Doctor of Philosophy, Miami University, 2024, Biology

CHAPTER 1: Nutrient excretion by fish supports a variable but significant proportion of lake primary productivity over 15 years. This chapter analyzes the long-term importance of excretion from gizzard shad for primary production in a midwestern reservoir using a supply:demand (S:D) approach and considers environmental and population variables that best predict the S:D ratio. Gizzard shad excretion supported a variable proportion of phytoplankton phosphorus demand, and it supported more demand during the summer than spring. Stream discharge, temperature, and gizzard shad population biomass best predicted S:D during the spring, while the biomass of the young-of-year best predicted S:D in the summer. CHAPTER 2: Combined influence of parasites and temperature on nutrient excretion rates and body stoichiometry of a freshwater fish. The rates of excretion from fish and the ratios of the nutrients excreted are expected to change as aquatic ecosystems warm. An experiment examined the excretion rates from bluegill under three climate scenarios and a range of natural parasite intensity. Carbon and phosphorus excretion increased with temperature but declined with parasite load, and the C and N concentrations in fish bodies declined with parasite load. CHAPTER 3: Ontogenetic changes in the gut microbiomes of Gizzard Shad and Bluegill and their relationship to nutrient excretion. The microbial communities within the guts of animals contribute to their health, but little is known about how these communities change with development and contribute to ecosystem processes. We conducted an exploratory study to learn about the gut microbiome of larval, young-of-year, and adult gizzard shad and bluegill as well as the relationship between microbiomes and excretion. We found that the two fish species had similar microbial communities as larvae, but the communities were different in the adults. The guts of adult gizzard shad contained taxa that are believed to fix nitrogen as well as s (open full item for complete abstract)

Master of Science in Environmental Science, Cleveland State University, 2024, College of Arts and Sciences

Despite the critical role of organic matter (OM) oxidation in depleting oxygen in the hypolimnetic waters of Lake Erie, uncertainties regarding the sources, quantity, and fate of OM continue to challenge our understanding and management of hypoxia in the lake. This study evaluates the effects of OM oxidation through the analysis of stable carbon isotopes (δ13C) of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in the central and eastern basins of Lake Erie. We disclose DIC contributions from OM oxidation and provide insight into the origins of OM in the hypolimnion. Our results reveal significant declines in δ13CDIC in hypolimnetic waters compared to surface waters, indicative of OM oxidation in the deepest portions of the lake. To further examine this process, we employed the Keeling plot method to estimate the composite isotopic signature of OM respiration (δ13CR). The good agreement between the respired source (-24.4‰) and the signature of the organic material (-24.6‰) support the idea that autochthonous material (internally produced OM) fuels OM oxidation in the central and eastern basins. Additionally, a binary mixing model was utilized to quantify the amount of DIC produced and the respective amount of oxygen required by OM oxidation. We estimate that 11.8 ± 1.6 % of DIC was produced in the central basin and 5.6 ± 1.2% in the eastern basin, which accounts, on average, for 89.3 ± 7.1 % of hypolimnetic oxygen depletion in the central basin and 99.2 ± 17.7 % in the eastern basin. This suggests OM oxidation accounts for most of the hypolimnetic oxygen depletion in the lake, however instances of hypoxia in the central basin may promote other mechanisms of oxygen depletion such as oxidation of CH4, Fe2+, and Mn2+. This study reveals a strong coupling between carbon cycling and oxygen depletion in Lake Erie. Our results underscore the applicability of δ13CDIC as a meaningful tracer to quantify the amount of oxygen-consuming OM in hypolimn (open full item for complete abstract)

PHD, Kent State University, 2024, College of Arts and Sciences / Department of Biological Sciences

