Our Students and Their Research

The wellbeing of the Chesapeake's Bay's diminished submerged aquatic vegetation (SAV) is closely tied to turbidity, but little is understood about the determinants of this water quality parameter. In order to refine SAV site-selection criteria, this study profiles the physical properties of suspended solids as they affect the scattering of light and cause turbidity. A device, the ACECam, was built to take images and collect water samples that contain suspended particles. Along with other tools, the ACECam provided data that was analyzed for particle properties, including size distribution and particle concentration. Such properties were used to define the particle behavior prior to and after agitation and how this affects turbidity. While there was little difference between the pre-suspension and post-suspension turbidity histograms, the "d50 vs. secchi depth" and "particle concentration vs. secchi depth" plots demonstrated a strong relationship between particle size and light scattering, as well as particle concentration and light scattering. Small particle size and higher particle concentrations more readily scatter light and reduce water clarity.

Freshwater tidal marshes are important ecosystems located between fresh and oligohaline waters. These ecosystems are constantly undergoing sediment changes, with sediment simultaneously being deposited, carried away, and/or captured by the vegetation present. In a wild rice-dominated part of the low marsh at the Jug Bay Wetlands Sanctuary in Maryland, we observed sediment dynamics over a tidal cycle with an emphasis on looking at particle capture by groups of wild rice. We then used much of this data to build a model for particle capture in a tidal freshwater wetland. A sensitivity analysis was done using this model, and the model was also parameterized with data from the Jug Bay/wild rice field work. In addition to concluding that morphology does affect sediment capture rates and that spatterdock have higher sediment capture rates than wild rice, we also concluded that the amount of particles captured per stem is most dependent upon water velocity, total suspended solids (TSS), and the percent particles captured.

This preliminary report is part of a broader study of polyfluorinated compounds (PFC) contamination in surface water that is incorporating a statewide survey of wastewater treatment plant (WWTP) effluents and three distinct watersheds (rural, urban, and suburban) to assess the contribution of PFCs from point and non-point sources. In this paper, we report that rural watersheds may contribute significant loads of various PFC species further downstream. St. Mary's Run in Central Maryland, a rural stream that receives a large proportion of its volume from an associated small wastewater treatment plant, displayed a total PFC concentration of 9.95 ng/ml. In comparison, a much larger WWTP in urban areas in Washington DC and Maryland, which serves a population of over one million displayed similar concentrations at 11.2 ng/ml for total PFCs. Although our sample analysis methods are still being refined and improved, the preliminary data indicates that rural watersheds may contribute more significantly to the PFC load then once previously acknowledged, especially when rural watersheds are viewed as a collective whole as in the case of the state of Maryland.

Water quality in Maryland's coastal bays has been declining in recent years with high nutrients and human and animal waste contaminants contributing greatly to the problem. 'Hotspots' for such anthropogenic inputs have been identified and include Johnson Bay; however, land use surrounding the bay offers little explanation as to why water quality is worsening so rapidly in the area. This study seeks to better understand regional anomalies through the enumeration of total bacteria, virus like particles (VLPs), and fecal bacteria at sites along four Johnson Bay tributaries, selected along a known eutrophication and land use gradient. This is the first study to assess such abundances within these creek ecosystems. Total bacterial abundances (0.49-2.83x10⁷ ml^-1) were slightly higher than those found within the Johnson Bay in 2007 but VLP abundances (0.23-3.34x10⁸ ml^-1) were more similar. Fecal bacterial abundances were found in excess of EPA primary contact standards at the majority of the sampling sites. Bacterial and VLP abundances differed at localized spatial and temporal scales which, together with high fecal bacterial contamination and high nutrient loadings, suggest that anthropogenic point-source inputs are prevalent. Changes in bacterial abundance following a rainfall event may suggest the presence of non point-source inputs. Fecal bacteria were found to be better spatial indicators of contamination than total bacteria or VLPs. These findings represent an important baseline from which to continue studying the specific types, locations, and ecosystem effects of inputs in the Johnson Bay area and may have implications for watershed land use management.

