Dissolved organic matter (DOM) is comprised of a complex array of molecular constituents that are linked to many globally-relevant processes and yet this material is still largely molecularly uncharacterized. Research presented here attempted to probe the molecular complexity of this material from both Arctic and temperate climates via multifaceted and novel approaches. DOM collected from remote Arctic watersheds provided evidence to suggest that permafrost-disturbed systems contain more photochemically- and biologically-labile material than undisturbed systems. These results have large implications for predicted increasing temperatures where widespread permafrost melt would significantly impact stores of organic carbon in polar environments. In attempting to address the complexities and reactivity of DOM within global environments, more information at the molecular-level is necessary. Further research sought to unravel the molecularly uncharacterized fraction via use of nuclear magnetic resonance (NMR) spectroscopy in conjunction with hyphenated and varied analytical techniques. Directly hyphenated high performance size exclusion chromatography (HPSEC) with NMR was explored. This hyphenation was found to separate DOM into structurally distinct fractions but proved limited at reducing DOM heterogeneity. Of the many high performance liquid chromatography (HPLC) techniques tested, hydrophilic interaction chromatography (HILIC) was found the most effective at simplifying DOM. HILIC separations utilizing a sample from Florida resulted in fractions with highly resolved NMR signals and substantial reduction in heterogeneity. Further development with a 2D-HILIC/HILIC system to achieve additional fractionation was employed. This method produced fractions of DOM that were homogenous enough to produce excellent resolution and spectral dispersion, permitting 2D and 3D NMR experiments to be performed. Extensive NMR analyses of these fractions demonstrated strong evidence for the presence of highly oxidized sterols. All fractions, however, provided 2D NMR spectra consistent with oxidized polycyclic structures and support emerging data and hypotheses suggesting that cyclic structures, likely derived from terpenoids, are an abundant, refractory and major component of DOM. Research presented within this thesis demonstrates that HILIC and NMR are excellent co-techniques for the analysis of DOM as well as that oxidized sterols and other cyclic components with significant hydroxyl and carboxyl substituents are major constituents in DOM.

Arctic regions are expected to be highly sensitive to climate change regarding the prediction of disproportionately large increases in surface temperatures and their related influence over the hydrological cycle and permafrost thaw. These modifications have the potential to impact biogeochemical cycles in these regions and in particular the mobilization of organic carbon into rivers. The most crucial period in arctic rivers hydrological cycle is the spring freshet that can account for most of the annual organic carbon transfers to the ocean in a very short window of time. The focus of this thesis was to monitor the dynamic of DOM in terms of quantity and quality along the hydrological cycle of the Yenisei river, through DOM characterization approaches to reveal seasonal variations in its composition, sources, age and degradation state. The first step was to make a review of the full range of existing DOM characterization approaches in worldwide river systems to identify the most widely used, the most relevant and reliable ones. Through the development of a DOM quality measurements database, we have been able to evaluate the geographical coverage of DOM characterization studies, to give estimates and ranges of values of the main reported DOM characterization variables and to observe global trends of DOM quality across latitudinal gradient. Second stage was to investigate DOC dynamic in the Yenisei river with regard to quantity and links with water chemistry and hydrology. We conducted sampling campaigns during three consecutive years (2014 to 2016), covering with a high sampling frequency the spring flood period to capture its very dynamic evolution. We reported DOC concentrations that followed the hydrograph with highest concentrations observed a few days before peak discharge. DOC concentration also responded to discharge variation (increase, likely due to higher precipitation) in early autumn. We reported average DOC flux over the three sampling years of about 4.53 Tg yr-1 which is within the range of values reported in the literature. We observed interannual variability with annual export estimates ranging from 5.45 Tg yr-1 in 2014 to 3.57 Tg yr-1 in 2016, likely driven by discharge amplitude. We confirmed the important role of spring freshet in DOC export with on average more than 65% occurring during this period (roughly May/June). Third point was to determine DOM quality combining characterization techniques. Combination of approaches helped to strengthen observations and cross validate interpretations. Most of the variables reported from the different characterization techniques confirmed one each other. The use of lignin biomarkers, optical properties and radiocarbon age of DOM allowed us to trace DOM main sources has primarily deriving from recently produced organic matter leached from boreal forest litter and top soil horizon during the spring flood and older organic matter derived from deeper soil horizons during low flow period.

