Master of Science, The Ohio State University, 2024, Evolution, Ecology and Organismal Biology

A major driver of eutrophication in aquatic ecosystems is phosphorus (P) pollution often derived from upstream agricultural or livestock production. While controlling P loss from these sources is essential, P export to lakes and estuaries may also be influenced by P storage and transformation within lotic ecosystems. At large scales P pools tend to be larger in places with high P inputs (i.e. agriculture and urban settings). However, spatial patterns in P storage in different pools (plants, algae, and sediment) across small watersheds with variable habitats has received little attention, but likely varies considerably with flow regime and stream size. I examined the form, mass, and location of phosphorus stored in an agriculturally dominated small watershed (20 km2) in northwest Ohio, USA. I measured the P stored in sediment, plant, and algae pools in 15 reaches varying in size and flow regime from grassed waterways to a third order stream. Sediment P was greater than 60% of the total benthic P mass in all reaches, suggesting processes determining streambed sediment storage also drive phosphorus storage. Additionally, measurements indicate that streambed sediment acted as a dissolved phosphorus sink across all reaches sampled. However, sediment tended to be saturated with P at downstream reaches, indicating that the role of sediment as a P sink may diminish in downstream reaches. Sites that were dry for some or most of the year contained a large portion of the benthic P located in this stream network, suggesting that wet/dry cycles are important drivers of P cycling in much of the stream network. Thus, the impact of streams on P exports may vary substantially within small watersheds.

Committee: Jim Hood (Advisor); Steve Hovick (Committee Member); Vinayak Shedekar (Committee Member) Subjects: Biogeochemistry; Ecology; Environmental Science

Master of Science (MS), Wright State University, 2024, Biological Sciences

Excess anthropogenic nitrogen (N), primarily from agricultural field fertilization, causes nutrient runoff that stimulates harmful algal blooms (HABs) in western Lake Erie. As a critical tributary to Lake Erie, nutrient loading from the Maumee River drives the intensity of the annual summer HABs in the western basin. Knowledge gaps around rates of N transformations in the Maumee River currently hinder the calibration of in-river parameters in Soil and Water Assessment Tool (SWAT) models for the Maumee watershed. To address these gaps, this research quantified rates of ammonium uptake, ammonium remineralization, nitrification, and bacterial respiration alongside physicochemical parameters of the river. Monthly sampling was conducted along the Maumee River at International Park (river mile 4.53), Mary Jane Thurston (river mile 31.88), and Independence Dam (river mile 59.31) over the course of a year. Ammonium uptake rates ranged from 1.2 to 8.7 µmol N L-1 hr-1 for water samples incubated under light conditions and from 0.2 to 1.9 µmol N L-1 hr-1 under dark conditions, while ammonium regeneration ranged from <0.01 to 12.0 µmol O2 L-1 hr-1. Bacterial respiration rates averaged 525.0 ± 28.5 µM O2. Respiration and both NH₄⁺ uptake & regeneration rates correlated overall with seasonal temperatures and biomass. Respiration rates closely followed temperature, with warmer months having the highest rates. November 2022 samples exhibited higher rates of respiration and both NH₄⁺ uptake & regeneration at all sites as chlorophyll was >200 µg/L during the fall river bloom. Despite not being at peak temperature in the study, the highest rates of microbial activity in April and May., with the lowest observed during the coldest months, January and March. The timing of peak rates at the three sites along the river-to-lake continuum shifted with biomass, indicating the importance of parameterizing the SWAT model with models with spatially and temporally dynamic values. These findin (open full item for complete abstract)

Committee: Stephen J. Jacquemin Ph.D. (Committee Chair); Silvia E. Newell Ph.D. (Committee Co-Chair); Katie Hossler Ph.D. (Committee Member) Subjects: Biogeochemistry; Environmental Management; Environmental Science; Environmental Studies; Hydrologic Sciences; Hydrology; Water Resource Management

Master of Science (MS), Ohio University, 2024, Civil Engineering (Engineering and Technology)

