Our Students and Their Research

Rates of denitrification and photosynthesis were measured in cores taken from Horn Point marsh, on the Choptank River and from Poplar Island, in the Chesapeake Bay. Denitrification was observed in all cores, causing an increase in the N₂ gas concentration measured in the water samples. Rates of photosynthesis were dependant on light conditions and the amount of photosynthetic algae and bacteria present.

A pilot study to investigate the effects of emergent freshwater wetland vegetation on sedimentation rates evaluated the impact of species composition, morphology, and distance from sediment source on accretion rates. Two transects were situated perpendicular to tidal creeks in the Jug Bay Wetland Sanctuary; one representing a diverse plant community composed predominantly of spatterdock (Nuphar advena), arrow arum (Peltandra virginica) and narrow leaf cattail (Typha angustifolia), and the other site dominated exclusively by spatterdock. Individual plants were collected along each transect to measure morphology, dry weight, and sediment captured on the surface of leaves and stems. Plant community measurements of percent cover, density, and biomass were also collected. Individual plant surface area or distance from tidal creek did not explain sediment capture rates. However, calculations of projected frontal area of the vegetation from plant density, water volume, and surface area estimates were related to increasing sediment capture in the spatterdock and arrow arum communities. Accretion rates attributable to plant capture were estimated using published bulk density values from the same locations and ranged from 0.7 mm year^-1 for spatterdock to 0.33 and 0.39 mm year^-1 for the low and middle marsh plant communities. High rates of sedimentation in spatterdock communities coincide with the lowest elevation zone of the marsh platform most susceptible to sea level rise.

An influx of nitrate (NO₃^-) from agricultural practices has altered the types and amounts of microbial respiratory processes occurring in the sediment downstream of agricultural fields. This study examined dissolved CO₂ in groundwater as a measure of microbial respiration, and compared it to dissolved N₂, O₂, N₂O, and CH₄. We found unusually high concentrations of CO₂ in nearly all groundwater samples, in relation to presently understood rates of aerobic respiration, denitrification, and methanogenesis. We believe that the excess dissolved CO₂ can be partially explained by the application of agricultural lime (CaCO₃) and the presence of cations in the soil, which stabilize HCO₃^- ions from air or soil in the groundwater. A large proportion of the excess CO₂ found in our samples is most likely a by-product of alternate anaerobic respiratory pathways (reduction of Mn⁴⁺, Fe²⁺, and SO₄^2-)that were not specifically examined in this study.

The number of surface functional groups of Ulva lactuca, their absolute concentrations, and acid dissociation constants (pKas) were determined through potentiometric titrations in sodium chloride solutions at various ionic strengths (0.01 M - 5.0 M). Dehydrated BCR-279 Ulva was compared to fresh Ulva specimens. Finally, a titration in seawater was compared to titrations in sodium chloride. It was determined based on the FITEQL 4.0 Fortran code that there are three (possibly four) surface functional groups. It was also determined that their zero ionic strength pKas were around 4.1, 6.3, and 9.5 and their absolute concentrations are approximately 4.6 x 10-4 mol/gram of Ulva, 5.1 x 10-4 mol/gram of Ulva, and 5.7 x 10-4 mol/gram of Ulva, respectively. Fresh Ulva was shown to have similar pKas, but lower concentrations. Finally, the seawater titration indicates that the non-carbonate alkalinity of seawater far exceeds the concentration of functional groups on the Ulva sample.

The ability of five wetland species to take up nutrients, nitrogen and phosphorus, were evaluated by examining initial and final whole plant nutrient concentration. They were grown in a 5% Hoagland's hydroponic solution. Plant samples were taken after three weeks and analyzed. The highest growth rate was seen in the species Kosteletzkya virginica. This species also exhibited the highest nitrogen tissue concentration. Panicum virgatum also exhibited the highest tissue concentration of phosphorus and second greatest nitrogen tissue concentration. The ability of these particular plants to take up large quantities of nutrients is beneficial for removal of these nutrients to alleviate pollution in and around watersheds like the Chesapeake Bay.

