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 2016

Project Title:

A Data-Driven Approach to Dynamic Spatio-Temporal Clustering

Climate data sets available currently, whether these are paleo-reconstructions, long-term weather monitoring records, or remote sensing data, contain a whelm of space-time information that needs to be analyzed under the pressure of computational and data storage requirements. This has led to a spark of interest in dynamic space-time clustering algorithms that are particularly suitable in the analysis of data streams. The trend-based clustering algorithm TRUST allows for space-time clustering in real time. However, this method requires the user to set a number of tuning parameters by hand. Here we propose a data-driven approach to automatically select the tuning parameters based on a penalized loss function. We focus on the two most important parameters of the TRUST algorithm: the current likeness of observations across the slide level and the temporal persistence within an analyzed window. We demonstrate the performance of the enhanced clustering procedure using simulated time series and illustrate its applicability using long-term records of water temperature in the Chesapeake Bay.

Project Title:

Improving Remotely Sensed Chlorophyll Concentration Estimates Using Hyperspectral Radiometers in the Chesapeake Bay

Throughout the last two centuries a variety of anthropogenic forces have drastically altered the Chesapeake Bay ecosystem. Because of their correlation to water quality, phytoplankton populations are useful gauges of restoration efforts and the changing biogeochemical properties of the Bay. Estuaries are dynamic environments, and traditional, in situ sampling lacks the spatiotemporal resolution necessary to effectively monitor water quality in general and phytoplankton populations in particular. In the past two decades, satellite technology has allowed for more resolved water quality measurements. However, extant ocean-observing satellites are best suited to the open ocean. In coastal and estuarine waters, high turbidity and land interference severely diminish the utility of satellite data. Hyperspectral instruments measure ocean color with much greater spectral resolution than the multispectral instruments currently deployed on ocean-observing satellites. Increased spectral resolution allows for better approximation of phytoplankton concentrations in optically complex waters. This research seeks to test optical inversion algorithms designed for the Chesapeake Bay. By pairing in situ measurements of chlorophyll with electromagnetic spectrum measurements, we determined the most accurate algorithms for use in the Chesapeake Bay. These algorithms can then be employed in future remote sensing studies to yield accurate chlorophyll measurements in fine temporal, and spatial time scales.

Class of 2015

Project Title:

The Impact of Irradiance and Ammonium on the Mixotrophic Response by the Winter Bloom Heterocapsa rotundata in the Chesapeake Bay

Mixotrophic plankton are capable of obtaining their energy through photosynthesis and phagocytosis, and have been observed to be common among marine and freshwater dinoflagellates. The role of mixotrophic dinoflagellates in the ‘microbial loop’ has received little attention.  Organisms that were only thought to introduce new carbon into the loop through photosynthesis may also consume fixed carbon by ingesting bacteria, making the ‘microbial loop’ more complex that originally conceived. The nanodinoflagellate Heterocapsa rotundata was cultured under various light and nutrient regimes to investigate the role of phototrophy and phagotrophy during winter conditions in the Chesapeake Bay. We quantified grazing rates of H. rotundata on bacteria using two feeding methods, ingestion of polycarbonate microspheres and prey removal experiments. Ingestion of fluorescent microspheres by H. rotundata revealed their ability to phagocytize particles. Using flow cytometry we calculated grazing rates of H. rotundata on bacteria under various light intensities and ammonium concentrations and found that H. rotundata increased phagotrophy at lower light intensities and ammonium was positively correlated with the grazing rates of H. rotundata. We conclude that H. rotundata uses mixotrophy as a primary source for obtaining carbon during the winter when there is limited light and low temperatures.

Blog post:

See Alison's post to Fellowship Experiences, Maryland Sea Grant's blog written by and about fellows and their research: "This Chesapeake Bay Phytoplankton Finds Multiple Ways to Snack."