Practical considerations for the design of an AMD treatment plant located in the Sunday Creek watershed were investigated. A mixed culture of bacteria originally from and AMD site located at Wolf Run, Noble County, OH, was enriched under various conditions in AMD from the Sunday Creek site. Following the work of Almomani (2023), the effects of inoculum size (1%, 2%, 5%, and 10%), nutrient enrichment conditions (reagent-grade ammonium and phosphate, no nutrient addition, and commercially available fertilizers), and temperature (8 °C, room temperature, and 32 °C) on the iron-oxidation kinetics of this culture were investigated. Inoculum size had no statistically significant effect on oxidation rates, although the oxidation rate at 5% and 10% inoculum (0.175 and 0.171 h^-1 , respectively) were observed to be nearly twice the oxidation rate at 1% inoculum (0.107 h^- 1 ). There was no significant difference between the oxidation rates of samples containing 0.1 M ammonium sulfate and 5 mM potassium phosphate (0.156 h^-1 ) and samples containing only inoculum (0.108 h^-1 ), and commercial fertilizer was observed to decrease iron oxidation rates (0.0547 h^-1 ), although the total time from inoculation to total iron oxidation was similar to that of the samples containing only inoculum. Iron oxidation rates increased with temperature, and the oxidation kinetics were fitted using the Arrhenius model yielding an activation energy of 70.1 kJ mol^-1 °K^-1 and a pre-exponential factor of 2.21 ∙ 10^11 h^-1 . A pilot-scale batch reaction experiment was conducted in field conditions at the Sunday Creek site in a 1250 gal clarifier. Oxidation rates were observed to be 0.012 h^-1 after the second subculturing, which was lower than any rate observed in the laboratory experiments. This was explained by a combination of suboptimal factors, including low temperatures and inclusion of commercial fertilizer as a secondary nutrient source. Finally, a process optimiz (open full item for complete abstract)

Committee: Guy Riefler (Advisor); Natalie Kruse-Daniels (Committee Member); Lei Wu (Committee Member); Daniel Che (Committee Member) Subjects: Biogeochemistry; Civil Engineering; Engineering; Environmental Engineering; Experiments; Microbiology

Master of Science, Miami University, 2024, Geology and Environmental Earth Science

Biological nitrogen fixation (BNF), the reduction of N2 to bioavailable NH3 by diazotrophs, is essential for all life on Earth. It is accepted that diazotrophs have existed since well before the Great Oxidation Event (GOE, 2.2Ga). Diazotrophs function through synthesis of nitrogenase enzymes with one of three metal cofactors: Mo, V, or Fe; Mo being the most efficient. However, before the GOE, oceanic Mo was theoretically mainly locked within crustal rocks and mineral precipitates. Despite extremely depleted aqueous Mo, phylogenetic and geologic evidence suggest that Mo-based nitrogenases developed first. To partially solve this “Mo paradox,” Methanosarcina Acetivorans, an N2-fixing, obligately anaerobic methanogen was cultured in an aqueous Mo-depleted medium with only solid Mo sources (molybdenite and basalt). Cell growth, methane production, and nitrogen fixation abilities were monitored. Mineral-cell interactions were imaged by scanning electron microscope. Results demonstrate greater nitrogenase activity and significantly higher growth yield when cultured with solid Mo sources than cultured with no solid or aqueous Mo. Cells attached to the surface of molybdenite and basalt through production of extracellular polymeric substances (EPS). These results implicate that ancient diazotrophs adapted to aqueous Mo-depleted conditions by utilizing solid Mo sources and passed this adaptation down to modern diazotrophs.

