Our Students and Their Research

We investigated the effectiveness of using flow cytometry parameters of light scatter and fluorescence as a means of measuring phytoplankton carbon per cell, chlorophyll per cell, cell volume, and cell abundance to monitor growth. As primary producers, phytoplankton are an important indicator of Chesapeake Bay ecosystem health. Common methods of monitoring phytoplankton do not take into account chlorophyll-to-carbon (ChlC) ratios or phytoplankton size spectra. We first considered the effects of mismatched sheath fluid and sample salinity on light scatter. We determined that matching sheath fluid to sample salinity gives the same forward light scatter (FLS) and side light scatter (SLS) values as using 0 salinity sample and sheath. Using 13 cultures, ranging in size from 1-30 m, we were able to produce a calibration curve for SLS to C/cell. Among our cultures, C/cell varied from 0.1 to 3600 pg/cell. The difference between the predicted and observed C/cell varied from 4 to 116% with an average of 41% and a median of 35%. This allowed us to create size spectra for our samples from the ACE-InC cruises of the Choptank and Patuxent Rivers. Size spectra data revealed the trend of larger cells tending towards the mid-river station and smaller cells tending towards the upper and lower stations in the river. This case study demonstrates that FCM parameters can provide complimentary information to chl a-biomass measurements and improve our ability to monitor phytoplankton as an indicator of Chesapeake Bay health.

In this study, a comparison was done between the Florida and Chesapeake Bays to better understand the biological and chemical influences of MCB on resuspension. Using a new erosion device, we were able to analyze eroded materials at different levels of shear stress, and better quantify the relationship of MPB, biomass and EPS concentration on resuspension. Our results showed that while EPS and chla are good determinants of erodability, other factors may be present which can override the influence of MPB.

PCBs are toxic, organic compounds found in the environment. They pose numerous threats to fish, wildlife and humans. Their hydrophobic nature makes them readily bind to organisms, soils and sediments. Determining binding constants, or how well PCBs bind to organisms or sediments, is integral in defining the extent of their potential harm on the environment. Therefore, binding constants for 18 PCB congeners from two samples, Cypress Swamp DOC water and a particle water sample from Fishing Bay, were found. Prior to finding the binding constants, however, several preliminary experiments were performed including a technique verification, PUF sample, and an exposure series using SPME fibers. Since the SPME technique is till relatively new, a new SPME verification experiment was also performed to ensure that SPME fibers only measure the dissolved, as opposed to the total concentration of PCBs in a given sample. Results show that the binding constants obtained generally followed expected trends and that they are comparable to other studies done in the Upper Hudson River. Results from the SPME verification reveal that indeed SMPE fibers only measure the dissolved phase concentration of PCBs in a given water sample.

Existing video data taken with the Video In Situ Settling Tube Apparatus (VISTA) was used to calculate particle sizes and settling speeds of suspended sediment particles found within the Estuarine Turbidity Maximum (ETM) region of the Chesapeake Bay. This information was used to determine the relationship between particle size and settling speed in order to calculate the fractal dimension, D3 and the reference particle diameter, dr. Observations of the settling speeds of suspended sediments in their natural environment have been estimated at 1 mm/s with fractal dimension values between 2 and 2.5. The preliminary results of this study show that particle settling speed increases with both size and depth, ranging between 0.5 and 4.5 mm/s and with sizes ranging between 71 and 549 microns. The calculated fractal dimension values decrease with depth ranging from 1.8 to 2.4, while the calculated reference particle diameter values increase with depth ranging between 0.5 and 4.9 microns.

The Eastern oyster, Crassostrea virginica is in trouble. The impact on the seafood industry and traditional fishing communities may be incalculable. Oysters play a vital role in helping to maintain water quality in estuarine ecosystems. Oyster reefs created by aquaculture can very rapidly take on the characteristics of healthy natural oyster reefs. The restoration of oyster reefs through aquaculture is an important part of the process of restoring the Chesapeake Bay. This study is to determine if there is a relationship between juvenile oyster size and resistance to mortality by desiccation to provide parameters of survival for oyster spat under transit conditions. Spat were marked to assure that replicates were easily identified. Replicates of each size class were subjected to timed desiccation in a drying oven. The percentage of dead oyster spat was determined after a recovery period. All data was plotted "raw" and then normalized using Microsoft Excel 2000 software. Our preliminary data analysis strongly suggests that there is a direct positive correlation between oyster-spat size and the spats resistance to mortality due to desiccation. A distinction occurs between <1mm and 3mm spat. This suggests that larger sizes (>3mm) may display an even greater tolerance to exposure.

