The University of Southern Mississippi The Aquila Digital Community Master's Theses Spring 2020 Nearshore Sedimentology of Eroding Microtidal Estuaries: Bon Secour Bay, Alabama and Perdido Bay, Florida Jennifer Simpson Follow this and additional works at: https://aquila.usm.edu/masters_theses Part of the Geology Commons Recommended Citation Simpson, Jennifer, "Nearshore Sedimentology of Eroding Microtidal Estuaries: Bon Secour Bay, Alabama and Perdido Bay, Florida" (2020). Master's Theses. 717. https://aquila.usm.edu/masters_theses/717 This Masters Thesis is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Master's Theses by an authorized administrator of The Aquila Digital Community. For more information, please contact [email protected]. NEARSHORE SEDIMENTOLOGY OF ERODING MICROTIDAL ESTUARIES: BON SECOUR BAY, ALABAMA AND PERDIDO BAY, FLORIDA by Jennifer L. Simpson A Thesis Submitted to the Graduate School, the College of Arts and Sciences and the School of Biological, Environmental, and Earth Sciences at The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Master of Science Approved by: Dr. Franklin T. Heitmuller, Committee Chair Dr. T. Markham Puckett Dr. Carl A. “Andy” Reese Dr. Davin J. Wallace ____________________ ____________________ ____________________ Dr. Franklin T. Heitmuller Dr. Jacob Schaefer Dr. Karen S. Coats Committee Chair Director of School Dean of the Graduate School May 2020 COPYRIGHT BY Jennifer L. Simpson 2020 Published by the Graduate School 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. ii ACKNOWLEDGMENTS I would like to express great appreciation to my committee chair and advisor, Dr. Frank Heitmuller, whose guidance and encouragement through this thesis has been irreplaceable. His positive attitude and unwavering willingness to help me through this challenging process has been a lesson in and of itself that I will take with me into my future ventures. I would also like to extend my gratitude to my committee members, Dr. Mark Puckett, Dr. Andy Reese, and Dr. Davin Wallace, whose collective generosity of equipment, advice, and extensive knowledge in their respective fields have contributed to the development and success of this project. Additionally, I would like to thank Dr. Scott Phipps and Shannon Walker from Weeks Bay National Estuarine Research Reserve; and Arthur Stiles with the Florida Department of Environmental Protection for their help in the facilitation of site locations for this project. I am also thankful for the support and camaraderie of the faculty and fellow students in the geology department at the University of Southern Mississippi. Finally, I am grateful for the inspiration, motivation, and confidence I unrelentingly received from my family and friends throughout this journey. iii TABLE OF CONTENTS ABSTRACT ........................................................................................................................ ii ACKNOWLEDGMENTS ................................................................................................. iii LIST OF TABLES ............................................................................................................. ix LIST OF ILLUSTRATIONS ............................................................................................. xi CHAPTER I – INTRODUCTION ...................................................................................... 1 1.1 Introduction ............................................................................................................... 1 1.2 Research Questions ................................................................................................... 4 1.3 Hypothesis................................................................................................................. 5 1.4 Thesis Scope ............................................................................................................. 6 CHAPTER II – LITERATURE REVIEW ......................................................................... 8 2.1 Geologic Setting........................................................................................................ 8 2.2 Depositional History ............................................................................................... 11 2.3 Climate .................................................................................................................... 12 2.4 Transgressive Systems Tract................................................................................... 13 2.5 Estuary Model ......................................................................................................... 14 2.6 Previous work ......................................................................................................... 17 2.6.1 Cedar Island, North Carolina ........................................................................... 17 2.6.2 Chesapeake Bay, Maryland ............................................................................. 18 CHAPTER III – STUDY AREA ...................................................................................... 20 iv 3.1 General Study Area ................................................................................................. 20 3.1.2 Bon Secour Bay ............................................................................................... 21 3.1.3 Perdido Bay ...................................................................................................... 24 CHAPTER IV – METHODOLOGY ................................................................................ 27 4.1 Preliminary Assessments Using Aerial Imagery .................................................... 27 4.2 Field Sampling and Data Collection ....................................................................... 30 4.2.1 Sample Locations ............................................................................................. 30 4.2.2 Nearshore Sediment Cores ............................................................................... 31 4.2.3 Piezometers ...................................................................................................... 36 4.2.4 Bottom Sediment Samples ............................................................................... 42 4.2.5 Erosion Pins ..................................................................................................... 45 4.3 Laboratory Analyses ............................................................................................... 47 4.3.1 Sediment Particle Size ..................................................................................... 48 4.3.2 Organic Matter ................................................................................................. 49 4.3.3 Calcium Carbonate........................................................................................... 49 4.3.4 Magnetic Susceptibility ................................................................................... 49 4.4 Statistical Analysis .................................................................................................. 51 CHAPTER V – RESULTS ............................................................................................... 52 5.1 Laboratory Results .................................................................................................. 52 5.1.1 Nearshore sediment cores ................................................................................ 52 v 5.1.1.2 BSB-C-01-1 .............................................................................................. 53 5.1.1.3 BSB-C-01-2 .............................................................................................