DOI
https://doi.org/10.25772/NG7M-G291
Defense Date
2023
Document Type
Thesis
Degree Name
Master of Science
Department
Biology
First Advisor
Julie Zinnert
Second Advisor
Donald Young
Third Advisor
Lesley Bulluck
Fourth Advisor
Jennifer Ciminelli
Fifth Advisor
Christopher Gough
Abstract
Located at the land-sea interface, barrier islands are important protective features that reduce wave energy and erosion from mainland areas. Further, barrier islands provide habitat for many different organisms and serve as popular areas for recreation and tourism. As sandy landforms, barrier islands are easily disturbed, but often recover after disturbance as a result of island plant communities, specifically dune building grasses. Disturbance on barrier islands is driven by storms, tides, and overwash events. After disturbance has occurred, dune grasses colonize the dunes allowing for dune building and habitat restoration. On the Virginia barrier islands, there are three dominant dune building grasses. These include Ammophila breviligulata, Spartina patens, and Panicum amarum. Uniola paniculata is also present in the region, but not in high abundance. Dune building has the potential to impact the entire barrier island ecosystem, and these grasses therefore serve as ecosystem engineers. Protection offered by dune ridges directly impacts the adjacent swale habitat, modifying both biotic and abiotic factors. In order to better understand how dune building impacts the island ecosystem as a whole, we quantified sediment accretion, plant percent cover, stem numbers, and soil characteristics (chlorides, bulk density, %OM, %C, %N). These characteristics were assessed on two islands with varied disturbance intensities. Hog island is infrequently disturbed, and resists change driven by storms and overwash. Metompkin island is frequently disturbed and undergoes high rates of overwash and island migration. In order to quantify these characteristics, 3 cross-shore transects were established on each island in 2020. Additional accretion plots were set on each island during fall 2021. Annual drone flights conducted over the islands provided for additional large-scale data collection and allowed for assessment of dune continuity through least cost paths. After one year, sediment accretion occurred at a higher rate on Hog compared to Metompkin. Dune face plots on Hog accreted sediment while dune face plots on Metompkin underwent high rates of erosion resulting in 9 of 15 plots transitioning from dune to open beach. On Hog, plots established in a newly formed dune hummock accreted sediment at a faster rate than those on the dune face. Species-specific effects were also observed on Hog, with Panicum accreting sediment at a significantly lower rate compared to Ammophila and Spartina. Larger, more continuous dunes on Hog offer enhanced protection for the swale habitat, reducing soil chlorides and increasing annual net primary productivity and soil carbon and nitrogen. As climate change continues to modify ecosystems globally, barrier islands will be at the forefront of increased severe weather and increased sea level. It is therefore crucial that we understand how these ecosystems respond to and recover from disturbance, and the many interconnected variables that exist among barrier island ecosystems. Understanding all aspects of the barrier island system will allow these data to be implemented into models to predict future barrier island scenarios.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
5-3-2023