Our Students and Their Research

 

You may search for students by class year and keywords found in the student's name, university, project title or abstract. Our first class was in 1989.

Our Students List

Class of 2019

Project Title:

Determining Fecundity and Genetic Differences of Neomysis americana in River Systems that Vary in Productivity Within the Chesapeake Bay

Small, pelagic crustaceans such as mysids are a central component of productive food webs in many estuaries and serve as a critical trophic link between primary production and larger consumers. Neomysis americana (Smith 1873) is a highly abundant mysid species found in temperate coastal habitats of the western Atlantic; although known to be an important prey item in the Chesapeake Bay (CB), basic understanding of its distribution, population dynamics, and ecology is lacking. This project investigated spatial patterns in relative abundance of N. americana by examining female fecundity and assessing genetic connectivity of mysids across space and time (seasons), focusing on two major tributaries of the CB, the Choptank and Patuxent Rivers. St. Lawrence River N. americana were used for regional genetic comparisons. Tests for length-specific fecundity differences between tributaries indicated the number of eggs per female was higher in the Choptank (ANCOVA, p= 0.002) and spring female fecundity was higher than fall fecundity (ANCOVA, p= 0.02). Preliminary analysis of CO1 haplotype networks using a median joining approach revealed strong regional structure (no sharing of haplotypes between St. Lawrence and CB), AMOVA results confirmed high variation among regions (Phi-St = 0.93). Within Chesapeake Bay, haplotypes were well-mixed and statistical analyses verified no significant spatial (Choptank vs Patuxent) or temporal (June vs. September) differences (AMOVA P >0.5). Given the absence of genetic differences between tributaries based on CO1 data, environmental factors likely play a large role in the fecundity differences observed across the tributaries. Future research into the drivers of spatial fecundity differences will help inform development of mysid population models, contribute to our understanding of estuarine food web controls, and build our capacity to better integrate forage into ecosystem-based fisheries management in CB.

Project Title:

Influences of Oyster Reef Restoration on Carbonate Dynamics in Chesapeake Bay: A Modeling Analysis

Anthropogenic CO2 emission have led to an effect known as ocean acidification. As a result, many coastal estuarine systems, such as the Chesapeake Bay, have seen major biogeochemical changes and large declines in biomass and biodiversity. Since pre-colonial times, oyster population in the Chesapeake Bay have declined by over 100-fold due to human associated activities such as over harvesting and water pollution. Oyster reefs are known to regulate carbonate system dynamics in their environments and their decline have likely led to the loss of any potential buffering capacity. This study quantified the potential pH and Ωaragonite buffering by oyster reefs in the Chesapeake Bay by running idealized simulations using the ROMS-RCA modeling system with multiple DIC/TA generated flux. Our study has found that oyster reefs have the potential to buffer ~15% of projected pH and Ω changes in their surrounding water. The effects buffered by oysters are relatively local to their environment with minimal spatial distribution. This is important as there are ongoing large-scale oyster reef restorations in the Chesapeake Bay. Our study and other future works on potential oyster reef buffering to water column carbonate system dynamics can serve as a framework to target ideal locations in the Chesapeake Bay as well as other estuarine systems for restoration and protect coastal waters from the effects of climate change.

Project Title:

An Analysis of Protist Diversity in Oxygen Deficient Zones: Understanding the Relationship Between Prochlorococcus and Grazing

The cyanobacteria Prochlorococcus is an integral part of oxygen deficient zone (ODZ) microbial ecology. In the Eastern Tropical North Pacific, Prochlorococcus displays two maxima, with one in the ODZ at ~100 meters (Low-Light IV ecotype (LLIV)). LLIV Prochlorococcus reproduces slowly, making populations vulnerable to grazing. Previous non-quantitative studies indicate that heterotrophic protists are in the ODZ. We investigated if ODZ LLIV Prochlorococcus are subject to heterotrophy from microbial eukaryotes. The two prevailing hypotheses predict that: (A) only symbiont-bearing mixotrophic protists, which consume fewer prey due to autotrophy, would be present at the second Prochlorococcus maximum, or (B) heterotrophic and mixotrophic protist populations would decrease along the oxycline, reducing grazing pressure on LLIV Prochlorococcus. We used 18S rDNA long amplicon sequences (1500 basepairs) to identify the protist community and create a phylogenetic tree. Metagenomic reads were placed on the phylogenetic tree. Results identified that both heterotrophic and mixotrophic protists were present at the second Prochlorococcus maximum, specifically high concentrations of the mixotrophic Radiolarian order, Spumellaria along with lower concentrations of heterotrophic Dinoflagellate orders: Prorocentrales and Gymnodiniales. However, nearly all protist population concentrations decreased dramatically near the lower bounds of the oxycline where LLIV Prochlorococcus is present, potentially signifying reduced grazing pressures.