Freshwater aquatic ecosystems, including lakes and wetlands, provide habitat for abundant and diverse animal communities, which can have large impacts on nutrient (nitrogen [N] and phosphorus [P]) biogeochemistry. Animals play an important role in nutrient recycling in freshwater ecosystems but are infrequently considered in nutrient management. It is broadly known that animals provide nutrients via excretion and egestion, however, less is known about how animals indirectly influence nutrient retention and release through interacting with aquatic sediments, and how their nutrient contributions shape aquatic communities and ecosystem functions such as primary production. Waterbirds (i.e., ducks, geese, wading birds, cormorants) and benthic invertebrates (i.e., benthic dwelling oligochaete worms, insect larvae such as mayfly and chironomid taxa) are common in Great Lakes aquatic ecosystems, yet their roles in shaping nutrient budgets and loading are often overlooked. The overall focus of this dissertation was to understand how sediment-surface water nutrient dynamics and ecosystem processes are shaped by aquatic animals and different water oxygen conditions in a variety of Great Lakes freshwater aquatic ecosystems. We demonstrate that multiple animal groups can measurably shape nutrient dynamics with implications on other ecosystem functions. In the first study, we investigated multiple internal load contributions, including net ambient and bioturbator-mediated sediment-surface water nutrient exchange, in Sandusky Bay, Lake Erie. We found that invertebrate bioturbation supplied P and N and made up a significant component of net internal fluxes, and internal sources made up a significant proportion of the total P load in this shallow, freshwater embayment. In the second study, we examined how the late-summer hypoxic event in Lake Erie shapes sediment oxygen and redox-sensitive indicators to better understand how hypoxia stressors affect sediment conditions and processe (open full item for complete abstract)

Doctor of Philosophy, Miami University, 2024, Biology

Midwestern North American lakes, including the Laurentian Great Lakes, are experiencing significant increases in water transparency due to invasive Dreissenid mussels and improved watershed management practices. Climate change loss of winter has reduced annual ice cover on the lakes. Increases in water transparency combined with the absence of ice cover in the winter may lead to an increased risk of exposure to damaging ultraviolet radiation (UV), which is known to regulate the early life stages of fish. Despite these potential increases in underwater UV, very little is known of the current day UV transparency throughout the Great Lakes, nor the UV tolerance or mechanisms of protection of the early life stages of a culturally, economically, and ecologically important subfamily of native Great Lakes fish: Coregonine (i.e., Lake Whitefish [Adikameg; Coregonus clupeaformis], Cisco [Otoonapi; C. artedi], and Bloater [C. hoyi]), nor an economically important invasive prey species of fish: Alewife (Alosa pseudoharengus). This dissertation investigated 1) the spatial and temporal UV transparency patterns across the Great Lakes, 2) the ability for UV to accelerate the hatching of native Cisco eggs, 3) the UV tolerance, mechanisms of protection, and sublethal consequences of exposure to UV among two life stages, four species and multiple populations of fish and 4) the influence of UV on the vertical distribution of larval Alewife and Bloater within Lake Michigan. Although long-term offshore UV data does not exist, long-term nearshore UV data suggest shallower UV exposure correlated with increasing dissolved organic carbon concentrations. Laboratory experiments revealed that developing Cisco embryos exposed to UV have the potential to hatch 30 days earlier than embryos unexposed to UV, the egg life stage of all native coregonines tested had a higher UV tolerance than the larval life stages, and the UV tolerance among species and populations of the same species varied. Field s (open full item for complete abstract)

Master of Science (MS), Ohio University, 2023, Environmental Studies (Voinovich)

Agricultural nutrient pollution is a significant cause of impairment in American surface waters. Wetland restoration projects in agricultural watersheds can provide an effective sink for excess nutrients and potentially improve downstream water quality. Ohio University has partnered with The Stream and Wetlands Foundation to conduct water quality monitoring during the restoration of Bloody Run Swamp, a wetland in a former agricultural field near Columbus, Ohio. This thesis serves as an analysis of the initial water quality impacts of this restoration project. The restoration of Bloody Run Swamp did not significantly impact total dissolved phosphorus, orthophosphate, TKN, or ammonia concentrations. In contrast, both nitrate/nitrate and total dissolved nitrogen concentration and loads were significantly reduced during construction. This may have been due to the dry weather during construction and the removal of drainage tiles from Bloody Run Swamp. Future water quality monitoring is needed to determine the long-term impacts of this restoration project.

