Date of Award
Level of Access Assigned by Author
Master of Science (MS)
Daniel F. Belknap
Second Committee Member
Joseph T. Kelley
Third Committee Member
Cynthia S. Loftin
Sea level has risen at a rate of ~2 mm/yr in eastern coastal Maine. Modern rates of sea-level rise surpass those of the long-term average by a factor of two to three. While numerous studies have focused on the effects of sea-level rise on the seaward edge of salt marshes, fewer studies have addressed the movement of the landward boundary of these marshes with adjacent freshwater wetlands that also are affected by sea-level rise. By shifting the landward boundary of salt marshes, continued sea-level rise will impose local geographic changes on the Maine coast. Given that sea level exerts such a strong influence on salt marshes, the chrono-stratigraphic record of marshes allows predictions of future changes at the edge of salt marsh and freshwater wetlands. Down East coastal Maine is unusual among the lower 48 states because it possesses extensive bogs, some of which are intersected by the leading edge of salt marshes. This study documents past behavior of the salt marsh–freshwater transition zone along the Down East coast in terms of rates of migration of the marine edge into terrestrial environments and the stratigraphic record left by this migration. Multiple techniques were employed to quantify succession rates of freshwater wetlands to salt marsh, establish the general stratigraphic signal, and begin to characterize the catalyst for transgression at the transition zone at several sites along the Down East coast (Jones Marsh, Mount Desert Island; Grand Marsh, Gouldsboro; Hay Creek, Jonesport; and Carrying Place Cove, Lubec). Ground-penetrating radar (GPR) revealed general substrate stratigraphy and guided coring and sampling transects to establish overall stratigraphy and rates of change. The interface of freshwater wetlands and salt marsh at depth corresponds with a blanking of the GPR signal by saltwater. Dutch cores generally penetrate salt marsh over freshwater peat, and refuse in glaciomarine mud or sand. The results from GPR and coring suggest that the ongoing transgression results in a clear erosional unconformity. By means of radiocarbon dating, the base of the section shows a break from a few hundred to thousands of years between the salt marsh and the underlying bog. At Jones Marsh, Grand Marsh and Hay Creek, where the freshwater wetland is buffered by a salt marsh, difficulties with photograph coregistration and boundary uncertainties did not allow for successful detection of measurable change with sequential aerial photography over the time span of ~50 years. The transgression rate of the salt marsh is not occurring on the order of decimeters of change per year, and thus the stratigraphy in that transition zone is >50 years old. Carrying Place Cove, the only site that directly abuts the open marine environment, experiences erosion rates of up to a meter per year. An age model from Hay Creek illustrates the distinct, order-of-magnitude difference in accumulation rates for the freshwater and salt marsh environments. The freshwater bog is accumulating at much slower rates than the salt marsh (~0.05 mm/yr and 0.5 mm/yr, respectively). These rates of accumulation lag current and likely future rates of sea-level rise. The rate of migration is not happening on the time scale of management interests.
Mansfield, Margot Elena, "The Critical Leading Edge of Gulf of Maine Salt Marshes: Interface with Freshwater Wetlands" (2012). Electronic Theses and Dissertations. 1778.
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