abstract: The focus of this thesis is to study dissolved organic carbon composition and reactivity along the Colorado and Green Rivers. Dissolved organic carbon (DOC) in large-scale, managed rivers is relatively poorly studied as most literature has focused on pristine unmanaged rivers. The Colorado River System is the 7th largest in the North America; there are seventeen large dams along the Colorado and Green River. DOC in rivers and in the lakes formed by dams (reservoirs) undergo photo-chemical and bio-degradation. DOC concentration and composition in these systems were investigated using bulk concentration, optical properties, and fluorescence spectroscopy. The riverine DOC concentration decreased from upstream to downstream but there was no change in the specific ultraviolet absorbance at 254 nm (SUVA254). Total fluorescence also decreased along the river. In general, the fluorescence index (FI) increased slightly, the humification index (HIX) decreased, and the freshness index (β/α) increased from upstream to downstream. Photo-oxidation and biodegradation experiments were used to determine if the observed changes in DOC composition along the river could be driven by these biogeochemical alteration processes. In two-week natural sunlight photo-oxidation experiments the DOC concentration did not change, while the SUVA254 and TF decreased. In addition, the FI and ‘freshness’ increased and HIX decreased during photo-oxidation. Photo-oxidation can explain the upstream to downstream trends for TF, FI, HIX, and freshness observed in river water. Serial photo-oxidation and biodegradation experiments were performed on water collected from three sites along the Colorado River. Bulk DOC concentration in all samples decreased during the biodegradation portion of the study, but DOC bioavailability was lower in samples that were photo-oxidized prior to the bioavailability study. The upstream to downstream trends in DOC concentration and composition along the river can be explained by a combination of photo-chemical and microbial degradation. The bulk DOC concentration change is primarily driven by microbial degradation, while the changes in the composition of the fluorescent DOC are driven by photo-oxidation. / Dissertation/Thesis / Masters Thesis Chemistry 2015

abstract: The influence of climate variability and reclaimed wastewater on the water supply necessitates improved understanding of the treatability of trace and bulk organic matter. Dissolved organic matter (DOM) mobilized during extreme weather events and in treated wastewater includes natural organic matter (NOM), contaminants of emerging concern (CECs), and microbial extracellular polymeric substances (EPS). The goal of my dissertation was to quantify the impacts of extreme weather events on DOM in surface water and downstream treatment processes, and to improve membrane filtration efficiency and CECs oxidation efficiency during water reclamation with ozone. Surface water quality, air quality and hydrologic flow rate data were used to quantify changes in DOM and turbidity following dust storms, flooding, or runoff from wildfire burn areas in central Arizona. The subsequent impacts to treatment processes and public perception of water quality were also discussed. Findings showed a correlation between dust storm events and change in surface water turbidity (R2=0.6), attenuation of increased DOM through reservoir systems, a 30-40% increase in organic carbon and a 120-600% increase in turbidity following severe flooding, and differing impacts of upland and lowland wildfires. The use of ozone to reduce membrane fouling caused by vesicles (a subcomponent of EPS) and oxidize CECs through increased hydroxyl radical (HO●) production was investigated. An "ozone dose threshold" was observed above which addition of hydrogen peroxide increased HO● production; indicating the presence of ambient promoters in wastewater. Ozonation of CECs in secondary effluent over titanium dioxide or activated carbon did not increase radial production. Vesicles fouled ultrafiltration membranes faster (20 times greater flux decline) than polysaccharides, fatty acids, or NOM. Based upon the estimated carbon distribution of secondary effluent, vesicles could be responsible for 20-60% of fouling during ultrafiltration and may play a vital role in other environmental processes as well. Ozone reduced vesicle-caused membrane fouling that, in conjunction with the presence of ambient promoters, helps to explain why low ozone dosages improve membrane flux during full-scale water reclamation. / Dissertation/Thesis / Ph.D. Civil and Environmental Engineering 2014

The majority of lakes on Earth are shallow, unproductive and located at high latitudes. These lakes are experiencing big changes due to climate change, where two environmental drivers operate simultaneously, browning and warming. How they affect lake ecosystems is not well understood. Here, I addressed this issue by using a theoretical and an experimental approach. In particular, I generated model predictions and compared them with the results of a realistic large-scale experiment, where browning and warming were manipulated in a factorial design. In addition, model outcomes were compared with data from 12 unproductive lakes sampled along a gradient of browning. Another novelty of my thesis is that it integrates benthic and pelagic food web components in the model and experimental approaches. I found that browning affected the resources availability for benthic and pelagic producers in the model and in the experiment. With browning, benthic primary producers became increasingly light limited and declined, while pelagic producers became less nutrient limited and increased. Pelagic nutrient limitation was alleviated by two non-exclusive mechanisms. Browning directly enriched the water with nutrients, and browning indirectly increased the nutrient flowing from the sediment to the pelagic habitat via suppression of benthic producers. To tease apart these two mechanisms I applied structural equation modeling (SEM). The indirect evidence by SEM suggests that both mechanisms contributed equally to the pelagic nutrient concentration in the experiment. Interestingly, a model food web with only primary producers shows similar qualitative behavior as a food web with grazers and carnivores included. This happens because carnivorous fish exert strong top-down control in the more productive habitat, which relaxes grazing pressure on primary producers and increases resource limitation in the adjacent habitat. Biomass of benthic and pelagic consumers followed the same pattern as their resources. The lake data were largely congruent with model expectations and supported the findings of the experiment. Furthermore, the model also predicted a negative relationship between total phosphorus and both primary and fish production, which was observed across the 12 lakes. Warming effects were more complex. The model predicts that warming effects should depend on browning and are expected to be strongest in the more productive of the two (benthic and pelagic) habitats. For example, at low levels of browning the biomasses of benthic algae and fish are expected to decline with warming, which was observed in the experiment. In contrast, observed warming effects at high levels of browning deviated from model expectations. The mechanisms by which browning and warming interactively affect lake food webs are still poorly understood. This thesis offers a conceptual foundation for their further study through the integration of within- and between-habitat interactions.

