Browsing by Subject "Estuary"
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Item Antecedent Geologic Controls on the Distribution of Oyster Reefs in Copano Bay, Texas(2011-08-08) Piper, Erin AlynnCopano Bay is a shallow (< 2-3 m), microtidal estuary in south central Texas. In an effort to both determine the distribution as well as investigate the controls on the distribution of oyster reefs, a geophysical survey of Copano Bay was conducted in June and July 2007. Surficial sediment analysis confirms that the recent sedimentation in Copano Bay is comprised of mostly estuarine mud with little sand or shell, large extents of oyster reefs and smaller areas of sand. Seismic stratigraphy analyses verify that the first oyster reefs in Copano Bay formed atop topographic highs in the Pleistocene surface. About 6 ka, sea level rise slowed to near its present rate and sediment supply decreased tremendously to Copano Bay decreasing the amount of suspended sediment. The first oyster reefs began forming around this time using these fluvial terraces as suitable substrate. Once the initial reefs were established, additional reefs began forming atop these initial reefs, or on the eroded shell hash material from the initial reefs. During this time of slow sea level rise and low sediment input to the bay, oyster reefs thrived and reef and shell hash material covered a majority of the bay surface. Once climate change increased sediment input to the bay, the reefs began to decrease in size due to siltation. The reefs have continued to decrease in size causing a 64 percent reduction in oyster reef and shell hash area from approximately 4.8 ka to today.Item Barrier island associated washover fan and flood tidal delta systems: A geomorphologic analysis and proposed classification scheme for modern washover fans and examination of a flood tidal delta complex in the Cretaceous upper McMurray Formation, Alberta, Canada(2013-12) Hudock, Jessica Wager; Wood, Lesli J.; Flaig, Peter PaulA detailed study of modern washover fan (fan) morphologies will clarify common fan geometries, lead to a better model for a “typical” fan, identify the preservation potential and probable geometries of fan facies in subsurface datasets and outcrops, and ultimately improve hydrocarbon recovery in barrier island reservoir systems. This study uses satellite imagery to conduct a spatial analysis of 118 modern fans to quantify geomorphologic attributes of fans. A new classification scheme for fans is proposed that refines the current fan model, dividing fans into channelized and non-channelized fans. Channelized fans are subdivided according to the location of primary deposition: barrier depo-center or lagoonal depo-center. Non-channelized fans are subdivided based on morphology: dissipative, lobate, or apron-sourced. Quantitative cross-plots of morphologic relationships are analyzed to define trends in fan morphologies. The most common type of fan encountered in our study is a non-channelized, line-sourced, lobate washover fan with an area of less than 1 km2 that is fully contained on a barrier and exhibits no subaqueous deposition in back-barrier waters. The Lower Cretaceous McMurray Formation is the primary reservoir of the Athabasca Oil Sands in Alberta, Canada. The upper McMurray is commonly interpreted as deposits of embayed coastal systems. Our location is in an under-studied area located 80 km northwest of Fort McMurray. Lateral and vertical facies changes, sedimentary structures, key surfaces, trace fossils, and bitumen saturation were documented in eight cores located along a 20 km transect situated paleo-landward of a Devonian paleo-high acting as a bedrock-barrier. Our data indicate that a flood tidal delta complex prograded landward into a back-barrier embayment through the stable, bedrock-controlled inlet. This system overlies middle McMurray fluvial sands and Devonian basement and was transgressed by marine waters prior to deposition of the overlying Wabiskaw Formation. Flood tidal delta sandbodies are bitumen saturated and therefore make good reservoirs; however, heavily bioturbated tidal flats can act as a barrier to flow where they encase flood tidal deltas, as encased sands were devoid of bitumen. This complex coastal paleogeography produced back-barrier deposits that contain a slightly more diverse, marine trace fossil assemblage than might otherwise be expected.Item Experimental and mathematical investigation of dynamic availability of metals in sediment(2009-12) Hong, Yongseok; Reible, Danny D.; Kinney, Kerry A.Contaminated sediments are periodically subjected to resuspension processes during either storm events or due to dredging. In sediments, metals are often contained in insoluble low bioavailability forms. Upon resuspension, however, biogeochemical processes associated with the exposure to more oxic conditions may lead