Date of Award
2026
Degree Name
Biological Sciences
College
College of Science
Type of Degree
M.S.
Document Type
Thesis
First Advisor
Dr. Kyle A. Palmquist
Second Advisor
Dr. Anne Axel
Third Advisor
Dr. Anita Walz
Abstract
Accelerating sea-level rise and storm surge events pose a substantial threat to salt marsh ecosystems, which provide critical ecosystem services. Classification and mapping of coastal vegetation through remote sensing can identify marsh dieback events and provide spatial context for patterns of marsh vulnerability. We used a multi-sensor approach that incorporated LiDAR data, multispectral imagery, and field-derived cover estimates to classify Spartina alterniflora (smooth cordgrass) dominated marsh types on Marine Corps Recruit Depot Parris Island (MCRDPI), a sea island in South Carolina, USA. In summer 2025, surveys were conducted within marsh classes to collect training and validation data. We used random forest models and Planet imagery to produce a time-series of salt marsh vegetation maps from 2016 to 2025. Models were assessed using spatial cross-validation and class accuracy values for vegetated salt and bare marsh classifications were 94% and 84%, respectively. We identified transitions between salt and bare marsh between years to highlight unstable areas with multiple conversion events. From 2016 to 2025, 83% of salt marsh remained stable but overall vegetated salt marsh area declined from 96.7% to 93.7% (-3%), while bare marsh coverage increased from 2.1% to 4.6% (+2.5%). Landscape metrics analysis results also showed a net increase in marsh fragmentation through changes in class aggregation and edge density values. We found that 43% of salt marsh to bare marsh conversion events from 2019 to 2025 were preceded by gradual declines in NDVI, while 43% were preceded by stable NDVI values. The remaining events (13%) were characterized as sudden dieback, where NDVI values increased before conversion.
From 2016 to 2025, we observed that mean yearly NDVI values declined while flooding frequency, a measure of how often the marsh was inundated, increased. We fit generalized linear mixed models with random intercepts and slopes to evaluate the influence of distance to infrastructure and natural barriers, elevation, and slope (fixed effects) on the likelihood of salt marsh to bare marsh conversion. Our results indicated that flatter, lower elevation marshes were more susceptible to transition to bare marsh and revealed a significant (p < 0.01) negative threeway interaction between infrastructure distance, elevation, and slope. Distance to infrastructure and distance to natural barriers alone were not significant (p = 0.4 and p = 0.08, respectively) and distance to natural barriers was only significant in two-way interactions with slope and elevation. These results provide context for spatial changes in salt marsh habitat, offer insight into factors affecting salt marsh loss, and provide a foundation to model marsh resilience under future sealevel rise scenarios.
Subject(s)
Ecology.
Remote sensing.
Climatic changes.
Global warming.
Salt marshes.
Sea level.
Spartina.
Vegetation classification.
Biotic communities.
Coastal plants.
Spartina alterniflora.
Recommended Citation
Bartholomew, Zak Henry, "Mapping coastal vegetation to evaluate salt marsh decline from 2016 to 2025 in South Carolina, USA" (2026). Theses, Dissertations and Capstones. 2111.
https://mds.marshall.edu/etd/2111
