La matière organique dissoute chromophorique (CDOM) est une fraction significative du pool global de matière organique dissoute (MOD) dans les océans. La CDOM absorbe une partie de la lumière dans le domaine du rayonnement ultraviolet (UV-R) et du visible. Une fraction de cette CDOM peut émettre une fluorescence lorsqu'elle est excitée par un UV-R. Cette fraction est alors appelée matière organique dissoute fluorescente (FDOM). La CDOM a donc d'une part, un effet positif, en protégeant les cellules contre les dommages causés par les UV-R, mais d'autre part, un effet négatif en réduisant la quantité de radiation disponible pour la photosynthèse. Les propriétés optiques de la CDOM, particulièrement sensibles aux processus physiques (abiotiques) et biologiques (biotiques), renseignent sur l'intensité des processus biogéochimiques en milieux aquatiques. Des suivis de la dynamique de la CDOM en zones côtière et hauturière en Méditerranée Nord occidentale ont permis de décrire différentes tendances temporelles claires, qui vont d’une faible à une forte saisonnalité et qui peuvent être découplées des variations du pool global de MOD caractérisé par les concentrations en carbone organique dissous (COD). Dans les zones tempérées, les événements météorologiques conduisent à des changements beaucoup plus brusques dans la frange littorale que dans l’océan, où les variations tendent à être plus progressives au cours de l'année. En outre, l'apport de nutriments et de polluants dans les zones côtières est fortement influencé par l'activité anthropogénique et ces entrées ne suivent pas nécessairement de tendances saisonnières nettes. Dans la présente étude qui effectue un premier bilan de la distribution et du devenir de la CDOM/FDOM aux stations d'observation à long terme du laboratoire Arago (stations côtière SOLA et hauturière MOLA) à partir respectivement d'un suivi hebdomadaire et mensuel, nous nous sommes attachés à extraire un signal cohérent et une variabilité claire des sources des différentes fractions de la MOD entre février 2013 et avril 2014 ceci, de manière à mieux comprendre les rôles respectifs des facteurs biotiques et abiotiques. Nos observations ont ensuite pu être replacées dans un contexte synoptique d'évolution climatologique des écosystèmes méditerranéens. / Chromophoric dissolved organic matter (CDOM) is a major fraction of dissolved organic matter (DOM). CDOM absorbs light over a broad range of ultraviolet (UV-R) and visible wavelengths. A small fraction of CDOM can emit fluorescence when excited by ultraviolet radiation; so called fluorescent dissolved organic matter (FDOM). CDOM plays a key role in regulating light penetration into the ocean, absorbing high-energy electromagnetic spectrum (visible and ultraviolet light) waves. On one hand, it protects aquatic organisms of potential photo-damage; in the other hand it induces a negative effect by reducing light for photosynthesis. The optical properties of the CDOM are sensitive to biological (biotic) and physical (abiotic) processes and for this reason the colored matter can provide valuable information about the biogeochemical processes in aquatic environments. CDOM monitoring in Mediterranean coastal areas has shown different temporal trends, which go from weak to strong seasonality. Interestedly, these temporal trends were uncoupled with those of the total dissolved organic carbon. In temperate areas, episodic meteorological events can induce much more abrupt changes in the littoral than in the open sea, where changes tend to be more gradual along the year. In addition, the input of nutrients and pollutants in coastal areas is strongly influenced by the anthropogenic activity on land, and those inputs do not necessarily follow seasonal trends. In the present study, weekly and monthly samplings were performed to investigate the temporal variability in SOLA and MOLA stations, respectively. The fluctuation of different fractions of dissolved organic matter (DOM) was evaluated from February 2013 to April 2014 and referred to long time-frame databases of SOLA and MOLA stations. Inorganic nutrients and chlorophyll shown the classical seasonal patterns, with a winter period characterized by an enrichment of surface waters favoring the spring bloom, followed by a calm period that allows the summer stratification and the depletion of nutrients in the photic zone. The stratification extended until autumn winds and low temperatures eroded the thermocline. In contrast, colored DOM fractions did not follow a clear temporal trend. Interestingly, dissolved organic carbon (DOC) exhibited the highest variability in summer, when the rest of parameters showed minimum variations. To explain this mismatch we proposed a sequence of abiotic and biotic phenomena driving the DOC dynamics. In the suggested conceptual frame, DOC dynamics depended strongly on episodic meteorological events (winds, rains, etc.) along the year, except in summer, where the biological factors were more relevant. In order to better understand the influence of biological factors, we examined the temporal trends of phytoplankton composition in relation to those of the different colored DOM fractions. We found that both phytoplankton and CDOM were strongly influenced by abiotic factors such as the intrusions of fresh waters, the vertical mixing due to convection and the light exposure. However we did not find a correlation between any of the CDOM fractions and any of phytoplankton groups. In addition, we use the dust deposition database of ADEPT project (ICM-CSIC, Barcelona) to investigate the potential role of atmospheric deposition in the CDOM temporal variability, and also performed two dust addition experiments with natural plankton communities collected in the Catalan coast.

