No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Uranium (U) contamination can be introduced to the environment as a result of mining and manufacturing activities related to nuclear power, detonation of U-containing munitions (DoD), or nuclear weapons production/processing (DOE facilities). In oxidizing environments such as surface soils, U predominantly exists as U(VI), which is highly water soluble and very mobile in soils. U(VI) compounds typically contain the UO22+ group (uranyl compounds). The uniquely structured and long-lived green luminescence (fluorescence) of the uranyl ion (under UV radiation) has been studied and remained a strong topic of interest for two centuries. The presented research is distinct in its objective of improving capabilities for remotely sensing U contamination by understanding what environmental conditions are ideal for detection and need to be taken into consideration. Specific focuses include: 1) the accumulation and fluorescence enhancement of uranyl compounds at soil surfaces using distributed silica gel, and 2) environmental factors capable of influencing the luminescence response, directly or indirectly. In a complex environmental system, matrix effects co-exist from key soil parameters including moisture content (affected by evaporation, temperature and humidity), soil texture, pH, CEC, organic matter and iron content. Chapter 1 is a review of pertinent background information and provides justification for the selected key environmental parameters. Chapter 2 presents empirical investigations related to the fluorescence detection and characterization of uranyl compounds in soil and aqueous samples. An integrative experimental design was employed, testing different soils, generating steady-state fluorescence spectra, and building a comprehensive dataset which was then utilized to simultaneously test three hypotheses: The fluorescence detection of uranyl compounds is dependent upon 1) the key soil parameters, 2) the concentration of U contamination, and 3) time of analysis, specifically following the application of silica gel enhancing material. A variety of statistical approaches were employed, including the development of multiple regression models for predicting both intensity and band structure responses. These statistical models validated the first two listed hypotheses, while the third hypothesis was not supported by this dataset. The combination of inadequate moisture levels and reaction times (≤ 24 hrs) greatly limited the detection of varying levels of U, depending on the soil.

Les dynamiques de l’activité photosynthétique du phytoplancton ont été caractérisées dans un écosystème côtier macrotidal (le Détroit du Pas-de-Calais, Manche orientale) et associées aux conditions environnementales. La variabilité spatiale et temporelle des paramètres photosynthétiques a été étudiée à différentes échelles, entre Septembre 2008 et Août 2010. Le niveau de variabilité et les facteurs de contrôle des paramètres photosynthétiques dépendent de l’échelle considérée. Au niveau spatial, aucun gradient des paramètres photosynthétiques n’a été trouvé entre la côte et le large. A l’inverse, au sein de la colonne d’eau, des variations du rendement quantique maximum (Fv/Fm), du taux de transport maximum des électrons (ETRm) et du coefficient de saturation lumineuse (Ek), en lien avec l’histoire lumineuse des cellules, ont été observées. Aux courtes échelles de temps (de l’heure à l’échelle d’un cycle de marée morte-eau/vive-eau), des variations considérables des paramètres photosynthétiques ont été observées. Les conditions lumineuses et la disponibilité des nutriments étaient les principaux facteurs de contrôle. Aux plus grandes échelles de temps (de l’échelle semi-mensuelle à l’échelle pluriannuelle), Fv/Fm, α (l’efficacité maximale d’utilisation de la lumière) et ETRm variaient sans cycle saisonnier clair. Par opposition, Ek suivait le cycle saisonnier de la lumière. A ces échelles, les interactions entre les successions des communautés phytoplanctoniques et les changements de lumière, de température et de disponibilité en nutriments contrôlaient la variabilité de l’activité photosynthétique. / Dynamics of phytoplankton photosynthetic activity were characterised in a macrotidal coastal ecosystem (the Strait of Dover, eastern English Channel) and related to environmental conditions. Spatial and temporal variability of photosynthetic parameters were studied at different scales, between September 2008 and August 2010. The level of variability and controlling factors of photosynthetic parameters depend on the scale considered. In space, no gradient of photosynthetic parameters was found between coastal and offshore waters. By contrast, within the water column, variations of the maximum quantum yield (Fv/Fm), the maximum electron transport rate (ETRm) and the light saturation coefficient (Ek) in relation to the light history of cells were observed. At short time scale (from hour to the scale of a neap-spring tide cycle), considerable variations of photosynthetic parameters were observed. Light conditions, temperature and nutrient availability were the main controlling factors. At longer time scale (from fortnightly to inter-annual scales), Fv/Fm, α (the maximal light utilization efficiency) and ETRm varied without any clear seasonal cycle. By contrast, Ek followed the seasonal variations of light except during summer where its changes of Ek were small compared to the light variability. At these time scales, close interplays between shifts of phytoplankton communities and changes of light, temperature and nutrient availability controlled the variability of photosynthetic parameters.

Dans le cadre de l'application de la Directive Cadre sur l'Eau il serait intéressant de mettre au point de nouveaux outils de surveillance de la qualité des cours d'eau. Dans le cas d'une pollution ponctuelle, certains d'entre eux pourraient être basés sur l'évaluation de l'état physiologique des communautés de diatomées périphytiques qui constituent souvent le premier maillon des écosystèmes aquatiques continentaux. L'objectif de ce travail était d'étudier l'effet de polluants communément retrouvés dans les milieux aquatiques (Cu, Zn, Cd, atrazine, isoproturon) sur la réponse de communautés périphytiques naturelles et de mieux cerner l'influence de la lumière. Nous avons mis au point une démarche méthodologique originale, basée sur l'estimation de leur activité photosynthétique à l'aide de la technique de mesure de la fluorescence chlorophyllienne en lumière modulée (fluorescence PAM). Nos résultats ont mis en évidence une certaine résistance à court terme des communautés aux différents polluants testés, variable selon le mode d'action du polluant (herbicides vs métaux lourds) et la structure du biofilm (biomasse, composition spécifique). En combinant des expérimentations originales en conditions naturelles et au laboratoire, nous avons montré que l'application d'un stress supplémentaire comme la lumière amplifie de manière significative la toxicité de ces contaminants. Ce travail confirme tout l'intérêt de l'utilisation de la technique de mesure de la fluorescence chlorophyllienne en lumière modulée dans le cadre de bioessais écotoxicologiques. Il offre également des perspectives intéressantes en vue de la détection in situ de pollutions ponctuelles par les herbicides. / Ln the context of the European Water Framework Directive implementation, new tools for river toxicity assessment have to be developed. Periphytic communities, which play a fundamental role in the trophic web in lotic systems, could be regarded as early wamings for detection of acute toxicant exposure by monitoring its physiological state. Several studies were then carried out by means of the chlorophyll fluorescence measurement in modulated light technique (P AM fluorescence) which helps to estimate the photosynthetic activity in a non-intrusive way. The aim of the present work was to study the effects of several pollutants commonly found in aquatic ecosystems (Cu, Zn, Cd, atrazine, isoproturon) on stream periphyton physiology and to highlight the role of light as an addition al potentially stressful parameter. Our results showed a relative resistance of the natural biofilms to the pollutants on a short term scale (< 1 day) which depended both on the mechanism of action of the toxicant (herbicides vs heavy metals) and the biofilms architecture. By combining novel experimental designs both in field and laboratory conditions, we also demonstrated that periphyton can be more affected when another stress, such as light, is applied. This work confmns the usefulness of chlorophyll fluorescence-based methods in ecotoxicological studies, particularly in order to detect in situ herbicide toxic effects.