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Dissolved organic matter (DOM) is a major component of natural waters and provides essential nutrients for aquatic organisms. However, excess DOM in the water results in water quality issues and affects the aquatic life negatively. The present research evaluated the source, composition, reactivity, dynamics, and the spatial distribution of DOM in diverse water bodies using spectrofluorometric methods in tandem with multivariate statistics. The study was conducted in the inland and coastal water bodies of Mississippi, Louisiana, and Alabama over a period of three years (2016 to 2018). Surface water samples were collected from spatially separated waterbodies with diverse land use and land cover classes. In addition, reactivity of DOM was assessed by conducting a series of laboratory experiments at varying magnitudes of sunlight and bacterial activity. Spatial distribution and mobility of DOM, nutrients and trace elements with respect to land cover classes and hydrology was evaluated using watershed delineation and multivariate statistics. Results suggest that microbial humic-like or protein-like DOM compositions derived from microbial/anthropogenic sources were less reactive than the terrestrial humic-like compositions originated from forests and woody wetlands. Furthermore, the sunlight was the major factor causing the degradation of DOM in the water bodies, while temperature had a minor effect. Additionally, the results also suggest that livestock fields in the pastoral and rangelands release a high amount of microbial humic-like DOM along with nutrients such as phosphates and nitrates into the water bodies. Present research identified the presence of four types of DOM in the study areas and were terrestrial humic-like, microbial humic-like, soil-derived humic-like and protein-like compositions. Additionally, trace element availability and mobility of coastal areas is influenced by local hydrology and precipitation. Research also identified forested areas as the major source of DOM to the water bodies of Mississippi. In conclusion, present research found that watershed land use and land cover, hydrology, and climate control the dynamics of DOM, other nutrients, and trace element delivery to the water bodies, while combined effects of light and bacteria are more efficient in reprocessing DOM chemistry within the waterbody.

River-floodplain connectivity is defined as the water mediated transfer of materials and energy between a river or stream and its adjacent floodplain. It is generally accepted that restoring and/or enhancing river-floodplain connectivity can reduce the downstream flux of reactive solutes such as nitrogen (N) and phosphorus (P) and thus improve downstream water quality. However, there is little scientific literature to guide ecological engineering efforts which optimize river-floodplain connectivity for solute retention. Therefore, the aim of my dissertation research was to examine feedbacks between inundation hydrology and floodplain biogeochemistry, with an emphasis on analyzing variation experienced along the river continuum and the cumulative effects of river-floodplain connectivity at the basin scale. This was completed through four independent investigations. Field sites ranged from the Atchafalaya River Basin, the largest river-floodplain system in the continental US, to the floodplain of a recently restored headwater stream in Appalachia. We also developed a method to examine river-floodplain connectivity across large- river networks and applied that methodology to US stream network. Largely, our results highlight the role floodwater residence time distributions play in floodplain biogeochemistry. In headwater streams, residence times restrict redox dependent processes (e.g. denitrification) and downstream flushing of reactive solutes is the dominant process. However, in large-river floodplains, redox dependent processes can become solute limited because of prolonged residence times and hydrologic isolation. In these floodplains, the dominant process is often autochthonous solute accumulation. Further, results from our modeling study suggest large-river floodplains have a greater impact on downstream water quality than floodplains associated with smaller streams, even when considering cumulative effects across the entire river network. / Ph. D.

