SAVE Currituck Sound: Submerged Aquatic Vegetation Evaluation in Currituck Sound, NC
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SAVE Currituck Sound: Submerged Aquatic Vegetation Evaluation in Currituck Sound, NC by Natasha G. Biarrieta May 2020 Director of Thesis: D. Reide Corbett, PhD Major Department: Geological Sciences ABSTRACT Submerged aquatic vegetation (SAV) provide numerous ecosystem services including enhanced biodiversity, erosion control and sediment stabilization, nutrient cycling, improved water quality, and organic carbon sequestration. Rapid environmental changes and increased coastal development have resulted in significant SAV losses globally. Currituck Sound, the northernmost estuary in North Carolina, was once known for extensive SAV beds serving as a refuge and food source to an abundance of fish and waterfowl that attracted anglers and hunters from all over the country. However, declines in water quality as a result of rapid population growth and development have led to massive declines in SAV habitats that have been devastating to the local ecology. This study investigated changes in historical and current SAV distribution and evaluated how these changes have been influenced by depth, light availability, and bed-sediment composition. The past and present relationship between depth and SAV cover was examined in several ways: (1) historical SAV cover maps, (2) hydroacoustic surveys, (3) quadrat transect surveys, (4) modeling using light attenuation data, and (5) comparisons with historical ground surveys. In Currituck Sound, SAV are not present beyond a water depth of 1.8 m and are preferentially located at depths shallower than 1.0 m. The median light attenuation for the combined 2016 and 2017 growing seasons was 1.99 m-1. The calculated minimum water-column light requirement was 2.8% and water-column light requirement for peak growth was ≥13.7%. Sediments were dominated by sand (average weight percent >90%) and had very low organic content (average percent loss on ignition ~1.0%). While some spatial and temporal variations in sediment composition were identified, no statistical relationships between SAV cover and sediment characteristics were observed. Light availability with depth proved to be the dominant factor limiting SAV growth and distribution in Currituck Sound. Therefore, the light and depth thresholds identified in this study are key to developing a sound management and mitigation plan. SAVE Currituck Sound: Submerged Aquatic Vegetation Evaluation in Currituck Sound, NC A Thesis Presented to the Faculty of the Department of Geological Sciences East Carolina University In Partial Fulfillment of the Requirements for the Degree Master of Science in Geology by Natasha G. Biarrieta May 2020 © Natasha G. Biarrieta, 2020 SAVE Currituck Sound: Submerged Aquatic Vegetation Evaluation in Currituck Sound, NC by Natasha G. Biarrieta APPROVED BY: DIRECTOR OF THESIS ______________________________ D. Reide Corbett, PhD COMMITTEE MEMBER ______________________________ Sidhartha Mitra, PhD COMMITTEE MEMBER ______________________________ Terri L. Woods, PhD EXTERNAL COMMITTEE MEMBER ______________________________ J. P. Walsh, PhD CHAIR OF THE DEPARTMENT OF GEOLOGICAL SCIENCES ______________________________ Stephen J. Culver, PhD DEAN OF THE GRADUATE SCHOOL ______________________________ Paul J. Gemperline, PhD ACKNOWLEDGEMENTS My sincere and deepest gratitude goes first and foremost to my advisor, Dr. Reide Corbett, whose constant guidance, support, and unrivalled enthusiasm made this work possible. I would also like to thank the members of my committee, Drs. Sid Mitra, J.P. Walsh, and Terri Woods, for their valuable insight and support throughout this process. Financial support was provided in part by the North Carolina Department of Transportation. Thank you to the U.S. Army Corps of Engineers Field Research Facility and CSA Ocean Sciences, Inc. for their collaboration in this research. A special thanks to Pat Dickhudt and Erin Hodel for their assistance with data collection and their scientific guidance on this project. I am very grateful to the faculty, staff, and students of the ECU Department of Geological Sciences and Coastal Studies Institute who made this work possible through their professional and personal support. I would especially like to thank Liz Mason for her help collecting and processing data, Paul Paris for his invaluable expertise and advice, Dave Sybert for his considerable assistance in the field, and all for their unwavering encouragement and friendship. Finally, I could not have done this without the incredible support and love of my family. Thank you most of all to my parents, Regis and Claudia Biarrieta, for all their sacrifices, patience, and relentless encouragement and to my brother, Leandro Biarrieta, for always being my fiercest friend. TABLE OF CONTENTS LIST OF TABLES....................................................................................................................... vii LIST OF FIGURES..................................................................................................................... ix 1.0 INTRODUCTION................................................................................................................. 1 1.1 SAV in Currituck Sound............................................................................................ 3 2.0 BACKGROUND................................................................................................................... 8 2.1 Currituck Sound......................................................................................................... 8 2.2 Mid-Currituck Bridge................................................................................................ 10 3.0 METHODS............................................................................................................................ 12 3.1 Study Design.............................................................................................................. 12 3.2 Historical SAV Cover................................................................................................ 14 3.3 Hydroacoustic Surveys.............................................................................................. 19 3.4 Quadrat Surveys......................................................................................................... 21 3.5 Light Attenuation Model........................................................................................... 23 4.0 RESULTS.............................................................................................................................. 26 4.1 Historical SAV Cover................................................................................................ 26 4.2 Hydroacoustic Surveys.............................................................................................. 28 4.3 Quadrat Surveys......................................................................................................... 30 4.3.1 Sediments.................................................................................................... 30 4.3.2 SAV Cover.................................................................................................. 33 4.3.3 SAV Species............................................................................................... 35 4.4 Light Attenuation Model........................................................................................... 37 5.0 DISCUSSION........................................................................................................................ 41 5.1 Spatial Variation in SAV: Changes and Sedimentologic Drivers............................. 41 5.2 Depth/Light Attenuation Influence on SAV Distribution.......................................... 52 6.0 FUTURE MANAGEMENT IMPLICATIONS..................................................................... 58 7.0 SUMMARY........................................................................................................................... 65 REFERENCES............................................................................................................................ 66 APPENDIX A: Statistical Analyses Result Reports.................................................................... 77 APPENDIX B: Maps of Past SAV Surveys in Currituck Sound................................................ 127 LIST OF TABLES Table 1. BioSonics surveys depth and relationship with SAV................................................. 30 Table 2. Summary statistics of SAV percent cover (% Cover), weight percent (wt. %) of sand, silt, and clay, and percent loss on ignition (% LOI) as measured from the quadrat surveys........................................................................................................... 32 Table 3. Mean weight percent (wt. %) of sand, silt, and clay and percent loss on ignition (% LOI) as measured from the quadrat surveys for northern and southern study areas and the absolute difference between the means of the two study areas...................... 33 Table 4. Mean SAV percent cover as measured from the quadrat surveys and results of the Student’s t-test comparing the northern and southern study areas.............................. 34 Table 5. Mean SAV percent cover as measured from the quadrat surveys and results of the Student’s t-test comparing the grouped transects found along the western shore, eastern shore, and middle marsh areas (i.e., west, east, mid)..................................... 35 Table 6. Frequency of occurrence of each species observed during the quadrat surveys........