Wetlands have been diminishing throughout the world due to poor management practices and sea-level rise. It is important to study the wetlands' ability to rebound from this, and accumulate sediment in order to keep up with sea-level rise. Research on freshwater tidal wetlands is much less cohesive in this area. This study seeks to determine what factors affect sedimentation rates in freshwater tidal wetlands both spatially and temporally. The wetlands studied in this research project are located in Dyke Marsh Preserve in Alexandria, VA. We hypothesized that sedimentation rates would be higher at sites with lower elevation, as well as over monthly time scales in comparison to decadal time scales. To analyze these nested time scales, ceramic tiles were placed in the sediment so they could collect sediment over a monthly scale. Decadal scale rates were determined by analyzing sediment cores for ²¹⁰Pb activity, and plotting the rates using linear regression. Sites at lower elevations did prove to have higher rates than the sites in the high marsh area. However, the monthly scale rates were actually lower than the decadal scale rates in most cases. This is likely because the sampling period did not include the prime depositional period of the year during the growing season. The major conclusion of this paper is that sedimentation rates are highest at sites in low elevation, located close to their sediment source, because they receive regular delivery of sediment through tidal flooding events.

Freshwater tidal marshes are transitional ecosystems between fresh and oligohaline waters. Stability of these ecosystems depends on a balance between marsh platform accretion rates and sea level rise. The capacity of a marsh to maintain this balance is strongly influenced by sediment deposition and capture, which in turn is influenced by the marsh vegetation. In a spatterdock dominated low-marsh at the Jug Bay Wetland Sanctuary, Maryland, we observed sediment dynamics over a tidal cycle with an emphasis on water column suspended sediment inputs, measurements of captured sediment on rinsed spatterdock leaves and stems, and sediment deposition. We took into consideration the distance from the water and sediment source and the variability of inundation depths and timing. We found that plants closer to the water source captured more sediment. Plant height was another determining factor, where leaves of taller plants were not submersed and had less surface area available to capture sediment. Sediment traps that were underwater for longer time periods captured exponentially more sediment. In addition to concluding that tidal inundation and plant morphology interact to influence sediment capture, we documented changes in sediment concentrations between flood and ebb tides that may indicate sediment loss and erosion.

Summer nitrogen limitation in the Sassafras River, a freshwater Chesapeake Bay tributary, selects for N₂-fixing cyanobacteria that could provide a "new" nitrogen source to this already nutrient enriched system. Despite the prevalence of these diazotrophic (N₂-fixing) blooms, little attention has been focused on the role of N₂-fixation in nutrient enriched, eutrophic estuaries like the Chesapeake Bay, nor has the role of cyanobacterial N-fixation been considered in N budgets. We analyzed weekly water samples from four stations for total suspended solids (TSS), volatile suspended solids (VSS), chlorophyll a, dissolved nutrients, and nitrogenase activity via the acetylene reduction assay. We performed two nutrient addition bioassay trials, monitoring the same parameters with additions of phosphate (5, 10 μM) and nitrate (10, 20 μM). Despite a cool, relatively wet summer without large cyanobacterial blooms, we found N₂-fixation to be present across the sample sites, with hot spots at Budd's Landing, a neighborhood marina, and Georgetown, an urban marina. Traditional water quality parameters such as suspended material and chlorophyll a were found to be poor indicators of N₂-fixation. In our bioassays, we found results consistent with N-limitation. Nitrogen additions stimulated phosphate uptake without increasing levels of N₂-fixation. Phosphate additions increased N₂-fixation without increasing chlorophyll a.

