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 2014

Project Title:

Factors Responsible for the Development of Fe Flocculate in Streams with and without Regenerative Stormwater Conveyance (RSC) Structures

A relatively new ecological engineering design developed to reduce stormwater runoff and pollutant loads is called a Regenerative Stormwater Conveyance (RSC). RSCs are implemented in degraded headwater streams using sand, woodchips, cobble, and ironstone boulders to create a series of stepped pool conveyance structures. Concern has been raised that RSCs exhibit excessive accumulations of flocculate mats created by iron-(Fe)-oxidizing bacteria. Iron sources and other factors responsible for mat formation are poorly understood, as well as how RSCs affect stream habitat and water chemistry. Leaching experiments were done on riparian soils and substrates used in RSC construction with and without added dissolved organic carbon (DOC) to identify Fe sources and the factors driving its release. Riparian and hyporheic ground- and surface-water chemistry, and physical habitat parameters, from six RSCs and three reference (control) streams in urban catchments of the Coastal Plain and Piedmont physiographic provinces of Maryland were compared. A longitudinal transect of one RSC was done to evaluate potential density changes of Fe-oxidizing bacterial mats and the solute composition of water in successive pools/riffles of the structure. This study suggests that both ironstone and riparian soils contribute to Fe bacterial mat formation, a process accelerated by the presence of DOC.

Class of 2013

Project Title:

Measured Responses of Gray Tree Frog (Hyla versicolor) Tadpoles to Selenomethionine and Selenium Dioxide

Selenium (Se) is a contaminant of concern in areas affected by coal ash disposal and runoff from seleniferous soils, and may occur in inorganic or organic forms. To quantify the different effects of organic and inorganic selenium, we dosed the food of gray tree frog (Hyla versicolor) tadpoles with selenium dioxide at concentrations of 16.27 and 34.2 μg g-1 Se dw and selenomethionine (SeMet) concentrations of 14.23 and 32.8 ug g-1 Se dw. As tadpoles accumulated Se throughout metamorphosis, we measured biological endpoints including metabolic rate, survival, and growth. A behavioral test was also administered. Chemical analyses on total accumulated Se and mercury (Hg) have yet to be completed. Analysis of food was done via chemical digestion and mass spectrometry. Midpoint respirometry analysis showed that SeMet high tadpoles had significantly higher metabolic rates in μl O2 g-1 min-1, with a mean of 3.26, than control (mean=2.20, p=0.0024), SeO2 low (mean=2.52, p=0.0337), and SeMet low (mean=2.66, p=0.0176) tadpoles. No further significance was found regarding respirometry, growth, survival, or behavior. However, survival to the end of the study was lowest for SeMet high and SeMet low tadpoles, suggesting organic Se had more toxic effects. SeO2 did not appear to be toxic, but because of the possibility of conversion to an organic form in a natural ecosystem, efforts to restrict release of Se rich wastes are warranted.

Project Title:

Factors Affecting Cyanobacterial Ecology in a Restoration Wetland on Poplar Island, Chesapeake Bay

A wetland habitat at the Poplar Island ecosystem restoration project (Cell 6) has recently become home to a variety of birds, which use the pond for its nearby food and protection from predators. Additionally, a variety of cyanobacteria inhabit the site, including Anabaena, Oscillatoria, and Microcystis. Toxins produced by some of these cyanobacteria resulted in bird fatalities after a Microcystis bloom in summer 2012. Here, we examine the role that temperature, nutrients, and species composition plays in predicting how blooms might occur, whether toxins are produced, and how nitrogen fixation is performed. We found that cultures of cyanobacteria (primarily Anabaena) grow well in temperatures as high as 30°C, and that Anabaena from Cell 6 produces low levels of microcystin. Nitrogen fixation levels in cultures tended to spike periodically, possibly in response to fluctuations in limiting nutrients. Finally, nutrient concentrations played an important role in cyanobacterial growth and nitrogen fixation.

Project Title:

The Effects of Nutrients on the Biomechanics of Spartina alterniflora on Poplar Island

Due to high nutrient content in dredge material encompassing Poplar Island significant amounts of lodging has resulted. Additions of silicon are used in order to determine their effect on Spartina alterniflora on Poplar Island. Biomechanical tests were performed in order to determine the elastic modulus and measurements were taken to determine the second moment of area. ANOVA statistical analysis was performed and determined there was no statistical significance in any mean values depicted in the bar graphs in average stem length.