N₂, O₂ and Ar are the three most concentrated gases in aerobic waters. N₂ and O₂ are affected by both biological and physical processes, whereas Ar is affected strictly by physical processes. Deviation of these dissolved gases from equilibrium concentrations are common and reflect biological activates such as denitrification and photosynthesis acting on the system. These deviations also reflect the presence of physical processes such as bubble formation. Current methods for measuring denitrification sediments are hampered by bubble formation which can occur under illuminated conditions with an algal layer on the sediment surface. Bubbles stop N₂ and affect the relationship between concentration of N₂ and denitrification. The project investigates the processes of denitrification, photosynthesis and respiration by measuring the intensity of dissolved gases in samples using the membrane inlet mass spectrometer (MIMS). Sediment core samples were taken from the Choptank River and were setup in a temperature-controlled cylindrical chamber with 170ml of headwater. Test tube samples were taken from the headwater and run by mass spectrometer, water temperature, salinity, and depth profile were monitored to determine the relationship of these factors with the results of the experiment.
The experimental results show that the concentration dissolved O₂ levels kept increasing and dissolved N₂ has insignificantly fluctuated, supporting the fact that that denitrifying bacteria in the sediment core do not denitrify during the day. The research project has identified both advantages and disadvantages of the MIMS and provides a method to measure to investigate an overall system metabolism of a natural aquatic system.

Vanadium (V) is a common byproduct of fossil fuel combustion in solid wastes of ash and is known to have a variety of effects related to metabolic function in vertebrates. In studies of captive mammals, V has been found to modify metabolic and bioenergetic processes. Selenium is essential to animals when present at low concentrations, but is toxic to aquatic life at somewhat higher concentrations. Along with entering the aquatic systems through natural weathering of rocks and soils, Se is also released from coal ash disposal in the same way V does. However, the effect of V, as well as Se, on wildlife in natural systems is largely unknown. In prior studies we found that dietary exposure to environmentally relevant concentrations of V reduced growth, lipid content, and survival to metamorphic climax in larval leopard frogs (Rana sphenocephala). In the current, follow up study, we examined dietary effects of a wider range in concentrations of V and Se on larval grey tree frogs (Hyla versicolor). We fed larvae of the grey tree frog V at two concentrations, 360 and 720 ppm and Se and 12 and 60 ppm. Metal bioaccumulation, growth rates, lipid content, and metabolic rates were measured to assess the impact of V and Se exposure. Metabolic rates measured mid-way through larval development did not differ, however several physiological traits of metamorphs appeared to be altered. The results from this and our prior study suggest that V and Se may pose risks to recruitment potential of amphibians in sites contaminated with fossil fuel-derived wastes.

American eel (Anguilla rostrata) harvests along the Atlantic coast of the U.S. have been declining since the late 1970s. It is thought that abundance may be declining to critically low levels. The objective of this study was to evaluate intra and inter-annual trends in catch-per-unit-effort (CPUE) and potential causes of trends. Catch and effort data were used to calculate CPUE as an index of abundance in order to evaluate whether American eels declined in the Potomac River during 1996-2007. Additionally, water quality parameters such as salinity, dissolved oxygen, and water temperature were examined to determine if they explained any of the variation in CPUE. Results showed an increase in CPUE for half of the years studied, indicating that the stock status is not in as dire a situation as implied by a study in the Potomac River during 2007. The overall yearly CPUE from 1996-2007 showed an increasing trend. There seemed to be a slight effect of salinity on CPUE, but dissolved oxygen and water temperature appeared to have little effect.

