Cyanobacterial harmful algal blooms are ubiquitous globally and can have enormous impacts on the environment, economy, and human health. These blooms have the potential to produce toxins such as microcystin (MC), cylindrospermopsin (CYN), and saxitoxin (STX). Currently, the standard method for toxin testing is by an Enzyme Linked Immunosorbent Assay (ELISA). This method is time consuming; LightDeck Diagnostics has developed a rapid and portable multiplexed assay to simultaneously test for MC, CYN, STX as an alternative to ELISA testing. During the summer of 2021, LightDeck's duplexed MC-CYN assay was successfully field validated in Sandusky Bay. A method of portable lysis was also tested but is undergoing further development prior to being used in additional testing. During the summer of 2022, a triplexed version of the LightDeck cartridge (MC-CYN-STX) was field validated in both Sandusky Bay and Springbrook Lake in Whitehouse, Ohio. The STX assay successfully detected toxin, however the triplexed MC assay did not perform as well as the previous duplex formulation. Additionally, toxin concentrations were correlated with water quality parameters and nutrients in both lakes to investigate potential environmental drivers of toxicity during bloom events. The LightDeck assay was also used as part of a research cruise in the Winam Gulf, Kenya. Though ELISA remains the gold standard for toxin detection, the LightDeck assay could be a valuable tool in monitoring and reporting toxin in water bodies that people interact with, whether they be recreational lakes or water that the community relies on for daily functions as demonstrated in the case of the Winam Gulf.

Sandusky Bay is both a valuable nursery for important sport and commercial fishes like Walleye and White Bass, and a degraded system with excessive sediment and nutrient inputs from the agricultural watershed. Proposed restorations could alter the bay from a uniformly turbid system to one capable of supporting submerged aquatic vegetation and accompanying changes in the fish community. The current bay conditions support rapid growth of larval and juvenile Walleye and Yellow Perch, but it also harbors Channel Catfish and Walleye fisheries. With the potential changes in habitat through restoration, I aimed to quantify the abundance and composition of large fish predators (piscivores) before proposed restoration begins, so the possible impacts to the bay as a nursery habitat can be assessed. Fish abundance was determined in early June 2021 when larval and juvenile fishes are in the bay. Using Dual Frequency Identification Sonar (DIDSON) and accompanying software, I quantified the abundance of fishes in Sandusky Bay (i.e., dividing the bay into four sectors, with multiple recordings in each sector). Due to species-specific size distributions, I divided the observations into size classes (100-250mm, 251-450mm, >451-mm total length (TL)) and then coupled these with proportions of species by size class from experimental gillnet sets in each sector to obtain abundance by species. By using the areal estimator in the ODNR Coastal Viewer and correcting for actual depth of water surveyed, I extrapolated these densities to determine that there were 29.6 ± 9.3 million (mean ± 1SE) fish >100mm TL in Sandusky Bay at the time we sampled. Gizzard Shad dominated the system (46% of all fish), but notably ~4.1 million Channel Catfish and ~2.9 million Walleye inhabit the bay. With absolute numbers, bioenergetic models may be built to predict community-wide impacts to larval and juvenile fishes and predict how restoration may affect this fish community.

Understanding the role of internal top-down trophic grazing interactions from zooplankton is necessary to better determine cyanobacterial algal bloom establishment as a parallel to more common investigation into the role of changes in nutrient concentrations, or bottom-up enrichment, on bloom structure and function. Bi-weekly samples were collected from two locations in Sandusky Bay, Lake Erie between March 2019 to October 2019 to capture pre-bloom, early-bloom, and late-bloom conditions. For microzooplankton analysis, dilution experiments were conducted to determine grazing rates using previously established methods. Mesozooplankton grazing rates were determined by concentrating natural populations to 8 times ambient levels, then measuring phytoplankton growth rate changes. After 24 hours samples for both experiments were collected for analysis of total chlorophyll ɑ pigment concentration using fluorometry and analysis of chlorophyll ɑ pigment concentration as well as phytoplankton community structure using a BBE Fluoroprobe. Phytoplankton cell enumeration using light microscopy was also conducted to determine cyanobacterial cell densities. This research also provided additional insights into correlations of chlorophyll ɑ data analysis between fluorometry and BBE Fluoroprobes. Results indicated that microzooplankton were actively grazing on the overall phytoplankton community in the majority of experiments conducted and that microzooplankton grazing rates were not negatively affected by increases in cyanobacterial density. In contrast mesozooplankton grazing rates were extremely low or no grazing was seen in the majority of experiments. Overall, this study indicated that while microzooplankton can play an important role, mesozooplankton grazing may not, in the top-down control of Planktothrix-dominated blooms in Sandusky Bay, Lake Erie.

