral wetlands. First, we quantify SOC stabilization (e.g., organo-mineral associations and aggregates) across a wetland–upland gradient. Second, we examine relationships between hydrologic regime and SOC stocks among wetlands. From wetland–upland, saturation was highly variable in the transition zone. Organo-mineral associations peaked in the transition zone while large macroaggregate SOC declined from wetland–upland. Across wetlands, indicators of drying (e.g., minimum water level and summertime recession rate) were more related to SOC than inundation duration. From wetland basin–upland, SOC stocks were significantly related to both mean water level and relative elevation. We highlight relationships between SOC and the dynamic hydrology of wetlands, emphasizing the need for research on how changing hydrologic regime may influence mineral wetland SOC.Item MODELING IMPACTS OF SUBMERSED AQUATIC VEGETATION ON SEDIMENT DYNAMICS UNDER STORM CONDITIONS IN UPPER CHESAPEAKE BAY(2019) Biddle, Mathew Michael; Sanford, Lawrence P; Palinkas, Cindy; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Submersed aquatic vegetation is an important modulator of sediment delivery from the Susquehanna River through the Susquehanna Flats into the Chesapeake Bay. However, the impact of vegetation coupled with the physical drivers of sediment transport through the region are not well understood. This study used a new vegetation component in a coupled flow-wave-sediment transport modeling system (COAWST) to simulate summer through fall 2011, when the region experienced a sequence of events including Hurricane Irene and Tropical Storm Lee. Fine sediment was exported under normal flows and high wind forcing but accumulated under high flows. The relative effect of vegetation under normal and high wind forcing depended on previous sediment dynamics. Vegetation doubled the accumulation of fine sediments under high flows. While further refinement of the bed model may be needed to capture some nuances, the COAWST modeling system provides new insights into detailed sediment dynamics in complex vegetated deltaic systems.Item PHENOLOGY OF ESTUARINE RESPONSE TO ANTHROPOGENIC AND CLIMATE DRIVERS, A STUDY OF THE CHESAPEAKE BAY AND CHESTER RIVER ESTUARIES(2019) Basenback, Nicole; Testa, Jeremy M; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The effects of nutrient loading on estuaries are well-studied, given the multitude of negative water quality, ecosystem, and economic impacts that have been attributed to the presence of excess nitrogen and phosphorous. A current gap in this knowledge is the consequence of changing climate variability on the seasonal patterns of estuarine processes related to eutrophication, potentially from direct (temperature) and indirect influences (nutrient load timing) of climate warming. A coupled hydrologic-biogeochemical model (ROMS-RCA) was used to investigate the spatial and temporal changes in the phenology of hypoxia and related biogeochemical processes in the Chesapeake Bay under three different hydrologic regimes. Shifts in nutrient load timing during idealized simulations dampened the overall annual hypoxic volume, resulting from discernable, but relatively small reductions in phytoplankton biomass and both sediment and water-column respiration in three regions of the Bay. Simulated increases in water temperature caused an increase in the spring/early summer hypoxic volume associated with elevated respirations rates, but this exhaustion of organic matter in the early summer caused a decrease in late summer/fall hypoxic volume due to lowered sediment respiration. Similar simulations in nutrient load timing were conducted using a model of the Chester River estuary, a smaller, shallower sub-estuary system to the Chesapeake Bay. Nutrient load timing and magnitude effects on hypoxia were much smaller in the Chester River as compared to Chesapeake Bay, which is likely due to high concentrations of nitrogen and phosphorus within the system. Therefore, cross-system comparisons are important for understanding the sensitivity of hypoxia to alterations in nutrient load across diverse estuaries. These idealized simulations begin the process of understanding the potential impacts of future climatic changes in the seasonal timing of key biogeochemical processes associated with eutrophication.Item ASSESSING THE IMPACTS OF NON-POINT SOURCE FRESHWATER AND NUTRIENT INPUTS ON A SHALLOW COASTAL ESTUARY(2019) Butler, Thomas; Hood, Raleigh R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Academic research models for Chesapeake Bay have, traditionally, been forced with USGS inputs, flows and nutrient loads from 10 major rivers. These tributaries fail to account for 100% of the inputs entering the Bay. In contrast, models used for determining Total Maximum Daily Load for Chesapeake Bay are forced with output from a watershed model at thousands of locations, presumably, accounting for all these inputs. Our aim is to increase understanding of the impacts different forcing schemes have on water quality model simulation. Simulations were completed using three forcing approaches: 1) using “traditional” USGS-derived input from 10 major rivers; 2) using “concentrated” input from 10 major rivers derived from watershed model output; and 3) using “diffuse” input from 1117 rivers derived from watershed model output. Comparisons of these schemes revealed large impacts on simulations in Chesapeake Bay during periods of high flow and extreme weather events under diffuse forcing.Item INVESTIGATING THE REGULATION OF GROWTH MECHANISMS IN TWO DISTINCT BRANCHES OF PHOTOSYNTHETIC LIFE(2019) Sittmann, John; Liu, Zhongchi; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Photosynthetic organisms often have limited mobility and rely on a variety of environmental, physiological, and chemical signals to regulate aspects of growth and development. In this thesis, I investigated how two such organisms, one a flowering plant and the other a heterokont alga, incorporate external signaling cues to make decisions regarding reproduction. My dissertation research is focused on 1) investigating molecular mechanisms of crosstalk between photoperiod and shade in regulating asexual reproduction in the wild strawberry Fragaria vesca, and 2) elucidating the mechanism of a bacterium-derived agent in the stimulation of cell division in the marine diatom Phaeodactylum tricornutum. First, strawberry, including woodland strawberry Fragaria vesca, is capable of a form of asexual reproduction by producing horizontal stems with daughter plants at the nodes. These horizontal stems, referred to as stolon, are derived from axillary meristems at the base of the leaves. Depending on the signals the axillary meristem receives, it will give rise to either a branch crown (a flowering shoot) or a stolon. Stolon allows for asexual reproduction to maintain the superior hybrid genotype and hence is of great significance agriculturally. Daughter plants derived from stolon are sold and propagated in strawberry farming. In this work, I have shown that a key regulatory protein FveRGA1 in GA signaling pathway functions as a repressor of stolon development. I further expanded this work by showing that the light quality (shade) signaling pathway interacts with the GA signaling to regulate stolon development. I identified and demonstrated FvePIF3 as a key transcription factor that positively regulates stolon initiation under far-red light (shade). Understanding the mechanisms underlying axillary meristem cell fate determination could advance biotechnology to increase strawberry production. Second, I have discovered and characterized a bacterium-based growth stimulation of the diatom Phaeodactylum tricornutum. Specifically, I noticed that a culture of P. tricornutum that had been accidentally contaminated with bacteria exhibited faster growth. I subsequently identified the responsible bacterium as Bacillus sp, which stimulated rapid Phaeodactylum cell division when added to the Phaeodactylum culture. I experimentally determined that the growth stimulating agent was heat labile and proteinase K-resistant. Further, I showed that the mother cell lysate of Bacillus sp. under sporulation was just as effective in promoting Phaeodactylum. In collaboration with Dr. Jon Clardy lab, we identified the growth-stimulating compounds as two distinct peptide-signaling molecules. The work revealed that the peptides may be previously under-reported signaling molecules for cross-kingdom communications. In addition to the fundamental discovery of novel signaling mechanisms between bacterium and algae, this work may facilitate large-scale diatom culture in biomass production for biofuel and biopharma.