Thesis (Ph. D.)--University of California, Berkeley, 2006. / Includes bibliographical references.

No description available.

No description available.

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.

The aim of this thesis was to improve our understanding of plant – flow interactions and to develop new remote sensing techniques that would allow a marsh scale assessment of flow modification due to the presence of salt marsh vegetation. The limitations of current approaches which improve our understanding and prediction of tidal flows centre around poor assessments of canopy structure and mechanical properties. The validity of such simplified and reductionist assessments of canopy structure were tested and found to contribute considerable error in estimations of canopy frontal area and canopy drag. New metrics to assess canopy structure were tested as part of a flume study using two salt marsh species with varying form and architecture. Results from this experiment found that biomass located immediately below the water surface are important for determining fluid momentum losses in salt marsh canopies. These results led to the development of a new empirical based model using vertical measures of biomass and approach (incident) velocity which can accurately (R2 0.71) predict flow momentum losses. This suggests that the characteristic vegetation parameter and the drag coefficient may be substituted with vertical canopy biomass and an empirical coefficient. This may lead to more accurate assessments of canopy structure and thus comparable results across the literature as well as potentially apriori assignment of parameters in the force drag model. Vertical canopy biomass (3D biomass) was then estimated at the marsh scale using a combined remote sensing approach and an empirical model. Accurate assessments of the marsh surface are critical for hydrodynamic models and important if we are to determine vertical changes in canopy structure. The approach first identified marsh surface returns by operating a moving average smoothing filter on Airborne Laser Scanning (ALS) data. The automated procedure detected vegetated and non–vegetated surfaces using aerial NDVI which calibrated the filter and ensured ALS returns were representative of marsh surface elevation. Using the marsh surface DEM, vegetation was reconstructed at 0.2 m grid cells. Terrestrial Laser Scanning (TLS) was found to accurately quantify maximum canopy height (RMSE 0.14m) whilst a regression model using aerial NDVI and spatial coordinates gave reasonable predictions (RMSE 0.08kg/m2) of total plot canopy biomass within each 0.2 m cell across a ~20,000 m2 area of marsh. Ground measurements found the vertical distribution of canopy biomass followed a power law increase with elevation from the marsh bed. Combining all the approaches allowed the creation of a 3D assessment of canopy biomass with an average error of 30% of the mean amongst plots exhibiting larger canopy biomass ( > 0.4 kg/m2). This vertical measure of biomass can be combined with the flow momentum loss model generated in the flume experiment to assess hydrodynamic canopy drag potential at the marsh scale. Roughness coefficients can also be calculated using this approach which can be easily fed into commercially available numerical flow models.

Thesis (Ph. D.)--University of Rhode Island, 2006. / Typescript. Includes bibliographical references (leaves 178-197).

Thesis (M.S.)--Oregon State University, 1971. / Partially funded by Oregon Agricultural Experiment Station. Includes bibliographical references (leaves 39-41). Also available on the World Wide Web.

No description available.

The coastal wetlands at Aransas National Wildlife Refuge near Austwell, Texas, support the last migrating population of whooping cranes during the winter months (October through April). With a population currently at 216 individuals, these are the rarest cranes in the world. The wetlands in which they winter are a part of the San Antonio Bay system, a bay that receives constant fresh water flow from the Guadalupe River. Currently there is a plan for using water diverted from the Guadalupe River just before it enters San Antonio Bay as a water supply for the greater San Antonio metropolitan area located 200 km to the northwest. The Guadalupe River delivers nutrients and sediment into the estuary along with fresh water. Because of the importance of sediment within a tidal wetland ecosystem, it is imperative to understand the sediment budget and underlying forces that drive it if one is to ultimately grasp how this ecosystem functions. To document natural and anthropogenic factors exerting control over sediment movement in this system, three sites on tidal creeks near the boundary between marsh and bay were chosen. The Gulf Intracoastal Waterwayparallels the marsh edge. Over six, non-consecutive weeks water level and velocity were automatically monitored in the tidal creeks. Automated water samplers extracted water samples that were analyzed for suspended sediment. In addition, bedload traps were deployed in one creek to monitor sediment movement along the channel bottom. Inflow exceeded outflow during the study. As a result there was a net influx of suspended sediments into the marsh. Bedload material also moves with current direction, and it appears to move in response to barge induced outflow currents. Barges passing on the Gulf Intracoastal Waterway exert influence on water level, flow direction, and velocity within tidal creeks. Natural factors such as winds, tides, and freshwater input from upland runoff or river discharge also impact suspended and bedload sediments.

Salt marsh food webs are complex systems, with high levels of in situ primary production supporting a wealth of resident and migratory species. In this study, we use stable isotopes as a tool to trace organic matter utilization within the Nueces Marsh food web. Specifically, we were interested in (1) the use of treated wastewater as a ¹⁵N tracer, and (2) seasonal and interannual variation in food web structure. We hypothesized that treated wastewater would selectively label detrital resourse use within the food web, allowing us to trace grazing vs. detrital pathways within the marsh system. We also hypothesized that marsh consumers would exhibit distinct differences in isotopic composition between summer and winter, and between different years. We found that the Nueces Marsh food web consists of 3.5 consumer trophic levels. The [delta]¹³C values of consumer organisms were similar across the spatial extent of the low marsh, regardless of proximity to wastewater inflow. However, a majority of the organisms collected from the wastewater channel were significantly (p<0.05) enriched in ¹⁵N compared to their reference counterparts. We propose that ¹⁵N-enriched nitrogen is entering the Nueces Marsh food web through detrital rather than grazing-based pathways, making wastewater effluent an effective tracer of detrital integration into a marsh food web system. Hydrologic data indicate that isotopic shifts between seasons and between years reflected larger scale shifts between drought and wet years. During drought years, decreased production by phytoplankton and emergent plants led consumers to rely more heavily on ¹³C-enriched cyanobacterial carbon. In contrast, wet years encourage phytoplankton and emergent plant production, making cyanobacterial carbon relatively less exploited. While the Nueces Marsh food web is supported by a stable detrital carbon pool, it may still be susceptible to larger scale hydrologic events. / text