Sandusky Bay and Lake Erie are plagued with harmful algal blooms every summer. Sandusky Bay is a drowned river mouth that is very shallow and turbid and is dominated by Planktothrix agardhii, while Lake Erie is dominated by Microcystis aeruginosa. Both species of cyanobacterium are non-diazotrophic and produce microcystin, a hepatotoxin. A competition experiment was conducted culturing both species alone and in coculture at nitrogen (nitrate) replete, nitrate restricted, and nitrogen-free environments. Planktothrix grew better alone at nitrogen restricted medium than in co-culture with Microcystis. In coculture, Microcystis was dominant over Planktothrix however, that dominance decreased as nitrogen was reduced in each treatment. In the nitrogen replete environment, the coculture produced significantly more toxin than the monocultures and in the no nitrogen environment the Planktothrix monoculture produced more toxin than the Microcystis monoculture or the coculture. The community composition in Sandusky Bay was monitored over the winter and spring months (January-April) to see how it changed as time progressed. Nutrient amendment experiments were also conducted adding nitrate, phosphate, and a combination of nitrate and phosphate to stimulate growth and identify any possible nutrient limitations. The initial community yielded low cell densities until the temperature increased and cell abundances followed shortly thereafter. Planktothrix dominated over the winter followed by a transitional period of cryptomonad and diatom dominations before transitioning back to Planktothrix. Both nitrate and phosphate were limiting Planktothrix growth in the spring, while nitrate alone was limiting the overall community.

Planktothrix sp. is less studied than other bloom-forming cyanobacteria. The aim of this study was to determine characteristics of the Planktothrix bloom in Sandusky Bay. Using the 2013 Sandusky Bay metagenome and 2014 summer samples, it was found that the bloom in Sandusky Bay has limited diversity and is continuously dominated by Planktothrix. Nutrient profiles of the Bay suggest nitrogen limitation throughout the bloom season. Physical parameters recorded in Sandusky Bay are suboptimal for many known bloom-forming cyanobacteria. Given this information, it is not yet understood how Planktothrix survives and dominates Sandusky Bay. Future work will look further at community members playing a role in the nitrogen cycle in the Bay. Additionally, the succession of genotypes will be determined over time as the environmental parameters will be monitored over a longer period of time to determine how survival of Planktothrix is supported.

I developed an ecological-economic model representing the Sandusky region of Lake Erie to explore the relationship between internal ecosystem change and management of external phosphorus loading. The model was comprised of two sub-models: an ecological unit model and a phosphorus management model reflecting the societal benefits and costs of phosphorus regulation. These two sub-models formed a dynamic feedback loop including freshwater ecology, ecosystem services, and phosphorus management. Climatic fluctuations in phosphorus loading caused significant variations in the quality of ecosystem services between years. Decreases in ecosystem resistance to eutrophication caused by dreissenid mussels created multiple stable states of management compromise. Adaptive management benefited ecosystem services during mussel invasion scenarios, while unresponsive management was biased towards groups discharging phosphorus. Large-scale wetland restoration shifted management compromise to states characterized by less on-site management and higher environmental quality. The perturbation-based approach taken here illustrates that equilibrium in ecological-economic systems over time is unlikely.

Studies of tributary-lake interactions most often consider only tributary nutrient stimulation of offshore phytoplankton growth. However, in freshwater ecosystems, input of tributary phytoplankton may directly affect offshore processes, such as nutrient cycling, phytoplankton-bloom formation, and hypolimnetic hypoxia. To explore these interactions, we propose the Algal Loading Hypothesis which predicts (1) tributaries contain phytoplankton; (2) tributary phytoplankton are light-limited due to high nutrient concentrations and high light attenuation; (3) offshore phytoplankton are nutrient-limited due to low nutrient concentrations and low light attenuation; and, (4) as tributary phytoplankton move offshore, productivity increases in response to greater light availability, using tributary-stored nutrients to drive offshore productivity. We used field sampling during April-September 2005 and 2006, phytoplankton physiological measures, and computer simulations to test these predictions and to determine the effect of loaded phytoplankton on offshore phytoplankton dynamics and hypolimnetic oxygen depletion in the Sandusky system (Sandusky River, Bay, and subbasin) of Lake Erie. We found extremely high phytoplankton biomasses in the Sandusky River and Bay (Chapter 2) including an invasive cyanobacterial phytoplankter, Cylindrospermopsis(Chapter 5). Phytoplankton biomass was best predicted by the ratio of total inorganic nitrogen to total phosphorus (Chapter 2) whereas Cylindrospermopsisbiomass correlated with increased temperatures and shallow depths (Chapter 5). River and bay phytoplankton communities were not phosphorus limited but the offshore phytoplankton community was (Chapter 3). Phytoplankton communities at all sites were not strictly light limited; however, simulated phytoplankton productivity was most sensitive to light availability. For example, when we simulated increased light for the bay phytoplankton community, productivity increased > 200% (Chapter 3). Hypo (open full item for complete abstract)