Committee: Hailiang Dong (Advisor); Claire McLeod (Committee Member); Jason Rech (Committee Member) Subjects: Agriculture; Biogeochemistry; Geobiology; Geology; Microbiology

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)

Committee: Michael Vanni (Advisor); Melany Fisk (Committee Member); Matthew Saxton (Committee Member); Roxane Maranger (Committee Member); Christopher Myers (Committee Member); María González (Committee Member) Subjects: Biogeochemistry; Biology; Environmental Science; Limnology; Science Education

Doctor of Philosophy, The Ohio State University, 2024, Earth Sciences

Atmospheric CO2 from global carbon emissions has increased at an unprecedented rate since the 1880s. Approximately 26% of atmospheric CO2 is absorbed into the surface ocean, resulting in a decrease in seawater pH referred to as ocean acidification. Additionally, increased atmospheric CO2causes the planet to warm, leading to ocean warming. Decreases in ocean pH and increases in ocean temperature negatively affect coral health, leading to decreased coral growth, cover, and biodiversity. Under future ocean acidification scenarios, the surface ocean is expected to decrease pH approximately 0.1 – 0.3 pH units, which leads to declining coral health. Calcification is energetically demanding, and when exposed to low pH corals need more fuel to maintain growth rates. Previous studies have shown a variety of responses to ocean acidification including decreased growth, decreased energy stores, or increased respiration. However, many of these effects are minimized when coral have access to food, which provides extra energy to the coral host. Most of these experiments are short or moderate-duration and do not study the long-term effects of ocean acidification to coral physiology and biogeochemistry. Therefore, volcanic CO2-vent ecosystems with naturally low pH can act as natural laboratories to study the effect of chronic ocean acidification on ecological time scales. The symbiotic coral Cladocora caespitosa and the asymbiotic coral Astroides calycularis grow at CO2-vents around the island of Ischia, Italy. To explore how these corals cope with low pH we 1) conducted a field survey of corals collected from ambient pH non-vent sites and low pH CO2-vent sites and 2) conducted a 6-month long experiment exposing corals collected from ambient and low pH sites to experimentally low pH. The field survey revealed that corals from CO2-vent sites have higher heterotrophic capacity than corals collected from ambient pH sites, allowing these corals to survive in a persistently low pH env (open full item for complete abstract)

Committee: Andréa Grottoli (Advisor); Jean-Pierre Gattuso (Committee Member); Elizabeth Griffith (Committee Member); William Lyons (Committee Member); Agustí Muñoz-Garcia (Committee Member) Subjects: Biogeochemistry; Biological Oceanography; Climate Change; Ecology; Environmental Science

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)

Committee: Fasong Yuan (Advisor); Brice Grunert (Committee Member); Julie Wolin (Committee Member) Subjects: Biogeochemistry; Environmental Science; Limnology

Doctor of Philosophy, The Ohio State University, 2024, Microbiology

Microbes are engines of ocean biogeochemical processes. Viruses influence and shape microbial communities via lysis, horizontal gene transfer, and metabolic reprogramming. Viral lysis facilitates the export of carbon from the surface into the deep ocean via aggregates of sinking particles. In fact, they outperform prokaryotes and eukaryotes as the strong predictor for carbon fluxes in the oligotrophic ocean. Viruses also impact the gene flow of their hosts, and the genes transferred from virus-host interactions can be fixed in viral genomes. Viruses are known to carry and express host-derived auxiliary metabolic genes (AMGs) that directly reprogram metabolisms within virus-infected cells, termed virocells. However, viral communities are poorly characterized in the oligotrophic ocean, and their AMG-driven metabolic reprogramming lacks systematic descriptions from the global oceans. The Sargasso Sea is highly stratified and nutrient-depleted each year in the summer months. This seasonal pattern makes the Sargasso Sea one of the ideal model ecosystems to study oligotrophic oceans. In the Sargasso Sea, abundance of viral-like particles has seasonal and depth-associated structuring patterns. Here, to better survey the Sargasso Sea viruses, we apply sequencing approaches to characterize viral communities via metagenomics and uncover their biogeographical and ecological structures locally and globally in the ocean. As described in Chapter 2, comparison with global viral metagenomics revealed that Sargasso Sea viruses were similar across warm oligotrophic oceanic regions but not represented globally. They form discrete populations in the viral and cellular fractions at the viral maximum (80m) and mesopelagic (200m) depths. Inclusion of long-read data captured 1,257 viral genomes in addition to the 1,044 viral genomes derived from short-read assemblies, resulting in the identification of ecologically important and microdiverse viral genomes. Having established lo (open full item for complete abstract)

