Date of Award

Spring 2020

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Franklin T. Heitmuller

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

T. Markham Puckett

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Carl A. "Andy" Reese

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Committee Member 4

Davin J. Wallace

Committee Member 4 School

Ocean Science and Engineering

Abstract

Estuarine shorelines along the northern Gulf of Mexico are dynamic geologic settings that provide numerous ecological and economic benefits. By definition, estuaries are semi-enclosed bodies of water that receive sediment from two sources: (1) fluvial systems feeding into the estuary and (2) sediment transported by wave action and tidal currents from adjacent marine sources. Erosion of estuarine shorelines resulting from rising sea level, storm impact, and anthropogenic influence has been increasingly evident in the microtidal Gulf Coast over recent decades. This study collects quantitative and qualitative data to better understand sedimentary dynamics associated with contemporary estuarine shoreline erosion in Bon Secour Bay, Alabama and Perdido Bay, Florida. Historical aerial imagery compared with modern imagery indicates an average land loss rate of 0.30 – 0.67 m yr-1 at Bon Secour Bay (1992–2018) and 0.55 m yr-1 at Perdido Bay (1994–2018). Selection of these two sites is based on their similar microtidal, sandy, forested, undeveloped, northwest-to-southeast trending shorelines; albeit Bon Secour Bay has a considerably longer fetch and greater fluvial sediment input as it is part of the greater Mobile Bay estuarine system. Particle size of five nearshore sediment cores (~0.75 – 1.00 m below seafloor) are dominated by fine- to medium-grained sand with intervals of very fine and coarse sand and silt (rare). Sedimentological characteristics of nearshore cores and surface sediment suggest eroding shorelines are being directly deposited to the nearshore. Occurrences of shell material, wood fragments, coarser particles, and reduced sorting quality at the base of some core locations indicate facies change and possible ravinement surfaces that have been buried by sediment from a Holocene transgression.

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