Project Title:

Binding of Mg and Ca with the Trihydroxamate Siderophore Desferrioxamine B at Seawater Ionic Strength

Organic ligands, which help micro-organisms obtain metals necessary for growth, remain largely unidentified in the ocean. Desferrioxamine B (DFOB) is a terrestrial, commercially available siderophore model for metal-ligand complexation in seawater. Calcium (Ca) and magnesium (Mg) are the only major cations in seawater that have a 2+ charge, allowing them to bind weakly to DFOB. However, they are in much greater abundance than trace metals in the ocean and may thus compete for complexation. DFOB has three stability constants (β) corresponding to its three hydroxamate groups. Previous regression models of DFOB titrations included β4, yet we omitted this parameter since most trace metals lack affinity for the terminal amine group. We measured DFOB complexation with Mg and Ca at various metal:ligand ratios in 0.7 M NaClO4 to simulate seawater conditions. DFOB is shipped with a mesylate (MSA) counter-ion, so MSA complexation with Mg and Ca also had to be considered. The three stability constants were used to re-evaluate the side-reaction coefficient (SRC) of DFOB in seawater. If, after proper correction for the SRC, stability constants of metal-DFOB complexes in seawater agree with those measured for unknown organic ligands, the latter may be siderophore-like.

Project Title:

Risky Business: Using the Perspective of Insurance Companies to Assess Climate Change Scenarios (Norway Example)

Climate change escalates frequency and intensity of extreme weather events such as excessive precipitation and high wind speeds. We use Norwegian data for insurance claims and precipitation levels to identify precipitation thresholds that trigger increased number of house insurance claim and develop a statistical time series model for the claims-precipitation relationship. We evaluate a new data-driven tail comparison method to quantify future change in extreme precipitation and forecast the future change of claims’ counts in the time series model framework. The results show a location-specific change in a number of flood related insurance claims expected based on different climate change scenarios.

Project Title:

The Effects of Low Oxygen Concentrated Waters on Male and Female Planktonic Copepods, Acartia tonsa

For this experiment, Acartia tonsa was collected from the Choptank River at the Horn Point Laboratory in Cambridge, Maryland. Five individual experiments were done on male and female A. tonsa copepods, each with 3 replicate vials. Filtered Penicillin-Streptomycin Solution antibiotic seawater was used in each experiment and treated with nitrogen gas to create oxygen concentrations ranging from 1 mg L-1, 2 mg L-1, 3 mg L-1, 4 mg L-1, and 6mg L-1. The vials were then connected to a Pyro Science FireStingO2 Optical Oxygen Meter and placed in a 23.5ºC ± 0.5 water bath, and the oxygen concentrations in each vial was recorded for 15 hours.

The results showed that above the critical environmental oxygen partial pressure value of 9.57 kPa, respiration for both male and females were independent of the environmental oxygen partial pressure. Additionally, adult A. tonsa continued to respire and maintained their target respiration rate, as their respiration was independent of oxygen concentration. However, at lower environmental oxygen partial pressures, adult female copepods continued to respire rapidly decreasing the oxygen concentration in the experimental vials. Adult female A. tonsa was found to have higher respiration rates than males. When exposed to hypoxia at 2 mg L-1, average female respiration rate was 0.00393 µg O2 L-1 µg dry wt.-1 d-1, while the average male respiration rate was 0.1876 µg O2 L-1 µg dry wt.-1 d-1.

Project Title:

Linking Salinity and Net Ecosystem Metabolism in Chesapeake Bay Wetlands

Sea level rise will increase the salinity in some coastal wetlands. Evidence suggests resulting metabolic shifts could increase the carbon loss from these systems. Cove Point Marsh in Calvert County Maryland experienced a saltwater intrusion and a monitored recovery to freshwater. We used in situ oxygen data to calculate respiration, gross primary production (GPP), and net ecosystem metabolism during the summers of 2011 to 2015. We incubated water and sediment samples to determine component benthic and pelagic metabolism. GPP increased with increasing salinity via a logarithmic relationship (p<0.05) as did respiration (p<0.05).  NEM was not affected by salinity. Water column chlorophyll averaged 1.46 mg m-2 while sediment chlorophyll was 3.5 mg m-2. Water incubations resulted in a depth-integrated pelagic primary productivity of 0.996 g O2 M-2. The lack of correlation between NEM and salinity contradicted predictions that increasing salinity would increase carbon loss. Our results do not indicate that future salinity intrusions will contribute to positive feedback cycles of climate change. Cove Point decreased in salinity throughout our study, so potential regime shifts and other contributing factors merit consideration in future studies. 