Master of Science, The Ohio State University, 2023, Environment and Natural Resources

Phytoplankton respond to environmental conditions through specialized adaptations and may proliferate to cause harmful algal blooms (HABs). Nutrient enrichment, largely linked to land-use, has been studied extensively in lakes, but less in streams and rivers. I investigated the influence of nitrogen (N), phosphorus (P), and environmental variables on phytoplankton community dynamics in streams and reservoirs in seven catchments representing a gradient of agricultural, forested, and mixed land uses in the upper Ohio River Basin. The main objectives of this study were to (1) examine the spatiotemporal variability of phytoplankton biomass and relative abundance and (2) identify environmental drivers associated with phytoplankton community structure. In reservoirs, total phosphorus (TP) ranged from 0.001 to 1.50 mg/L and did not differ among catchments, whereas total nitrogen (TN) ranged from 0.084 to 1.91 mg/L and differed significantly among catchments. Total chlorophyll a ranged from 2.56 to 150 µg/L, with Indian Lake exhibiting the highest concentrations (150 chl a µg/L). Cyanobacterial chlorophyll a concentrations were highest in Indian Lake (143.2 chl a µg/L) and positively correlated with percentage agriculture and ammonium concentrations, and were negatively correlated with total phosphorus and TN:TP ratio. There were noticeable differences in the relative abundance of phytoplankton taxonomic groups across catchments and years. Percentage agriculture was identified as a strong predictor of total and cyanobacteria chlorophyll a concentrations. In streams, TP ranged from 0 to 1.32 mg/L, and TN ranged from 0.093 to 4.72 mg/L. Indian Lake exhibited the greatest total chlorophyll a concentrations, with the highest concentrations of both cyanobacterial (76.1 µg/L) and chlorophyte (30.8 µg/L) chlorophyll a. Non-metric multidimensional scaling (NMDS) and permutational multivariate analysis (PERMANOVA) showed differences in phytoplankton communities between years and amo (open full item for complete abstract)

Master of Science, University of Akron, 2023, Geology

In 1967, Wolman modeled how human land-use modification affects sediment yield in the U.S. Middle-Atlantic. This study uses the sediment of Wyoga Lake, Summit County, Ohio to quantify the impacts of land use change on sediment yield, to determine if there is a relationship between land use and the sedimentary heavy metal record, and to test if Wolman's model is applicable to northeast Ohio. Mud Brook flows into and out of Wyoga Lake, thus the lake traps much of the sediment yield from the upper Mud Brook watershed. Based upon wave base models and lakefloor sediment properties, lacustrine sediment accumulates in water deeper than 2.8 m. Sediment cores were collected from deep-water basins and dated by correlating to absolute-dated cores from other Ohio kettle lakes and by using event chrono-stratigraphy to identify lithologic features associated with events of known age. The 266.5 cm-long composite core contains a 220-year environmental history record that was divided into 5 periods of varying human-induced land use change to the Wyoga Lake watershed. The oldest Period, the Pre-Settlement Period (pre-1804) extends from 266.5 to 240.5 cm below lake floor (cmblf) and has organic-rich mud, low Ti concentrations, and a low mass accumulation rate (MAR) of 0.026 g/cm2/yr that accumulated when the forested watershed limited sediment yield. The Settlement and Agriculture Period (240.5─147.6 cmblf; 1804─1964) begins with an initial decline in organic matter followed by elevated arsenic concentrations later in the Period, and a MAR of 0.323 g/cm2/yr which is 12X greater than the Pre─Settlement Period. The sediment properties are interpreted to represent increased terrigenous influx due to deforestation when Stow and Hudson, OH were settled, followed by agricultural activities that applied arsenic-based insecticides to orchards. The Lakeside Housing and Construction Period (147.6 to 94.0 cmblf; 1964─1984) occurred prior to the use of construction-site erosion control practices (open full item for complete abstract)