Project Title:

Characterizing Flow at the Susquehanna Flats

The Chesapeake Bay (CB) is the largest estuary in the United States. Water quality models in the CB depend on a predictive understanding of the physical, chemical, and biological processes that influence the transport and fate of sediments and nutrients. This study characterized flow at the Susquehanna Flats (SF) in the upper CB to show how submerged aquatic vegetation (SAV) influences hydrodynamics. The SF lie at the mouth of the Susquehanna River, which is the primary source of fresh water for the CB. From July 7-12, 2013, we deployed tide, wave, current velocity, and pressure gauges at seven sites around the SF to gather time series data on flow and its attenuation in and around the SAV bed at the SF. The design shows how spatial features including bathymetry, delta geometry, and grass bed geometry affect patterns of flow and transport. Data were processed and analyzed using standard MATLAB time series analysis techniques. Our hypothesis was that the flow would predominately be diverted around the grass bed into adjacent deep, unvegetated channels. Seagrass was minimally present during the deployment. Analysis shows that tide, river flow, and wind all play key roles in the physical processes at the SF.

Project Title:

Wind-induced Lateral Circulation and Mixing in the Chesapeake Bay

The lateral salinity gradient responds to wind and tidal forcing in the Chesapeake Bay with spatial variation in salinity. The layers of isohalines tilt to the western shore during flood tide and slack before ebb tide, while the isohalines flatten during ebb and slack before flood tide, creating a semi-diurnal seesaw motion of the salinity gradient. The degree of the tilt correlates to the sensitivity of the tide to the Coriolis Effect, a phenomenon previously not well understood spatially. Sensitivity to wind forcing occurs on a more drastic scale and results in tilting to the Eastern shore. Up-welling and down-welling zones appear on the shallow shoals during wind events. The shallow shoals also experienced regularly changing salinity from 11-15 PSU within the interval of six hours. Both up-welling and down-welling zones and the seesaw motion of the salinity gradient may indicate lateral mixing.

Project Title:

The Microbial Effects of the Addition of Oil to the Anoxic Layers of Benthic Sediments from the Chesapeake Bay

The Macando oil spill three years ago released an unprecedented amount of oil into the Gulf of Mexico. The environmental impacts of this massive influx oil are still being studied today. This project focuses on the effects oil has on microbes in deep-sea anoxic sediments. In the anoxic sediments, three major microbial zones exist due to competitive-substrates. The primary microbes studied within each of the three zones respectively are the sulfate reducing bacteria, the methanotrophs, and the methanogens. In this experiment, incubations were done to produce a time series for each zone tracking the changes in concentration of sulfate and methane. It was hypothesized that the addition of oil will cause sulfate to be depleted faster in the sulfate reduction zone and methane to be produced sooner in the methane production zone. The results showed that sulfate remained constant throughout the time series despite oil being added, and that methane was produced sooner for the oil groups than the control groups in two of the three zones. These results contradicted the idea of competitive substrates. In conclusion, a new hypothesis was formed stating that the addition of oil has a greater effect on methane production via non-competitive substrates.

Project Title:

Bioaccumulation of Synthetic Musk Fragrances in Northern Diamondback Terrapins (Malaclemys terrapin terrapin) of Jamaica Bay, New York, USA

Synthetic musk fragrances are found in almost all scented personal care products. They have been measured in water, air, sewage sludge, and various biota all over the world. However, no studies have measured the maternal transfer of musk fragrances. The northern diamondback terrapin was selected as a bioindicator because of its long life span, high trophic level, high nest fidelity, and its ability to live across a wide salinity gradient. In this preliminary study we targeted one nitro-musk (musk xylene [MX]) and one polycyclic musk (galaxolide [HHCB]). We assessed their presence in eggs of terrapins inhabiting a contaminated site (Jamaica Bay, NY, USA) and compared those results to a less impacted site (United States Patuxent Naval Air Station along the Patuxent River in Maryland). We developed a method for extraction and used gas chromatography-mass spectrometry to analyze these parent compounds in terrapin eggs. We found that MX maternally transferred to the offspring. Work is still being done to measure the accumulation of HHCB and quantify the concentration of the musk fragrances in individuals. This field-based study is the first step in assessing the degree of exposure of terrapin embryos to synthetic musk fragrances accumulated by their parents.