Project Title:

Determination of the Stability Constants for the Complexation of Yttrium Rare Earth Elements with Silicate at Seawater Ionic Strength

Inorganic ligands dominate aqueous complexation of yttrium and rare earth element (YREE) within the marine environment. Therefore, the stability constant of several important ligands has been characterized to discover more about YREE complex speciation. Little attention has been directed towards evaluating silicate. This may be due to silicate undergoing polymerization at pH 8 making it difficult to work with. Here, we present a method to determine the logβ1 and logβ2 for Eu-silicate complexes through conducting potentiometric titrations at seawater ionic strength (I=0.7). To prevent Eu-hydroxide precipitation, titrations have to be conducted in the presence of the strong ligand desferrioxamine B (DFOB). Using a computer program called FITEQL 4.0, non-linear regressions were produced from the raw titration data. The acid dissociation constants for silicic acid are pKa1 = 9.45±0.02 and pKa2 = 11.4±0.1. The stability constants were found to be logβ1 = 6.1±0.4 and logβ2 = 11.4±0.8. These values show a good correlation with stability constants obtained from static potentiometry, a linear free energy relationship (LFER) with Fe3+, and reanalyzed data from the literature. These results indicate that silicate only affects the speciation within the deep Pacific Ocean. 

Project Title:

Determining the Photochemical Fate of Organic UV-filters Commonly Found in Sunscreen in Natural Waters

Chromophoric dissolved organic matter (CDOM) holds the potential to drastically change the light field of aquatic environments. Once in solution, organic UV-filters commonly found in sunscreen such as oxybenzone, octocrylene, and octinoxate fall within the definition of CDOM, dissolved organic matter that absorbs UV and visible light. Thus, these compounds hold the potential participate in photochemical reactions, altering both the chemical makeup and light field of an aquatic environment. To date, limited information exists on the photochemical degradation of sunscreen organic UV-filters in natural waters. Thus, we used a custom designed photodegradation system to continuously photo-irradiate samples with simulated sunlight and quantify changes in optical properties throughout long-term experiments. We utilized excitation-emission matrix spectroscopy to determine absorbance and fluorescence spectra. Additionally, sub-samples were collected during 24h irradiation experiments to determine the change in concentrations of the examined UV-filters using LC-qqq MS. Results revealed exponential decrease in concentration of the parent compound during photoirradiation, no OpenFluor database comparison matches, a variety of photo-products, and suggest the possibility of secondary photo-products.

Project Title:

Remote Sensing in the Chesapeake Bay: A Focus on Harmful Algal Blooms

In the Chesapeake Bay (CB), harmful algal blooms (HABs) have become more commonplace due to nutrients from agricultural and urban runoff entering the Bay. HAB data (location, date, species abundance reported as cells/mL) were mined from the Maryland Department of Natural Resources (MDDNR) Eyes on the Bay program. Given the inherent variations in the optical properties (e.g. algal biomass) of CB through space and time, we first constructed spatially explicit monthly composites of chlorophyll-a (chl-a) using the red-band difference (RBD) algorithm commonly used for detecting HABs in coastal waters. For each HAB event (2016-2019) with corresponding cloud-free imagery, we then compared RBD chl-a of a given event to its climatology to ultimately derive and report chl-a as a standardized anomaly. Contrary to our expectations, HABs cell concentrations were not correlated with satellite-derived chl-a anomalies. All satellite data analysis was performed using Google Earth Engine (GEE), and the code is an important deliverable of this project.  One drawback of GEE is that Sentinel 2 data is currently not atmospherically corrected, which diminishes the accuracy of satellite-derived chl-a and is a potential source of error in our analysis.

Project Title:

Determining the Abundance of Bacteria on Marine Particles of Different Size Classes

Microbes that live in association with marine particles have significant involvement in the remineralization of particulate organic carbon in the deep ocean within the biological pump. To better understand this process of carbon movement, it is important to study these microbes and the types of particles on which they live. Diverse particle characteristics can influence the microbes that inhabit them. This study aimed to examine the relationship between the size of particles and the number of microbes living on them. Previous studies have found the relative microbial abundance on various sized particles, but this experiment calculated the total abundance of cells per particle, in order to better understand the preferred particle habitats of different microbial species. Particles were collected with different sized filters and DNA was extracted for quantitative PCR and sequencing. Though it was hypothesized that cell number would scale with particle size, this relationship was not found. Rather, the abundance of microbes on each particle size depended on the specific type of microbe. 

