No description available.

Thesis advisor: Noah P. Snyder / Nitrogen is an important component in the biogeochemical processes of freshwater systems. Likewise, it is unknown if, and to what magnitude, changes in land use in the watersheds of New England lakes have affected nitrogen availability. This study examines the effects of land-use change on the present and historic isotopic signatures of nitrogen in three New England lakes of varied histories, Lower South Branch Pond, Little Kennebago Lake, and Sennebec Pond. The histories of all three sites indicate minimal discernible disturbance before the onset of Euro-American-induced land use change. For two sites, the dominant mechanism of change was timber harvest, which began in the latter half of the 19th century. Sediment cores for each site were examined and variations in geochemical and sedimentological indicators were evaluated in the context of changes within respective basins. Statistical analysis indicates significant shifts in the means and variance of the geochemistry within the Little Kennebago Lake and Sennebec Pond watersheds after the incursion of Euro-American settlers, while the Lower South Branch Pond watershed displays similarities to a more widespread signal of anthropogenic nitrogen that has been deposited remotely. The record of magnetic susceptibility in Little Kennebago Lake displays the largest variation compared to the other two lakes, which may indicate that the magnitude of land-use change within the basin was more impactful relative to Lower South Branch Pond and Sennebec Pond. This is significant in that all three sites experienced some level of land-clearance. / Thesis (MS) — Boston College, 2023. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

The objective of this study was to determine the origin of sediment currently collected in Black Lake, an extremely productive salmon fishing environment located along a remote section of the Alaska Peninsula, AK. To meet the goals of this project, soil cores were collected at the site during an extensive field study. The field investigation was based on a prior numerical study, which revealed the most erodible areas and the hydrologic patterns in Black Lake and its tributaries, namely the Alec River. From this study, select locations of the catchment were chosen for coring. These included the Alec River Delta, Black Lake, and four tributaries in the catchment. These samples were analyzed for the radionuclides 137Cs and 210Pb to determine soil deposition rates using Gamma Spectroscopy. To determine the sedimentation rate of each coring location, spikes in the 137Cs activity were connected to the known cesium deposition peak in 1964 and the depth of soil above the peak was divided by the number of years that have passed. This gave a spatially averaged deposition rate within the lake of roughly 0.25 cm/y. This result closely compared to the numerical study of Elhakeem and Papanicolaou (2008) and to a study done in close proximity to Black Lake in the early 1990s (Stihler et al. 1992). The rate of each location was then validated by visually analyzing each core using soil color demarcation lines to determine the soil composition. This analysis resulted in the discovery of a variety of soil types ranging from silts and clays, to coarse sands, to volcanic tephra. It was concluded that the lake flow patterns, the introduction of volcanic material from nearby Mt. Veniaminof, and back water resulting from deposition occurring down stream of Black Lake at the Black River's junction with the West Fork River are some of the main contributors for the deposition in the lake.

Les systèmes carbonatés lacustres salins présentent un fort potentiel d’enregistrement des changements paléogéographiques et paléoclimatiques. Ce manuscrit présente une méthode d’analyse pluridisciplinaire (sédimentologie, écologie, stratigraphie, paléontologie, géochimie et paléomagnétisme) et multi-échelle (µm au km) appliquée au bassin lacustre d’Alès et des régions limitrophes au cours du Priabonien (–38 à –33,5Ma). Cette approche a permis d’apporter de nouveaux éléments dans les reconstitutions paléoenvironnementales, paléogéographiques et paléoclimatiques du sud–est de la France au Priabonien. De nouveaux concepts sédimentologiques et stratigraphiques transposables à d’autres systèmes lacustres sont mis en avant. Enfin, les observations permettent de reconstituer, dans un cadre temporel bien contraint, l’histoire de la détérioration climatique précédant la limite Eocène–Oligocène qui correspond à la plus grande crise climatique de ces 50 derniers millions d’années. / Lacustrine carbonate systems are of great interest to record the paleogeographic and paleoclimatic changes. This manuscript provides a multi-disciplinary (sedimentology, ecology, stratigraphy, paleontology, geochemistry and paleomagnetism) and a multi-scale (from µm to km) analysis dedicated to the Alès Basin and the neighboring areas during the Priabonian (–38 to –33.5Ma). Such joint approach has already allowed us to bring new elements regarding the paleoecological, paleoenvironmental and paleoclimatic interpretations. New sedimentological ideas and stratigraphic concepts emerge and could be transposed to such saline lacustrine systems as analogues. Finally, the well-defined chronostratigraphic framework can be used to decipher the climatic deterioration recording prior to the Terminal Eocene Event at the Eocene–Oligocene boundary (the most profound climatic change of the past 50 million years.