Master of Science (MS)
Oceanography and Coastal Sciences
River discharge pulses, wind, waves, tides, and the presence of dense vegetation are factors that interact and regulate the transport and retention of sediment in coastal regions. In particular, vegetation structural and physiognomic traits promote fine sediment trapping during tidal and river flow, maintaining the balance between soil elevation and relative sea level rise on coastline stability and land building. Mike Island, located within Wax Lake Delta, Louisiana, USA, is part of a deltaic system created by a man-made freshwater diversion (1941) and one of few coastal areas where land is expanding in coastal Louisiana as result of pulsing river sediment discharge. Acoustic and optical sensors at upstream and downstream locations in Mike Island were deployed for 30-60 days during spring and late summer in 2015 to evaluate spatiotemporal changes in turbidity, waves, tides, current speed and direction. Sediment traps were installed 30 cm above and on the sediment surface to identify spatiotemporal differences in sediment texture and deposition. During a flood stage, most of the island is dominated by overbank flooding and high discharge from a secondary channel located upstream. When vegetation biomass was low, the downstream station received more wave influence than the upstream station. Current speeds during the spring deployment were approximately 23 cm/s at the upstream station and only 6 cm/s downstream. During peak productivity in August-October, current speeds decreased markedly in early September 2015 due to the presence of dense vegetation interference. Spatial and temporal differences in total inorganic nitrogen (TIN) and orthophosphate (PO43-) nutrient concentrations in overlying and soil surface water were evident and indicate complex nutrient availability patterns controlling vegetation production. Surficial sediments (0-5 cm) collected in April and August (2014) were comprised of approximately 20% sand and 80% mud. Bulk density (BD) in sediment cores increased with depth (50 cm) at the downstream location while BD in the upstream location peaked at shallower depths (<20 cm), indicating differences in sediment deposition history and rates. This study contributes toward the long-term goal of developing and parameterizing biophysical models to manage and recommend freshwater and sediment diversions in Louisiana wetland restoration programs.
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Elliton, Courtney Erin, "Interactions among Hydrology, Sediment and Vegetation in Accreting Wax Lake Delta: Physical and Biogeochemical Implications for Coastal Louisiana Restoration" (2016). LSU Master's Theses. 1730.