Project Title:

High Resolution Biogeochemical Distributions in the Chesapeake Bay Pycnocline

The Chesapeake Bay’s water quality has been affected over many years of human activity. Agricultural runoff and wastewater deposits has resulted in eutrophication of the bay which have affected the chemical make-up of the bay. In this study, vertical biogeochemical distributions of the bay were determined. Observations included vertical distributions of ammonium (NH4+), hydrogen sulfide (H2S), oxygen (O2) concentrations and consumption rate and dissolved inorganic carbon (DIC) and its rate of production. As in other studies, the results showed that the O2 content of surface water was drastically higher than deeper waters. However, this approach captures the O2 and H2S transitional regions in detail that has not previously been observed. Such detailed vertical distributions provide essential clues about underlying biogeochemical processes. 

Project Title:

Ocean Exploration: Understanding the Biogeographic Regions of the Indian Ocean

This is a descriptive paper analyzing the biogeographic regions of the Indian Ocean. The Ocean was delineated into nine regions based on the physical characteristics of flow based on satellite sea surface height anomalies (SSHA) and estimates of geostrophic velocity. It introduces new hypotheses analyzing the physical oceanography of each region in order to explain the biogeochemical, ecological, and biological processes of the Indian Ocean. This paper further discusses the effects of eddies, velocity shearing, low oxygen, and the impact that topography has on a region displaying elevated levels of productivity, such as the Seychelles-Chagos Thermocline Ridge (SCTR). Currents, such as the South Equatorial Counter Current (SECC) and the South Equatorial Current (SEC), and topographical regions, such as the Chagos-Laccadive Ridge (CLR), are studied to aid in the hypothesis of nutrient sustenance for the SCTR.

Project Title:

Phosphorus Uptake in Floating Wetlands: A Mass Balance Approach

The health of marine environments situated near developing coasts, like the Chesapeake Bay, is threatened by mass-inputs of nutrients that run off the land. In an attempt to mitigate eutrophic events in aquatic environments, scientists have deployed Floating Treatment Wetlands (FTWs), which mimic a natural wetland’s ability to remove excess nutrients from flowing water. Scientific literature on the behavior of FTWs in lakes and stormwater ponds supports the success of this innovation, however, studies testing the potential of FTWs in estuarine waters is lacking. This study utilized mesocosms to imitate the behavior of FTWs in brackish environments. Mesocosms consisted of a tank filled with ambient estuarine water, an FTW in which Spartina patens was established, and a plumbing system that kept water flowing in and out at a consistent rate. Wetland mesocosms were compared to control mesocosms, which did not contain Spartina patens. The nutrient of interest for this experiment was Phosphorus (P), and uptake of P within wetland mesocosms was determined by calculating the difference between the concentration of P in inflowing and outflowing water. We hypothesized that wetland mesocosms would show greater uptake P than control tanks over the entire 5-week experiment. Results showed wetland mesocosms removing less P than control mesocosms until the fourth week. It was determined that this outcome was likely due to fertilizer leeching into the tanks containing the Spartina patens at the beginning of the experiment, but further research is necessary to support this assumption.

Project Title:

Anticyclonic Eddies and Their Influences on Temperature and Salinity in the Mid-Atlantic Bight

Eddies are large, circular, temporary currents that trap water and marine life in their center and carry them far away from their origin (Chelton et. al 2011). The Gulf Stream in the North Atlantic Ocean sheds eddies of two different types: anticyclonic (clockwise rotating) eddies to its north and west, and cyclonic (counterclockwise rotating) eddies to its south and east (https://marine.coastal.edu/gulfstream/p6.htm). When anticyclonic eddies impinge upon the shelf break in the Mid Atlantic Bight, they quickly dissipate, and the material that was trapped in their center is released and dispersed (Zhang and Gawarkiewicz 2015).

Until recently, little was known about the extent of water exchange between the shallow shelf water in the Mid Atlantic Bight, which is a relatively cold, fresh, nutrient dense water mass, and warm, salty, nutrient poor water from the deep ocean released when anticyclonic eddies impinge upon the shelf break (Zhang and Gawarkiewicz 2015). This study sought to explore the relationship between anticyclonic eddies (also called warm core rings) that impinge upon the continental shelf and salinity variability within the shelf.

Upon analysis, it was revealed that there is a moderate correlation between the number of anticyclonic eddies that impinge upon the shelf per year and salinity changes along the continental shelf. Further analysis revealed that there is an even stronger correlation between eddy numbers weighted by amplitude and salinity. The strongest correlation was established between eddy numbers weighted by radius and salinity.