Seasonal jellyfish blooms are ecologically important events that affect food web dynamics in coastal systems throughout the world. Additionally, high concentrations of jellyfish can cause significant economic losses by interfering with fisheries, aquaculture operations, nuclear power plants, and tourism. The paucity of existing information on bloom development and diminution exacerbates the task of reducing or avoiding the associated problems. This work is part of a larger goal to improve our understanding of the causative factors that influence jellyfish blooms and to utilize this information for forecasting purposes. Data from recent years shows a relationship between temperature and the disappearance of sea nettles from both the surface and the riverbed. This study focuses on further understanding this relationship by exposing sea nettles to low temperatures and observing the vertical position and locomotion of each medusa. Our findings show low temperatures significantly influence the vertical position of Scyphomedusan Chrysaora quinquecirrha in the water column. Results suggest that below a threshold value of 15°C, the swimming ability of the medusae is significantly impaired causing them to sink to the bottom of the water column. This provides the basis for future studies to assess the fate of organic carbon associated with the biomass of this top predator, which may have significant implications for pelagic-benthic processes including carbon cycling and trophic interactions.

The copepod Acartia tonsa dominates the mesozooplankton in the Chesapeake Bay at certain times of the year, providing a link between primary producers and higher trophic levels, including commercially important fish species. We evaluated the use of a DNA stain (DAPI) to measure egg development and explore the effects of low dissolved oxygen (hypoxia) on A. tonsa eggs. Stage distributions were determined from vertically stratified samples. Larger amounts of late stage eggs were observed in deeper water. Incubated samples also showed shifts in development distributions. Low staining success was observed, ranging from 19.6% to 37%. Possible reasons for the low staining success could be due to methodological or biological reasons, but these were not evaluated. The vital stain neutral red was tested to determine if non-viable eggs weren't staining, but the eggs did not take up the neutral red stain efficiently. Overall we found that the use of DAPI was effective in staining the eggs and allowed for the distribution of eggs in a particular site to be quantified. This technique could be used, along with controlled lab experiments, to determine egg development rates for A. tonsa in the future, and look at the variation of egg distributions and rates in different environmental conditions in the Bay.

While it is known that krill are very important in the food web of the Bering Sea and that their transfer of lipids from organism to organism is paramount to a healthy ecosystem, it is unknown to what extent that this takes place. It was discovered that krill were eating phototrophic organisms by way of finding phytol, a chlorophyll breakdown product, in their bodies. It is also evident that the krill were eating assorted species of diatoms from the diatom-exclusive sterols found in the krill. While this work may have continued and produced more conclusive evidence, I was offered an opportunity to board a polar science research vessel manned by the United States Coast Guard in the Bering Sea. As this is a very valuable opportunity and not one to pass up, I accepted and spent the month of July performing genuine oceanographic field work with krill.

The goal of this study was to determine whether increasing acidic conditions in coastal waters will affect the calcification rate of the bivalve Mya arenaria. Acidification is caused by anthropogenic emissions of carbon dioxide, sulfur and nitrogen and subsequent dissolution in coastal waters, thereby lowering pH and decreasing the availability of calcium carbonate. Our experiment created three different pH levels by bubbling carbon dioxide into the experimental flasks and measured biocalcification of juvenile M. arenaria. The experiment ran for 28 hours and 5 samples where taken throughout the duration of the study. The lowered saturation state caused M. arenaria to experience a decrease in biocalcification rate and suffer from a slight dissolution effect due to high concentrations of CO₂ bubbled in the low treatment throughout the experiment. The medium and the high treatments, however, were not significantly different.

This study examined trophic niche aspects of three meso-predatory elasmobranchs abundant within the shallow neritic waters of coastal Maryland: smooth dogfish (Mustelus canis), clearnose skate (Raja eglanteria) and bullnose ray (Myliobatis freminvillei). Graphical analysis assessed major prey items and foraging strategy, while dietary overlap measurements determined possible competitive interactions. Lastly, trophic level for each species was estimated using proportions of differing prey categories within the diet. Smooth dogfish and clearnose skate gut content biomass were dominated by small fish and crabs (Anomura and Brachyura). Gut contents indicated a generalist foraging strategy for smooth dogfish and clearnose skate. Conversely, bullnose ray gut contents indicated a diet almost exclusively composed of mollusks, specifically gastropods, suggesting that the bullnose ray is a specialized molluscivore. Estimates of trophic level indicate clearnose skate occupied the highest trophic level (3.97), bullnose ray the lowest (3.67), and smooth dogfish were intermediate (3.71). Finally, significant dietary overlap was only evident between smooth dogfish and clearnose skate. This significant overlap indicates similar ecological niches for the smooth dogfish and clearnose skate; however, competition for food sources may not greatly affect the abundance of the two species given their generalist feeding patterns. The results suggest a minimal potential interaction with large teleost species, specifically with competition for food sources or predation of juvenile fish. Thus changes in abundance in these elasmobranch species may not affect commercially important teleost species.