Project Title:

Influence of Microphytobenthos on Denitrification And Nutrient Fluxes in Shallow Coastal Systems: A Modeling Approach

The sediments of shallow coastal estuaries play important roles in storing, transforming, and removing nutrients from coastal ecosystems, and using quantitative models to accurately predict the response of sediment nutrient fluxes to environmental changes is crucial to environmental regulation. Microphytobenthos (MPB), photosynthetic microalgae inhabiting the sediment, are widespread in shallow areas and substantially alter the oxygen and nutrient dynamics of photic (illuminated) sediments, but past efforts to model ecosystem-scale sediment nutrient fluxes have largely neglected their effects. This study presents a sediment nitrogen model that computes seasonal cycles of diagenesis, nitrification, and denitrification, and includes a layer of MPB on the sediment surface that performs photosynthesis to characterize the effect of light exposure. Model outputs are validated against data from sediment core incubations at two sites in Chesapeake Bay. The model reproduces observed oxygen dynamics well; sediments exposed to light take up less oxygen during midsummer peaks in oxygen consumption than sediments in the dark, and become net sources of oxygen during spring and fall. Measured sediment nitrogen fluxes are more variable, and the model reproduces seasonal patterns less effectively, but overall both measured and modeled illuminated sediments supply less nitrogen to the water column than dark sediments. This model can be applied to water quality management to help develop recommendations for total maximum daily load of nitrogen to coastal systems. 

Project Title:

Photochemistry of Cyanobacteria Derived Fluorescent Dissolved Organic Matter

Cyanobacterial-derived dissolved organic matter (DOM) was analyzed using excitation emission matrix (EEM) fluorescence spectroscopy and the statistical Parallel Factor Analysis (PARAFAC) technique. The samples were exposed to simulated sunlight, which matches closely the solar spectrum, for a total of 20 hours while recording EEMs every twenty minutes to observe the photodegradation of the fluorescent DOM (FDOM). PARAFAC analysis was applied to deconvolute the EEM matrices into six separate components. The photodegradation kinetics was then calculated for each component and compared with previously obtained photodegradation data of marine and terrestrial FDOM. This 6 component PARAFAC model was similar to those generated from open ocean data and global DOM data sets. Regions previously considered “humic-like” FDOM showed similar fluorescence intensities and percent fluorescence loss when compared to marine DOM. However, the degradation kinetics of the “humic-like” and photo-labile component of bacterial-derived DOM was faster than that of terrestrial-derived DOM. This indicates significant differences in chemical composition. While it was previously believed the majority of marine FDOM was of terrestrial origin, marine FDOM samples showed degradation kinetics more similar to the bacterial derived FDOM.  This supported the hypothesis that a significant portion of marine FDOM is produced in situ

Project Title:

Replication of a Coral Strontium/Calcium-based Medieval Ocean Temperature Record from the Caribbean

Coral Sr/Ca is often used to reconstruct past ocean temperatures in order to extend our knowledge of climate variability beyond the scope of instrumental records. Two sub-fossil corals with overlapping time record that grew in different reef settings on the island of Anegada, British Virgin Islands were used to test the replicability of a coral Sr/Ca record from different reef zones. Coral Sr/Ca was measured from coeval sections of core using ICP-OES and the geochemistry data were compared. Seasonal cycles of Sr/Ca in the corals were nearly identical, but the data differed in mean Sr/Ca. High levels of interannual variability in one of the corals contributed to low correlation between the two Sr/Ca records, likely as a result of the different environmental conditions in which the corals grew. Diagenesis is unlikely to have played a role in differing Sr/Ca data based on lack of evidence of diagenesis in observations of the surface of the corals and the coral x-radiographs. Data from this study suggests seasonal patterns of SST are the most robust feature of Sr/Ca-based SST records in Anegada from the two corals. 

