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)

Committee: Michael Wilkins (Advisor); Steven Lower (Advisor); Audrey Sawyer (Committee Member); Elizabeth Griffith (Committee Member) Subjects: Biogeochemistry; Earth; Ecology; Environmental Geology; Environmental Science; Geobiology; Geochemistry; Geology; Hydrology; Limnology; Microbiology; Mineralogy

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

The Theis Environmental Monitoring and Modeling Site is a field research facility, located on the Great Miami River in southwest Ohio, dedicated to the study of hyporheic zone processes. The site is underlain by an aquifer on the order of 21 meters thick, comprised of fluvial deposits. The permeability of the aquifer sediments was quantified both from one large scale hydraulic test (~100 m radial distance) and from grain-size analysis of 119 small-scale core samples (~20 cm length each). The permeability determined from the large-scale hydraulic test is 98.9 Darcies. The test also gave a value for specific yield of 0.25. The geometric mean of the small-scale measurements is 88.3 Darcies, close to the value of the large-scale measurement, and within the central tendency of the distribution of previously published measurements. The aquifer contains an inferred hierarchy of sedimentary architecture, with compound bar deposits comprising unit bar deposits, and unit bar deposits comprising stratasets with different grain-size facies, including sand, gravelly sand, sandy gravel, and gravel. The stratasets are less than a meter thick and less than 10 meters in length. Intervals of sand facies make up 18.5% of the aquifer, have a mean thickness of 0.75 m (standard deviation (σ) of 0.37 m), a mean permeability of 86.8 Darcies (σ of 47.8 Darcies), and a mean porosity of 36% (σ of 4%). Intervals of gravelly sand facies make up 25.2% of the aquifer, have a mean thickness of 0.96 m (σ of 0.46 m), and a mean permeability of 73 Darcies (σ of 49.9 Darcies), and a mean porosity of 28% (σ of 3%). Intervals of sandy gravel facies make up 36.1% of the aquifer, have a mean thickness of 1.00 m (σ of 0.79 m), and a mean permeability of 84.9 Darcies (σ of 49.7 Darcies), and a mean porosity of 25% (σ of 3%). Intervals of gravel facies make up 20.2% of the aquifer, have a mean thickness of 1.10 m (σ of 0.74 m), and a mean permeability of 670 Darcies (σ of 1170 Darcies), and a me (open full item for complete abstract)

Committee: Robert W. Ritzi Jr., Ph.D. (Committee Chair); David A. Schmidt Ph.D. (Committee Member); David F. Dominic Ph.D. (Committee Member) Subjects: Geological; Geology; Hydrologic Sciences; Hydrology

Master of Science, The Ohio State University, 2015, Earth Sciences

Hydraulic conductivity (K) heterogeneity and channel morphology both control surface water-groundwater exchange (hyporheic exchange), which influences stream ecosystem processes and biogeochemical cycles. Here I show that K heterogeneity is the dominant control on exchange rates, residence times, and patterns in hyporheic zones with sharp lithologic contrasts. I simulated hyporheic exchange in a representative low-gradient stream with 300 different bimodal K fields composed of sand and silt. K realizations span five sets of sand-silt ratios and two sets of low and high K contrasts (one and three orders of magnitude). K heterogeneity increases interfacial fluxes by orders of magnitude relative to homogeneous cases, drastically changes the shape of residence time distributions, and decreases median residence times. The positioning of highly permeable sand bodies controls patterns of interfacial flux and flow paths. These results are remarkably different from previous studies of smooth, continuous K fields that indicate only moderate effects on hyporheic exchange. The results also show that hyporheic residence times are least predictable when sand body connectivity is low. As sand body connectivity increases, the expected residence time distribution (ensemble average for a given sand-silt ratio) remains approximately constant, but the uncertainty around the expectation decreases. Including strong heterogeneity in hyporheic models is imperative for understanding hyporheic fluxes and solute transport. In streams with bimodal sediments, characterizing stark facies contrasts is more critical for predicting hyporheic exchange metrics than characterizing channel morphology.