Committee: Matthew Sullivan (Advisor); Joseph Tien (Committee Member); Virginia Rich (Committee Member); Igor Jouline (Committee Member) Subjects: Biogeochemistry; Bioinformatics; Biological Oceanography; Biology; Climate Change; Ecology; Environmental Science; Microbiology; Statistics; Virology

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

Wetlands act as a filter between the terrestrial land and a body of water, regulating the flux of nutrients between these. An overabundance of nutrients, such as phosphate, can lead to a harmful algal bloom (HAB), which is known to deplete oxygen from aquatic ecosystems and produce harmful toxins. The goal of this study was to determine the effect of different vegetation patches on the amount of bioavailable phosphorus, measured as soluble reactive phosphate (SRP), in both the surface water and sediment. We sampled surface water and sediment from Turtle Creek Bay located in Magee Marsh Wildlife Area, Ohio, where we identified four distinct vegetation patches: grasses, hardwoods, Typha spp. (cattail), and submerged aquatic vegetation (SAV). Results of this study showed that the SAV patch exhibited significantly less SRP than the other patches (p<0.05). However, there was no significant difference in SRP concentrations for the rest of the patches. Additionally, we experimentally incubated intact sediment cores sampled from a diagonal transect across Magee Marsh. The cores were incubated with four different SRP concentration treatments based on in situ SRP measurements. We found that at ambient SRP concentrations (4 ug/L), sediments released 455.2 ± 518.3 ug SRP/m2/d into surface waters, but when SRP concentrations in the surface water increased (to 18, 39, and 60 ug SRP/L), sediments removed SRP at increasing rates (-919.9 ± 278.7, -2062.3 ± 1001.61, -7378.5 ± 4267.1 ug SRP/m2/d, respectively).The increasingly negative mean flux rates suggest that these coastal wetland sediments can sequester increasing amounts of SRP as surface water concentrations increase.

Committee: Lauren Kinsman-Costello PhD (Advisor); Mark Kershner PhD (Committee Member); Andrew Scholl PhD (Committee Member); David Costello PhD (Committee Member) Subjects: Biogeochemistry; Biology; Conservation; Ecology; Environmental Science; Freshwater Ecology; Plant Sciences

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)

Committee: David Costello (Advisor); Lauren Kinsman-Costello (Committee Member); Ferenc de Szalay (Committee Member); Michael Vanni (Committee Member); Allyson Tessin (Committee Member) Subjects: Biogeochemistry; Ecology; Environmental Science; Freshwater Ecology; Limnology

Master of Science, The Ohio State University, 2024, Environment and Natural Resources

It is important to understand how environmental factors drive variability in aquatic nutrient cycling in streams. Controls on variability in production and transformation of dissolved organic matter (DOM), a carbon-based nutrient, are not well understood on spatial scales spanning many streams. This knowledge gap leaves questions as to how environmental factors influence DOM characteristics. In water year 2023, we investigated nitrogen and carbon chemistry seasonally in 80 tributaries on the United States side of Lake Erie. Watershed area and modeled discharge had no clear effect on total dissolved nitrogen (TDN) or DOM concentrations. Land use was a significant factor influencing stream chemistry; watersheds with different dominant land uses produced different seasonal chemistry patterns and had different environmental factors influencing stream chemistry. In watersheds dominated by agricultural land use, nitrate was the dominant form of nitrogen contributing to high TDN concentrations, likely driven by fertilizer use. DOC concentration and chemistry varied moderately with season and were impacted differently in watersheds with greater forest cover as compared to watersheds with greater cover of anthropogenically impacted land uses. Dominant land use of a watershed dictated how watershed factors, such as soil hydrology, watershed size, and degree of natural or anthropogenic land use, influenced stream chemistry, indicating that differences in DOM chemistry may be due to differential processes controlling DOM source and transformation.