Project Title:

Measuring Temporal Variability of Methyl Mercury and Methane in the Pore Waters of a Chesapeake Bay Tidal Marsh

This study assesses the use of OsmoSampler technology to monitor methylmercury (MeHg) production in a tidal marsh and examines temporal variability of MeHg in relation to controlling factors. We collected pore water samples in a Chesapeake Bay marsh using continuous pore-fluid sampling devices called OsmoSamplers. OsmoSampler technology has not previously been used in a coastal wetland or to investigate mercury cycling. We designed systems using OsmoSamplers to collect pore water samples for MeHg, methane, chloride, and sulfate analysis, sampling in a vegetated area and an area devegetated by clipping. Samples were collected over a 27 day period and stored in coils to create a temporal data set of in situ concentrations. This time series allows us to explore the methane-MeHg connection and the effects of vegetation removal on MeHg production. Some methanogens are known to methylate mercury, but the relative importance of the methane community in mercury methylation is not well understood. We hypothesized a positive correlation between methane and MeHg production, a decrease in MeHg production corresponding to vegetation removal, and that vegetation removal would inhibit sulfate reduction. We also sought to demonstrate the feasibility of using OsmoSamplers to look at MeHg flux in relation to these controls on mercury methylation. We conducted a lab experiment with a MeHg standard, comparative to the field experiment, to assess yield rate and resolution. This study is a preliminary exploration of OsmoSampler technology in a marsh environment. Using our system we have successfully collected samples from the vegetated area for methane, sulfate, and chloride analysis and collected and preserved samples from the devegetated area for MeHg and sulfate analysis. A number of issues arose when adapting the OsmoSampler technology to the collection of pore water in a terrestrial environment. We present the variability of measured concentrations with a discussion of adjustments for future long-term deployment.

Project Title:

Carbonate Chemistry in the Chesapeake Bay: The Effect of the Eastern Oyster, Crassostrea virginica

There are ongoing oyster reef restoration projects in the Chesapeake Bay and these new ecosystems have yet to be fully explored. The carbonate system in an oyster reef is complex with contributions from respiration, calcium carbonate precipitation and dissolution, and other organic and inorganic processes. This experiment aimed to determine the overall effect of all of those processes by looking at the carbonate chemistry balance in a restored oyster reef. D filled with varying amounts of oyster reef material were left in the field for about a month before they were collected and an ex-situ incubation was performed over several hours. The trays with high densities of oysters had significantly higher rates of dissolved inorganic carbon increase and total alkalinity increase compared to trays with low densities or no oysters. High density trays had DIC fluxes of 29776.8±7593.2 µmol DIC m-2 hr-1 and TA fluxes of 20119.1±11107.6 µmol TA m-2 hr-1. High densities of oysters resulted in respiration controlling the carbonate system and forcing oyster shell dissolution. 

Project Title:

Seagrass Beds and Sediment Transport in the Susquehanna Flats

The Chesapeake Bay (CB) is the largest estuary within the United States. Sediment dynamics within this water body rely on comprehending the physical processes that determine the fate of fine sediments and nutrients. This study investigated seasonal and spatial changes in sediment erodibility at the Susquehanna Flats (SF) to show its interaction with the seasonal growth of Submerged Aquatic Vegetation (SAV). Positioned at the mouth of the Susquehanna River, the Flats receives approximately half of the total freshwater and suspended sediment flowing into the CB. From May 28-30, 2015, I assisted in collecting samples using sediment cores at six different sites around the Flats, accounting for an even grain size distribution. This ensured an unbiased data collection. Data were processed and analyzed using MATLAB scripts to process an implicit erosion equation, displaying results in the form of semi-logarithmic graphs. Our hypothesis stated that seasonal and spatial changes in SAV abundance were reflected in seasonal and spatial differences in sediment erodability. Analysis revealed that the presence of SAV biomass played a salient role in the erosion processes in the SF.