In-water biogeochemical constituents and bio-optical properties of the St-Lawrence Gulf and Estuary were monitored during 5 cruises conducted between 1997-2001 accross different seasons. Measured inherent optical properties (IOPs) included vertical profiles of the absorption and attenuation coefficients and the volume scattering function as well as absorption by particles, non-algal particles, phytoplankton and coloured dissolved organic matter (CDOM). Apparent Optical parameters (AOPs) included vertical profiles of the upwelling radiance and downwelling irradiance. The spectral shape of the major IOPs like absorption by phytoplankton, CDOM and non-algal particles as well as the particulate backscattering were parameterized using conventional models and adaptations of conventional models. Descriptive statistics of each variable in the collected dataset were analysed and compared with previous findings in the literature. The optical coherence of the measurements was verified using a radiative transfer closure approach. A complete set of IOP cross-sections for optically significant biogeochemical variables were generated. The magnitude and the spatial, temporal and spectral variation exhibited by the optically significant inwater biogeochemical constituents as well as the bio-optical parameters was consistent with our current knowledge of the ecosystem. The variation of the bio-optical parameters throughout the seasons was also coherent with our expectations. All the measured and derived parameters were found to vary within the ranges reported in the literature. Evidence was presented wherein the Gulf waters, which are usually considered as case I waters could also behave like case II waters. Moreover, spectral signatures exhibited by the IOPs and AOPs were coherent with the variation detected in the concentrations of the measured (optically significant) constituents. The extracted IOP cross-sections were consistent with the results of similar studies previously performed and could eventually be used in the estimation of the biogeochemical constituent concentrations given the related component IOPs. First-order radiative transfer closure was achieved; this underscored the validity of our experimental dataset based on considerations of higher level, integrative, physics. We argue that the current data collection campaign succeeded as a comprehensive framework for describing the behavior of the St-Lawrence bio-optical provinces within the context of remote sensing objectives. This bio-optical dataset should provide the basis for the development of a rigorous, satellite-based, remote sensing algorithm for the retrieval of near surface chlorophyll, fine-tuned to the local characteristics of the St-Lawrence system.

Earth observation satellites cover large areas with frequent temporal repetition and provide us with new insight into ocean and coastal processes. Ocean colour measurements from satellite remote sensing are linked to the bio-optics, which refers to the light interactions with living organisms and dissolved and suspended constituents in the aquatic environment. Human pressures have changed the aquatic ecosystems, by, for example, the increased input of nutrient and organic matter leading to eutrophication. This thesis aims to study and develop the link between bio-optical data and the remote sensing method to the monitoring and management of the Baltic Sea. The results are applied to the European Union’s Water Directives, and the Baltic Sea Action Plan from the Helsinki commission. In paper I indicators for eutrophication, chlorophyll-a concentration and Secchi depth were evaluated as a link to remote sensing observations. Chlorophyll-a measurements from an operational satellite service (paper I) were compared to conventional ship-based monitoring in paper II and showed high correlations to the in situ data. The results in paper I, II and IV show that the use of remote sensing can improve both the spatial and temporal monitoring of water quality. The number of observations increased when also using satellite data, thus facilitating the assessment of the ecological and environmental status within the European Union’s water directives. The spatial patterns make it possible to study the changes of e.g. algae blooms and terrestrial input on larger scales. Furthermore, the water quality products from satellites can offer a more holistic and easily accessible view of the information to decision makers and end-users. In paper III variable relationships between in situ bio-optical parameters, such as coloured dissolved organic matter (CDOM), dissolved organic carbon, salinity and Secchi depth, were found in different parts of the Baltic Sea. In paper IV an in situ empirical model to retrieve suspended particulate matter (SPM) from turbidity was developed and applied to remote sensing data. The use of Secchi depth as an indicator for eutrophication linked to the concentrations of chlorophyll-a and SPM and CDOM absorption was investigated in paper V. The variations in Secchi depth were affected differently by the mentioned parameters in the different regions. Therefore, one must also consider those when evaluating changes in Secchi depth and for setting target levels for water bodies. This thesis shows good examples on the benefits of incorporating bio-optical and remote sensing data to a higher extent within monitoring and management of the Baltic Sea. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