Dissolved organic matter (DOM) is one of the largest carbon reservoirs on this planet and is present in aquatic environments as a highly complex mixture of organic compounds. The Florida coastal Everglades (FCE) is one of the largest wetlands in the world. DOM in this system is an important biogeochemical component as most of the nitrogen (N) and phosphorous (P) are in organic forms. Achieving a better understanding of DOM dynamics in large coastal wetlands is critical, and a particularly important issue in the context of Everglades restoration. In this work, the environmental dynamics of surface water DOM on spatial and temporal scales was investigated. In addition, photo- and bio-reactivity of this DOM was determined, surface-to-groundwater exchange of DOM was investigated, and the size distribution of freshwater DOM in Everglades was assessed. The data show that DOM dynamics in this ecosystem are controlled by both hydrological and ecological drivers and are clearly different on spatial scales and variable seasonally. The DOM reactivity data, modeled with a multi-pool first order degradation kinetics model, found that fluorescent DOM in FCE is generally photo-reactive and bio-refractory. Yet the sequential degradation proved a “priming effect” of sunlight on the bacterial uptake and reworking of this subtropical wetland DOM. Interestingly, specific PARAFAC components were found to have different photo- and bio-degradation rates, suggesting a highly heterogeneous nature of fluorophores associated with the DOM. Surface-to-groundwater exchange of DOM was observed in different regions of the system, and compositional differences were associated with source and photo-reactivity. Lastly, the high degree of heterogeneity of DOM associated fluorophores suggested based on the degradation studies was confirmed through the EEM-PARAFAC analysis of DOM along a molecular size continuum, suggesting that the fluorescence characteristics of DOM are highly controlled by different size fractions and as such can exhibit significant differences in reactivity.

abstract: I present for the first time a broad-scale assessment of dissolved organic matter in the continental hot springs of Yellowstone National Park. The concentration of dissolved organic carbon in hot springs is highly variable, but demonstrates distinct trends with the geochemical composition of springs. The dissolved organic carbon concentrations are lowest in the hottest, most deeply sourced hot springs. Mixing of hydrothermal fluids with surface waters or reaction with buried sedimentary organic matter is typically indicated by increased dissolved organic carbon concentrations. I assessed the bulk composition of organic matter through fluorescence analysis that demonstrated different fluorescent components associated with terrestrial organic matter, microbial organic matter, and several novel fluorescent signatures unique to hot springs. One novel fluorescence signature is observed exclusively in acidic hot springs, and it is likely an end product of thermally-altered sedimentary organic matter. This acid-spring component precipitates out of solution under neutral or alkaline conditions and characterization of the precipitate revealed evidence for a highly condensed aromatic structure. This acid-spring component serves as a reliable tracer of acidic, hot water that has cycled through the subsurface. Overall, dissolved organic carbon concentrations and fluorescent features correlate with the inorganic indicators traditionally used to infer spring fluid mixing in the subsurface. Further, the fluorescence information reveals subtle differences in mixing between fluid phases that are not distinguishable through classic inorganic indicator species. My work assessing dissolved organic carbon in the Yellowstone National Park hot springs reveals that the organic matter in hydrothermal systems is different from that found in surface waters, and that the concentration and composition of hot spring dissolved organic matter reflects the subsurface geochemical and hydrological environment. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2020

The photosensitized processes significantly enhance photolysis of various chemicals in the aqueous system with dissolved organic matter (DOM) as sensitizer. The excitation of chromophores on the DOM molecule further generates reactive species as triplet states DOM, singlet oxygen, hydroxyl radical, carbonate radical etc. We investigated the photosensitization properties of Beaufort Fulvic Acid, Suwannee River Fulvic Acid, South Platte River Fulvic Acid, and Jeddah wastewater treatment plant effluent organic matter with a sunlight simulator. DOM photochemical properties were characterized by observing their performances in 3DOM*, singlet oxygen, hydroxyl radical production with indirect probing protocols. Sensitized degradation of 0.1 μM and 0.02 μM 2, 4, 6- Trimethylphenol exhibited higher pseudo-first-order rate constant than that of 10 μM. Pre-irradiated DOMs were found to be depressed in photochemical properties. Photolysis of 5 different contaminants: ibuprofen, bisphenol A, acetaminophen, cimetidine, and caffeine were found to be enhanced in the presence of sensitizers. The possible reaction pathways were revealed. Long time irradiance induced change in contaminants degradation kinetics in some DOM solutions, which was proposed to be due to the irradiation initiated indirect transformation of DOMs. Key Words: Photolysis Dissolved Organic Matter, Triplet State DOM, Singlet Oxygen, Hydroxyl Radical, Contaminants Degradation.