Project Title:

Climate Change Effects on Respiration Rates of Blue Crab (Callinectes sapidus) from the Patuxent River, Chesapeake Bay

A rise in atmospheric CO2 induces a greenhouse effect that also causes ocean temperatures and CO2 levels to rise. These environmental changes may represent an additional energetic cost for blue crabs because they rely on the concentration of CO2 in the water to deposit calcium carbonate in their shells. We conducted a respiration experiment to measure the effect of climate change on crab metabolism. Crabs were collected from the Chesapeake Bay and exposed to different heated and acidified conditions. After crabs had been exposed to the environmental conditions in the chambers for two molts, they were placed in respiration chambers to measure rates of oxygen consumption. Results indicated different trends in respiration rates between the treatments, although the patterns were not statistically significant. Crabs exposed to higher temperatures showed elevated respiration rates, while crabs exposed to high CO2 demonstrated decreased respiration rates. The two factors of climate change (high temperature and high CO2) did not demonstrate the highest respiration rate, but rather the crabs exposed to high temperatures and ambient CO2 showed the highest mean respiration rate. These data suggest that crab metabolism may not change as much as expected due to climate changes. 

Project Title:

Fortnightly Variability of Sediment Dynamics In Tidal Freshwater Marshes

Salt and freshwater marshes exist at the interface of terrestrial and aquatic systems. Key differences exist between salt and freshwater marshes and even among marshes experiencing similar salinity; however, these differences are often not examined when drawing inferences about sustainability in the face of sea-level rise. The main purpose of this study was to examine five key parameters at play in both Monie Bay (salt water) and Jug Bay (freshwater): grain size, organic content, vegetative community, sedimentation rate, and turbidity over a period of two weeks. Previous studies have examined these parameters when studying marshes, although turbidity is often disregarded. In reality, the amount of sediment transported within the water column can have large implications on whether a marsh is likely to survive future sea-level rise or suffer heavy losses to erosion. Because of the complex nature of these systems, it is wise to be cautious of making long-term assumptions off of short-term data collection. 

Project Title:

Salinity Tolerance of Early-Stage Oyster Larvae in Low Salinities

The eastern oyster (Crassostrea virginica) is ecologically and economically important to the Chesapeake Bay, Maryland, USA. Its population, however, is currently estimated to be less than one percent of what it was historically. To restore oyster populations, techniques such as larval transport modeling are being implemented to aid the selection of sanctuary locations. These models can incorporate biological factors such as salinity-induced mortality, but no data from low-salinity areas such as the oligohaline Choptank River, a major focus of oyster restoration efforts, exist. The purpose of our study was to generate salinity-induced mortality data for oyster larvae from the Choptank River and compare their tolerances to those of oysters from different salinity regimes. We performed three experiments looking at the effect of salinities from 3 to 26 on the survival of larvae from ~4 to 48 hrs post-fertilization. While overall survival differed across experiments, we found a consistent minimum survival threshold between 5-7 and peak survival window between 9-16. These salinity values were about 7 lower than those of oysters from the polyhaline Long Island Sound (threshold: 12.5-15; peak: 17.5-27). This research has direct application to oyster restoration in the Choptank River and similar low-salinity areas by improving larval transport model predictions.

Project Title:

Origins of Low Oxygen Zone Water Masses and Their Link to Nitrous Oxide Production in the Eastern Pacific Ocean

Nitrous Oxide, a potent greenhouse and ozone depleting gas, is produced in large quantities over oceanic oxygen minimum zones as a result of nitrification and denitrification. A majority of oceanic N2O is produced at O2 concentrations of less than 30 μmol/L, which are primarily located below the mixed layer. As a result, the time scales and pathways over which it effluxes into the atmosphere are poorly understood. Subsurface N2O data collected at five stations by Dr. Alyson Santoro during a 2010 research cruise over the Eastern Tropical South Pacific low oxygen zone were analyzed in this study. In order to better understand the mid-depth ocean circulations that transport N2O rich waters to the surface over this region, we used the Hybrid Coordinate Ocean Model (HYCOM) in conjunction with a Lagrangian float model. We found that the combination of coastal upwelling and horizontal advection of N2O rich waters was responsible for both spatial distributions of atmospheric N2O effluxes and their magnitudes. Station analyses also uncovered denitrification as the primary method for N2O production in oxygen minimum zones.

The Blue Crab: Callinectes Sapidus

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