Term of Award

Summer 2025

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

J. Checo Colon-Gaud

Committee Member 1

Stephen Vives

Committee Member 2

John Carroll

Abstract

Saltwater intrusion, the movement of ocean water into freshwater, is a significant global threat to coastal freshwater ecosystems linked to both climate change and anthropogenic influences. Alterations to coastal landscapes can increase intrusion. Sapelo Island has an extensive history of agricultural landscape alteration, but freshwater flow decline increased the movement of saltwater inland by tides. Intrusion is expected to increase in frequency and magnitude due to rising sea levels and storms. Salinization puts inland habitats and the humans relying on them at risk. As saltwater is denser than freshwater, more pressure is placed on benthic organisms (i.e., macroinvertebrates) that will be forced into higher salinity conditions and, higher trophic levels rely on macroinvertebrates for food. Previous studies show that saltwater intrusion negatively affects freshwater communities and the essential process of decomposition. I hypothesized that habitats exposed to an increasing gradient of salinity would exhibit reduced diversity and function (as measured by lower decomposition rates). I monitored hydrology, measured decomposition rates using leaf packs, sampled benthic macroinvertebrates with the Rapid Bioassessment Protocols (RBP), and set traps for larger aquatic organisms to assess impacts of saltwater intrusion in three sites across a salinity gradient. As salinity increased, communities significantly shifted from intolerant to tolerant, with the intermediate site overlapping both. RBP scores for sites with saltwater were significantly lower than those without. Diversity metrics were not effective due to seasonal variability, but the intermediate site had higher average richness than the fresh site. Leaf pack decomposition was not significantly different among sites from summer to winter but was significantly faster in the chronic site from winter to spring; the lack of macroinvertebrates collected in leaf packs at that site and accumulation of biofilm suggest strong bacterial decomposition. Traps captured euryhaline fish in the chronic site and the freshwater obligate two-toed amphiuma in the fresh site. I showed that community replacement is occurring across the salinity gradient, and evidence indicates a potential lateral tidal canal connection to the chronic site. Problems associated with saltwater intrusion tied to anthropogenic impacts have been outlined by this study, and these data should help the management of imperiled habitats.

OCLC Number

1528835671

Research Data and Supplementary Material

No

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