to transformation and release of the metals, giving rise to exposure and risk in the water column. Batch experiments suggested that oxidation of reduced species and corresponding pH decrease were the most importance processes controlling metals release upon sediment resuspension. A mathematical model was implemented to better understand the complex underlying biogeochemical reactions that affect metals release. The model described the metals dynamics and other inter-related important biogeochemical factors well and was successful at predicting the metals release from different sediment reported in the literature. Tidal and other cyclic variations in oxygen, pH and other relevant parameters in the overlying water may also lead to cyclic transformations and release of metals from surficial sediments. In simulated estuarine microcosm experiments, cyclic variations in pH and salinity due to freshwater/saltwater exchange were shown to lead to cyclic variations in metal release. Both pH and salinity were important factors controlling interstitial dissolved metals concentrations, however, in terms of freely dissolved metals concentrations, which have been considered to be more related with toxicity and bioavailability, pH was the single most important parameter. The mathematical model was extended to the conditions of the cyclic behavior in an estuary and successfully described metals release under such conditions. It is believed that the model can be used to predict the metals behavior in other sediments and conditions by model calibration with a similar experimental approach to that used in this study.Item Flow around a dredge spoil island in a shallow estuary during peak tidal currents(2013-12) Christiansen, David Aaron; Hodges, Ben R.A vessel-mounted ADCP study focusing on channel-scale flow patterns in Galveston Bay near the Houston Shipping Channel and Mid-Bay Island is described. Winds of 5-7 m/s at 215-230◦ from N were present during data collection. For both peak ebb and flood conditions, the tidal circulation forced flow in a direction opposing the wind, perhaps due to a large-scale flow divergence forced by Mid-Bay Island. The strongest such currents were measured closest the island. During peak flood flow, the shape of the along-channel velocity profile for the open water upwind of the channel at Mid-Bay Island indicated uniform flow, and the salinity profile indicated a well-mixed water column. The near-island along- channel velocity profile showed a near-linear trend, and the salinity profile indicated a stratified water column. This suggested that the stratification had some effect the velocity profile shape, but further research is needed to better quantify this effect. During peak ebb flow, the near-island along-channel velocities were highly variable with respect to the mean velocity, indicating an area of active turbulence. Salinity profiles collected in the open water and near-island both showed stratification, something that was not seen during flood conditions. Differences in observations between flood and ebb flows can possibly be attributed to the survey location with respect to the chain of dredge spoil islands. During flood flows Mid-Bay Island is the first of the islands, and the flows surrounding the island may part of a developing horizontal boundary layer. During ebb flows the island is last in the chain relative to the direction of flow, and therefore the surrounding flows are well back from the leading edge of a horizontal boundary layer.Item Modeling hydrodynamic fluxes in the Nueces River Delta(2011-08) Ryan, Andrea Johanna; Hodges, Ben R.Increasing municipal and regional water demands have reduced freshwater inflows to the Nueces Delta. These flow reductions impair the marsh ecosystem’s functionality. As part of a United States Army Corps of Engineers multi-agency collaboration to restore the Nueces River and its tributaries, we have developed a mass-conservative hydrodynamic model to analyze fate and transport of freshwater and tidal inflows to the Nueces Delta. The model is built upon the LIDAR bathymetric data collected by the Coastal Bend Bays and Estuaries Program (CBBEP). Input data includes tidal, salinity, and wind data obtained from the Texas Coastal Ocean Observation Network (TCOON), pumping data from the Nueces River Authority, precipitation data from NOAA, and river flow from the USGS. The underlying modeling method uses conservative finite-difference/volume discretization on a Cartesian rectangular grid to simulate the movement of water and salt fluxes across the delta. Sub-models to represent the hydraulic influence of flow constrictions (e.g. railroads trestles, culverts) have been developed. The model’s response to forcing from wind, precipitation, and roughness were analyzed. The time to spin up for the model was analyzed and found to be approximately