Project Title:

Modeling of Blue Crab Catchability in Chesapeake Bay using Winter Dredge Surveys

Project Title:

Calibration of Modern Coral Climate Signals to Ensure Accuracy of Paleoclimate Determinations in Anegada, British Virgin Islands

Three modern Diploria strigosa corals from Anegada, British Virgin Islands were analyzed for Sr/Ca ratios over their lifetime to create a modern calibration between Sr/Ca and sea surface temperature (SST) for use in climate reconstructions of subfossil coral specimens from the same site. Results were compared to those of Hetzinger et al. 2006 and Giry et al 2010. Average mean Sr/Ca between the three corals was 9.03 mmol/mol, yielding an expected intercoral mean Sr/Ca range in the Caribbean for this species of approximately 9.00±0.15 mmol/mol when the other studies are incorporated. The average Sr/Ca-SST relationship for the three corals using ordinary least squares regression was -0.043 mmol/mol/°C using the monthly Sr/Ca from corals and gridded temperature from the ERSST 3b data set (Smith et al. 2008), which agrees with previous findings. The average Sr/Ca-SST relationship for the three corals using reduced major axis regression was -0.0564 mmol/mol/°C, whereas the average Sr/Ca-SST relationship was -0.122 mmol/mol/°C based on the monthly anomalies of both data sets. This calibration informs further work reconstructing Medieval climate data from subfossil corals at this site.

Project Title:

Marine Chromophoric Dissolved Organic Matter Distribution in the Atlantic Ocean

Seawater samples (200) containing dissolved organic matter (DOM), collected in the Atlantic Ocean, have been solid-phase extracted, analyzed by EEM Fluorescence Spectroscopy and used to create a robust Parallel Factor Analysis (PARAFAC) model. Using a 24 bottle rosette and CTD profiler aboard the R/V Atlantic Explorer, a total of 24 samples (10 liter volume), were collected at the Bermuda Atlantic Time Series Station (BATS) at every 200 m down to 4,530 m. Each sample was then solid-phase extracted. The quinine sulfate normalized fluorescent peaks that represent humic-like and fulvic-like peaks showed a continuous increase until constant levels were reached at about 1,400 m depth. The protein-like fluorescent peak showed exactly the opposite trend, indicating that this fluorescent component is correlated with the abundance of marine biota (autotrophic and heterotrophic organisms) as there is more marine life in the surface waters of the ocean. The source of the humic and fulvic-like fluorescence at greater depths is not yet known, but it is still plausible that it is related to heterotrophic microorganisms. Additionally, sunlight would severely photobleach these fluorescent dissolved organic matter (FDOM) components at the surface ocean and deplete them. The PARAFAC model was then applied to determine the relative contribution of the six PARAFAC components found for Atlantic solid-phase extracted marine FDOM. The components established for humic-like, fulvic-like and protein-like fluorescence followed the same trends as described above, indicating that the PARAFAC model nicely resembles the results obtained through the quinine-sulfate normalized method. These trends have also been confirmed in previous studies using direct water samples and hence the solid-phase extraction method, combined with PARAFAC analysis used in this study is suitable to obtain representative fluorescent data with the advantage of using much more concentrated samples and therefore a greatly improved signal.

Project Title:

Effects of N:P Ratio Variation on Feeding of Dinoflagellate K. veneficum on Cryptophyte Rhodomonas sp.

Harmful Algal Blooms (HABs) are a global problem in marine and freshwater systems, leading to adverse environmental, economic, and health effects. HABs are increasing in frequency, due largely to the eutrophication of marine and freshwater ecosystems caused by increased runoff of nitrogen and phosphorus. Many HABs are formed by mixotrophic algal species, and may change their behavior based on their nutrient conditions, or the nutrient composition of their food. We experimented with one species of algae, Karlodinium veneficum that can form harmful blooms. Karlodinium veneficum and a cryptophyte food source, Rhodomonas sp., were grown separately under two different nitrogen to phosphorus ratios, and feeding crosses were done to see the effect of these different nutrient conditions on the growth and feeding of K. veneficum. The results of this experiment showed differences between K. veneficum grown at an N:P ratio of 4 and K. veneficum grown at an N:P ratio of 24 when both were fed Rhodomonas sp., as the K. veneficum grown at an N:P of 24 showed growth similar to that of the control, and K. veneficum grown at an N:P of 4 showed negative growth compared to the control. Although the results of this project were inconclusive, continued research in this area is important for collecting data on growth of harmful algal species under different nutrient conditions. These data can then be incorporated into models that attempt to successfully predict when and where HABs may occur.