Master of Science / Department of Civil Engineering / Natalie Mladenov / The detrimental health effects of arsenic (As) contamination have motivated the study of As mobility around the globe. The variability in naturally occurring As concentration is due to variation in geology and climate. In arid environments with high evaporation, ecohydrology and As desorption under alkaline pH are thought to be responsible for high As concentrations. In reducing groundwater, on the other hand, microbial iron (Fe) reductive dissolution is known to release As into solution. In such environments, As-sulfide minerals precipitation and vegetation uptake could contribute to re-distribution of As. The Okavango Delta is an arid-zone wetland punctuated by ten of thousands of islands, and the reducing groundwater beneath these islands have dissolved As as high as 3000 µg•L[superscript]-1. Ecohydrologic controls are thought to contribute to the elevated As level; however dissolution of Fe-containing sediments has been proposed as the initial step in releasing As from sediment to the groundwater. To test the consistency of the hypothesized mechanisms, four islands were sampled in January 2013. The goal of this thesis is to: 1) provide more evidence on the zones of elevated As in groundwater of four islands, 2) gain understanding on the influence ecohydrology (i.e., evapotranspiration) on high As in groundwater, 3) evaluate the sediment of microbial community composition, and 4) gain new insights into the behavior of DOM along the groundwater flow path. The findings show zones of elevated As in all four islands. The ecohydrologic controls provide information on the location of high As and solute accumulation. Microbial analyses suggest DNA sequences collected were grouped within lineages that contain organisms capable of dissimilatory Fe reduction and sulfate reduction. This supports evidence from previous study that sulfide produced by microbial sulfate reduction is available for As-sulfide mineral formation. The variation of DOM characteristics could influence As solubility and reactivity. In addition, carbonate alkalinity and increase pH may contribute to As mobility further along the flow path. In this arid and reducing groundwater, we find that ecohydrologic and biogeochemical processes have a fundamental role in As mobility.

Les BioRéacteurs à Membranes (BàM) sont une technologie adaptée à l’un des challenges du 21ème siècle : la réutilisation des eaux usées.En combinant un traitement biologique et une filtration membranaire, ce procédé permet d’atteindre une qualité d’eau adaptée à la réutilisation en permettant une désinfection physique totale. Néanmoins, son essor économique est fortement limité par le colmatage membranaire qui, quand le système est optimisé, est dû principalement à la Matière Organique Dissoute (DOM). Afin de comprendre et de maitriser ce colmatage, des outils ont été développés pour identifier les composés de la DOM responsables du colmatage. Ainsi, au cours de cette thèse, la DOM de deux BàM, alimentés par des effluents réels, a été étudiée ; un BàM traitant des eaux usées urbaines(station d’épuration de La Grande Motte) et un BàM échelle pilote traitant des urines réelles. La matière organique dissoute issue du premier BàMa ainsi été fractionnée par taille et par hydrophobicité pour identifier les mécanismes de colmatage associés à chaque fraction.Des tests de filtration, réalisés sur les différentes fractions, ont permis d’identifier les colloïdes (protéines) comme responsables majeurs du colmatage externe (gâteau) et les substances humiques comme responsables du colmatage interne. En combinant ces tests de filtration avec des mesures de fluorescence3D (3DEEM), étant une méthode rapide dont le signal facilement exploitable, il a été possible de définir des indicateurs qualitatifs pour ces deux familles de colmatants. Par la suite, en combinant la 3DEEM avec une méthode de séparation et quantification par taille (LC-OCD), le signal de 3DEEM qualitatif a été calibré pour donner une information quantitative et de taille au travers d'une analyse rapide.Ces nouveaux indicateurs ont ensuite été mesurés sur site et ont permis d’établir des liens entre les paramètres opératoires ou la qualité de l’intrant pour le suivi global de la DOM et son impact sur le colmatage. Ces outils soulignent toute la potentialité de la fluorescence 3D comme indicateur en temps réel du suivi, du contrôle et de l’optimisation de l‘étape de séparation membranaire. / Membrane BioReactors (MBR) are suitable technology to face one of the major 21th century challenges : wastewater reuse.Combining biological treatment with membrane separation step, MBR produce reusable water through total physical disinfection. Nevertheless, it democratization is limited by membrane fouling that is mainly caused by Dissolved Organic Matter (DOM) compounds when the system is optimized.In order to understand and control membrane fouling, tools were developed to identify DOM compounds responsible for this phenomenon.Thus, this PhD work, focused on studying the DOM taken from two MBR fed with real wastewater: a full-scale MBR treating urban wastewater (La Grande-Motte wastewaster treatment plant) and a lab-scale MBR treating urine from source-separated toilets.Dissolved organic matter collected in the first MBR was fractionated by size and hydrophobicity to identify fractions’ fouling mechanisms. Then, filtration tests performed on the different fractions highlighted the role of colloids (proteins) in external fouling (cake) and humic substances in internal fouling. Filtration tests were combined with fluorescence3D (3DEEM) measurements, which is a quick identification method with an easy extracted signal, allowing to define qualitative indicators for both foulants classes.After, coupling 3DEEM with a size separation and quantification method (LC-OCD), qualitative signals from foulants indicators were calibrated. Thus, using 3DEEM it was possible to obtain a quantitative and size information about DOM foulants. These new indicators were used on-site and allowed establishing links between DOM and operating parameters or influent quality, which is necessary for DOM global control and its impact on membrane fouling. These tools highlight the potentiality for 3DEEM on-line application for separation step monitoring, control and optimization.