The copepod Acartia tonsa serves as a critical link between primary production and higher trophic levels in the Chesapeake Bay ecosystem. In this study, we investigated the sub-lethal effects of hypoxia (low dissolved oxygen content <2.0 mg/L) on the development of A. tonsa eggs. We tested the relationship between incubation time, oxygen concentration, and egg developmental stage. We expected to observe increased egg development time with decreasing dissolved oxygen concentration and increased incubation time. A. tonsa eggs were incubated for two, four, or six hours in various oxygen concentrations or normoxic water, with one experiment having eggs incubated for two hours in normoxic water and then transferred to hypoxic conditions. At the end of the experiment, all eggs were incubated in normoxic conditions for a minimum of 30 hours to determine hatching success. The data showed that hypoxia had a significant effect on egg development (compared to normoxic controls) when incubated for as few as 2 hours, and the effect increased with longer incubation times as evidenced by unhatched eggs after six hour incubations. This research suggests that increased severity and duration of hypoxic events may confer both sub-lethal and lethal effects on A. tonsa eggs, thereby altering population dynamics.

To determine the role of the marshes in the sediment cycling of the Corsica River, ²¹⁰Pb analyses were carried out and accumulation rates were calculated. Organic matter percent and total phosphorous analyses were also done to the samples. Four cores were collected from different sites in the marsh for comparison. Site one was in the bank and site two in the inside of the marsh. Site three is located upstream and site four is downstream. Accumulation rates from the sites one and two were ~7-9mm/y, which is higher than the average rate of sea level rise in this region ~3-4 mm/yr. Site three changed its rate through the core; in the top we calculated 2.0 mm/y and at the bottom 5.8 mm/y, with a long-term average of 3.8 mm/y. Because of this decrease, this marsh site may disappear with time. Site four showed the highest of all the accumulation rates; 2.3 cm/y. The organic matter percent increases generally upward in cores. We also did total phosphorus analysis while the data should be considered qualitative, values do increase upward with the highest values observed at the base of site 4.

Excessive nutrient input is a known cause to the poor health quality of the Chesapeake Bay. Variability in the nutrient concentration signal, at frequencies as high as the semi-diurnal tidal signal, falls through the gaps of the bi-weekly to monthly sampling record that currently exists. We found that collecting samples less frequently than every three days is not enough to consistently estimate the true nutrient concentration mean of a seasonal period within plus or minus 20% error. Because each nutrient has natural frequencies and reacts differently to rainfall events, sampling biases such as sampling during the day, or not sampling on days of rainfall events, skew the reported nutrient concentrations. In terms of sampling techniques, not sampling at exact intervals increases the confidence that the datas mean falls within a 20% error range because the samples are less likely to hit on the resonant frequencies of the time series. We have also shown that bi-weekly to monthly samples taken over a long period of time (~50 years) are unlikely to confidently recognize a 40% decrease in nutrient inputs to the Chesapeake Bay.

Marine bacteria produce siderophores in order to acquire iron (Fe), which has concentrations on the nanomolar scale in the ocean. Desferrioxamine B (DFOB), one type of siderophore, is readily available due to its use in chelation therapy for patients with iron-overload diseases. Like Fe(III), the rare earth elements (REE) have a 3+ charge. This allows complexation to also occur between DFOB and REE. The nature of complexation between DFOB and REE was investigated through the use of acid-base titrations as well as a cation-exchange resin and ICP-MS technique. Titrations were used to determine acid dissociation constants of the acidic functional groups on DFOB. The other method provides insight into the trend of complexation that occurs between DFOB and REE.

Three cores were collected from the shallow waters (<2m) of the tidal Sassafras River to examine the history of environmental pollution. Sediment dating and geochemical profiles were determined through analysis of ²¹⁰Pb, total and inorganic phosphorus, iron and trace metals. Additionally, the cores were examined for algal induction and presence/absence of submerged aquatic vegetation seeds. Sedimentation rates were determined for 2 cores, with rates of 0.7 and 4 cm per year; the third core was not dateable. Moderate concentrations of trace metals were found with an indication of higher inputs in the past. Phosphorus concentrations were generally higher than observed in other Chesapeake Bay sediments.