Master of Science, Miami University, 2022, Biology

Lakes in the northeastern US are browning or increasing in dissolved organic carbon (DOC) as they recover from acidification and experience an increase in precipitation from climate change. DOC attenuates ultraviolet radiation (UV), reducing exposure of lake zooplankton to damaging wavelengths in browner lakes. Additionally, some zooplankton can detect and avoid UV. DOC's role in the cladoceran Holopedium's survival was tested by exposing organisms to natural solar radiation in the presence vs. absence of DOC. It was hypothesized that when exposed to natural UV, the presence of DOC would increase survival in Holopedium. Additionally, if Holopedium could behaviorally detect and avoid UV or visible light was also investigated. Survival was significantly higher in treatments exposed to UV in the presence vs. absence of DOC. There was no evidence of behavioral response to UV or visible light. These results convey the importance of DOC protecting Holopedium from UV damage as they can inhabit in the surface waters of some lakes, partially due to a defense against tactile predators. Browning may also mediate the potential for resource partitioning between Holopedium and its competitor Daphnia. Predicted increases in browning caused by climate change may continue to alter these patterns.

Master of Science, University of Akron, 2022, Geology

Summit Lake is an urban kettle lake located in Akron, Ohio. Once used by industry, Summit Lake is currently being revitalized to provide recreational opportunities. It is important to study the lake's overall health to ensure it is suitable for increased recreational use. Seasonal water column profiles were measured and reveal that from May to October the lake is thermally stratified, the hypolimnion becomes anoxic, and orthophosphate as phosphorus is released from the sediment into the hypolimnion and averages 1100 μg/L by October. This phosphorus release may contribute to harmful algal blooms (HABs). During the sunny productive season, the drawdown of CO2 by algae and increased temperatures results in the precipitation of calcite in the epilimnion and deposition of a white calcite-rich sediment layer. During the remainder of the year organic matter deposition produces a brown sediment layer. The white-brown sediment rhythmites observed from 0-58.7 cm composite core depth have been shown to be varves based upon correlation to year 2003 sediment cores and 210Pb dating. Productive season meteorological precipitation was assessed to determine if heavy rain events increased algal productivity and in-turn produced thicker brown sediment layers. Results were inconclusive, but years with extreme rain events (2003, 2004, and 2011) corresponded to thicker brown layers the following non-productive season. The varve-age model allowed the sediment record to be divided into three time periods. The Industrial Period is defined by sediment with no calcite laminations below 58.7 cm composite core depth which varve-dated to 1980. At this time the residence time of Summit Lake water was short due to high input and extraction of water by industry and resulted in unfavorable conditions for abundant calcite precipitation. A massive brown mud layer from 58.7-96.2 cm composite core depth is interpreted as dredged spoil or possibly sediment disrupted by the 1977 bor (open full item for complete abstract)

Master of Science (MS), Bowling Green State University, 2022, Biological Sciences

Grand Lake St. Marys (GLSM) is a lake located in western Ohio, USA and is utilized for recreation, boating, fishing, and swimming. GLSM is a regionally important center for tourism and recreation bringing in nearly $150 million in annual revenue, but after three years of algal blooms and public health advisories, water-based recreation has reduced significantly in the region. Summer cyanobacterial blooms thrive due to both external and internal loading of phosphorus and are of great concern given that the city of Celina uses the lake as a water source for their community. Planktothrix agardhii, which dominates GLSM, can produce microcystin toxins that are known to be harmful to humans and animals. It is important that we understand the mechanisms driving and influencing these blooms. In this study, we examine Chytridiomycota (chytrids) and how these aquatic fungi can infect P. agardhii blooms. Rhizophydium sp. are known obligate parasites to Planktothrix, and these species have been found and isolated from the waters of Sandusky Bay (McKindles et al. 2021a). We investigated the spatial distribution of infections along with the effect that turbulence has on infectivity. Results of in-lake mesocosms, coupled with lab experiments, suggest that low levels of water turbulence can significantly reduce the infectivity of chytrids. Furthermore, infectivity is dependent on water temperature. Understanding different environmental conditions and the effect they have on infectivity provides valuable insights into controlling factors that may be limiting chytrid pathogenesis.

