Our Students and Their Research

Predominantly used in sunscreens, organic ultraviolet filters (OUVFs) are becoming water pollutants of emerging concern. Studies on the photochemistry of OUVFs are increasingly concerned with their environmental fate as opposed to the maximization of effectiveness and safety of consumer products. OUVFs have been associated with bactericide, bioaccumulation and toxicity to marine organisms, in addition to photodegradation—the symmetrical cleavage of a covalent bond under UV conditions to form multiple degradates that may experience further recombination reactions. A thorough understanding of the environmental fate of OUVFs requires knowledge of their photostability, of the kinetics of their degradation reactions, and of their photodegradates’ identities in a variety of aqueous media. In addition, natural water and wastewater components such as inorganic photocatalysts, free chlorine, chromophoric dissolved organic matter (CDOM), inorganic cations and anions, and acids and bases may influence OUVFs’ stability and the outcomes of their photochemical reactions. This comprehensive review concerns three of the most used OUVFs worldwide: octocrylene (OC), the dibenzoyl methane avobenzone (BMDBM), and the salicylate homosalate (HMS). To overall provide a sense of what has been studied on OUVFs’ fate in the hydrosphere, knowledge on the behavior of these compounds in various aqueous matrices is consolidated with knowledge on their behavior on human skin and in organic solvent. Every effort is made to classify the reaction kinetics and photoproducts of OC, BMDBM, and HMS based on previous experiments, many of which rely on the artificial irradiation of OUVF samples and the characterization of photoproducts by gas chromatography-mass spectrometry (GC-MS) or liquid chromatography-mass spectrometry (LC-MS). Finally, future research objectives are outlined based on the findings of this review.

Cable bacteria are long filamentous sediment-associated microbes capable of electron transport along their filaments from sulfide to oxygen. Their activity is often responsible for a majority of the oxygen consumption and sulfide depletion in sediments. They may also serve as electron acceptors, where oxygen is not available, potentially stimulating the activity of other beneficial microbes in the sediment environment. A previous experiment suggested there may be enhanced activity of cable bacteria following an experimental cutting treatment. However, this was not observed directly. A stimulation of activity could occur if a cutting treatment stimulated cable bacteria to migrate upward in the sediment, to re-connect with oxygen. Here, using pH and electric potential (EP) microsensors, I assessed the activity of cable bacteria before and after manipulating the sediment to directly observe if cable bacteria activity may be stimulated by a cutting treatment. To a subset of sediment cores, I performed a cutting treatment by passing a fishing line horizontally through the sediment, and I left control sediment cores intact. Unexpectedly, I found that moving the sediment prior to our targeted experimental treatment inhibited the activity of the cable bacteria, and counter to my hypothesis, that the cutting treatment did not detectably influence the activity of cable bacteria. I suggest several improvements that should be considered for future experiments, including reducing salinity gradients between the overlying water and the sediments, and setting up the sediment initially with an extra piece of acrylic core liner already in place to minimize pre-treatment manipulations.

Synoptic climatology describes the relationship between the climate system and certain surface conditions. Past synoptic relationship studies have focused on longer and broader surface conditions. This project aims to provide results that will benefit near-shore communities by focusing on extreme weather events, climate extremes. Correlations made between climate modes and climate extremes are seen to be stronger than with average weather patterns (St. Laurent et al., 2022). Climate extremes are more harmful due to their severity of effects than shifting average weather behaviors. For that reason, we correlated the climate modes North Atlantic Oscillation and Pacific Decadal Oscillation to 16 climate extreme indices. We first connected 39 years of historical sea level pressure (SLP) to weather data, temperature and precipitation. We utilized the principal component analysis (PCA) to reduce high dimensionality among the SLP data. The self-organizing map (SOM) algorithm created sets of grids of pressure patterns and seasonal (monthly) distribution histograms were also generated. The weather data was fitted against the 16 climate extreme indices and grouped within three categories: extreme cold, heat, and precipitation. We then visualized the probability of climate extreme occurrence during the SOM’s seasonal distribution with star plots. Finally, scatter plots were created to represent the correlation between climate extreme probability and climate mode index. These final plots provide us with the likelihood of extreme events occurring and the respective state of climate mode. 