Committee: Audrey Sawyer Dr. (Advisor); Michael Wilkins Dr. (Committee Member); Franklin Schwartz Dr. (Committee Member) Subjects: Geology; Hydrology

PhD, University of Cincinnati, 2024, Arts and Sciences: Geology

Per- and polyfluoroalkyl substances (PFAS) contamination presents one of the most pressing environmental challenges that humanity will face in the coming years to decades. PFAS have emerged as significant environmental pollutants due to their extreme persistence, global distribution, ability to bioaccumulate and bioconcentrate, as well as potential adverse impacts on human and ecosystem health. These compounds, characterized by their environmentally stable carbon-fluorine bonds, are resistant to natural degradation processes leading to their accumulation in various environmental matrices. The complexities inherent in the fate and transport of PFAS in subsurface environments pose substantial challenges for environmental management and remediation efforts. To effectively address these contaminants, a detailed understanding of their behavior in different geological settings is essential, particularly given their ability to migrate through and impact groundwater quality. This dissertation addresses the urgent need for comprehensive insights into PFAS dynamics by utilizing a multidisciplinary approach to study their fate and transport in subsurface systems. The research encompasses an extensive review of existing literature to frame the current understanding and gaps in PFAS environmental science. Building on this foundation, the study employs advanced numerical modeling techniques to simulate PFAS behavior in variably saturated heterogeneous sedimentary environments. Batch sorption experiments were also conducted to assess the sorption characteristics of PFAS on various sediment types, examining factors such as organic carbon content, mineral composition, and the chemical properties of the contaminants. Additionally, field geophysical measurements were coupled with a variety of field and laboratory analyses to elucidate the impacts of heterogeneity on groundwater-surface water interactions. Perhaps the most significant contribution of this body of work is the cor (open full item for complete abstract)

Committee: Reza Soltanian Ph.D. (Committee Chair); Daniel Sturmer Ph.D. (Committee Member); Robert Ford Ph.D M.A B.A. (Committee Member); Drew McAvoy Ph.D. (Committee Member); Dylan Ward Ph.D. (Committee Member) Subjects: Geology

Master of Science, The Ohio State University, 2021, Earth Sciences

Log jams are natural features in mountain streams that promote stream-groundwater interactions, or hyporheic exchange, through a variety of mechanisms. Log jams alter gradients in hydraulic head, increase the area available for exchange by creating backwater areas, and lead to the formation of branching channels and bars that drive additional exchange. Here, I numerically simulated stream-groundwater interactions for two constructed flume systems—one without jams and one with a series of three jams—to understand the effects of interacting jam and channel structures on hyporheic exchange. Jams increased stream-groundwater connectivity, or decreased the turnover length that stream water travels before it enters the hyporheic zone, by an order of magnitude and drove long flow paths that connected multiple jams and channel threads. The increased turnover of stream water through the bed was due mainly to the increase in the average hyporheic exchange rate, though the wetted surface area available for exchange also increased slightly. Jams with larger volumes had longer hyporheic residence times and path lengths that exhibited multiple scales of exchange. Additionally, the longest flow paths connecting multiple jams occurred in the reach with multiple channel branches. These findings suggest that large gains in hydrologic connectivity can be achieved by promoting in-stream wood accumulation and the natural formation of both jams and branching channels.

Committee: Audrey Sawyer (Advisor); Michael Durand (Committee Member); Joachim Moortgat (Committee Member) Subjects: Geomorphology; Hydrologic Sciences; Hydrology