Project Title:

The Evaluation of Basic Calculations Concerning the Effects of Non-Storm Waves on Offshore Sediment at Jefferson-Patterson Park, MD

Project Title:

Hypoxic Impacts on Egg Respiration Rates of the Copepod Acartia tonsa

The Chesapeake Bay has experienced extensive areas of hypoxia (< 2 mg O2 L-1) in the past half-century as a direct result of eutrophication. The copepod Acartia tonsa, serves as a valuable prey item to higher trophic levels in the Chesapeake Bay and past studies have detected negative hypoxic effects on reproductive success and egg development rates. Little is known, however, on the physiological mechanism causing increased egg hatching time by hypoxia in A. tonsa. The goal of this study was to examine if lowered A. tonsa respiration rates may be a potential physiological mechanism impacted by hypoxia in the Chesapeake Bay. Egg development rates of female A. tonsa and egg hatching success were measured in hypoxic (< 2 mg O2 L-1) and fully oxygenated (> 5.99 mg O2 L-1) waters. Egg respiration rate and development were measured in two-hour intervals for a total of eight hours using a Pro2030 Professional Series YSI probe. We expected lowered respiration rate in hypoxic conditions to contribute to decreases in A. tonsa egg production, sinking rates, and ultimately egg hatching success. Results of this study may inform how future A. tonsa populations will be impacted in a changing environment and how those changes impact the future health of their predators.

Project Title:

Levels of PAHs in Marine Biofouling Organisms Attached to Oil Rigs in the Gulf of Mexico

The Deepwater Horizon oil spill was a tragedy resulting in multiple people losing their lives and millions of gallons of oil being leaked into the Gulf of Mexico. This spilled oil contained compounds known as polycyclic aromatic hydrocarbons that are known for their toxicity, specifically, their carcinogenic properties. In this study, Orange Cup Coral and Crested Oysters were collected from oil rigs located around the oil spill on two different sampling dates after the oil well was capped. These samples were analyzed for their concentrations of polycyclic aromatic hydrocarbons. Results were then compared through temporal and spatial analyses to determine where the polycyclic aromatic hydrocarbons were originating.

Project Title:

Quantifying Growth Variation of Juvenile Blue Crab (Callinectes sapidus) using RNA:DNA in Response to Elevated Water Temperature and Nutritional Rations

The blue crab (Callinectes sapidus) is both ecologically and economically important in the Chesapeake Bay. It supports the most valuable fishery in the Chesapeake Bay and plays a key role in coupling energy flow between the benthic and pelagic ecosystems. As a result, future management is needed to maintain a sustainable habitat quality for the blue crab. To estimate the value of individual habitats, we must be able to estimate the production of blue crab. Yet, currently we lack knowledge on the growth of blue crab. The goal of this project is to evaluate the utility of a biochemical assay of nucleic acid concentrations as an index of growth. Although the amount of RNA and DNA in tissue varies between species, the quantity of DNA is constant in cells, but the level of RNA fluctuates with metabolic activity. This study explored the potential for RNA:DNA ratios to measure crab growth in laboratory settings, based on elevated water temperature and nutritional ration. Data indicated that concentrations of RNA, DNA, and RNA:DNA could be measured with precision. The experimental results showed a growth response to temperature and ration treatment. However, results indicated that the relationship between RNA:DNA and growth was equivocal. Based on these results RNA:DNA does not appear to be a valid index of growth in blue crab.

Class of 2012

Project Title:

Investigating the Effects of Unusual Weather Patterns on Water Quality, Sediment Composition, and Submersed Aquatic Vegetation Biomass at the Susquehanna Flats

Our data have quantified and characterized the composition of sediment and water quality parameters at the Susquehanna Flats. These variables are important factors in determining the rate of growth of submersed aquatic vegetation (SAV) for a given year. This summer, the SAV has had a much weaker growth than previous years. An unusual year of weather, with heavy fall storms and warm winter temperature, appears to have contributed to lower SAV growth and abundance. During the summer of 2012, we found that there were higher concentrations of suspended solids and phytoplankton chlorophyll inside the bed and down-bay from the bed than would be expected (based on conditions measured in previous years). The suspended solids are mostly made up of inorganic materials, suggesting that input of these materials into the water column from the fall storms discharge was more important than the eutrophication effects from nutrient inputs. Elevated levels of sediment down-bay are attributed to continual resuspension and deposition of bottom sediments inside the bed. It is likely that this increase in suspended particles caused decreased water clarity which in turn caused reduced SAV growth. Biomass samples collected in this study revealed lower SAV growth associated with increased epiphyte levels. Understanding how environmental changes influence the growth and abundance of SAV can help to explain both disappearance and resurgence of SAV in the Susquehanna Flats.

The Blue Crab: Callinectes Sapidus

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