Master of Science (MS), Wright State University, 2021, Earth and Environmental Sciences

Cyanobacteria are important primary producers, but large cyanobacterial harmful algal blooms (HABs) have many negative ecological and health impacts and are becoming increasingly common. Honeoye Lake (New York, USA) is a shallow, eutrophic lake characterized by increasingly frequent HABs. Nitrogen (N) and phosphorus (P) loads often drive HABs in lakes, and sediment processes can contribute to N removal (e.g., denitrification) or loading (e.g., N fixation, remineralization). Sediment cores and lake water were collected during May–October (2016–2018) at two sites and incubated with no amendments (controls) or 15N stable isotopes to measure sediment nutrient fluxes and N cycling dynamics in Honeoye Lake. Sediments were a strong source of ammonium (NH4+; 200 ± 56 µmol N m-2 hr-1) and soluble reactive P (SRP; 1.60 ± 0.67 µmol P m-2 hr-1). Internal loading of NH4+ was greater than previous estimates of external and internal TN loads. In situ denitrification (mean 17 ± 7 µmol N m-2 hr-1) was the main N removal pathway but was limited by NO3- availability and a lack of nitrification (mean 0.007 ± 0.002 µmol N L-1 hr-1). Potential dissimilatory nitrate reduction to ammonium rates (DNRA; 30 ± 11 µmol N m-2 hr-1) suggested sediments may play an important role in internal loading and recycling of N. Water column NH4+ uptake (mean 0.23 ± 0.02 µmol N L-1 hr-1) rates indicated high NH4+ demand, with only 50% of potential uptake being supplied by regeneration (mean 0.11 ± 0.01 µmol N L-1 hr-1) within the water column, while the other 50% can be accounted for from sediment NH4+ loading. Scaling these rates to the whole lake area suggests internal loads of bioavailable N and P are greater than external loads and promote primary productivity and HABs within Honeoye Lake. Shallow lake sediments can be a significant source of reduced N and SRP, which can be mixed periodically supporting HABs. N loads dominated by chemically reduced forms may limit denitrification and favor non-N-f (open full item for complete abstract)

Doctor of Philosophy (PhD), Wright State University, 2021, Environmental Sciences PhD

Attached algae are ubiquitous components of lake benthic habitats wherever sufficient light reaches submerged surfaces. Attached algae interact with heterotrophic bacteria and fungi to form complex biofilms (“periphyton”) that provide a nutritious food source for consumers and influence biogeochemical cycling by regulating redox potential at the sediment-water interface. Despite their ecological importance, there are limited data on the role of periphyton in the Laurentian Great Lakes. I quantified wave exposure and light availability in rocky nearshore habitats in Lake Erie and Lake Huron. Periphyton biomass and productivity in nearshore Lake Erie was very high while algal biomass and productivity in Lake Huron were uniformly low irrespective of depth. Regression modeling demonstrated that wave disturbance and light availability control periphyton biomass and productivity in nearshore areas of the Great Lakes. To better understand how attached algal diversity and abundance vary with depth and substrate, I measured the biomass and composition of sediment algae and periphyton growing on Dreissena across broad depth gradients in Lake Ontario and Lake Erie. Sediment and mussel shell algal biomass were greatest around 20 m and declined with depth. Algal photosynthesis on sediments and mussels declined with depth down to approximately 40 m in both lakes. I found that sediments from both lakes were dominated by benthic diatoms and settled phytoplankton. In contrast, mussel shells harbored diverse filamentous algal assemblages. I analyzed the stable isotope signatures of Dreissena tissue and biofilms collected in Lake Ontario and Lake Erie, discovering enrichment of nitrogen isotopic signatures in both organisms with depth. DNA metabarcoding data from Lake Erie revealed that Dreissena biofilms harbor greater abundances of putative nitrifying and denitrifying bacteria than surrounding sediments, suggesting that Dreissena may be hotspots for nitrogen cycling in the Great Lak (open full item for complete abstract)

Doctor of Philosophy, Miami University, 2021, Ecology, Evolution and Environmental Biology