seven days. Preliminary validation of the model was qualitative but the overall trend of the tide coming in appears correct at the monitoring stations analyzed, indicating that the lowest frequency forcing of the tide and wind are correct. The effects of pumping into the delta were investigated under different pumping conditions to reveal the area inundation and impacts on salinity from pumping.Item Regional water planning and the National Estuary Program(2006) Slovak, Sarah; Butler, Kent S.Water availability, supply, accessibility, and quality issues are becoming urgent issues around the globe. Planning and management of water resources is both complicated and different in every state for every type of water resource. Estuaries are among the most important ecosystems in the world, in terms of their ecological and economic value. The many problems facing estuaries across the nation led to an effort by the Environmental Protection Agency (EPA) to protect these valuable resources and to characterize their conditions. The National Estuary Program (NEP) was established in 1987, under an amendment to the Clean Water Act to address estuarine issues and planning. Three NEP case studies, Galveston Bay Estuary Program, San Francisco Bay Estuary Program, and Tampa Bay Estuary Program provide insight into the functions, capacities and potential of the NEP. Estuary Programs can be located in a variety of institutional settings, and these case studies evaluate the institutional structure of the individual estuary program in the context of their state political environments. These programs provide interesting management and planning challenges, as estuaries do not conform to exact political jurisdictions, so NEP’s define their management areas according to watershed boundaries and their ecosystems in an effort to provide comprehensive estuarine planning and management. This professional report will evaluate these three case studies to determine the role of the NEP in regional water planning and estuarine management.Item Water quality and eukaryotic plankton dynamics in the Mission-Aransas Estuary, Texas from 2011-2012(2013-08) Lashaway, Aubrey Rain; Erdner, Deana L.As the base of the food chain, plankton affect the cycling of nutrients and organic matter within ecosystems and support production at higher trophic levels. The overall goal of this project was to examine how natural water quality fluctuations, such as changes in nutrients, temperature, and salinity, influence estuarine plankton community structure. To achieve this, I examined water quality as well as the diversity and biomass of eukaryotic plankton communities in a subtropical estuary located within the Mission-Aransas National Estuarine Research Reserve. The sampling sites included in this study consisted of three bay (Copano Bay West, Copano Bay East, Aransas Bay) and two river (Mission River Estuary, Aransas River Estuary) estuary sites. Water samples were collected monthly at the five sites from September 2011 to August 2012 and analyzed for a suite of abiotic and biotic variables. Eukaryotic plankton diversity and community structure were evaluated by using the terminal restriction fragment length polymorphism (t-RFLP) method. Although a narrow salinity gradient was present at the sampling sites, seasonal changes in water quality conditions were observed. In the river estuaries, water quality parameters defined three significant temporal periods at the Mission River Estuary site, whereas only one month differed at the Aransas River Estuary site, indicating little seasonal variation. The Copano Bay sites exhibited a seasonal pattern consisting of four periods, marked by a distinct fall (October, November, December) grouping, while Aransas Bay showed a seasonal pattern consisting of three periods, with no fall group. Even though the water quality conditions define different monthly groupings in the bay and river estuary sites, the same parameters – DOC, TDN, and pH – are the strongest drivers of the patterns at all of the sites. Seasonal and spatial distinctions in the Mission-Aransas Estuary eukaryotic plankton community composition were determined using t-RFLP. Frequent shifts in composition were apparent across samples collected at approximately bi-weekly to monthly intervals. There were significant differences (ANOSIM, p < 0.05) in community composition between the Aransas and Mission River Estuary and Aransas Bay sites. Although the overall ANOSIM tests show significance between eukaryotic plankton communities monthly and between the bay water quality periods, none of the pairwise comparisons were significantly different. However, the ANOSIM R-statistic for the monthly pairwise comparisons displays a general increasing trend over time from sampling, further highlighting the dynamic nature of the microbial eukaryotic assemblage within sites.