Carbon dioxide (CO₂) is a potent greenhouse gas, and its overabundance in the atmosphere contributes to climate change and ocean acidification, negatively impacting marine and terrestrial life. Estuaries like the Chesapeake Bay are nutrient-dense, so increased rates of photosynthesis and respiration affect the flux of dissolved inorganic carbon (DIC) in the estuarine system. Recent studies have identified the Bay as a source of CO₂ to the atmosphere and continue to monitor temporal and spatial variability over time. To support these efforts, the Chesapeake Biological Laboratory (CBL) has established a long-term monitoring program at its research pier, to assess the partial pressure of CO₂ (pCO₂) in the Bay at surface and bottom depths over time. The data from this study reveal where CO₂ preferentially resides in the water column and can be correlated to water chemistry data to contribute to a more holistic understanding of carbon cycling in the Bay. Throughout the summer, a time series of pCO₂ measurements was produced, and revealed that bottom-water measurements greatly increased toward the end of the time series, while those from surface-water were frequently at equilibrium with pCO₂ values collected from ambient air samples taken over the same time period. Additionally, isotopic data was collected from the pCO₂ samples, and values were frequently lower than air. These findings suggest respiration as the source of CO₂ from the Bay to the atmosphere. The experimental measurements of pCO₂ and isotopic signatures were only weakly correlated to secondary water chemistry variables such as pH, dissolved oxygen (DO), and total algae concentration. However, these findings are preliminary in the scope of the greater monitoring project, so more data and multivariate analyses should be conducted to lengthen the time series and improve the robustness of data analysis.

Water flow impacts many oyster reef processes, such as food availability and the transport and composition of particulate matter. The three-dimensional structure of the reef in turn creates feedback on local hydrodynamics and particle transport processes, generating drag on current velocities that slows down particles in the water column. This drag allows for more concentrated particle settling and increased filtration rates. Here we describe an effort to deploy tilt meters to document hydrodynamic conditions on oyster reefs alongside water quality measurements of chlorophyll and turbidity. Typically, current velocity is measured using Acoustic Doppler Current Profilers (ADCP) which utilize sound waves. For our study, we explored tilt meters as a low-cost alternative. Previous studies have suggested that tilt meters and ADCP can yield similar water velocity readings in saltwater systems. However, there is not much prior work done utilizing tilt meters in mesohaline systems such as the Chesapeake Bay. This gap in application led to two components of this study. First, we evaluated the accuracy of tilt meters in a mesohaline setting. Tilt meter and ADCP water velocity data were collected at the Chesapeake Biological Laboratory research pier. Timeseries and regression models were then created to observe patterns and correlations of the two sensors. Second, we deployed the tilt meters and analyzed the relationship between water quality and water velocity in a restored oyster reef in the St. Mary’s River. Three tilt meters and a water quality sonde were deployed at various locations around the reef. Timeseries and regression models were created to observe trends and relationships between water quality parameters, such as turbidity and chlorophyll concentrations, and water velocity. Tilt meters were found to overestimate ADCP readings by an average of 0.56 cm/s. Preliminary results from the oyster reef suggest there was no significant relationship between water quality and velocity. 

Chesapeake Bay has a history of varying nutrient fluxes that lead to periods of eutrophication. During these times of nutrient overabundance, phytoplankton blooms can have negative consequences on bay health including hypoxia in bottom waters, which affect species up the food chain. Mesozooplankton (>200µm), mainly copepods, are consumers of phytoplankton, making them vital species for trophic energy transfer. While various research has focused on how phytoplankton are affected spatially and temporally by environmental conditions, less is understood about how copepod grazing may be impacted by such influences across time and space. Thus, this study sought to determine if there is a significant relationship between salinity or nutrient levels, which vary throughout the bay, and rate of mesozooplankton grazing. Water samples were collected from six sites across Chesapeake Bay’s main stem, and the >200µm size fraction were filtered out. Phytoplankton biomass was measured after an incubation period between these treatment groups and controls where mesozooplankton were not removed. Results reflect a shifting influence of salinity on mesozooplankton grazing between June and July. Furthermore, NOx concentration was found to be positively correlated with grazing, whereas ammonium and phosphate levels showed no significant relationship with grazing. While grazing data from June and July broaden the current understanding of interactions between abiotic environmental factors and biotic species, further research should observe higher trophic species alongside shifts in other environmental factors over a longer time period with larger sample sizes. 

