Browsing by Subject "estuary"
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Item Aggregation and transport kinetics of crude oil and sediment in estuarine waters(Texas A&M University, 2004-09-30) Sterling, Michael Conroy, Jr.Modeling the transport and fate of spilled crude oil is important for estimating short and long-term toxicity effects in coastal ecosystems. This research project investigates the partitioning of hydrocarbons from a surface crude oil slick, the resurfacing of chemically dispersed crude oil droplets, the suitability of in-situ field instruments for oil and sediment characterization, and the aggregation and settling of dispersed oil and suspended sediments. An initial laboratory study was conducted to investigate apparent hydrocarbon solubility in petroleum/water systems. Mixing shear and initial crude oil layer thickness were related empirically to oil entrainment rate. A model describing hydrocarbons partitioned in colloidal and soluble phases was consistent with experimental data. A second laboratory study was conducted to investigate the influence of coalescence kinetics on mean droplet size and resurfacing rate of chemically dispersed crude oil droplets. Increased mean shear rates resulted in mean droplet diameters and oil resurfacing rates. A third laboratory study was conducted to compare particle size and fractal dimension measurements obtained using a submersible flow cytometer, an electrozone particle counter, and a light scattering particle sizer. Measured particles included latex beads, crude oil, clay, crude oil-clay aggregates, and crude oil-silica aggregates. Tested instruments gave consistent size measurements for all particle systems, suggesting their suitability for sizing marine particles. To describe the aggregation kinetics of oil-sediment systems, a modified Smoluchowski model based on coalesced sphere (CS) assumptions was developed. Observed collision efficiency values (?OBS) were related to collision efficiency values for single particle type systems (?HOMO) and those for two particle type systems (?HET) using a probabilistic approach. For clay and crude oil, ?HOMO values were higher than the ?HOMO value for silica. Clay-oil and silica-oil have similar ?HET values. Thus, crude oil can significantly increase the aggregation rates of noncohesive sediments such as silica. The CS model above was modified to incorporate sediment fractal geometry. The ability of this modified coalesced fractal sphere (mCFS) model to fit experimental data sets was better than that of a coalesced sphere (CS) model. Because of their reduced settling rates, sediments with lower fractal dimension form more aggregate with dispersed oil.Item Aquatic macrophyte and animal communities in a recently restored brackish marsh: possible influences of restoration design and the invasive plant species Myriophyllum spicatum(2012-07-16) Bell, Michael ThomasThe numerous benefits that wetlands provide make them essential to ecosystem services and ecological functions. Historically, wetland losses have been caused by natural and anthropogenic changes. In Texas, nearly 50% of coastal wetland habitat has been lost since the 1930s and losses in the Lower Neches watershed have been some of the most extensive. Restoration is a way to mitigate these losses and can be accomplished in many ways. Each restoration design creates different aquatic habitats that can influence both submerged aquatic vegetation (SAV) and faunal communities. The restoration of the Lower Neches Wildlife Management Area (LNWMA) has created the conditions for the growth of the invasive submerged macrophyte, Myriophyllum spicatum (Eurasian watermilfoil) which may be competing with the native aquatic grass, Ruppia maritima (widgeongrass) for essential nutrients. In this study, an attempt was made to link restoration design with both SAV and aquatic fauna community structures by using a throw trap to characterize assemblages observed in three different types of restored marshes. We also performed two controlled mesocosm experiments in 0.5 gal aquariums to determine growth inhibition by M. spicatum on R. maritima. Analyses using Kruskal-Wallis non-parametric test determined that temporal variations in fauna and SAV community composition was greater than any restoration effect. Discriminant Function Analyses (DFAs) determined two to three key faunal species that best predicted association among restoration designs, but linear regressions could not determine any consistent relationship between individual species density and biomass of the dominant SAV species, M. spicatum. For the mesocosm experiments, M. spicatum inhibited the biomass production and branch count of R. maritima when the two species are grown together (ANOVA, p = 0.004 and 0.003, respectively). Changes in SAV assemblages due to competition and habitat characteristics could play a major role in determining faunal community. In order to minimize the temporal effect observed and better determine any habitat pattern that may be present, a much longer study is necessary.Item Controls on the sulfur cycle in estuarine sediments on the Central Texas coast(2009-06-02) Thomson, HeatherThe sedimentary sulfur cycle is one of the main components of estuarine biogeochemical systems. It is initiated by the oxidation of organic matter via sulfate reducing bacteria which produce hydrogen sulfide (H2S). The S(II) then reacts via both abiotic and biotic pathways to form sulfur with other oxidation states. The three most widely-studied ?operationally??defined components of the sedimentary sulfur system are total reduced (inorganic) sulfur (TRS), acid volatile sulfide (AVS), and dissolved (=filter-passing) sulfide. This study focused on several parameters that are widely held to be important in determining TRS in sediments and the relative proportions of TRS, AVS and dissolved S(II) forms. The formation of iron sulfide minerals requires metabolizable organic matter and SO4 2- to produce S(II) and ?reactive?