MS, University of Cincinnati, 2021, Arts and Sciences: Geology

Interactions between surface water and groundwater (hyporheic exchange) influence water quality and control numerous physical, chemical, and biological processes. Despite its importance, hyporheic exchange and the associated dynamics of solute mixing are often difficult to characterize due to spatial (e.g., sedimentary heterogeneity) and temporal (e.g., river stage fluctuation) variabilities. This study coupled geophysical techniques with physical and chemical sediment analyses to quantify hyporheic exchange dynamics in a compound bar deposit within a gravel-dominated river system in southwestern Ohio. Electromagnetic induction (EMI) was used to quantify variability in electrical conductivity within the compound bar. A zone of high electrical conductivity was clearly identified as a fine-grained cross-bar channel fill. Differences in the physical and geochemical characteristics of such channel fills play an important role in hyporheic flow dynamics and nutrient processing. EMI informed locations of electrode placement for time-lapse electrical resistivity imaging surveys to examine changes in electrical resistivity driven by hyporheic exchange, revealing preferential flow paths through high-permeability sediments. Grain size analyses confirmed interpretations of geophysical data, and loss on ignition and x-ray fluorescence identified more favorable locations for enhanced geochemical and microbial activity as cross-bar channel fills identified through EMI measurements. These findings provide fundamental insights into hyporheic exchange, and the technical framework presented in this study has implications for improving future studies of hyporheic dynamics and numerical model development through more accurate representation of geomorphologic features and sediment heterogeneity.

Committee: Reza Soltanian Ph.D. (Committee Chair); Dimitrios Ntarlagiannis Ph.D. (Committee Member); Daniel Sturmer Ph.D. (Committee Member); Corey Wallace Ph.D. (Committee Member) Subjects: Geology

Doctor of Philosophy, The Ohio State University, 2019, Earth Sciences

In coastal rivers, tidal changes in streamflow and water table elevation influence river-groundwater exchange (hyporheic exchange), with important consequences for nitrogen transport and water chemistry. Excess nitrate, one of the most bioavailable forms of nitrogen, can have adverse environmental effects on surface waters and disrupt coastal ecosystems. Here, I use field observations and numerical models to quantify how hyporheic exchange and nitrogen transport in tidal rivers vary with river stage fluctuations and sediment properties. Using spectral analyses in the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA), I link continuous redox measurements to hydrologic perturbations within the streambed and banks. Redox potential indicates the energetic favorability of reactions such as nitrification and denitrification, which in tidal systems are strongly coupled near the fluctuating water table. Storms perturb redox potential within both the bed and banks over timescales of days to weeks, while tides drive semi-diurnal oscillations in redox potential within the streambed. Tidal redox oscillations are greatest during the late summer when river stage fluctuations are large and microbial activity is likely high. Using numerical models, I next demonstrate that nitrate removal capacity initially increases towards the coast with increasing tidal range but then declines as sediment grain size and permeability decrease, which limits the supply of nitrate to the riparian aquifer. Nitrification is a significant source of nitrate to the variably-saturated zone, but new nitrate produced by nitrification within the shallow stream bank is removed via denitrification before discharge to the river. Nitrate is also removed from groundwater sources, but little nitrate is removed from surface water. Heterogeneity in permeability and organic matter influences the distribution of reactants and transport rates. Nitrification is more efficient along high permeability sand pa (open full item for complete abstract)

Committee: Audrey Sawyer (Advisor); Thomas Darrah (Committee Member); Michael Durand (Committee Member); Rachel Gabor (Committee Member) Subjects: Geochemistry; Geology; Hydrology

Master of Science, The Ohio State University, 2019, Earth Sciences

The hyporheic zone, where surface water and groundwater mix, is an important microbial habitat where biogeochemical reactions influence water quality. I show that spatial variability in hyporheic flow in the East River near Crested Butte, CO, drives heterogeneity in streambed geochemical conditions and microbial community assemblages, but the diversity of assemblages remains nearly constant throughout the reach. In July-August 2018, I collected approximately 100 pore water samples at 20 cm depth and analyzed them for anions, cations, dissolved organic carbon, dissolved organic matter (DOM) quality, and standard water quality parameters. Vertical hydraulic head gradients were also measured to assess the potential for upward or downward water flow. I found that regions of the streambed that are more groundwater-dominated contain less dissolved oxygen, higher concentrations of reduced metals, and more microbially-processed, recalcitrant DOM, while more surface water-dominated locations contain higher dissolved oxygen concentrations and terrestrially-derived, labile DOM. 16S rRNA gene sequencing of extracted DNA revealed that microbial community composition varies with geochemical conditions related to hyporheic flow. These findings provide a better understanding of hyporheic controls on streambed biogeochemistry during the base flow season, which is expected to lengthen with climate change in alpine watersheds due to earlier snowmelt onset and reduced snowpack