La baie de Marseille est impactée par des apports d'eau douce issus du Rhône et d'effluents. Leur impact sur la composition et sur la dynamique saisonnière de la matière organique dissoute (DOM) naturelle et anthropique (hydrocarbures et biocides) présente dans le Rhône, delta du Rhône ainsi qu'en baie de Marseille est encore peu documenté. Une partie de la DOM possède des propriétés de fluorescence (FDOM) et peut être caractérisée et quantifiée par spectrofluorimétrie. Le but de cette thèse est d'enrichir les connaissances sur la composition et la dynamique de la FDOM naturelle et anthropique dans les eaux continentales du bassin du Rhône et en Méditerranée côtière nord-occidentale. Des solutions de composés standards ont permis de définir les propriétés de fluorescence (λEx, λEm, temps de vie), les limites de détection d'hydrocarbures et de biocides d'intérêt et de montrer que la spectrofluorimétrie permet de caractériser et de quantifier la FDOM anthropique dans des milieux contaminés. Ces contaminants ont été recherchés dans l'environnement à l'aide de techniques chromatographiques et mis en évidence dans le milieu durant un suivi d'une année. Cependant, la spectrofluorimétrie a réussis de mettre en évidence la présence de contaminants uniquement dans le golf de Fos. Concernant la FDOM naturelle, elle a permis de montrer que la DOM d'origine terrigène prédominait dans les eaux continentales, alors que la DOM produite par l'activité biologique était plus abondante en mer et que le Rhône jouait un rôle majeur en augmentant la quantité de DOM réfractaire et labile par des apports directs et en stimulant la production primaire par des apports de sels nutritifs. / The Marseille bay is impacted by inputs of freshwater from the Rhône River and effluents. Their impact on composition and seasonal variability of anthropogenic (hydrocarbons and biocides) and natural dissolved organic matter (DOM), present in the Rhône river, the Rhône delta and in the Marseille Bay is still poorly documented. A part of the DOM has fluorescence properties (FDOM) and can be characterised and quantified by spectrofluorimetry. The goal of this thesis was to supply knowledge about composition and dynamic of anthropogenic and natural FDOM in inland waters of the Rhône basin and in the North-western coastal Mediterranean Sea. Standard solutions allowed to define fluorescence properties (λEx, λEm, lifetime), detection limits of hydrocarbons and targeted biocides and to show that spectrofluorimetry allow to characterise and to quantify anthropogenic FDOM in contaminated environment. These contaminants were searched in the environment with chromatography analyses and bring out in the environment during a one year monitoring. However, the spectrofluorimetry not succed to bring out contaminants only in the Fos gulf. Concerning natural FDOM, it allowed to show that terrigenous DOM predominated in continental waters, whereas the DOM produced by the biological activity was more abundant in seawater and that the Rhône River played a major role by increasing both refractory and labile DOM through direct inputs and by enhancing the primary production by nutrient inputs.

A Ilha Comprida formou-se no Quaternário tardio e é uma ilha barreira arenosa composta de um conjunto de superfícies de rugosidade moderada à plana, nas quais se formaram Espodossolos com padrões variados de desenvolvimento e morfologia. Essa pesquisa utilizou a abordagem multiescalar, com observações e descrições através de sensoriamento remoto, topocronossequências, perfis, horizontes e seções delgadas de solo. O levantamento cartográfico com o auxílio de fotografias aéreas 1:16.000 do setor sul da Ilha Comprida permitiu mapear as feições geomorfológicas de cordões praiais, áreas planas, reentrâncias de manguezais, dunas frontais (cordões eólicos), rupturas de deflação (blow-outs) e bordas de terraços. O estudo baseou-se em dois perfis transversais (leste-oeste) com 3 km de extensão, onde foi possível identificar diversas unidades de crescimento sedimentar. As transeções A-B e C-D estão situadas no interior e na falésia sul da ilha, respectivamente. Comparando-se os solos dessas transeções é possível constatar o papel desempenhado pela evolução da drenagem na formação, manutenção e degradação dos horizontes espódicos. A degradação dos horizontes espódicos da transeção C-D está ligada à abertura de canais de raízes onde se instalam fluxos preferenciais de água, somado a atividade decompositora de Acidobactérias. Foram realizados levantamentos topográficos e da configuração vertical e lateral dos horizontes dos solos das transeções, sendo instalados 14 poços de monitoramento do nível freático