| Summary: | This dissertation is an investigation into the interplay between vegetation and aeolian processes in the coastal embryo dune environment at Padre Island National Seashore, Texas. Vegetation is a geomorphic agent, altering aeolian process dynamics. This research adopted a three-pronged approach to improving our understanding of ecogeomorphodynamics in the coastal environment.
The first study analyzed large-scale spatiotemporal trends in the vegetation community of the embryo dune environment in order to contextualize smaller scale aeolian processes. Results of this study demonstrated that there was a clear transition in community assemblage from the seaward edge of the embryo dune zone, where species functioned as pioneer builders promoting deposition, to foredune toe, where species stabilized and protected the substrate from erosion.
The second study documented morphology of different vegetation types (tall grass, short grass, and shrub) as well as their response to wind velocity. While tall grass occupied the greatest area, it also had the highest porosity. Short grasses occupied less space than the tall grasses, with roughly half the optical porosity. Shrubs occupied the lowest volume but were the densest roughness element with the highest optical porosity.
The final study documented spatial patterns of fluid flow and sediment erosion and deposition around vegetation of different morphology types (tall grass, short grass, and shrub). Tall grasses and shrubs were more effective at reducing velocity in their lee than short grasses, with tall grasses creating a larger deceleration zone than shrubs. However, the greatest deposition occurred around patches of short grass, which was the shortest morphology type.
Findings of this dissertation suggest that both optical porosity and element size influence patterns of aeolian flow and sediment deposition. There is a tradeoff between overall size of a roughness element in the flow field and the porosity of that element. Objects with lower optical porosity but smaller size are less effective at trapping sediment than elements with greater size and higher optical porosity. Results indicate that large, continuous patches of short, dense vegetation are in fact more effective at trapping and retaining sediment than tall grasses which obtrude into the boundary layer and cause greater flow deceleration.
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