CHAPTER 1: Deeper waters are changing less consistently than surface waters in a global analysis of 102 lakes. As global climate change influences lake physical structure, this chapter analyzed long-term trends and drivers of five metrics of vertical thermal structure across 102 globally-distributed lakes. While increases in surface water temperatures and strength of stratification were common, trends in deepwater temperatures and thermocline depth were highly variable and poorly explained by geomorphological lake characteristics. CHAPTER 2: Attenuation of photosynthetically active radiation and ultraviolet radiation in response to changing dissolved organic carbon in browning lakes: Modeling and parametrization. Lake ecosystem models have limited capacity to address how changes in dissolved organic carbon (DOC) influence light attenuation and consequent vertical structural responses. We developed an update to the MyLake model to dynamically link light attenuation at multiple wavelengths, including the first parameterization of ultraviolet attenuation, with changing concentrations of DOC at the daily time step. CHAPTER 3: Earlier ice breakup induces changepoint responses in duration and variability of spring mixing and summer stratification duration in dimictic lakes. As ice cover duration has shortened in lakes worldwide, the subsequent periods of spring mixing and summer stratification are likely to change in response. We modeled the relationships between these two phenological periods vs. timing of ice breakup by "moving" a single lake across a latitudinal gradient. A key changepoint in the timing of ice breakup on May 9 determined the relative response of longer spring mixing vs. longer summer stratification duration. CHAPTER 4: High-frequency data reveal lake phenology is more strongly associated with oxygen depletion during winter than in summer. Using year-round high-frequency data from 14 lakes, we assessed the role of lake phenology on deepwate (open full item for complete abstract)

Master of Science, University of Toledo, 2021, Biology (Ecology)

Chapter 2: Stratification and hypoxia in the western basin of Lake Erie (WBLE) has been shown to result in phosphorus flux from the underlying sediment, which could provide necessary nutrients for harmful algal bloom (HAB) growth. Studying the duration and frequency of hypoxic events would provide pivotal information for estimations of phosphorus flux from underlying sediments. However, due to the ephemeral nature of hypoxic events in the WBLE, planned weekly vessel-based sampling trips are inadequate for alerting researchers of the onset of hypoxia, making sampling such events difficult. Instead, water quality instruments can be deployed to collect and relay live data to researchers in a much more frequent timeline. In this study, a buoy equipped with a thermistor string and an EXO3 sonde (Yellow Springs Institute) was deployed to monitor for potential stratification and depleting lake bottom oxygen concentrations. This system measured water quality parameters and posted the data online every 20 minutes. Using these data, immediate vessel-based sampling trips to 7 sites were made according to observed hypoxia. Data captured show a hypoxic event occurred in the WBLE during early July 2020 that persisted for several days before being mixed by a storm on July 11, 2020. This hypoxic event coincided with 8 days of stratification. In addition, hypolimnion water warmed to over 23 ℃ while remaining stratified from the overlying waters, which could facilitate higher phosphorus flux from sediments. On average, phosphorus concentrations in the hypolimnion were 1.06 µ/L (~43%) higher than in the epilimnion by the end of the event, suggesting that sediments were releasing phosphorus into the overlying waters. Chapter 3: The western basin of Lake Erie (WBLE) has been experiencing Harmful Algal Blooms (HABs) for over a decade. These blooms have been detrimental to the health of Lake Erie and the safety of drinking water for surrounding communities. Nutrient inputs (namel (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2021, Evolution, Ecology and Organismal Biology