Committee: Rachel Gabor (Advisor); Rachel Eveleth (Committee Member); Gil Bohrer (Committee Member); Matt Davies (Committee Member) Subjects: Aquatic Sciences; Biogeochemistry; Environmental Science

Master of Science, The Ohio State University, 2024, Civil Engineering

Estuarine marshes occur at the interface of terrestrial riverine flows and oceans or lakes. As such, they play a crucial role in the movement, storage, and fluxes to the atmosphere, of carbon. We monitored CH4 fluxes, and the concentration of dissolved organic carbon (DOC) in the Old Woman Creek (OWC) estuary, Ohio. Gas exchange chamber measurements and sampling of surface water for DOC concentration were conducted simultaneously at three locations with distinct hydraulic characteristics: the outflow, mid-flow, and backflow areas, and at three different relative depths (deep, intermediate, and shallow) within each location. Samples were conducted monthly, over the summer and autumn of 2023 (i.e., month 1 to month last). We investigated the temporal and spatial correlation between DOC and CH4 fluxes in OWC, with a focus on the inflow dynamics from nearby rivers and the wetland's hydrological regime. We hypothesized that the high CH4 flux levels observed in OWC are driven by the wetland's intake of DOC, and short-term depth changes (due to barrier opening and closing) and long-term depth changes (due to changes in water levels and inundation) influences methane emissions. We found that DOC in the wetland's inflow positively correlates with the river stage, but contrary to our initial hypothesis, elevated DOC levels within the wetland did not significantly contribute to methane emissions. However, we found that DOC concentrations varied by depth, but not temporally when other factors (temperature, depth, river stage) were considered. Spatially, the outflow area had the highest DOC concentration, with deep depths in each hydrological location exhibiting higher DOC concentrations. CH4 fluxes varied spatially, with the outflow area recording the least methane emissions, while the mid-flow area exhibited higher methane concentrations. Intermediate depths in each hydrological location recorded higher methane emissions. Interestingly, we found that long-term trends of CH4 fl (open full item for complete abstract)

Committee: Gil Bohrer (Advisor); Andy May (Committee Member); James Stagge (Committee Member) Subjects: Atmospheric Sciences; Biogeochemistry; Climate Change; Environmental Engineering; Environmental Science; Freshwater Ecology

Doctor of Philosophy, The Ohio State University, 2024, Civil Engineering

Earth System Models (ESMs) are common tools for simulating mass and energy exchange between the surface and the atmosphere, thus constituting an important component of climate studies that set the necessary scientific background for future decision-making. Wetlands are the highest biogenic emitters of methane flux globally, where this latter is the second most important greenhouse gas after carbon dioxide, with raising concerns of rapidly increasing methane concentration in the atmosphere. Wetlands ecosystems have been represented in ESMs, although coupled with high uncertainties in their estimations of greenhouse gas emissions, as in these ecosystems small-scale spatial heterogeneities play a major role in resulting fluxes, where these fine scale heterogeneities are usually smaller than the model's grid resolution. In this study, we use the US DOE's Energy Exascale Earth System Model (E3SM) Land Model (ELM), and attempt to improve its representation of wetlands by adding one sub-grid layer within the wetland land-unit that allows the representation of within-wetland eco-hydrological patches, while resolving its effect on total carbon and methane fluxes. ELM-Wet, our developed version of ELM with a specific focus on wetlands, introduces a wetland-specific hydrology that could vary between plant functional types and presents a new diffusion model for plant-mediated transport of methane flux based on field observations of methane flux and soil concentrations. ELM-Wet is coupled with a recently developed method for classifying within-wetland eco-hydrological patches distribution using the Harmonized Landsat and Sentinel-2 (HLS) remote sensing product. HLS-based classification is used as input to provide ELM-Wet with necessary information about yearly vegetation cover. ELM-Wet is run and evaluated at two coastal wetlands in Louisiana that were extensively studied through chamber measurements of methane flux, methane soil concentration, and ecosystem-scale estimation of (open full item for complete abstract)