na transeção A-B. As informações do relevo, solo e dinâmica atual do lençol freático permitiram identificar cinco compartimentos morfopedológicos. Os compartimentos I, II e IV, com maior rugosidade do terreno, possuem Espodossolos bem desenvolvidos providos de ortstein na zona próxima ao limite de oscilação do lençol freático, enquanto o compartimento III é mais plano e apresenta Espodossolos Hidromórficos e Organossolos. No compartimento V, mais recente, a podzolização é incipiente. As análises de estatística da distribuição das areias e micromorfologia indicam que a granulometria e o ajuste espacial dos grãos de areia de certas camadas sedimentares, atuam no acúmulo de Matéria Orgânica Dissolvida (MOD) através do acentuado gradiente de condutividade hidráulica ou por quebra de capilaridade. O resultado é a formação de bandas e horizontes cimentados (Bhm) em determinados contatos estratigráficos. Os cordões e entre-cordões praiais convergentes para à Ponta da Trinheira (sudoeste da ilha) controlam a direção dos fluxos hídricos superficiais e subsuperficiais do local, funcionando como escoadouro de MOD, cujo aporte contínuo e lateral explicaria a formação dos horizontes Bhm gigantes que sustentam o limite territorial em forma de \"L\". A descida gradual e contínua do NRM e o efeito de borda na falésia sul ocorrido após sua erosão colaboraram para o dessecamento e hiperdesenvolvimento do ortstein deste local. O horizonte glei (2Cg) é um paleomangue e ocorre de forma pontual na face lagunar da ilha. Seu impedimento à drenagem limita o avanço da podzolização em profundidade, formando o horizonte Bhm acima do horizonte 2Cg. Algumas raízes e paleogalerias tubulares de Callichirus major, preenchidas por areia, promovem bioturbações capazes de condicionar o acúmulo e cimentação de MOD. As galerias formadas pelo crustáceo são holocênicas e a manutenção de seus vestígios até os dias atuais se deve ao processo de pedofossilização por podzolização. / Formed since the late Quaternary period, the Ilha Comprida is made up by a set of geomorphological units depicted whether by rough or smooth surfaces, where both have Spodosols with a range of morphology and development stages. Multiscale approach has been applies through the spatial representation of topochronossequences, soil profiles, soil horizons and soil thin sections. Cartography survey of the south Ilha Comprida has been aided by aerial photos, allowed to mapping geomorphological features: beach ridge and swales; plan surfaces; coves with mangrove recesses; and edge of terrains. The study was based on two transversal profiles (east-west) with nearly 3 km of width, located at southernmost of Ilha Comprida, where there are several growth units. There transections A-B and C-D are located inland and at the cliffs, respectively. The soils from these transections show the role play by drainage conditions on formation and degradation of spodic horizon. The degradation of spodic horizons through transection C-D is linked to the preferential flow channels created by roots growth, plus by the decomposition activities of Acidbacterias. Traditional topography survey and lateral configuration of soils has been draw to depict these transections, where 14 wells were deployed for water table monitoring (transection A-B).The relief, soil, and water table information allowed the delimiting of five morphopedologic compartments. The compartments I, II and IV has rough surfaces (higher and close beach ridges) with Spodosol well developed provided with ortstein at oscillation zone of water table, while compartment III is a flat surface with Hydromorphic Spodosol and Histosols. Compartment V is the youngest surface and has incipient podsolization. Statistic of sand grain size and micromorphology analysis indicates that granulometry and spatial sand arrangement of some sedimentary package, deal with Dissolved Organic Matter (DOM) accumulation through high hydraulic conductivity gradient or capillarity breaks. It results in formation of bands and commentated horizons (Bhm) at some stratigraphic boundaries. The presence of beach ridges and swales alignments convergent towards southwest of Ilha Comprida, plus the directions of local hydrography flows, implies that the swales are channels of DOM, which contribute to ortstein formation at Ponta da Trincheira. The slow decreasing of sea level along the Holocene, in addition to the edge effect upon erosion of the south sandy cliff, also played a role to ortstein genesis. Gley horizon (2Cg) with mineralogical assemblage similar to the soils found in the mangrove, suggest that some mangroves has been buried by the costal dynamics typical in infra-tidal environment. Currently, these buried horizons occur locally and plays a impediments for drainage, which is expressed in accumulation and cementation by organic matter (Bhm horizon). Some roots and Callichirus major fossils entail bioturbation that also enable accumulation and cementation of DOM. This icnofossils might have been preserved through pedofossilization by the podsolization process itself.