Committee: Audrey Sawyer (Advisor); David Cole (Committee Member); Rachel Gabor (Committee Member) Subjects: Biogeochemistry; Geology; Geomorphology; Hydrology; Microbiology

Master of Science, The Ohio State University, 2019, Earth Sciences

Manganese (Mn) plays a critical role in river water quality since Mn-oxides serve as sorption sites for contaminant metals such as copper, zinc, and lead. Here, I measure and model annual changes in river water-groundwater interaction and Mn(aq) transport in an alpine streambed influenced by spring snowmelt (East River, Colorado). In field observations and models, oxygenated river water containing dissolved organic carbon (DOC) mixes with groundwater rich in reduced manganese in the riverbed. The depth of mixing is greatest during spring snowmelt when river discharge is greatest, leading to an influx of DOC, dilution of Mn(aq), and net respiration of Mn-oxides, despite an enhanced supply of oxygen. Conversely, a shift to upwelling conditions over the subsequent baseflow period allows for groundwater rich in Mn(aq) to mix with oxygenated river water in the shallow subsurface, resulting in net accumulation of Mn-oxides until the bed freezes in winter. To explore potential responses of Mn transport to different climate-induced hydrological regimes, I model three hydrograph scenarios (Historic, Low-snow, and Storm) for the Rocky Mountain region. In a warming climate with less snowpack and a longer baseflow season, Mn(aq) oxidation will be favored in the upper riverbed sediments over more of the year, which may increase the sorption capacity of the streambed for other metals.

Committee: Audrey Sawyer (Advisor); Elizabeth Griffith (Committee Member); Allison MacKay (Committee Member) Subjects: Biogeochemistry; Environmental Science; Hydrologic Sciences

MS, Kent State University, 2016, College of Arts and Sciences / Department of Earth Sciences

Hundreds of streams in the eastern US are impaired by acid mine drainage (AMD) due to historical coal mining. Remediation efforts usually focus on stopping AMD from reaching the stream but the accumulation of AMD precipitates on the streambed may prevent the overall ecological health of the area from rebounding even after extensive off-channel efforts. Dredging the AMD deposits has been proposed as a way to improve stream health, but the efficacy of doing so while preventing further iron buildup and the potential release of trace metals during such an operation is uncertain. Huff Run in Mineral City, Ohio, is one stream heavily affected by AMD, where a watershed restoration group has made progress remediating surface water contributions to the stream and dredging is being considered as a next step. Two areas were studied within the Huff Run: (1) the Farr Tributary, an impacted tributary that is actively transporting AMD into the Huff Run, and (2) a section of Huff Run where a debris dam is present. Sediments from beneath these two areas show large differences in mineralogy and pH. Sediment cores from the Farr Tributary presents a mineralogy dominated by iron oxides, goethite, with notable amounts of quartz and minor amounts of magnetite, jarosite, kaolinite and illite. The pH in this area is also acidic, ranging from 3.6 to 5.32. The dam section contains mainly quartz with minor concentrations of goethite, kaolinite and illite and contains neutral pH values, ranging from 6.2 to 7.34. 2 Despite geochemical variations both areas contain the geomorphological features that should promote hyporheic exchange, including step-pool sequences in the tributary and the debris dam in the Huff Run. Around these features downwelling and upwelling were observed. Finally, hydraulic conductivity was generally in the range of silty sands, with averages in the tributary and the dam section of 5.6 x 10-6 and 3.85 x 10-5 m s-1 . The combination of mineralogical (open full item for complete abstract)

Committee: David Singer PhD (Advisor); Anne Jefferson PhD (Advisor); Elizabeth Herndon PhD (Committee Member) Subjects: Geochemistry; Geology; Hydrology