abstract: Dissolved organic matter (DOM) is an important part of aquatic foodwebs because it contains carbon, nitrogen, and other elements required by heterotrophic organisms. It has many sources that determine its molecular composition, nutrient content, and biological lability and in turn, influence whether it is retained and processed in the stream reach or exported downstream. I examined the composition of DOM from vascular wetland plants, filamentous algae, and riparian tree leaf litter in Sonoran Desert streams and its decomposition by stream microbes. I used a combination of field observations, in-situ experiments, and a manipulative laboratory incubation to test (1) how dominant primary producers influence DOM chemical composition and ecosystem metabolism at the reach scale and (2) how DOM composition and nitrogen (N) content control microbial decomposition and stream uptake of DOM. I found that differences in streamwater DOM composition between two distinct reaches of Sycamore Creek did not affect in-situ stream respiration and gross primary production rates. Stream sediment microbial respiration rates did not differ significantly when incubated in the laboratory with DOM from wetland plants, algae, and leaf litter, thus all sources were similarly labile. However, whole-stream uptake of DOM increased from leaf to algal to wetland plant leachate. Desert streams have the potential to process DOM from leaf, wetland, and algal sources, though algal and wetland DOM, due to their more labile composition, can be more readily retained and mineralized. / Dissertation/Thesis / Masters Thesis Biology 2018

Black carbon (BC) is an organic residue formed primarily from biomass burning (e.g., wildfires) and fossil fuel combustion. Until recently, it was understood that BC was highly recalcitrant and stabilized in soils over millennial scales. However, a fraction of the material can be solubilized and transported in fluvial systems as dissolved BC (DBC), which represents on average 10% of the global export of dissolved organic carbon (DOC) from rivers to coastal systems. The composition of DBC controls its reactivity, and it has been linked with a variety of in-stream processes that induce both carbon sequestration and evasion of CO₂ from aquatic systems, which suggest DBC may have a significant contribution within the global carbon cycle. The primary objectives for the thesis were to elucidate environmental factors that control the fate and transport of DBC in fluvial systems. Ultra-high resolution mass spectrometry was used to characterize DBC on a molecular scale whereas benzenepolycarboxylic acids were used to quantify and characterize BC in both dissolved and particulate phases (PBC). Sinks for polycondensed DBC were linked to a series of in-stream biogeochemical processes (e.g., photodegradation, metal interactions); whereas photooxidation of particulate charcoal led to production of DBC, suggesting photodissolution as a previously unrecognized source of DBC to fluvial systems. Coupling of DBC with PBC, however, was hydrologically constrained with sources varying over temporal scales and land use regimes. For DBC in particular, an enrichment of heteroatomic functionality was observed as a function of anthropogenic land use. Furthermore, land use coupled with stream order (a proxy for in-stream processing as defined by the River Continuum Concept) could explain significant spatial variability in organic matter (e.g., DOC) composition within an anthropogenically impacted system. With an increase in wildfire frequency projected with on-going climate change trends, parallel projections for increases in BC production are also expected. Furthermore, conversion of natural landscapes for urban and agricultural practices is also expected to continue in the coming decades. Thus, it is imperative to reach a comprehensive understanding of processes regulating the transport of DBC in fluvial systems with efforts to constrain future BC budgets and climate change models.

