Date of Award

Summer 8-19-2016

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Earth Sciences

Advisor

Joseph T. Kelley

Second Committee Member

Daniel F. Belknap

Third Committee Member

Lawrence M. Mayer

Abstract

The tidally dominated Damariscotta River estuary is located on the south-central Maine coast. The elongate, north-south orientation of the estuary is characteristic of the indented shoreline in this region and a consequence of the bedrock structural framework, comprised of Paleozoic high-grade metasedimentary rocks. Pegmatite sills form bedrock constriction points that divide the estuary into seven distinct basins. The narrow, bending geometry and sill and basin morphology impact the distribution of sediment within the estuary and the hydrodynamics of the system. This study employs multibeam bathymetry surveys, sediment grab samples and radionuclide analysis (210Pb and 137Cs) of sediment cores to evaluate the impact of the bedrock framework on sediment accumulation patterns in the estuary. Sedimentation rates in the estuary are lower than those of other estuaries in the region, indicative of a sediment-starved system. As a result of extensive reworking of sediment within the estuary, the inner estuary is sediment choked and the volume and distribution of sediment control the hydrodynamics in this region. Current lineations mark a transition from the inner to middle and outer estuary, where the volume of sediment is reduced and constriction points formed by bedrock sills dominate the morphology of the system.

The role of the bedrock framework in the morphology of the system is not unique to the Damariscotta River but also applies to other estuaries in the region. Despite its absence from many published conceptual models, bedrock framework is critical to development of estuaries in rocky, formerly glaciated regions. Furthermore its role in the distribution of sediment, as well as pollutants and contaminants, is significant in the context of global climate change, continued shoreline development in the region and expansion of Maine’s aquaculture industry.

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