UVM Theses and Dissertations
Format:
Print
Author:
Palmer, Johanna E.
Dept./Program:
Geology
Year:
2012
Degree:
M.S.
Abstract:
Undisturbed lake sediments record information on the changing nature of lakes, their watersheds, and climate through time. This information can be retrieved through sediment core collection, and subsequent analysis of established proxies can provide information about sediment and organic matter sources, lake productivity, water depth, and more. St. Albans Bay (SAB) is currently one of the most eutrophic regions of Lake Champlain (northeastern United States/Canada). Short cores and historical accounts suggest that the current level ofproductivity has been maintained for at least a half-century, yet long cores spanning the pre-settlement period display high organic matter content at depth, suggesting the bay may have experienced eutrophication pre-settlement.
This study examines the sediment record in SAB over ~8600 years of deposition, with an objective to determine whether productivity in the bay was in fact relatively stable pre-settlement, or varied widely in response to climatic change and environmental perturbations. One core from each of the two sub-basins in the bay was examined and radiocarbon dated. Measured proxies included magnetic susceptibility, C and N content, CIN ratios, biogenic silica, particle grain size, X-Ray diffraction of mineralogy, and stable carbon isotopes. SAB results are compared to a study of cores extracted from Missisquoi Bay (Koff, 2012), which is another shallow segment of Lake Champlain that currently experiences severe eutrophication problems.
Results indicate that SAB responded to multiple natural perturbations during the Holocene, including variations in temperature, precipitation, lake level, internal nutrient loading, and watershed hydrology. For example, periods of high productivity were generally related to warmer conditions, and periods of low productivity to cooler conditions. The inner, shallow bay seems to have been dominated by macrophytes throughout most of its history, in contrast with the deeper, outer bay, which was dominated by algae. During lake high-stands, productivity was generally lower, with decreased influx of macrophyte material to the central parts of the bay, while lake low-stands forced the zone of macrophyte productivity to migrate to the offshore parts ofthe bay. In addition, the inner sub-basin of SAB was more susceptible to changes in climate and environment than the outer bay, most likely due to its proximity to river inputs and wetlands, and its shallower depth.
Early episodes of productivity at or above the levels present since permanent settlement in the basin can be confirmed in both St. Albans and Missisquoi Bays. The role of climate and environment as drivers of SAB productivity in the past may serve as a harbinger of future productivity increases during global warming and increased human activity in the watershed.
This study examines the sediment record in SAB over ~8600 years of deposition, with an objective to determine whether productivity in the bay was in fact relatively stable pre-settlement, or varied widely in response to climatic change and environmental perturbations. One core from each of the two sub-basins in the bay was examined and radiocarbon dated. Measured proxies included magnetic susceptibility, C and N content, CIN ratios, biogenic silica, particle grain size, X-Ray diffraction of mineralogy, and stable carbon isotopes. SAB results are compared to a study of cores extracted from Missisquoi Bay (Koff, 2012), which is another shallow segment of Lake Champlain that currently experiences severe eutrophication problems.
Results indicate that SAB responded to multiple natural perturbations during the Holocene, including variations in temperature, precipitation, lake level, internal nutrient loading, and watershed hydrology. For example, periods of high productivity were generally related to warmer conditions, and periods of low productivity to cooler conditions. The inner, shallow bay seems to have been dominated by macrophytes throughout most of its history, in contrast with the deeper, outer bay, which was dominated by algae. During lake high-stands, productivity was generally lower, with decreased influx of macrophyte material to the central parts of the bay, while lake low-stands forced the zone of macrophyte productivity to migrate to the offshore parts ofthe bay. In addition, the inner sub-basin of SAB was more susceptible to changes in climate and environment than the outer bay, most likely due to its proximity to river inputs and wetlands, and its shallower depth.
Early episodes of productivity at or above the levels present since permanent settlement in the basin can be confirmed in both St. Albans and Missisquoi Bays. The role of climate and environment as drivers of SAB productivity in the past may serve as a harbinger of future productivity increases during global warming and increased human activity in the watershed.