Project Title:

Northern Caribbean Sea Surface Temperatures During the Medieval Climate Anomaly from Pseudodiploria strigosa Sr/Ca Ratios

Anthropogenic climate change may alter the variability of Earth’s climate patterns during the 21st century in ways we are only beginning to understand. By analyzing past conditions through proxies, we can understand the climatic system and make better models to predict climate variability under future warming trends. We measured strontium to calcium ratios in approximately monthly samples of a Pseudodiploria strigosa coral to reconstruct sea surface temperatures (SST) at Anegada, British Virgin Islands, in the northeastern Caribbean. The coral was uranium-series dated to the 11th century, and grew during approximately 1005-1049 C.E. with an uncertainty of 2.3 years. The data revealed seasonal cycles over the lifetime of the coral, allowing us to create a seasonal climatology from 22.7 years of data. Comparing the seasonal climatology of Medieval coral 13AN4 with three modern corals measured by Xu et al. 2015, we found the Sr/Ca values of the fossil coral to be substantially higher than the modern corals, indicating cooler temperatures relative to modern at the time of coral growth. These results are consistent with previous work indicating that the climate system may have been more often in a positive North Atlantic Oscillation (NAO) state and an El Nino Southern Oscillation- cool phase (La Nina- like) during the Medieval period.

Project Title:

Modeling the Distribution of Bottlenose Dolphins (Tursiops truncatus) in the Chesapeake Bay as a Function of Environmental Factors

Bottlenose dolphins (Tursiops truncatus) are wide-ranging marine mammals that live in open-ocean habitats as well as coastal areas. However, little is known about their seasonal occurrence within the Chesapeake Bay, U.S.A, a highly urbanized region. The goal of this study was to determine the spatial and temporal distribution of bottlenose dolphins in the Chesapeake Bay using geospatial and statistical modeling techniques. Two years (2017-2018) of observational dolphin sighting data from a citizen-science initiative, Chesapeake DolphinWatch, was mapped using ArcGIS 10.5 to visually characterize dolphin occurrence. Sightings were then integrated with water quality data to identify factors significantly influencing dolphin occurrence in this area. We found a distinct seasonal occurrence pattern with dolphins being most commonly sighted in July. Using a generalized additive model, the probability of dolphin presence was found to be significantly affected by the tidal phase, water temperature, salinity levels, and dissolved oxygen. These results provide a better understanding of the geographical distribution and seasonal occurrence of bottlenose dolphins in the Chesapeake Bay. The relationship between dolphin occurrence and environmental conditions can be used to support conservation efforts and inform population management.

Project Title:

Effect of Nutrients on Phytoplankton Biomass in the Ocean City, MD Inlet

Ocean City’s inlet is a conduit for nutrients and pollutants between the Atlantic Ocean and Maryland’s coastal bays. This study investigated the response of phytoplankton to increased nutrient availability and temperature as part of a larger investigation of phytoplankton dynamics, in relation to eutrophication and climate change effects. Three nutrient bioassays were conducted on phytoplankton biomass in the Ocean City Inlet, with additions of 10μM nitrate, 10μM ammonium, 5μM phosphate, and 10μM Nitrate+5μM Phosphate. The first two bioassays were subjected to natural light and temperature while bioassay 3 was conducted in two temperature control rooms averaging 22.1C and 36.5C. Chlorophyll a and phycocyanin were measured using a handheld fluorometer; Chlorophyll a was extracted to standardize the in-situ measurements. All bioassays showed a strong positive increase in phytoplankton biomass with nitrogen treatments, supporting the hypothesis that nitrogen is the major limiting nutrient for marine phytoplankton. There was no significant response with phosphate additions alone, however, N+P additions were highest in bioassay 1, suggesting co-limitation of phosphorus when excess nitrogen is supplied. There was no significant difference between nitrate and ammonium treatments. Phytoplankton biomass did not increase with temperature. However, temperature had synergistic effects on nutrient intake. This data, as part of the larger study, will allow for improved management and preservation of coastal ecosystems.

Project Title:

The Temperature Inside the Nests of the Diamondback Terrapin, Malaclemys terrapin, and Its Relationship with the Air Temperature of the Nesting Site

The diamondback terrapin (Malaclemys terrapin), is an estuarine turtle found within brackish marshes of the eastern and gulf coasts of the United States and it is the official state reptile of Maryland. The diamondback terrapin unfortunately may become a victim of increasing global temperatures due to its temperature-dependent sex determination (TSD). Species that display TSD may produce more female than male hatchlings or vice versa depending on the temperature of the individual nest. This study used several individual nest temperatures along with the air temperatures at the nesting site, recorded in the summer of 2018, to select a predictive model with R software package rstanarm, to predict nest temperatures using known air temperatures. The regression spline mixed model was selected for having the lowest leave one out information criterion. Its accuracy was determined by using air temperatures recorded during the summer of 2019 to predict 2019 nest temperatures, and comparing the predictions to field recorded values. The RSMM had a predictive capability of 83.6-98.7% coverage of five actual nest temperatures recorded in 2019, with a predictive interval of 95%. The resulting model will inform a collaborative project evaluating climatic influence on individuals and populations of diamondback terrapins.

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