We studied the importance of benthic habitat structural complexity to grass shrimp and determined if shrimp utilized habitat of varying complexity differently in the presence and absence of predators. We constructed habitats with differing complexities using PVC tubing that were placed on a sand base (sand control and a medium and high complexity tube structure) in large laboratory tanks. Shrimp were placed in these tanks for a 34 hr period and after each trial their location was measured as being on or off the test habitat. Trials were done in the presence and absence of white perch, which is a predator of grass shrimp. We found that shrimp were only significantly attracted to the high complexity habitat, whereas in the medium complexity and sand control tanks, the shrimp moved about the habitat area. In the predator/sand control and predator/medium complexity treatments, shrimp were found to be higher in the water column. In contrast, in the predator/high complexity treatments shrimp stayed lower in the water and on the reef. However, there was no interaction between habitat complexity and the presence of predators.

Due to recent advances in nanotechnology, it is important to determine if the nanoparticles being released into the environment are toxic. Aquatic environments are the ultimate sink for these nanomaterials, yet little research has been done on the effects for aquatic organisms. In this present study, three species of larval amphibians were assessed for toxicity of copper: the spotted salamander, Ambystoma maculatum, the American bullfrog, Rana catesbeiana, and the Gray tree frog, Hyla versicolor. Copper was chosen because it is already known to be toxic to fish and amphibians in dissolved form. To understand how toxic nanoparticles are, we performed 96 hour toxicity tests on the amphibians using dissolved copper chloride and copper oxide nanoparticles. Our results indicate that dissolved copper is toxic to all species, whereas one type of copper nanoparticle was highly toxic to the Gray tree frogs only. The second type of nanoparticle used, which stayed suspended in the water rather than settle to the bottom like the first, had no effect on the tree frogs.

Urbanization and climate change are occurring globally. These environmental changes can increase stream temperatures through rising air temperatures and urban heat island effects. We measured dissolved oxygen in streams draining a land-use gradient (forest, suburban, urban) in the Gwynns Falls watershed of the Baltimore Long-Term Ecological Research site in Baltimore, Maryland. In each stream, we exposed incubations to 4 different temperatures, 4°C, 20°C, 30°C, and 35°C. Incubations lasted 3 - 5 days with 2 experiments conducted during June and July of 2009. The experiment consisted of measuring biochemical oxygen demand, respiration and carbon consumption in a 3 day experiment on June and a 5 day experiment on July. For all sites, we observed significant increasing trends in respiration and carbon consumption with increasing temperature. Although urban streams showed higher biochemical oxygen demand during ambient temperatures before experiments, we did not observe significant differences in respiration rates across sites. The ratio of primary production to respiration decreased with increasing temperature as did net generation of dissolved and particulate organic carbon. The activation energy for respiration decreased with increasing temperature at all sites. Increases in stream temperatures due to urbanization and climate change may influence respiration dynamics and influence carbon cycling in small streams.

Growth rates of Prorocentrum minimum and Karlodinium veneficum were determined in laboratory experiments using varying N:P ratios and under different light intensities. Two experiments were done each with a different nitrogen source. Growth rates were found to be higher when using urea as the nitrogen source than with nitrate for both species of algae. The three light levels (300μE m²s^-1, 150μE m²s^-1, 50μE m²s^-1) had an affect on the rate of growth for P. minimum in the first experiment and second experiment but not for K. veneficum. There was no significance when looking at the different N:P ratios. In the second experiment rate of growth for K. veneficum was significantly different with the N:P ratios.