A method is presented, using calculations of the underwater light field, to examine viability of phytoplankton at depth. For this study, viability is defined as the ability of phytoplankton to harvest, and efficiently convert enough photons into primary production to overcome metabolic demands. How the available light field influences the production environment is examined. Changes in water column constituents, such as chlorophyll and colored dissolved organic matter (CDOM) concentration, alter the spectral quality and quantity of the light field at depth. Certain species with specialized survival strategies, such as assemblages of photoprotective and light-harvesting accessory pigments, may be better-suited to 'making a living' at depth in response to the spectral quality of the underwater light field. Stations for study were identified from various cruises off the West Florida Shelf that exhibited variations in chlorophyll and/or CDOM concentration, including an optically complex, red-tide station. Optical and water column constituent measurements from these stations were used to develop input parameters to Hydrolight 4.1, a radiative transfer theory model, to simulate the underwater light field and to calculate absorbed radiation by phytoplankton (ARP). Values for respiration and quantum yield from the literature were used to calculate comparative values of net photosynthesis at these stations. The effect of differences in spectral light harvesting (pigmentation), photosynthetic efficiency rates, and respiration, on viability through the water column was examined.

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.

In aquatic ecosystems, dissolved organic matter (DOM) is an important source of detrital energy on which microorganisms rely. However, its dynamics are not well understood in an ecological context. By isolating watershed sources, the work reported in this thesis has attempted to characterize the seasonal patterns of DOM in the hyporheic zone of a temperate stream and to find the likely sources that contribute to this pool of organic carbon. Hyporheic DOM characteristics described by UV spectroscopy indicated temporal rather than spatial dependence. Excitation-emission matrices (EEMs) showed that hyporheic DOM was mainly comprised of fulvic- and humic-like fluorescence with small amounts of protein-like fluorescence. Increases in dissolved organic carbon (DOC) concentrations from birch litter isolates were greater than those from cedar litter in early autumn, but less in late autumn. Although streambed biofilm was not significant in increasing DOC concentrations, it was also a source of protein-like fluorescence.

The effects of different types and amounts of dissolved organic matter (DOM) on the isotope fractionation of Hg isotopes during aqueous photo-reduction of monomethylmercury (MMHg) were investigated to assess whether mass-independent fractionation (MIF) signatures can be used to track photo-degradation of MMHg in natural waters. From experiments conducted with different amounts of reduced organic sulfur (Sred-DOM), it appears that MIF during photo-reduction may be dependent on whether MMHg is dominantly bound to Sred-DOM. Similar fractionation factors were observed for experiments where Sred-DOM was in far excess of MMHg, while significantly lower fractionation factors were observed with lower Sred-DOM. We also characterized the signature of MIF (i.e. Δ199Hg/Δ201Hg) during MMHg photo-degradation to assess if it was similar in different matrices. The experimental Δ199Hg/Δ201Hg was very similar for different matrices. However, the experimental slope is slightly but statistically different than the slope observed in freshwater fish, which preserve MMHg in nature.

The effects of different types and amounts of dissolved organic matter (DOM) on the isotope fractionation of Hg isotopes during aqueous photo-reduction of monomethylmercury (MMHg) were investigated to assess whether mass-independent fractionation (MIF) signatures can be used to track photo-degradation of MMHg in natural waters. From experiments conducted with different amounts of reduced organic sulfur (Sred-DOM), it appears that MIF during photo-reduction may be dependent on whether MMHg is dominantly bound to Sred-DOM. Similar fractionation factors were observed for experiments where Sred-DOM was in far excess of MMHg, while significantly lower fractionation factors were observed with lower Sred-DOM. We also characterized the signature of MIF (i.e. Δ199Hg/Δ201Hg) during MMHg photo-degradation to assess if it was similar in different matrices. The experimental Δ199Hg/Δ201Hg was very similar for different matrices. However, the experimental slope is slightly but statistically different than the slope observed in freshwater fish, which preserve MMHg in nature.