Browsing by Subject "tidal creek"
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Item Characterization of sediment movement in tidal creeks adjacent to the gulf intracoastal waterway at Aransas National Wildlife Refuge, Austwell, TX: study of natural factors and effects of barge-induced drawdown currents(Texas A&M University, 2005-08-29) Allison, John BryanThe 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.Item Spatial and Temporal Dynamics of Salt Marsh Vegetation across Scales(2010-10-12) Kim, DaehyunBiogeographic patterns across a landscape are developed by the interplay of environmental processes operating at different spatial and temporal scales. This research investigated dynamics of salt marsh vegetation on the Skallingen salt marsh in Denmark responding to environmental variations at large, medium, and fine scales along both spatial and temporal spectrums. At the broad scale, this research addressed the importance of wind-induced rise of the sea surface in such biogeographic changes. A new hypothetical chain was suggested: recent trends in the North Atlantic Oscillation index toward its positive phase have led to increased storminess and wind tides on the ocean surface, resulting in increased frequency, duration, and magnitude of submergence and, hence, waterlogging of marsh soils and plants, which has retarded ecological succession. At the mid-scale, spatial patterns of vegetation and environmental factors were examined across tidal creeks. Sites closer to tidal creeks, compared to marsh interiors, were characterized by the dominance of later-successional species, higher bulk density, and lower nutrient contents and electrical conductivity. This finding implies that locations near creeks have experienced a better drainage condition than the inner marshes, which eventually facilitated the establishment of later-successional plants that are intolerant to physical stress. At the micro-scale, this research examined how the extent and mode of facilitation and competition vary for different combinations of plant species along physical gradients. Both positive and negative relationships were spatially manifested to a greater degree on the low marsh than on the mid marsh. This insight extends our current knowledge of scale-dependent interactions beyond pioneer zones to higher zones. On the low marsh, different types of bivariate point pattern (i.e., clustered, random, and regular) were observed for different combinations of species even at similar spatial scales. This finding implies that it is difficult to generalize at which scales competition and facilitation occur. To conclude, this research stresses the need for a holistic approach in future investigations of salt marsh biogeography. For example, based on results of this current research, it would be meaningful to develop a comprehensive simulation model that incorporates salt marsh ecology, geomorphology, and hydrology observed across scales.