Anthropogenic activities, including deforestation, waste water output, agricultural land use, developed land use, and atmospheric deposition, all contribute towards river nitrogen and phosphorus concentrations. Water quality data from USGS for 8 subbasins within the Hudson River basin, the Delaware River basin, and the Chesapeake basin was analyzed with 2000 population data from the US Bureau of the Census and 2001 land cover data from the National Land Cover Database. Population density, percent developed land, and percent agriculture varied concentrations of N and P in rivers, reducing water quality within the basins. Forests, agriculture, and developed lands were the most prominent land uses within all basins. Long term regressions show minor improvement in water quality during 1970-2005, despite attempts to reduce anthropogenic impacts. Short-term regressions show similar improvement from 1995-2005. The 1995-2005 time-frame was wetter than the long-term mean at every basin site, and water yield increased as site latitude increased due to mean temperature and evapotranspiration. Human presence on land still has large negative effects on water quality.

The purpose of this study is to analyze the projected climate over the Chesapeake Bay Watershed by the IPCC AR4 models.  As a mean of doing this the A2 and B1 emission scenarios were chosen because they represent the largest range of direction in all the emission scenarios.  The mean model is the average of all individual models and is often used as a tool for the most accurate future climate projections. By removing some poorly performing models versus the 20th century data, the mean model was able to undergo a statistically significant improvement.  With an improved mean model, it is projected that mean annual temperature will increase across the watershed by 4.65 degrees Celsius under the A2 emissions scenario and 2.49 degrees Celsius under the B1 scenario.  Additionally, annual precipitation is projected to increase by 5.04% under the B1 scenario and 7.18% under the A2 scenario with the greatest increases projected for winter and spring.  With no concrete relationship exists between precipitation and streamflow, it is possible only to speculate that changes in precipitation may alter the time and duration of the spring freshet.  Flooding events and drought conditions could be an even greater future concern as there appears to be an upward trend for the amount of 5 day rain fall, consecutive dry days, and extreme temperature events—particularly under the A2 scenario.

Management of white perch (Morone americana) populations in the Chesapeake Bay requires knowledge of demographic parameters, including age, growth and mortality. Spatial variation in vital rates may be genetically based, the result of differences in habitat or harvest across populations, or some interaction of these factors. Age was determined by examination of otolith thin-section, growth was analyzed using von Bertalanffy growth model, and mortality estimated through catch-curve analysis. Comparisons of vital rates were made within and between populations occurring in the James, York, Potomac, Patuxent, and Choptank rivers. Growth of white perch from the James, Patuxent, and Choptank rivers were best fit by sex-specific models, whereas growth of York and Potomac river white perch was best described by models including both sexes combined. Across rivers, growth was best described by separate Maryland (Potomac, Patuxent, and Choptank rivers) and Virginia river models (James and York rivers). Similarities in growth within Maryland and Virginia rivers may be a function of connectivity between these populations or similarities in habitat. For most river systems, excluding the Potomac and Choptank, mortality was best estimated by sex-specific models rather than combined sex models. Mortality was found to be similar across populations, however, bias in fish collection and violation of the assumptions of catch-curve analysis may have affected our estimates. Similarities in growth suggest that white perch populations in the Chesapeake Bay may benefit from management as two units (MD and VA rivers), however, further research is required to draw definitive conclusions.

