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acase@tulane.edu / Ecogeomorphology is the study of interactions and feedbacks between the physical surface processes and biological communities in an ecosystem. These interactions are under-studied in wetlands associated with river deltas, and are of vital importance to the deteriorating wetlands of South Louisiana. As the state of Louisiana implements its Comprehensive Master Plan for a Sustainable Coast, which relies heavily on diverting Mississippi River water in order to create new wetlands, a detailed understanding of ecogeomorphological relationships is required to create accurate predictive models to design and assess future projects. This research is comprised of three studies of such relationships in the West Bay Sediment Diversion near Venice, LA, and has resulted in the following key findings: 1) the composition of the buried seed bank suggests a shift from river-derived to within-system propagules as the marsh develops, 2) emergent plant roots increase the cohesion of marsh soils, especially when grasses, sedges, and woody species dominate the vegetation, and 3) a competition experiment between the native sedge Schoenoplectus deltarum and the invasive grass Phragmites australis indicated that the two species performed approximately equally in mixture, regardless of abiotic stressors, while the stressors did affect productivity of each species grown in monoculture. These three studies are unified by the role of wetland vegetation as an increasingly important autogenic modifier of other wetland processes during the early development of the marsh. / 1 / Alexander D Ameen

Thesis (Ph.D.) -- University of Rhode Island, 2008. / Typescript. Includes bibliographical references (leaves 170-184).

Accelerating sea-level rise (SLR) poses an imminent threat to salt marshes, which sit within meters of mean sea level. In order to assess marsh vulnerability to SLR, we must first understand the fundamental processes governing marsh response to SLR. The objective of this dissertation work is to examine how marsh sedimentation and erosion affect the morphological development of marshes as sea level rises, over a broad range of spatial and temporal scales. At the smallest scale, the effects of bioturbation by Sesarma reticulatum crabs on sediment erodibility are examined using a laboratory flume. Measurements of surface elevation, erosion, and turbidity show that S. reticulatum bioturbation repackages formerly compacted sediment and deposits it above the surface, decreasing the threshold velocity for erosion and increasing eroded volume. S. reticulatum-induced sediment erosion can have broader impacts on creek development and marsh morphology. S. reticulatum has facilitated drainage network expansion in salt marshes at Sapelo Island, GA and Cape Romain, SC in response to local SLR. Burrowing by this crab directly adjacent to tidal creeks at these locations leads to rapid headward growth. The effects of site-specific conditions on creek expansion are examined through comparison of sediment properties, surface elevations, and historical rates of creek growth at each site. Results suggest that while similar processes are occurring at both locations, the higher elevation of the marsh in GA leads to greater shear strength and a larger volume of material to be eroded by creeks. These combined effects have led to slower creek growth compared to SC. At the largest spatial scale, and projecting forward over a 100-year period, a model for marsh response to SLR at the Great Marsh in Massachusetts is developed. This model takes into account limitations imposed by both low sediment availability and steep topography in the surrounding uplands. Results indicate that while the marsh may persist for several decades, it undergoes a dramatic shift in ecology and hydrology. As the rate of SLR accelerates, marsh loss increases due to the lack of sediment available for accretion and the physical barriers to migration presented by surrounding topography.

Thesis (M.S.) in Marine Biology--University of Maine, 2006. / Includes vita. Includes bibliographical references (leaves 77-82).

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