Committee: Gil Bohrer (Advisor); Matthew Sullivan (Committee Member); James Stagge (Committee Member); Andy May (Committee Member) Subjects: Biogeochemistry; Climate Change; Ecology; Environmental Engineering

PHD, Kent State University, 2023, College of Arts and Sciences / Department of Biological Sciences

Climate change is exerting profound and far-reaching impacts on ecosystems worldwide, encompassing both aquatic and terrestrial environments. The evolving precipitation patterns and shifting temperature regimes impact fluctuations in hydrology, resulting in shifts in redox conditions which can impact the availability of nutrients like phosphorus (P). Phosphate, the bioavailable form of P, is only present in small amounts within soils, making the biological demand greater than soil phosphate availability. The majority of soil P is present in non-labile forms including organic P and phosphate sorbed to metal oxides like iron (Fe). Microorganisms must content with geochemical and other abiotic factors to access phosphate from these non-labile sources through the use of various strategies including the secretion of enzymes, the production of phosphate solubilizing acids, as well as indirect mechanisms associated with the reduction of Fe oxides. The primary goal of this dissertation was to advance our understanding of how microorganisms access both labile and non-labile forms of P in the presence of changing hydrologic and redox conditions which impact the speciation of Fe that is present, altering phosphate availability. Specifically, I investigated 1) how phosphate availability changes across a permafrost thaw gradient (palsa, bog, and fen) in the presence of iron oxides, 2) how microorganisms access and mobilize chemically diverse phosphorus sources under contrasting redox conditions, and 3) how changes in hydrology, redox, iron mineralogy, and phosphate availability drive shifts in microbial community composition, specifically iron oxidizers, reducers, and phosphate solubilizers. In our first study assessing microbial phosphate accessibility across a permafrost thaw gradient, we found that near surface redox conditions changed as a function of permafrost thaw which impacted phosphate availability. Reducing conditions in the bog promoted the dissolution of Fe oxides, (open full item for complete abstract)

Committee: Lauren Kinsman-Costello (Advisor); Christie Bahlai (Committee Member); David Costello (Committee Member); Christopher Blackwood (Committee Member); Elizabeth Herndon (Committee Member); Timothy Gallagher (Committee Member) Subjects: Biogeochemistry; Climate Change; Ecology; Geobiology; Geochemistry; Microbiology; Mineralogy; Soil Sciences

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

Miscanthus x giganteus (miscanthus) is considered an ideal biomass energy crop because of its carbon (C) sequestration potential, water use efficiency, and low fertilizer requirements. Few US studies have measured long-term C sequestration of miscanthus on marginal lands on a decadal scale, and none have been conducted in southeast Ohio. The objective of this study was to measure the potential for C sequestration on abandoned agricultural land, the change in plant and soil nitrogen (N) over a decade, and the photosynthetic capacity in the tenth year of growth. The results revealed that after a decade, C was accumulated in the soil and the sequestration rates were estimated to be 0.20 Mg C ha-1y-1 and 0.54 Mg C ha-1y-1. However, the amount of C accumulated in the miscanthus plots were not statistically different from the adjacent unmanaged plots. There was also no statistically significant change in the amount of N in the baseline soils and after tillage and plowing when compared to the tenth year of growth. There was no statistically significant change in the amount of N found in plants over seven years, but variability in plant N was greater in some years relative to others. Even though the crop of miscanthus was grown without N fertilizers in this study, soil N at 0-30 cm depth was not depleted. There was no difference in plant C between sites, but the C concentration in stem tissue was statistically different over seven years. The photosynthetic capacity of miscanthus measured in this study indicated that the plants were thriving, and C assimilation for growth was consistent with the findings of prior work that evaluated the maximum photosynthetic rates of this species. The combination of soil C sequestration and sustained soil N over a ten-year period has important implications for the sustainability of biomass crops. Ultimately, this study addresses the net environmental benefit of using a perennial grass as a dedicated biomass crop on abandoned agricultural l (open full item for complete abstract)