Etablir un lien entre le dépôt atmosphérique et le réservoir de matière organique dissoute (DOM) en mer Méditerranée est rendu difficile en raison: (1) d’une faible connaissance du réservoir de phosphate (P) dissous de surface, principalement contraint par les faibles concentrations en phosphate inorganique dissous (DIP), (2) d’un manque critique de données de dépôt atmosphérique de C, N et P organique et (3) d’une absence d’information sur sa biodisponibilité. Cette thèse a tenté de pallier ces manques. (1) A l’aide d’une mesure sensible du DIP, le recouvrement des données valides de phosphate organique dissous a été augmenté de 70% par rapport à la méthode classique, permettant de révéler la dynamique biogéochimique du P dissous dans les eaux de surface. (2) Les flux atmosphériques en C, N et P organique soluble ont été quantifiés et ont été de 59 mmol C m-2 an-1, 16,4 mmol N m-2 an-1 et 23,6 μmol P m-2 an-1. La contribution de la fraction organique aux flux totaux en N et P est respectivement de 40 et 25%. La fraction labile du dépôt atmosphérique en P organique soluble a également été quantifiée et a montré une importante variabilité, allant de 0 à 97%. (3) La biodisponibilité de la DOM atmosphérique a été étudiée expérimentalement. La DOM contenue dans une pluie saharienne peut soutenir l’activité des bactéries hétérotrophes marines, avec une quantité de C labile de 29%. La fraction labile de C contenue dans les aérosols désertiques et anthropiques est également importante, 26 ± 2 et 15 ± 5%, respectivement. Les résultats issus de cette thèse soulignent le caractère non négligeable du dépôt atmosphérique et son rôle déterminant dans le cycle de la DOM océanique. / Establishing a link between atmospheric deposition and the dissolved organic matter (DOM) pool in the Mediterranean Sea is currently hampered by: (1) a poor knowledge on the surface dissolved phosphate (P) pool, mainly due to low concentrations of dissolved inorganic phosphate (DIP), (2) a critical lack of data on atmospheric fluxes of organic C, N and P and (3) the lack of information on their bioavailability. This PhD thesis aimed at filling these gaps. (1) Relying upon a sensitive determination of DIP, the coverage of the valid dissolved organic phosphate data was enhanced up to 70%, revealing a vertical pattern in the dissolved phosphate biogeochemistry in surface waters. (2) Atmospheric fluxes of soluble organic C, N and P were quantified and were 59 mmol C m-2 yr-1, 16.4 mmol N m-2 yr-1 and 23.6 μmol P m-2 yr-1, respectively. The contribution of the organic fraction to the total atmospheric fluxes of N and P was of 40% and 25%, respectively. The labile fraction of atmospheric deposition of organic phosphate was also quantified during the study period and showed a wide variability, ranging from 0 to 97%. (3) The bioavailability of atmospheric organic matter was experimentally assessed. DOM contained in a Saharan rainwater could support the activity of marine heterotrophic bacteria, with an amount of labile carbon of 29%. The labile fraction of carbon contained in desert dust and anthropogenic aerosols was also substantial, 26 ± 2% and 15 ± 5%, respectively. The results obtained from this PhD thesis emphasize the non-negligible character of atmospheric deposition and highlight the key role that this external source could have on the oceanic DOM cycle.