Thesis (Ph.D.)--University of Southern California, 2006. / (UMI)AAI3257832. Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1482. Adviser: Donal T. Manahan.

Thesis (Ph.D.)--Boston University, 2007. / (UMI)AAI3259864. Source: Dissertation Abstracts International, Volume: 68-04, Section: B, page: 2036. Adviser: Jelle Atema.

Thèse (Ph.D.)--Université de Sherbrooke (Canada), 2008. / Titre de l'écran-titre (visionné le 1 février 2007). In ProQuest dissertations and theses. Publié aussi en version papier.

Thesis (Ph.D.)--The College of William and Mary, 2007. / (UMI)AAI3272659. Source: Dissertation Abstracts International, Volume: 68-07, Section: B, page: 4312.

Seabirds are an important link between their marine feeding areas and their terrestrial breeding environments, transporting both marine-derived nutrients and contaminants to land via their excreta, feathers and carcasses. The importance of seabird-derived nutrients is particularly apparent in nutrient poor regions like the Canadian High Arctic, where biological oases form in the area surrounding a colony. While providing the nutrient subsidies that shape the terrestrial ecosystem of many Arctic sites, seabirds may focus contaminants into their nesting sites at potentially toxic levels. Here, we investigated the impact of a large northern fulmar (Fulmarus glacialis) colony on nearby ponds spanning a broad gradient of seabird influence at Cape Vera, Devon Island. Nutrient concentrations were significantly higher in ponds receiving guano than in reference ponds. The ponds closest to the cliffs, and thus receiving the highest seabird subsidies, were the most contaminated, and in some cases exceeded Canadian Sediment Quality Guidelines for the Protection of Aquatic Life for As, Cd and Zn. This study demonstrates that seabirds can transport contaminants bioaccumulated from the ocean and funnel them into receptor sites to potentially toxic levels thousands of kilometers from industrial centers.

Abstract not available.

The partitioning of methyl mercury (MeHg) to dissolved organic carbon (DOC) and the photodegradation of mercury by UVB radiation (280-320nm) are two important processes that influence the availability of MeHg to the base of the aquatic food chain. Water samples from 20 sites across Eastern Ontario and Western Quebec were filtered sequentially using tangential flow ultrafiltration to determine the size distribution of MeHg and DOC and to test whether the concentrations and distribution of these two variables varied in wetlands, lakes and rivers. These filtrates were also analyzed for DOC fluorescence and absorbance. The highest proportions of mean MeHg (47.3 +/- 25.4%), DOC (56.8 +/- 14.5%) and DOC FL (74.5 +/- 11.4%) were found in the low molecular weight fractions (<5 kDa). Significant differences in the distribution and concentration of MeHg amongst filtered samples were found between wetlands, lakes and rivers. MeHg was related to DOC at all size fractions. The low molecular weight organic compounds may be an important contributor to MeHg biomagnification through uptake by bacteria and/or algae. St. Lawrence river water was collected to test factors that affect the rate of photodegradation of MeHg. Samples exposed to UVB irradiance from a fluorescent lamp and spiked with MeHg(5 ng/L) illustrated significant decreases in concentration with a 31% average loss after 6 hours. No significant difference in photodegradation was found between samples with and without added Fe(II). MeHg concentrations decreased 35.4% and 41.7% after 6 hours of exposure at pH 3 and 5, respectively. It appears that photo-demethylation is a function of UVB exposure, is more rapid in acidic conditions and likely occurs slower under most natural freshwater conditions due to the attenuation of UVB.

In recent years, reaction transport models have gained importance in the study of diagenesis, which describes the chemical, biological and physical processes that take place in sediments. This project reports on factors influencing chemical profiles in lake sediments through an exploration of a generic reaction transport model which includes representations of the major reactions involved in the cycling of iron, sulfur and phosphorus. We have performed a global sensitivity analysis examining the steady state effects of physical, kinetic and thermodynamic factors on the magnitude, shape and burial concentrations of chemical profiles of iron, sulfur and phosphorus-bearing species. The environmental conditions were varied within a broad range typical of lake sediments. The exploration demonstrates the importance of the nature of boundary conditions (i.e. characteristics of the water column) and their coupling to the water column dynamics. The study additionally points to some chemical mechanisms such as precipitation of vivianite and scavenging of vivianite by sulfide having a dominant influence on the depth profiles of chemical species. Investigation also shows the importance of physical transport processes such as bioturbation near the sediment water interface and sedimentation velocity. Additionally, the distribution of reaction rates with depth and their role in shaping the profiles of chemical concentrations under typical environmental conditions were investigated.

No description available.

My research was designed (1) to examine the role of predatory decapods as an organizing force in grassbed prey distribution and abundance patterns, and (2) to compare the importance of vegetation as a prey refuge with its importance in providing increased living space for prey populations in seagrass meadows. My approach was first to catalogue the feeding ecology of the larger shrimps and crabs in Apalachee Bay, Florida. This study revealed great overlap among trophic niches of the 14 decapod species examined, nine feeding categories based on different proportions of prey consumed by 25 age-related ontogenetic trophic groups, trophic niche similarity that was unrelated to taxonomic similarity, and that living plants, especially algal epiphytes, are more important in diets than has been realized. The pink shrimp, Penaeus duorarum, was clearly the most important predatory decapod. / After evaluating the predator-exclusion effectiveness of a new cage design by defaunating and monitoring faunal recruitment into cages during a 2-mo period of high predator densities, I initiated a 1-mo manipulative field experiment designed to test the refuge hypothesis. Replicate predator inclusion (treatment) and exclusion (control) cages were established across a vegetation gradient and Penaeus duorarum were enclosed in treatment cages. Cages successfully excluded larger decapods and fishes and a significant predation effect was detected for total densities of all major prey taxon groups in a simple (low plant biomass) habitat. The general consequence of increasing microhabitat complexity on the outcome of predator-prey interactions was a reduction in Penaeus effects on total prey densities across the vegetation gradient. Vegetation provided more protection for amphipods and mollusks than for decapods and polychaetes. These results extend the premise that vegetation affords protection for prey from the laboratory to nature. These experiments also reveal that living space (on vegetation) alone can account for microhabitat distributions of some grassbed fauna without invoking predation as a causal mechanism. / Source: Dissertation Abstracts International, Volume: 44-07, Section: B, page: 2041. / Thesis (Ph.D.)--The Florida State University, 1983.