Committee: Sarah Davis PhD (Committee Chair); Rebecca Snell PhD (Committee Member); Jared DeForest PhD (Committee Member) Subjects: Agriculture; Alternative Energy; Biogeochemistry; Climate Change; Ecology; Environmental Studies; Plant Biology; Soil Sciences; Sustainability

Master of Science, The Ohio State University, 2022, Earth Sciences

Agricultural headwater ditches and streams are frequently maintained by removing woody riparian vegetation, leading to seasonal growth of aquatic vegetation that influences the transport of water and nutrients from cropland to larger rivers. This study examined seasonal changes in the transport of phosphorus (P) in an agricultural drainage ditch in the Maumee River Basin (Ohio, USA) by conducting constant rate injections of a novel tracer mixture [conservative salt (Cl as NaCl), dissolved P (KH2PO4), and a fluorescent fine particle (Dayglo AX-11-5 Aurora Pink®)] in spring, summer, and fall as aquatic vegetation grew and decayed. I modeled retention and transport behavior for solutes and particles using a traditional transient storage approach consisting of mobile and immobile storage zones, connected by a first-order exchange rate constant. Transient storage of solutes and particles was greatest during the spring, when thicker vegetation stands caused more pooling and flow stagnation, while transient storage decreased through fall as reed grasses decayed and vegetation stands became thinner and smaller. Nutrient spiraling lengths were 8.7 times longer in fall than spring, likely due to declines in both biological uptake rates with fall senescence and transient storage in shrinking vegetation stands. With the increasing eutrophication of major waterbodies like Lake Erie and the Gulf of Mexico, it is crucial to better understand how nutrients move through agricultural headwater systems. This study highlights the physical and biological roles of aquatic vegetation in creating immobile zones that slow the downstream movement of nutrients, increasing the assimilation of dissolved nutrients, and filtering particle bound nutrients. Because these processes are seasonal, the relationships between travel times of soluble and particle-bound nutrients are also strongly seasonal, with the greatest disparity in travel times occurring in the spring, when nutrient export is typical (open full item for complete abstract)

Committee: Audrey Sawyer (Advisor); Gil Bohrer (Committee Member); James Hood (Committee Member) Subjects: Biogeochemistry; Hydrology

PHD, Kent State University, 2022, College of Arts and Sciences / Department of Biological Sciences

Plant-soil feedback, a phenomenon where plants alter their soil environment in ways that either hinder or bolster reproductive success and growth, can shape plant community composition and ecosystem function. Under negative feedback, plants induce the buildup of antagonistic soil microorganisms that reduce growth and increase mortality. This can prevent more competitive plant species from excluding less competitive community members, which promotes diversity and increases productivity. Under positive feedback, beneficial soil microorganisms that facilitate access to soil resources build up over time, increasing growth and the recruitment of progeny while lowering diversity and reducing productivity. These complex interactions between plants, their soil environment, and soil microorganisms have traditionally been studied with grass species in greenhouse environments. Due to this limited scope, there is a need to expand research into other systems such as temperate hardwood forests. In these ecosystems, trees form species-specific root symbioses with one of two distinct groups of soil fungi: arbuscular mycorrhizal (AM) fungi or ectomycorrhizal (ECM) fungi. Different tree species of each mycorrhizal type often share similar root and leaf litter traits that play direct roles in soil nutrient cycling (a.k.a., the “Mycorrhizal-Associated Nutrient Economy (MANE)” framework). Within this framework, AM tree species are hypothesized to generate rapid rates of nutrient cycling through their labile leaf litter and reliance on saprotrophic fungi for litter decomposition. Conversely, ECM tree species are hypothesized to slow nutrient cycling rates through recalcitrant leaf litter and competitive suppression of fungal saprotrophs. Given their effects on soil biogeochemistry, large individuals of either mycorrhizal type may influence the soil environment – and thus feedback potential – experienced by surrounding community members (coined “spillover effects”). However, interactions (open full item for complete abstract)