Phytoplankton are pivotal in aquatic ecosystems, influencing trophic dynamics and global biogeochemical cycles. In the Chesapeake Bay, shifts in phytoplankton community composition have occurred over centuries due to effects of anthropogenic activities, particularly eutrophication. While past studies tend to monitor phytoplankton by general biomass, this study attempts to look at phytoplankton changes on a population level, assessing changes within floral composition in response to nutrient inputs. This work can be done via automated plankton imaging tools, and this project looked at the Imaging Flow CytoBot (IFCB) and the Planktoscope. A nutrient bioassay was conducted on samples taken from the main stem of the Bay and run through these instruments to determine nutrient limitation across taxonomic groups. Diatoms, dinoflagellates, and zooplankton counts were recorded for each nutrient-treated sample and control. Results indicate that diatom abundance increases significantly with nitrogen additions, underscoring nitrogen as a key limiting nutrient in this region. These findings align with previous studies, which also observed heightened diatom proliferation during wet years with elevated nutrient runoff. The study highlights the potential for increased diatom blooms under ongoing eutrophication. Automated imaging technologies, such as the Planktoscope and Imaging FlowCytobot (IFCB), demonstrate their utility in advancing phytoplankton monitoring. This research ultimately contributes to a growing image database, aiding in the development of taxonomic classifiers and providing critical insights into the future impacts of nutrient management and climate change on the Bay's phytoplankton communities.

This study aimed to investigate seasonal and site-specific variations in the abundance and isotopic composition of various taxa between an oyster sanctuary reef and an actively fished oyster reef. Water quality parameters (dissolved oxygen, salinity, temperature) were measured in April and June across each reef type, concurrent with assessments of mysid, crab, amphipod, isopod, shrimp, and fish abundances. Additionally, carbon and nitrogen isotope analyses were conducted on fish and mysid samples to evaluate trophic niche differences between reef types. ANOVA identified significant interactions between site and season for mysid and shrimp abundances. For both taxa, abundance declined from April to June at the sanctuary site but increased over the same period at the harvested sites. Fish abundance was significantly affected by site, with higher abundance observed in the harvested site. Crab, amphipod, and isopod abundances showed no significant effects. Water quality data indicated distinct seasonal variations, with April exhibiting higher dissolved oxygen and salinity values, and June showing  elevated temperatures. Site-specific differences were also noted, particularly in dissolved oxygen levels with the lowest dissolved oxygen concentrations observed at the sanctuary reef in June. Isotope analysis revealed variations in carbon (δ13C) and nitrogen (δ15N) isotopic signatures among fish and mysids. Fish exhibited a range of δ13C values from -24.3‰ to -17.1‰ and δ15N values from 13.4‰ to 16.2‰. Mysids showed δ13C values from -23.5‰ to -18.2‰ and δ15N values from 15.2‰ to 17.6‰. Isotopic niche analysis suggested larger niche widths in sanctuary reefs for both mysids and fish. The results suggest that both seasonal changes and site-specific factors significantly influence the abundance and trophic niche of taxa in oyster reef ecosystems. These findings underscore the potential for both sanctuary and harvested oyster reefs to continue providing ecosystem services for estuarine environments. Future research should further explore the mechanisms driving these observed differences between reef types to inform conservation and management strategies for oyster reef habitats.

