Our Students and Their Research

Due to its painful sting, dense blooms that clog fishing gear and pumps, and voracious predation of mesozoplankton and ichthyoplankton, the sea nettle Chrysaora quinquecirrha, is an important species in Chesapeake Bay. Temperature and salinity influence inter-annual variability in the distribution of sea nettles, but the causes of smaller scale, intra-annual variability, remain unknown. Current efforts at understanding patchiness include visual surface and vertical net-haul counts. Here, we compare the abilities of a digital video camera to capture images of sea nettles at the water surface to those of a human observer in an attempt to automate the observing process so that visual counts could be made more frequently in time and simultaneously at multiple locations to better comprehend this patchiness. Translucent plastic disks were deployed at different depths to determine the limit of the camera's depth of view. The results showed that the camera was not able to visualize the disks as well as an observer on location, and it likely will not provide a quantitative measure of sea nettle abundance; however, we feel that it can be used as a continuous semi-quantitative data collector, and the data can be analyzed for trends in variability of sea nettle abundance.

Nitrite can accumulate in the water in natural and hatchery settings and elevated levels are toxic to many fish. This study evaluated effects of 1 mg/L nitrite on methemoglobin, PCV (packed cell volume), hemoglobin and plasma chemistry in Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus). Juvenile fish (0.544 kg ± 0.126 SD) were divided into two treatment groups of chloride concentrations of 0 mg/L and 50 mg/L. The percent methemoglobin in the 0 mg/L chloride group was 81.936 (68.182, 87.719), median (1st quartile, 3rd quartile), at 96-hours post exposure and was significantly different from the 50 mg/L chloride group which had a percent methemoglobin of 7.895 (4.762, 10.811) (P < 0.05). Two weeks after removal from nitrite, elevated methemoglobin was observed in the 0 mg/L chloride group with a percent of 71.429 (62.963, 90.476). PCV decreased significantly in both groups (P < 0.05). The 0 mg/L treatment group dropped in percent PCV from 30 (29, 32) to 7 (5, 9) and the 50 mg/L treatment group dropped in percent from 29.5 (28, 32) to 15 (13, 18) over the duration of the study. Total hemoglobin decreased significantly from 6.6 g/dL (6.2, 6.8) to 5.6 g/dL (5, 7.1) in the 0 mg/L chloride group and from 6.2 g/dL (5.9, 6.6) to 4.3 g/dL (3.5, 5.3) in the 50 mg/L chloride group (P < 0.05). Nitrite resulted in severe hemolytic anemia and mortality of 60% in the 0 mg/L chloride group and was less severe with no mortality in the 50 mg/L chloride group. Nitrite accumulation at a chloride level close to 0 mg/L is toxic and multiple stressors can result in significant mortality.

Excessive anthropogenic nutrient inputs from both point and non-point sources have contributed to a number of problems currently plaguing the Chesapeake Bay. Nitrogen compounds in particular have resulted in extremely high levels of phytoplankton production, causing hypoxia, and increased turbidity in certain parts of the Bay. In this study, we explore how denitrification rates may be influenced by processes that occur naturally within an oyster reef community. We conducted a three day laboratory experiment with sediment core samples to quantify nitrogen flux rates in the presence of two oyster reef associated organisms; polychaete worms (Alitta succinea) and amphipods (Leptocheirus plumulosus, Melita nitida, Gammarus spp., and Apocorophium spp.). Our results indicate a significant enhancement of denitrification rates in the presence of both polychaetes and amphipods, however, due to unforeseen influences within amphipod treatments, we were unable to attribute flux rates entirely to the treatment. We conclude that oyster reef communities with high densities of polychaetes and amphipods significantly enhance removal of nitrogen compounds.

This study was designed to determine whether denitrification was occurring in stream beds within the Choptank River Basin. Denitrification was measured by the amount of excess N₂ found in the groundwater flowing into piezometers installed 20-60 cm below the stream bed of a channelized farm stream. I hypothesized that the groundwater flowing into the stream from adjacent lands was the primary source of excess N₂ in the stream sediments, meaning denitrification is primarily occurring in soils and groundwater distant from the stream and not within the streambed. My alternate hypothesis was that denitrification is occurring within the stream sediments and augments the vertical distribution of excess N₂ entering the stream from groundwater. Sampling in July 2010 produced results, which showed significant inverse correlations between NO₃, O₂, and excess N₂ that indicated an environment suitable for denitrification. However, excess N₂ concentrations decreased from 40 cm to the surface of the streambed, suggesting that advective loss to the surface waters flowing above was the most important process influencing the vertical distribution of excess N₂ concentrations. Thus, denitrification was only concluded to be occurring in the deeper layers at one sampling site.

Chicken manure-based fertilizers are extremely popular with not only the farming community, but everyday home-gardeners as well. These types of fertilizers are known to contain a suite of heavy metals (As, Ag, Cd, Cr, Cu, Pb, Ni, Se, V, and Zn) and organic compounds. Yet the effects that these contaminants have on the environment have not been well studied in a laboratory setting. For this study, grey tree frogs (Hyla versicolor) were assessed for toxicity to chicken manure-based fertilizer. Hyla versicolor was chosen, due to their availability, rapid developmental period, and their sensitivity to certain toxins. To determine the effects of heavy metals on H. versicolor two controls were set up (one containing sediment consisting of soil, the other containing no sediment), as well as two experimental groups. One experimental group contained sediment consisting of one hundred percent fertilizer, and the other containing an equal mix of fertilizer and soil. The frogs were closely monitored, and by the end of the experiment several heavy metals such as arsenic, copper, and lead were found to have accumulated at significantly higher concentrations in the fertilizer treated groups. However, many biological traits of the frogs were not significantly affected, including metabolic rate, lipid content, and rate of metamorphosis.

Establishing biomarkers for a particular species at a specific area is very important to determine the significance of contamination, and it can help identify pollutants and their source. There are many known types of PAHs in oil that are toxic to marine organisms hat range in their toxicity. Neptunea heros, an arctic whelk found in Northwest Alaska was used as a bioindicator to establish baseline levels to test for antioxidant and PAH exposure with a GST and EROD assay. Small activity were found in the EROD and GST assays, as compared to controls.

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.