Arctic ecosystems are vulnerable to human-induced changes such as increases in contaminant levels and climatic warming. To predict effects of these changes, it is important to understand trophic relationships among Arctic organisms and how they change in response to time and environmental perturbations. Seabird diet can reflect relative availability and abundance of planktivorous fish and zooplankton in remote areas. The measurement of naturally occurring stable isotopes presents an alternative approach to evaluating dietary patterns of seabirds at both an individual level and at a larger, ecosystem level. Relative changes in δ13C values provided an indication of changes in consumption of benthic vs. pelagic prey and changes in δ15N values provided an indication of changes in trophic level.<p>I investigated trophic positions of four seabirds (Thick-billed Murres (<i>Uria lomvia</i>); Northern Fulmars (<i>Fulmarus glacialis</i>); Black-legged Kittiwakes (<i>Rissa tridactyla</i>); and Glaucous Gulls (<i>Larus hyperboreus</i>)) at Prince Leopold Island, Nunavut, 1988 2003, using my own and previously measured stable isotope measurements in blood samples. Trophic level and space use among years differed within and among species and may be related to ice conditions and species-specific foraging strategies. The species with the most flexible foraging methods, Thick-billed Murres, varied their foraging location and trophic level the most. In 2002, fewer chicks than average for all species were fledged and Thick-billed Murre chicks were lighter than in other years; however, only murres showed a concurrent decrease in the proportion of fish in their diet. Adult body condition of murres in 2002 was positively correlated with trophic level. Breeding season dietary patterns of Thick-billed Murre adults and chicks were examined on Coats Island, Nunavut, Canada, in 2004. Adult trophic level increased slightly through the breeding season and δ13C values indicated a switch from benthic to pelagic foraging locations. Chick and adult murres did not differ in either δ15N or δ13C values; however, within a family (two parents, one chick), chicks were fed at or slightly below adult trophic level. I found little variation in stable isotope values which suggests adult murres did not preferentially select prey for either themselves or their chicks. <p>Finally, stable isotope analysis was used to investigate winter foraging ecology of three species of alcids (Thick-billed Murres; Common Murres (<i>U. aalge</i>) and Razorbills (<i>Alca torda</i>)), off Newfoundland, Canada, 1996 2004. Thick-billed Murres fed at a higher trophic level than Common Murres. Razorbill δ15N values were highly variable and overlapped those of both murre species. I found no significant differences in δ13C values among the three species confirming a common spatial feeding pattern. Both murre species became depleted in 13C during winter suggesting foraging location or prey species shifted from nearshore to offshore. For Common Murres, hatching-year individuals fed at a higher trophic level and foraged farther offshore than after-hatch year birds. For Thick-billed Murres, I contrasted trophic level determined for the breeding colony at Prince Leopold Island with those determined for winter over four years and found considerable inter-annual variation in patterns of seasonal difference in trophic level. However, the proportion of lower trophic level (amphipod) vs. higher trophic level (fish) prey was generally greater in the winter than the summer.