International shipping is critical for transporting goods around the world but commercial vessels are also known to be a major vector for aquatic invasive species. While solutions to ballast water invasive species have been studied extensively for over 20 years, ship hull fouling has received relatively little attention and there are few solutions beyond specialized coatings. This study explores the option of low salinity exposure as a means to remove fouling organisms on the hulls of ocean-going vessels thus minimizing the risk of hull fouling invasive species. A laboratory experiment was conducted exposing high salinity (32 psu) fouling organisms found in the coastal bays of the Chesapeake Bay region to either (1) an immediate drop in salinity to 5 psu, remain for 24 hours and then an immediate return back to 32 psu, or (2) a slow reduction in salinity to 5 psu and slow increase back to 32 psu, mimicking a vessel's voyage from the Atlantic Ocean up to the Port of Baltimore, then back down the Chesapeake Bay to the ocean. While significant mortalities were found, no significant difference existed between the rapid and slow salinity treatments and some taxa of fouling organisms appeared to withstand low salinity exposure. Although transit into low salinity water by ocean going vessels could kill some hull fouling organisms thereby reducing the risk of invasive species, this approach would not eliminate the problem.

Accurate surveying techniques are necessary for the creation and enforcement of fisheries management practices. Previous creel surveys used to estimate angler effort have had large amounts of variance, mostly due to day to day variation in effort. Effort data taken from a creel survey, performed on nine Chesapeake Bay tributaries, was compared to weather data from National Oceanic and Atmospheric Administration (NOAA) weather stations. The three weather patterns investigated were daily rain fall, average wind speed, and daily precipitation. Various prediction models were created using all possible combinations of these three variables. These models were then compared via Akaike Information Criterion (AIC) for each model. Out of the eight systems optimal prediction models all used temperature as a predicting variable. Additionally, two models used wind data and three models used precipitation data. The variables used for prediction appeared not only to depend upon what environmental conditions were seen, but also depended on the fishing population and the locations available for fishing. In the future, these prediction models may provide more accurate total angler effort predictions by explaining some of inter-day effort variation.

We determine the dissolution rate of three different types of eastern oyster shell as well as determining the growth rate of spat on different substrates under four different pH levels reflective of estuarine conditions in the Chesapeake Bay. Wet weights were taken every three days to determine dissolution rates of fresh, fossil, and weathered shell by loss of mass. To determine oyster growth rate pictures were taken of spat on PVC and fossil shell every three days and linear measurements. We found that both pH and shell type had a significant effect on dissolution rate of non living oyster shell, (F_3,48 = 9.67, P < 0.0001) and (F_2,48 = 17.86, P < 0.0001) respectively. The difference in dissolution was likely due to variations in surface characteristics of the shell. Oyster growth rate decreased with increasing acidity and a difference was seen in the growth rates between treatments. Our experiments illustrate that increasing acidity has the potential to decrease lifetime of oyster shell in the estuary. Furthermore, oyster growth on shell versus PVC were found to be higher under lower pH, with the implications that growing oysters can grow under acidic conditions if there they are attached to a calcium carbonate substrate.

The drastic decline of seagrasses and other submerged aquatic vegetation (SAV) in the Chesapeake Bay over the last century is a major concern and has sparked both research and restoration efforts to combat the problem. Due to previous studies, distribution is known to be heavily affected by water quality factors such as light availability, salinity, temperature and depth. Sediment type, although secondary, also seems to be a contributing factor. In this study, pushcores were taken at two sites with stable SAV beds, Trippe Bay and Crab Alley Bay, and at two sites that had previously contained historical beds, Casson Point and Herring Bay. Samples were then separated at 0.5-1 cm depth increments and each interval wet sieved at 64 μm and dried to determine the mud and sand portions. Dry sieving was used to determine the particle size distribution within the sand component for each interval. Both stable sites were found to have well-sorted surface sediment with the majority of particles falling between 106-150 μm. The historical site Casson Point did have a slight fining trend, while Herring Bay remained constant. The grain-size profiles for the stable sites Trippe Bay and Crab Alley Bay were also relatively constant (except for the fine top layer which may have been deposited because of the current-slowing beds). Total sand content near the surface was variable between all sites, ranging from 78-96%.