The experiences an individual has during early development may have life-long effects (“experiential legacies”) which can also have population-level consequences. However, since experiential legacies are difficult to measure in populations, how experiential legacies of individuals affect cohort- and population-level outcomes (i.e., buffering or amplifying population responses) remains difficult to discern. The objective of my dissertation research is to evaluate the extent to which experiential legacies affect individual performance and alter population dynamics. By exploring the importance of individual life events to populations, we can better understand the interconnectedness of life stages and better anticipate how environmental change may alter population and community dynamics. Specifically, I examined individual experiential legacies across a range of animal species with the goal of identifying generalizable patterns in response to early-life nutritional stress (Chapter 2), and then I focused on experiential legacies within individuals (Chapter 3), cohorts of individuals (Chapter 4), and a population consisting of multiple cohorts (Chapter 5) in Lake Erie Walleye (Sander vitreus). Lake Erie Walleye present a population for which understanding the long-term impacts of early-life experiences may be particularly valuable due to current human-induced environmental changes within its ecosystem. Since experiential legacies can produce unanticipated changes in the kinds as well as proportions of subsequent (i.e., later in life) phenotypes, examining patterns across multiple species may expose underlying trends. Patterns in experiential legacies across 81 studies of 65 animal species demonstrated generally consistent negative or neutral impacts of early nutritional stress on later-life phenotypes, indicative of energy depletion as a mechanism for the long-term consequences of early-life conditions (Chapter 2). Yet, overall, my results emphasize the existence of c (open full item for complete abstract)

Master of Science, Miami University, 2020, Biology

Zooplankton in reservoirs within agricultural landscapes exhibit unique dynamics due to highly variable discharge as well as elevated nutrient inputs and productivity. Here we explore the long-term response of crustacean zooplankton biomass and phenology and relate these to long-term trends and interannual variability (IAV) in environmental factors in a eutrophic reservoir over a 24-year period. We also investigated bidirectional effects among zooplankton taxa, chlorophyll, and larval fish using convergent cross mapping (CCM). Cyclopoids increased and rotifers decreased over time, while the center of gravity (COG, week of peak biomass) of calanoids advanced over time. We detected the largest number of significant correlations between the IAVs of crustacean taxa and temperature, and between the IAVs of crustacean taxa COG and chlorophyll COG. CCM identified numerous interspecific relationships among zooplankton taxa and effects of inorganic turbidity, temperature, and food quality. Bottom-up effects of chlorophyll on cyclopoids and rotifers as well as rotifers on copepods were significant, while top-down effects were marginally significant. Our findings suggest phytoplankton and temperature likely drove long-term changes in the zooplankton community. Management of eutrophic reservoirs should consider the temporal scale and complexity of food web dynamics to understand effects from climatic factors and watershed inputs.

Master of Science, Miami University, 2020, Microbiology

The McMurdo Dry Valleys is a polar desert ecosystem which composes the largest ice- free area in Antarctica, with the exception of perennially ice-covered lakes and ponds. The lakes in the valleys are the only landscape unit that support metabolic activity year- round. Recent increases in air temperature and solar radiation have led to a chain of disturbances altering the environmental conditions of these lakes. In this study, we test the impact of climatic disturbances on microbial communities in Lake Bonney, one of the lakes in the MDV. Through an integrated approach of combining field studies on natural communities in the lake (in situ) and laboratory experiments on algal isolates (ex situ), this study will attempt to understand how phytoplankton, eukaryal and bacterial communities respond to simulated disturbances. Results from the in situ experiments showed that the moat is a unique and stressful environment for under-ice communities and that under-ice shallow communities are highly sensitive to climatic disturbances. The ex situ experiments showed that certain phytoplankton species, like the chlorophytes, are more resistant to environmental alterations and thus will outcompete other phytoplankton species.

Doctor of Philosophy, Miami University, 2020, Ecology, Evolution and Environmental Biology

How spatiotemporal variability modulates ecosystem structure and function has long been a fundamental question of ecology. This issue is particularly topical, as climate and land use change operate in concert to alter aspects of environmental variability. In this dissertation, I examine how watershed land use and climate change interact with in-lake processes to mediate ecosystem function, specifically nutrient cycling and ecosystem metabolism. I employ a combination of observational and experimental techniques across a range of spatial and temporal scales to address these questions. In Chapter 1, I examine the relative contributions of internal (fish excretion) and external (watershed) nutrient loading in a hypereutrophic reservoir. I found that annual watershed nutrient loading exceeded fish excretion. However, fish excretion became more important in the growing season (April - October) and summer (July - September), and during shorter timescales (weeks - months). Within these shorter timescales and seasonal periods fish excretion frequently exceeded watershed nutrient loading. In Chapter 2, I examine how hydrology and discrete disturbance events (storms) mediate spatiotemporal patterns of nutrient cycling and metabolism. I captured two consecutive years (one wet, one dry) that varied markedly in watershed discharge and nutrient loading. I found that temporal variability usually exceeded spatial, but spatial increased in dry years. I also found that storms produce large, yet sometimes ephemeral and spatially explicit effects. Further, wet years may shift the lake from net carbon sink to a net carbon source. In Chapter 3, I build upon observations from reservoir ecosystems to experimentally simulate storms in aquatic mesocosms. Specifically, I examine if detritus pools in conjunction with sediment and nutrient resource pulses increase ecosystem resilience and resistance following perturbations. I found that detritus pools increased resilience and (open full item for complete abstract)