Polybrominated diphenyl ethers (BDEs) have been used for years as flame retardants in plastics, electronic equipment, and textiles. It has been found that BDEs can leach from these materials and contaminate terrestrial and aquatic ecosystems. Once in the environment, BDEs bioaccumulate in sediments and tissue, but it is not clear what harmful effects this accumulation has on exposed individuals. Studies have shown that BDEs potentially act as endocrine-disrupting compounds and estrogen mimics; there is also a possible link between BDEs and single-strand breaks in DNA. This study, therefore, sought to investigate these three potential effects of BDEs on snapping and red-eared slider turtles. A significant difference was found in the number of DNA single-strand breaks between those snapping turtles fed BDE-99 contaminated food and the negative control. A species difference was also found in which BDE-47 and BDE-99 contaminated snapping turtles showed significantly more DNA damage than BDE-47 and BDE-99 contaminated red-eared slider turtles, respectively. The results of both the thyroid and gonadal studies showed no significant differences among treatment groups. Further investigations of other species and endpoints are required to comprehensively evaluate threats of BDEs to wildlife.

Ichthyoplankon were collected during a cruise at the mouths of Chesapeake and Delaware Bays. Larval fish from these collections were identified and their vertical distributions were mapped. The species included significant numbers of striped anchovy, bay anchovy, weakfish, Atlantic croaker, and naked goby. While Delaware Bay collections were more diverse, Chesapeake Bay had a greater abundance of larval fish overall. Larvae were found in highest concentrations close to the surface near the mouth of Chesapeake Bay but were found throughout the water column near the mouth of Delaware Bay. The differences in vertical distribution could be related to the differences in water column structure which was well mixed in the Delaware and stratified in the Chesapeake. Imaging techniques and protocols were developed during the laboratory work. The library of images of larval fish will help future researchers identify larval fish indigenous to Middle Atlantic Bight region. This research also will increase our understanding of the influence of varying environmental conditions on larval fish distribution and transport.

A preliminary study done on the biogeochemistry of the pond of Blackwater National Wildlife Refuge explored the rate of benthic nutrient fluxes and concentrations of porewater constituents. In a series of incubation experiments conducted in June and July, it was found that flux rates in the refuge pond are low with the exception of one location characterized by submerged intact peat. Of primary interest were the rates of denitrification and the possible presence of benthic microalgae. Denitrification was measured by changes in N₂ in the water column over a period of 8 hours. Rates of denitrification (in μmol m^-2h^-1) were high at site 1(the submerged peaty site) and lower, but > zero at sites 2-4. Oxygen flux rates into the sediment were high, showing significant heterotrophy in the system. Following illumination, most oxygen fluxes remained negative, but a change in the rate at site 1 showed positive gross photosynthesis in both June and July, indicating the presence of benthic photosynthesis. Significant positive ammonium fluxes in the pond result from high levels of organic degradation, and were substantially higher at site 1 as well. Porewater profiles were analyzed for the presence of soluble reactive phosphorus, iron, ammonium, H₂S, and methane gas at sites 1 and 4. Differences at each location were evident in the porewater profiles, as SRP was higher at site 1 than site 4. Porewater iron showed the opposite trend with higher levels at site 4. H₂S and methane gas were both present in high levels at site 1. Results show that Blackwater is a unique and highly variable system, and more studies must be done to further investigate these parameters.

The Coastal Bays of Maryland, USA are affected by eutrophication resulting from increased nutrients into the system due to anthropogenic activities. The Coastal bays of Maryland are characterized by high nutrients, poor water quality, high residence times, and high mixing. This is the first study enumerating viruses and bacteria in the Coastal Bays using SYBR Green I staining and epi-flourescent microscopy. Bacteria concentrations ranged from 106 to 107 ml^-1 during sampling periods in May and July, 2007. Viruses ranged from 107 to 108 ml_-1 over the same time period. These numbers are similar to or greater than comparable coastal eutrophic systems. Significant correlations (p<0.05) with bacteria were found for viruses, surface salinity, chlorophyll a, total nitrogen, total phosphorous, and surface temperature. These findings should be considered in subsequent analysis of the Coastal Bay region that regard nutrient cycling, primary production, and the microbial loop.