Master of Science, The Ohio State University, 2016, Earth Sciences

In coastal rivers, tidal pumping enhances the exchange of oxygen-rich river water across sediment-water interfaces, controlling nitrogen cycling in suboxic riverbed sediments. I developed a one-dimensional, coupled fluid flow and solute transport model that quantifies the influence of tidal pumping on redox zonation and nitrate removal in the hyporheic zones of coastal rivers, and applied it to the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA). At high tide when oxygen-rich river water infiltrates into the bed, denitrification rates decrease by ~20% relative to low tide when nitrate-rich anoxic groundwater discharges to the channel. Tidal pumping deepens the aerobic zone by a factor of 6, decreasing denitrification rates by 10%. Therefore, along TFZs nitrate removal rates decrease as tidal amplitude increases due to enhanced oxygen exchange across the sediment-water interface. Sensitivity analyses suggest that denitrification hot spots in TFZs will occur in less permeable, organic-rich sediment under lower tidal ranges and higher rates of ambient groundwater discharge. Tidal pumping is not efficient at removing surface water nitrate but removes up to 81% of groundwater nitrate that would discharge to White Clay Creek. Given the high population densities of coastal watersheds and thus the tendency towards high nitrate inputs from groundwater to rivers, the hyporheic zones of TFZs play a critical role in mitigating new nitrogen loads to coasts.

Committee: Audrey Sawyer PhD (Advisor); William Lyons PhD (Committee Member); Joachim Moortgat PhD (Committee Member) Subjects: Earth; Environmental Geology; Geology; Hydrology

Doctor of Philosophy, The Ohio State University, 2013, Geological Sciences

My dissertation research utilizes stable isotopes as tracers of water and solute sources to study specific geochemical (solute origin) and hydrological (glacier meltwater source across a season comparing water contributions from hyporheic zone and/or glacier melt and residence time of precipitation within a managed water supply) problems within McMurdo Dry Valleys (MCM), Antarctica, and Central Ohio, USA. In Chapter II, δ11B isotopic and dissolved B measurements are used to infer the origin of B within MCM aquatic system. Boron stable isotopic values span the range of +12.3‰ to +51.4‰, varying from glacier meltwater streams to the hypolimnion of a highly evaporated hypersaline lake. These data demonstrate that the major sources of B are chemical weathering of alumniosilicates within the stream channels, and a marine source, either currently introduced by marine-derived aerosols or from ancient seawater. In-lake processes create a more positive δ11B through adsorption or mineral precipitation. The glacier meltwater streams, Lakes Fryxell, Hoare, and upper waters of Lake Joyce display a mixture of these two sources, with Lake Joyce bottom waters primarily of marine origin. Lakes Bonney and Vanda and Blood Falls brine are interpreted as having a marine-like source changed by in-lake processes to result in a more positive δ11B, while Don Juan Pond displays a more terrestrial influence. In Chapter III, δ18O and δD are used to trace water source variation via hyporheic zone or glacier melt within two MCM streams over an entire melt season. The isotopic variation of these streams was more negative at the beginning of the season and more positive later. D-excess measurements were used to infer mixing between hyporheic storage and glacier meltwater. It was supported that Von Guerard Stream has a large, widespread hyporheic zone that changes with time and discharge amounts. The chemistry of Andersen Creek also displayed hyporheic zone influence at certain times of (open full item for complete abstract)

Committee: William Berry Lyons (Advisor); Anne E. Carey (Committee Member); Bryan G. Mark (Committee Member); John Olesik (Committee Member) Subjects: Environmental Geology; Environmental Science; Geochemistry; Geology; Hydrologic Sciences

Master of Science (MS), Wright State University, 2012, Earth and Environmental Sciences