As oysters filter water, they produce biodeposits made up of their feces and pseudofeces. There is concern surrounding how suspended oyster farms concentrate biodeposits and the effect that this may have on submersed aquatic vegetation (SAV) health. This study collected sediment push cores between April and June 2024 from an oyster farm in the Choptank River in Maryland. Cores were collected underneath and in between oyster floats as well as slightly offshore from the floats in the SAV bed area. This study found that the mud and organic content underneath the floats is slightly higher in June. Mud and organic content percentages at every site during this study were within the limits for SAV growth. Also, there was a positive linear correlation between mud and organic content with an R² value of 0.738 in April/May and 0.7479 in June. This study and future research will provide insight on how oyster farms may affect SAV.

We investigated the size to volume relationship of Rhizaria, and specifically focused on Collodaria, a Rhizaria morphotype, in the Sargasso Sea during the summertime. Rhizaria, and specifically Collodaria, play an important role in many different biogeochemical cycles through uptake and sinking of elements including strontium, sulfate, carbon, nitrogen, and more. Rhizaria were collected on a research cruise during the month of June at the Bermuda Atlantic Time-series Study (BATS) site in the Sargasso Sea. The samples were collected using plankton tows as well as a Multiple Opening-Closing Net and Environmental System tow. The Rhizaria were sorted, filtered, and weighed to determine the mass of each of the Rhizaria morphotypes. Our method was insufficiently sensitive to measure the mass of smaller Rhizaria, such as Acantharea and Foraminifera; however, we successfully measured the mass of most individuals of the large Rhizaria morphotype, Collodaria. We found a strong linear relationship between volume and mass of Collodaria, suggesting a dry density of 4.3 mg/mm³. This relationship allows conversion of image-based measurements of volume into mass estimates. These data and density estimates will enable future biogeochemical models and studies to better parameterize the role of Collodaria in oceanic biogeochemical cycles. 

Poplar Island is an island restoration site with wetland and upland habitats. The tidal marshes have a thick layer of edaphic algae present on the surface of areas without macrophytes. To increase our understanding of the role of edaphic algae in carbon cycling in the marshes, we measured algal production and respiration rates using two methods. We evaluated oxygen cycling under a range of light intensities and under flooded versus unflooded conditions. We collected a total of 23 sediment cores throughout June-July 2024. Twelve unflooded cores were subjected to light levels of 0, 120, 200, 300, and 350 µmol m^-2 s^-1 photosynthetically active radiation (PAR); in addition, six cores were incubated under flooded and unflooded experimental conditions. In all eighteen cores oxygen concentrations were measured to estimate rates of photosynthesis. We found that the rate of photosynthesis increased when PAR increased, and the mean rate of photosynthesis was not significantly different between flooded and unflooded cores. Higher amounts of chlorophyll a were not correlated with higher rates of photosynthesis. 

Crassostrea virginica, commonly known as eastern oysters, are integral to the environment and economy surrounding the Chesapeake Bay, North America’s largest estuary. Many restoration efforts are underway to protect this critically endangered species. However, there’s a significant challenge associated with these restoration efforts: finding a place for the oyster larvae to settle. They prefer to settle on oyster shell, but there is a serious shortage when it comes to this material. Therefore, restoration efforts seek out alternate substrates, which are other materials besides oyster shell that larvae can settle on. There are many studies underway to test the effectiveness of a variety of alternate substrates but a huge challenge is associated with this is how to equally compare these different types. Throughout this study, we looked at three different methods of measuring the surface area of alternate substrates, as well as comparing the measurement of surface area to volume. This is part of a larger study to determine the effectiveness of nine alternate substrates in comparison to the standard oyster shell. We found that the most effective method of measuring surface area involved tin foil, ensuring the maximum surface area was captured for each substrate. We found that if other methods in this study are used, there will be an inaccurate surface area, which will cause an artificial inflation of larvae settlement preferences. 

Atlantic Menhaden and Striped Bass are key economic and ecological species in the Chesapeake Bay; however, the effects of increasingly frequent rare weather events on both species are unclear. This study aims to first identify rare weather and fish catch per unit effort events and then identify linkages between the two. Isolation forest and density-based clustering algorithms were used on residuals generated from Loess and Fourier smoothing to identify rare events, and 𝜒2 tests were used to identify significant relationships. The results showed a strong relationship between rare minimum temperature events and catch per unit effort events but  a less prominent relationship with precipitation and catch per unit effort. More research into the role of positive versus negative anomalies is needed to better assess the relationships and implications of climate change.