Mercury (Hg) transport in streams is typically facilitated by dissolved organic matter (DOM), however, the dynamics of Hg and DOM during snowmelt in montane watersheds are poorly understood. Hg transport during snowmelt is widely recognized as a significant source of Hg to downstream lakes and reservoirs, such as Jordanelle Reservoir where fish consumption advisories are in effect due to elevated Hg concentrations in certain species of fish. For this study, total mercury (THg), methylmercury (MeHg), and DOM samples were collected at three sites in the upper Provo River, northern Utah, during the 2016 and 2017 water years. To evaluate Hg and DOM sources, samples were collected from snowpack and ephemeral streams in the watershed. In-situ fluorescent DOM (fDOM) data and other parameters were measured in the river to characterize high-frequency variation in water chemistry. Excitation-emissions matrices (EEMs) were used to determine changes in DOM characteristics during snowmelt. Hg concentrations increased in the upper Provo River from /L during baseflow to >;7 ng/L during the snowmelt period (~April-July), with filtered THg concentrations approximately ~75% of the unfiltered concentrations. In the watershed, filtered THg concentrations ranged from ~0.4 ng/L in snowpack to ~8 ng/L in ephemeral streams. Annual THg loading from the Provo River to Jordanelle Reservoir was approximately 1 kg/yr with ~90% of the flux occurring during the snowmelt period. High correlations between filtered THg and fDOM allowed for the development of a high frequency filtered THg proxy using in-situ fDOM sensors. DOM characteristic during the snowmelt period showed that Hg transport was facilitated by humic substances which was sourced from upland soils. Fractions of filtered methylmercury (MeHg) and filtered THg (filtered MeHG:filtered THg) were ~0.1 during baseflow and reduced to ~0.01 during snowmelt, implying that snowmelt runoff has little impact on the MeHg flux to Jordanelle Reservoir. The results suggest that Hg and DOM are flushed from soils during snowmelt, and that a significant majority of the Hg flux occurs the snowmelt period. Our study has implications for understanding Hg sources and transport mechanisms in other snowmelt dominated watersheds.

Heterotrophic bacterioplankton dynamics have seldom been assessed in the Red Sea, an exceptionally warm oligotrophic basin, which could be used as a model for the future ocean. To understand the function of heterotrophic bacteria in biogeochemical cycles and the flows of matter and energy to higher trophic levels, it is peremptory to understand how bacterial growth is controlled. Bottom-up (resources availability), top-down (mortality by predators and viruses) and temperature are the main hypotheses of control of bacterial activity and stocks. This dissertation aims to assess the spatial-temporal variability of heterotrophic bacteria and their interactions with diverse sources of dissolved organic matter (DOM) through the observed effects on bacterial growth rates and productivity in coastal environments of the central Red Sea. To that end we conducted a total of 66 shortterm incubations (4-6 days) concurrently with the whole microbial community and predator-free (by filtration) in various shallow ecosystems characterized by different dominant sources of DOM. Frequent sampling combined flow cytometry and biogeochemical analysis allowed us to measure bacterial standing stocks, including the carrying capacity (maximum abundances), growth rates, characterize DOM concentrations and lability, assess bacterial DOM consumption rates and biomass production and ultimately quantify bacterial growth efficiencies. Our findings suggest that although bacteria seemed to thrive in nutrient-sufficient waters, the central coastal Red Sea is characterized by unusually low bacterial standing stocks (4.05 ± 0.31 x105 cells ml-1), probably controlled by protistan grazing. At the same time, bacterioplankton showed high potential to grow (0.35-1.75 d-1, reaching 4.16 d-1 when dilution and pre-filtration were performed). Even though the highest specific growth rates were observed during the warmer periods, we did not find any consistent relationship with temperature. While temperature seemed not to constrain bacterial specific growth rates, we observed a tight link between bacterial growth and resource availability in terms of both quantity and quality. Overall, by surveying one of the warmest marine regions on Earth, this dissertation provides detailed insights into heterotrophic bacterioplankton dynamics and how bottomup, top-down and temperature regulate them in tropical waters, a vast geographical extension of the world oceans that had remained strongly undersampled to date.