Subsurface heat flow was simulated to study the effect of hyporheic exchange on groundwater intake temperatures of open-loop geothermal wells in glacigenic-outwash aquifers in the North American midcontinent. The model represents an aquifer kilometers wide, on the order of 100m thick, and directly connected to a perennial river. The aquifer has bimodal hydraulic conductivity with a geometric mean on the order of 100m/day, an effective thermal conductivity of 2.33W/mK, and specific heats on the order of 106J/(m^3 K) for water and 103J/kgK for solids. The aquifer is initially set to a temperature of 12.85 ¿¿¿¿C and the river is fixed to 26.85 ¿¿¿¿C. Results show that the ambient zone of hyporheic thermal influence spans the entire depth of the aquifer and extends laterally for approximately a half a kilometer from the river. Temperatures within this zone decrease, as a linear approximation, at about 1 ¿¿¿¿C per 50 m distance from the river. Aquifer heterogeneity strongly influences the extent of and the temperatures within the hyporheic zone. A well pumping at 500 m^3/day had intake temperatures as much as 2¿¿¿¿C greater than ambient levels and, depending on location, slightly extended the range of the river's thermal influence. However, this increase of intake temperature was not instantaneous, drifting upward on the order of 1 ¿¿¿¿C per century before achieving thermal equilibrium. A realistic distribution of 25 wells pumping at variable rates extended the range of thermal influence to a kilometer, produced intake temperatures as much as 16 ¿¿¿¿C greater than ambient levels, and increased spatial variability in aquifer temperatures.

Committee: Robert Ritzi PhD (Committee Chair); David Dominic PhD (Committee Member); Chris Barton PhD (Committee Member) Subjects: Environmental Engineering; Environmental Geology; Environmental Management; Environmental Science; Environmental Studies; Hydrologic Sciences; Hydrology

Master of Science (MS), Wright State University, 2012, Earth and Environmental Sciences

Hyporheic exchange can be influenced by channel meanders, by streambed topography, and by the heterogeneity within subsurface sediments. Fluvial systems with streambed sediments composed of sandy gravel can be heterogeneous and contain open-framework gravel stratasets that comprise roughly one-third of the sedimentary deposit by volume. The open-framework gravel stratasets have an average lateral length scale on the order of 10 m, average thickness on the order of a decimeter, and an average dip on the order of 10 degrees downstream. The hydraulic conductivity of open-framework gravel stratasets is on the order of 10-1 m/s, and for the larger volume of sandy gravel it is on the order of 10-3 m/s. Connected open-framework gravel stratasets form tortuous higher-permeability pathways throughout the sub-streambed sediment. The results of modeling show that the heterogeneity within the sub-streambed sediment influences the location and magnitude of the interfacial flow (flow across the streambed) more than the effect of meanders, and more than the effect of streambed topography. The heterogeneity gives rise to regions of positive and negative interfacial flow (flow over areas on the order of 50 m by 50 m) scattered across the streambed surface, which are not present in an equivalent but homogeneous system. The heterogeneity also gives rise to interfacial fluxes that are more than an order of magnitude higher than would occur in an equivalent but homogeneous system. These highest-magnitude interfacial flows are typically found at the location of connected open-framework gravel.

Committee: Robert W. Ritzi PhD (Advisor); Dominic F. David PhD (Committee Member); Mark N. Goltz PhD (Committee Member) Subjects: Environmental Science; Geology; Hydrologic Sciences; Hydrology

MS, University of Cincinnati, 2010, Engineering and Applied Science: Environmental Engineering

Excess nitrogen in rivers and lakes is a well known problem which leads to eutrophication and can leave water bodies neither aesthetically pleasing nor a healthy ecosystem. 95% of all stream miles in the United States are small streams, and they have a significant capability to prevent excess anthropogenic nitrogen from reaching larger, impaired bodies. Instead of modifying natural streams to test engineering solutions and toxicity of pollutant loads, stream mesocosms and computer models have been used to analyze the processes of natural streams. A computer model was developed using nutrient data obtained from a stream mesocosm at the USEPA's Experimental Stream Facility (ESF) in Milford, OH to examine the processing of nitrogen by the stream mesocosm, and by extension, natural streams. The model showed that, for the ESF mesocosms, sediment, temperature, and light are very important factors in determining how much nitrogen is either stored or passed on to receiving bodies.

Committee: Paul Bishop PhD (Committee Chair); Margaret Kupferle PhD, PE (Committee Member); Christopher Nietch PhD (Committee Member) Subjects: Environmental Engineering