The increasing impact of eutrophication and climate change on phytoplankton populations poses significant ecological risks, particularly in the Chesapeake Bay where harmful algal blooms (HABs) are a growing concern. This study leverages the advanced imaging capabilities of the PlanktoScope to monitor and classify plankton populations in the Choptank River. By developing a comprehensive annotated image library on EcoTaxa, this research enhances the identification and tracking of HABs, contributing to the Maryland Department of Natural Resources' efforts to mitigate these blooms. Standard operating procedures (SOPs) for data collection and analysis have been established to ensure consistent and scalable monitoring efforts. The study demonstrated the efficacy of the PlanktoScope in capturing and analyzing phytoplankton images in real-time, enabling early detection of HABs. Notably, a significant increase in diatom populations following a rainstorm indicated the device's capability to track ecological changes and predict potential HABs. The integration of citizen science through the PlanktoScope, alongside the creation of a publicly accessible Chesapeake Bay HAB Atlas, supports better ecosystem management and public health strategies. Continued data collection and the development of machine learning models to classify plankton images will further refine these monitoring efforts, ultimately contributing to the protection of aquatic environments and the communities that depend on them.

The Arctic is warming two to three times more rapidly than the global average, causing benthic communities in the region to undergo rapid and pronounced ecological changes. Researchers have compiled time series of benthic biological, biogeochemical, and physical data in the Bering and Chukchi Seas which document northward shifts among benthic species. However, Arctic data collection is expensive. Our work has two objectives: (a) to minimize costs of future research by identifying redundant information reported among research stations; (b) to augment existing knowledge of how Arctic benthic communities are responding to rapidly changing conditions. Conventional Euclidean distance metrics for comparing time series can only provide simultaneous comparisons; however, Arctic research stations may report similar information at a time lag due to changing conditions. In this study, we applied dynamic time warping (DTW) to these time series of Arctic water column and benthic community data, realigning their time indices to highlight similarities in their shapes. A cluster analysis was then performed using the distance values output by DTW for each time series comparison. For each variable under study, we produced two clusterings using one globular and one density-based clustering algorithm. The time series of water column variables were largely clustered by region, highlighting the existence of similar spatial dynamics within, but not across, regions. For each of the sedimentary and benthic community variables, the stations were grouped into one large cluster with the exception of one or two extreme observations. Removing these outliers could improve the clustering results, rendering them more informative. Further research which integrates a holistic approach (e.g. multidimensional DTW) with a region-specific analysis (e.g. formal tests for trend synchrony) will be necessary to conclusively identify sources of redundancy among the stations of study.  

Visual estimation is a technique used to measure vegetation cover in marshes and is crucial to perform effectively to monitor marsh health and the progression of restoration projects. However, there are two vastly different existing techniques that are both ‘visual estimation,’ and that is the ungridded and gridded quadrat. Both techniques require the user to place the quadrat over a plot and give total and species-specific cover. The ungridded quadrat covers a larger area (1.0 m² vs. 0.25 m²), but the gridded quadrat has physical guidelines to help the user (25 cells of equal size). There is a lack of comparative studies of these two methods which can cause inconsistencies in data. In this study, we aimed to compare the two methods for estimating total cover and diversity across marsh types and observers. Multiple observers went to marshes of various zones (low/high) and ages (natural, 8 to 20 y/o, and >1 y/o) and gave their ungridded and gridded quadrat estimates. We also investigated observer biases between different observers and within the same observer by analyzing the same sites and on two different occasions. A regression analysis of the composite data produced an equation of conversion between the two methods. Our results revealed no significant difference between the ungridded and gridded quadrat total cover and diversity estimates between different marsh zones and ages. Significant observer bias was detected but within the same observer there were not significant differences between observations in the same locations. Further investigation is needed to confirm these results and to fine-tune the conversion factor. It is also strongly suggested to train observers prior to the field to avoid biases.  