Committee: Christopher Blackwood (Advisor); David Ward (Committee Member); Andrea Case (Committee Member); Kurt Smemo (Committee Member); David Singer (Committee Member) Subjects: Biogeochemistry; Bioinformatics; Botany; Ecology; Environmental Science; Evolution and Development; Molecular Biology; Plant Biology; Plant Pathology; Plant Sciences; Soil Sciences

Master of Science (MS), Ohio University, 2022, Geological Sciences

Currently, there is a lack of quantification to the hydrogeologic sensitivities (groundwater level, soil textures, waters chemical condition, precipitation quantities, soil, and air temperature) that contribute to the fluctuating emissions from wetlands. Focusing on nitrous oxide (N2O) production rates within a palustrine groundwater-dependent ecosystem in Gunsan South Korea named Baeksukjae, a novel methodology has been applied to measure the emission rates of N2O and N2 gases from the field site. Five sampling sites were utilized where a total of 246 gas, 59 water, 38 soil, and 52 kinetic cell samples were collected. During sample collection, field parameters of pH, conductivity, dissolved oxygen, redox potential, soil, air temperature, and groundwater levels were measured daily over a 4-week field survey conducted in summer, 2021. Field data were then used within a denitrification and decomposition (DNDC) model for calibration. Water ion data at all sites reinforced several expected relationships such as the diminishment of nitrification during moments of high silicon concentration, increased delivery of alkaline earth metals during moments of higher acidity, and strong positive correlations between water electrical conductivity and alkalinity. Although the chemical diversity of water samples taken during the sampling stint are high, investigation revealed only a few significant parameters that vary NO2 emissions. Dramatic changes in water chemistry can be attributed to high precipitation events. Precipitation events diluted chemical constituents directly, as well as delivered nutrients to the wetland through runoff. Site mA consistently showed increases in nitrate (NO3-) concentrations (maximum values of 19.1 mg/L) in the groundwater and increased N2O gas production rates that mirror the frequency of precipitation and temperature variations. Analyzing kinetic cell data confirmed initial hypotheses that the production (open full item for complete abstract)

Committee: Eung Lee (Advisor); Dan Hembree (Committee Member); Katherine Fornash (Committee Member); Dan Hembree (Committee Member); Katherine Fornash (Committee Member) Subjects: Biogeochemistry; Chemistry; Climate Change; Geochemistry; Geological; Geology; Hydrology

Master of Science, Miami University, 2022, Biology

With ongoing anthropogenic N and P deposition worldwide, understanding the effects these added nutrients are having on nitrogen cycling in soils is necessary in anticipating changes in ecosystem functions such as nutrient availability, N sequestration and retention, CO2 emissions, and the movement of nutrients through soils. In northern hardwood forests, alleviating P limitation can increase tree growth and also decrease available N pools in soil. This study tested two alternate hypotheses: plant uptake of N increases with elevated P, and microbial and organic matter uptake of N increases with elevated P. Using a 15N tracer, the movement of N through the soil was quantified over one year under fertilization with N, P, N+P and a control. Both roots and microbes responded to N and P fertilization. Microbial N uptake increased in response to P addition in the short term, and over the next few weeks a combination of the two nutrients increased the rate of immobilization of N in roots and microbes. Forest floor organic matter was the greatest sink for N regardless of nutrient addition treatment and transfer to organic N was rapid.

Committee: Melany Fisk (Advisor); Michael Vanni (Committee Member); Jonathan Bauer (Committee Member) Subjects: Biogeochemistry; Biology; Ecology

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)

Committee: John Peck (Advisor); John Senko (Committee Member); Caleb Holyoke (Committee Member) Subjects: Biogeochemistry; Environmental Geology; Environmental Science; Geochemistry; Geology; Hydrology; Limnology; Sedimentary Geology