Master of Science (MS), Bowling Green State University, 2020, Biological Sciences

Cyanobacterial harmful algal blooms (cHABs) have occurred regularly in Lake Erie for the past two decades. The blooms are commonly dominated by Microcystis aeruginosa, a cyanobacterium with the ability to produce a group of hepatotoxins known as microcystins (MC). Current forecasting of the blooms predicts the spatiotemporal biovolume based on chlorophyll-a concentrations collected via remote sensors and known drivers of cyanobacteria cell growth. Forecasting however, cannot predict MC concentration of a bloom. The focus of this research was to examine MC production and loss rates to provide information that would be useful to develop forecasting of MC concentration for Microcystis blooms in the western basin of Lake Erie. Throughout 2018 and 2019 summers, 26 microcosm experiments were conducted at a near river mouth and off-shore location to quantify rates of MC production and loss. Eleven trials of production experiments with nutrient amendments were conducted each year during the annual cHAB. Nutrient additions of phosphorous with different nitrogen sources were added to 2 L of whole lake water at the beginning of the experiment to understand the effects of nitrogen on MC production. Bottles were incubated in-situ at each site for 72 hours with daily sample collection. Four trials of MC loss experiments were conducted monthly in 2019 to understand if loss of MC was due to biotic factors. Triplicate two liters of whole (biotic treatment) and 0.2µm filtered lake water (filtered control) were spiked with 1µg/L of 15N-labeled dissolved microcystin LR to quantify loss rates of this congener under ambient incubation. Subsamples were collected every 3 hours for the first 24 hours, then at hour 36 and 48 for measurement of microcystins. Production studies with nutrient amendments indicated various nitrogen sources did not significantly impact the production of MC during 2018 and 2019. Ambient rates of MC production were higher earlier in the bloom season and decreas (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2020, Earth Sciences

Upland catchments play an outsized role in the processing and export of water, sediments, nutrients, and organic matter, thus strongly influencing downstream water quality. In Chapter 1, an overview of biogeochemical cycling within upland fluvial sediments is presented, focusing on key regional biogeochemical cycling patterns and solute export processes. Additionally, anthropogenic influences on this environment, such as historical mining activities and climate change, are briefly reviewed in this chapter. Chapter 2 explores the relationship between spatial hydrologic heterogeneity and microbial community assembly and functional potential within the hyporheic zone. The region of groundwater and river water mixing, known as the hyporheic zone, is a hotspot of microbial activity that influences solute export and cycling in rivers. Hyporheic mixing patterns can vary over small spatial scales, leading to heterogeneity in fluid chemistry and microbial community composition and function. Here, we integrate new mass-spectrometry data, metagenomic insights, and ecological models with previous analyses of microbial community composition and dissolved organic matter (DOM) quality to understand spatial relationships between hyporheic flow and microbial community assembly, metabolism, and DOM processing at high-resolution (100 locations) along a 200 m meander of East River, Colorado (USA). Ecological modeling revealed a strong linkage between community assembly patterns and underlying hydrologic and geochemical drivers, including the impact of physical heterogeneity (riverbed grain size) on microbial community structure. Geochemical profiles associated with upwelling groundwater suggest the influence of underlying geology, specifically Mancos-derived solutes, in driving community assembly. Distinct microbial community profiles and functional potential in zones of upwelling groundwater suggest that groundwater chemistry may have a greater influence on biogeochemical cycling wi (open full item for complete abstract)