Date of Award

Spring 5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Biological, Environmental, and Earth Sciences

Committee Chair

Dr. Gregory Carter

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Dr. George Raber

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Dr. Frank Heitmuller

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Committee Member 4

Dr. David Cochran

Committee Member 4 School

Biological, Environmental, and Earth Sciences

Abstract

Salt marshes are critical ecological gems that serve as habitat for many specialized species of flora and fauna, while providing a natural buffer to human populations from tropical cyclone impacts. However, rises growth of coastal populations has led to greater strain on the natural services these ecosystems provide. To better understand and project the future of coastal evolution, the physical, mechanical, and biological feedbacks between the natural and human coupled systems need to be more defined and thoroughly understood. Human encroachment towards naturally retreating shorelines will lead to coastal communities being more susceptible to nuisance tidal flooding and minor tropical cyclone impacts well into the future. Further, the natural system is reliant on the human system for ecological balance due to land use practices and resource depletion. The need to quantify and understand the precise elevation at which the natural salt marsh system occurs is essential in achieving a balanced natural-human ecosystem in coastal areas. The goal of this study was to determine the relationship between precise elevation (cm-scale) and slope associated with salt marsh plant communities along Mississippi’s Gulf Coast (diurnal, microtidal). In particular, the marsh-upland ecotone is of increasing importance due to its sensitivity to environmental stressors. Elevations (NAVD88) were measured using survey-grade GNSS solutions integrated with high-precision leveling. Associated plant species were documented at approximately 1-meter intervals along 33 transects extending from the intermediate marsh through the marsh-upland ecotone. Elevation thresholds associated with plant community change were determined based on the relevant quartiles of the data, and probabilities of occurrence of each plant community were computed for elevations at the centimeter scale. Additionally, first and second derivative extrema were determined from smoothed elevation profiles. Results indicated transitions from marsh to ecotone and ecotone to upland at elevations of approximately 0.40 m and 0.60 m, respectively. Further, plant community transitions occurred in near proximity to slope maximum, which proved effective in modeling model ecotone spatial position. Quantifying the precise dependencies of marsh vegetation with elevation and slope will help facilitate marsh stability and migration prediction models in response to land use change, alterations in sediment flux, and relative sea level rise.

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