Seasonal eutrophication occurs throughout Chesapeake Bay, leaving the bottom waters to be anoxic. Eutrophic waters lead to higher production of methane in the sediments, which is a powerful greenhouse gas that can contribute to global warming if released into the atmosphere. Methane oxidation, a process done both aerobically and anaerobically, transforms methane into carbon dioxide, which is a less powerful greenhouse gas. If the rising temperatures associated with global warming continue on a similar trend, it is possible methane oxidation rates will increase with it. To test this, anoxic and oxic sediment slurry incubations using ¹³C-enriched methane were conducted under varying temperatures using surficial sediment from the lower Chesapeake Bay. While there was an increase in carbon dioxide associated with increasing temperatures both aerobically and anaerobically, the production of methane measured and the lack of ¹³C-isotope incorporation into the CO₂ pool suggest that methane oxidation was not observed under these experimental conditions. As such, rising temperatures will increase carbon dioxide levels in the sediments of Chesapeake Bay, but it cannot be concluded that these increased temperatures will have a direct effect on methane oxidation.  

Dissolved Organic Matter (DOM) is a dynamic carbon pool with largely unknown molecular composition. We are focused on the subset of DOM that fluoresces (FDOM) and can be linked to overall DOM molecular signatures derived from ultrahigh resolution mass spectrometry (HRMS). Complex HRMS and fluorescence data were collected from samples at Bermuda Atlantic Time-series Station (BATS) and Hawaii Ocean Time-series (station ALOHA). Using sparse orthogonal factor regression (SOFAR), a method previously used in genetic analysis, we aim to learn underlying association networks between the HRMS and fluorescence datasets (Uematsu et al. 2019). Increasing sparsity in a large dataset minimizes noise and promotes selection of the most significant latent factors. On the other hand, orthogonality ensures independence.  SOFAR applies these two concepts to select smaller sets of predictor m/z ions while increasing independence of the fluorescence response variable. This project is one example of a growing collaboration between big data and environmental sciences that showcases the powerful role of machine learning techniques across disciplines, from genetics to analytical chemistry.  

Aquatic and marine viruses are present in all known aquatic environments. A proportion of these viruses infect cyanobacteria including the invasive filamentous cyanobacteria Lyngbya. In the Chesapeake Bay and other ecosystems, Lyngbya can produce toxins that are hazardous to the organisms in their surrounding environment. However, viruses have been shown to be associated with bloom decline or termination and with toxin production. Our study aimed to determine if Lyngbya in the Susquehanna Flats are producing viruses and to estimate their production rates. Lyngbya from one location in the Susquehanna Flats appeared to produce viruses, while Lyngbya from another location did not. As the location with detectable virus production was also the one with higher Lyngbya abundance, we hypothesize that viral production may only be possible when the density of Lyngbya is sufficiently high in the environment. We recommend further studies to observe viral production by Lyngbya later in the summer when there are denser mats. We also advocate determining the taxonomic identity of the viruses infecting Lyngbya, as well as exploring their effects on the blooms, as they could alter toxin production and regulate bloom termination.  

Solomon’s Harbor, MD, a shallow water estuary connected to the Chesapeake Bay, is suffering from a lack of dissolved oxygen. The two primary drivers of this oxygen depletion are the introduction of excess nutrients and climate change, which are known to increase temperatures and decrease dissolved oxygen (DO) levels. To better understand the factors that influence DO, we performed a univariate analysis of a 36-year-long historical dataset, deployed temperature sensors at seven sites for a month, and conducted dark box incubations on water samples collected on-site. Temperature was determined to be the strongest factor that explains DO, especially in bottom waters. Hydrodynamics were also impactful on DO and temperature because they determine water mixing, residence times, and variability at individual sites. Temperature was also strongly impacted by distance to the mouth of Solomon’s Harbor, with sites further away having higher temperatures than sites close to the mouth. The sites furthest from open water have less mixing, higher residence times, more variability, are more heavily impacted by sunlight and weather, and have higher average temperatures, so these sites contain the most vulnerable habitat and should be closely monitored and made a conservation priority.