Exposure of aquatic animals such Palaemonetes pugio to contaminated sediments of aquatic animals such Palaemonetes pugio can cause these animals to increase their metabolic rates and thus change their energy budgets to better cope with the higher accumulation of toxic contaminants in their bodies. Inability to cope with contaminated conditions can lead to increased mortality. To examine changes in the energy budget of the grass shrimp P. pugio under contaminated conditions, we exposed shrimp to a concentration of 12% Elizabeth River sediment. We looked for effects on survival, standard metabolic rate measured by mean oxygen consumption at rest, growth measured by RNA:DNA ratios, lipid storage, and reproduction. We found no significant difference between contaminated and reference tanks for survival, reproduction, or growth. We also found no significant difference between tanks for oxygen consumption rates with the exception of week six, where shrimp from the contaminated tanks had a lower metabolic rate. We found a significant difference between treatments for adult lipid content, with shrimp from the contaminated tanks having higher lipid content. Thus, we did not see any conclusive negative effects of exposure to contaminated sediments on the energy budget of P. pugio.

One of the most predominant problems facing the Chesapeake Bay and its tributaries today is that of excess nutrient loading, which can lead to several detrimental ecological effects. However, although the results of high nutrient concentration have been studied in detail, few quantitative studies on nutrient sources have been conducted. This paper concentrates on the development of a one-dimensional advection-diffusion model for the Choptank River, the largest Eastern Shore Chesapeake Bay tributary. The model is based on the salt balance equation:

Using salinity data collected from the CISNet cruises between 1999 and 2001, the diffusion coefficient K was calculated once with time dependence, and once without. Currently, it does not appear that time-dependence makes a significant contribution to the diffusion coefficient, but it may play a larger role in the final model. The preliminary results of the model show that a one-dimensional model can accurately estimate salinity in a well-mixed sub-estuary such as the Choptank River. In order to complete this nutrient transport model, the model will need to be calibrated with the CISNet data and verified with an independent data set. A conservative tracer will then be added to the model to represent transport. Finally, a non-conservative tracer will be added to represent nutrient transport.

Benthic organisms respond to chemical and physical cues that prompt them to settle or deter them from settling at a particular sedimentary site. Disturbance to the sediment from deposit-feeding, burrowing, human activity, or numerous other sources releases sulfides and ammonium from the lower sediment layers. Since these chemicals are often toxic to benthic animals, they can act as negative chemical cues for settling larvae or mobile meiofauna. In this experiment, ambient porewater ammonium concentrations in Tom's Cove in Chincoteague Bay, VA were manipulated through the burial of acrylatnide gels containing Ammonium sulfate in the muddy sediment in an intertidal zone. Porewater and sediment samples were taken above the gels four days later and analyzed for ammonium concentration and animal content, respectively. It was found that the porewater ammonium concentrations were successfully increased above the high ammonium gels, with significant difference from the control gels. There was also a significant difference in meiofaunal abundance above those two types of gels. Only nematodes and polychaetes were found in the samples. The results indicate that acrylatnide gels are useful for chemical manipulation in the field. They also reaffirm previous findings that ammonium is a negative chemical cue for settling meiofauna.

Seagrass beds may influence sediment biogeochemical cycling through enhancing nitrification, ammonification, phosphate regeneration, and sulfate reduction as compared to unvegetated sediments. In addition, seagrass health (i.e. die-back) may influence biogeochemical cycling as well. This study was conducted in Florida Bay and Chincoteague. In Florida Bay, I found that concentrations and rates were higher in healthy beds than in unhealthy ones for relative nitrate concentrations and ammonification. No difference in rates between vegetated and unvegetated sediments in Florida Bay were observed. In Chincoteague Bay, differences between vegetated and unvegetated for relative nitrate concentration and ammonification were observed. Sulfate reduction and phosphate regeneration were indeterminate for both study sites. Methods need to be further improved so that reasonable rates can be determined. Once improved, further investigation will be able to elucidate these processes.

Seagrass decline worldwide is generally attributed to eutrophication. However, in the future global climate change may increase sea-surface temperatures, increasing the frequency and severity of storms. Increase in severe storms may also cause an increase in overwash events along barrier islands. Overwash events increase deposition, burying seagrasses and altering their habitat. The seagrasses Zostera marina and Ruppia maritima occur in patchy distributions in Sinepuxent Bay, a shallow coastal barrier island lagoon south of Ocean City, MD affected by overwashes approximately every 5 to 7 years. We hypothesize that overwash events will cause a short-lived setback on local seagrass populations as they quickly recolonize the area. We determined through organic matter, grain size, and GIS analysis that an overwash in 1998 altered seagrass habitats by changing topography, sediment type, and bottom cover. However, new seagrass habitat is being created as seagrasses slowly recolonize the area.

An in-situ camera system was created to investigate particle size distributions and the dynamics of flocculated particles within the Estuarine Turbidity Maximum zone of the Chesapeake Bay. The Video In Situ Settling Tube Apparatus (VISTA) displayed images of sediments within a settling tube. The images were recorded and later transferred to a computer and analyzed to determine particle characteristics. A Laser In Situ Scattering and Transmissometry (LISST) was deployed simultaneously with the camera setup in order to validate the outputs of both instruments. The preliminary results indicate that the two instruments agree reasonably well, but the VISTA misses some of the larger particles. The dynamics of flocculated particles were evaluated by investigating the sources of macroflocs within the water column. Of the two cruises, one data set indicated that macroflocs are present due to resuspension from the current shear. The data from the second cruise concluded that macroflocs are actively forming immediately following the decrease in current shear when the maximum tides pass.