Arctic ecosystems are vulnerable to human-induced changes such as increases in contaminant levels and climatic warming. To predict effects of these changes, it is important to understand trophic relationships among Arctic organisms and how they change in response to time and environmental perturbations. Seabird diet can reflect relative availability and abundance of planktivorous fish and zooplankton in remote areas. The measurement of naturally occurring stable isotopes presents an alternative approach to evaluating dietary patterns of seabirds at both an individual level and at a larger, ecosystem level. Relative changes in δ13C values provided an indication of changes in consumption of benthic vs. pelagic prey and changes in δ15N values provided an indication of changes in trophic level.<p>I investigated trophic positions of four seabirds (Thick-billed Murres (<i>Uria lomvia</i>); Northern Fulmars (<i>Fulmarus glacialis</i>); Black-legged Kittiwakes (<i>Rissa tridactyla</i>); and Glaucous Gulls (<i>Larus hyperboreus</i>)) at Prince Leopold Island, Nunavut, 1988 2003, using my own and previously measured stable isotope measurements in blood samples. Trophic level and space use among years differed within and among species and may be related to ice conditions and species-specific foraging strategies. The species with the most flexible foraging methods, Thick-billed Murres, varied their foraging location and trophic level the most. In 2002, fewer chicks than average for all species were fledged and Thick-billed Murre chicks were lighter than in other years; however, only murres showed a concurrent decrease in the proportion of fish in their diet. Adult body condition of murres in 2002 was positively correlated with trophic level. Breeding season dietary patterns of Thick-billed Murre adults and chicks were examined on Coats Island, Nunavut, Canada, in 2004. Adult trophic level increased slightly through the breeding season and δ13C values indicated a switch from benthic to pelagic foraging locations. Chick and adult murres did not differ in either δ15N or δ13C values; however, within a family (two parents, one chick), chicks were fed at or slightly below adult trophic level. I found little variation in stable isotope values which suggests adult murres did not preferentially select prey for either themselves or their chicks. <p>Finally, stable isotope analysis was used to investigate winter foraging ecology of three species of alcids (Thick-billed Murres; Common Murres (<i>U. aalge</i>) and Razorbills (<i>Alca torda</i>)), off Newfoundland, Canada, 1996 2004. Thick-billed Murres fed at a higher trophic level than Common Murres. Razorbill δ15N values were highly variable and overlapped those of both murre species. I found no significant differences in δ13C values among the three species confirming a common spatial feeding pattern. Both murre species became depleted in 13C during winter suggesting foraging location or prey species shifted from nearshore to offshore. For Common Murres, hatching-year individuals fed at a higher trophic level and foraged farther offshore than after-hatch year birds. For Thick-billed Murres, I contrasted trophic level determined for the breeding colony at Prince Leopold Island with those determined for winter over four years and found considerable inter-annual variation in patterns of seasonal difference in trophic level. However, the proportion of lower trophic level (amphipod) vs. higher trophic level (fish) prey was generally greater in the winter than the summer.

Les mécanismes d’interactions entre uranium et colloïdes ont été étudiés à partir d’échantillons provenant d’un site d’intérêt pour le Commissariat à l’Energie Atomique (CEA). La mobilisation de l’uranium depuis les sols a été appréhendée par lixiviations statique et dynamique. Le transfert et le transport ont été investis en considérant les eaux de nappe et de surface (drain). Les résultats confirment que l’uranium anthropique est plus mobile que l’uranium naturel. Le comportement (mobilisation, distribution) de l’uranium ne diffère cependant pas selon son origine. La phase colloïdale joue un rôle non négligeable dans la migration dans le sol et le transfert vers les eaux, représentant de 10 à 90 % de l’uranium suivant les échantillons. Les phases porteuses de l’uranium sont dans un continuum de taille allant jusqu’à environ 200 nm de diamètre hydrodynamique. Elles sont principalement composées de matière organique, de fer et d’aluminium. Le long du drain, de l’amont à l’aval du site, un réarrangement des associations colloïdales uranium-matière organique se fait en défaveur de celles uranium-fer, la proportion d’uranium colloïdale lié à l’aluminium restant elle inchangée. / Mechanisms of interaction between uranium and colloids were studied by samples taken from a site of interest for the “French Nuclear Agency” (CEA). The mobilization of uranium from soils was apprehended by static and dynamic leaching experiments. The transfer and transport have been studied by considering pondwaters and drainwaters. Results confirm that anthropogenic uranium is more mobile than natural uranium. However mechanisms of mobilization and distribution of uranium, does not differ depending on its origin. The colloidal fraction plays an important role on the migration in soil and the transfer into water by representing from 10 to 90 % uranium depending on samples. The colloidal fractions of uranium are in a continuum of size up to about 200 nm hydrodynamic diameter. They are mainly composed of organic material, iron and aluminum. Along the drain, from the upstream to the downstream of the site, rearrangement of colloidal associations between uranium and organic material occurs in disfavor of colloidal associations between uranium and iron, the proportion of colloidal uranium bound to aluminum remains unchanged.