-Fe as a source for the iron in iron sulfide minerals. One of these components is generally the limiting factor in TRS formation (e.g., Berner 1970). Nine different sites from three locations on the Central Texas coast were studied for a variety of parameters including organic matter, sulfate concentrations, sulfate reduction rate, solid ?reactive? and dissolved iron, and grain size, as well as TRS, AVS, and ?H2S. At each site five sediment cores were taken to a depth of 20 cm whenever possible. The cores were sectioned in 2 cm intervals. The porewater was extracted and both solid and dissolved components were analyzed using a variety of methods, including carbon and sulfur coulometry, acid extraction, chromium extraction, and drying the sediment. The results of he analyses showed that the central Texas coast is a widely diverse system. Some sites were very sandy while others were fine-grained. This variety was especially true for the Nueces Bay and Baffin Bay sites. The East Matagorda Bay sites showed more homogeneity in almost all analysis. While the heterogeneity of locations along the Central Texas coast makes it difficult to make a definitive statement about the controls on TRS in this area, most sites are controlled by the low amounts of iron in the system, which limits the amount of iron sulfide that can form. Low reactive iron concentrations and high degrees of pyritization (DOPs) support this argument. Exceptions exist for low-salinity (sulfate-limited) or very fine-grained (organic matter limited) sites.Item Late Pleistocene New Jersey Shelf sedimentation as a response to glacio-eustatic sea level rise(2009-08) Stackhouse, Stanley B.; Fisher, W. L. (William Lawrence), 1932-; Goff, John A.; Steel, Ronald J.Shallowly-buried channel systems have been imaged on the New Jersey Shelf with high-resolution seismic imaging. These channels formed as riverine systems that occupied the exposed shelf during the Last Glacial Maximum, ~18 ka. Subsequent sea level rise ~15-12 ka modified the valleys, forming estuaries and filling the channels with estuarine sediments. The infill sediments within the channel provide evidence for the response of the shelf to the Late Pleistocene glacio-eustatic sea level rise, but little work has been done on samples from these strata. This study aids in the ground-truthing of previous stratigraphic results by analyzing the cores collected within the infill sediments. The seismic stratigraphy of fill sediments from the mid-shelf and outer-shelf channels are structurally dissimilar. The mid-shelf channel fill stratigraphy is dominated by finely-laminated U-shaped reflectors throughout the section, with cut and fill geometries. In contrast, the outer shelf channel fill stratigraphy is a well-ordered sequence of 4 identifiable, primarily flat-lying seismic units. We collected five cores in mid-shelf channels (~30 m water depth), one in an outer shelf channel (~80 m of water depth) and one core in the trangressive ravinement surface. Cores were logged for density and seismic velocity. Grain size analysis was conducted by settling column and laser particle size analyzer. Radiocarbon analysis of the stratigraphy was conducted with the shell fragments and organic mud within the samples. The foraminiferal assemblages aided in determining the depositional environment. Using these data I investigated the differences in depositional environment of the mid- and outer-shelf channels systems, and consider these results in the context of sedimentary models for estuarine processes. The radiocarbon dates and foraminiferal are consistent with channel infill in an estuarine environment. Grain size and density log data indicate that the mid-shelf channel fills are sandier than the outer-shelf channel fills, which leads me to infer that the sediment from the mid-shelf channels was deposited in a higher energy environment than that of the sediment in the outer shelf channels. The stratigraphic differences and locations of the channel systems are similar to the Zaitlin (1994) model of incised valley infill, but infill of the mid-shelf channel system could possibly be the result of a catastrophic meltwater flood event occurring ~14 ka as glacial lakes to the north broke their dams and flooded the mid-shelf.Item Mercury speciation in Galveston Bay, Texas: the importance of complexation by natural organic ligands(Texas A&M University, 2005-02-17) Han, SeungheeThe major goal of this research is the development of a competitive ligand equilibration-solvent solvent extraction (CLE-SSE) method to determine organically complexed mercury species in estuarine water. The method was applied to estuarine surface waters of Galveston Bay and the water column of Offatts Bayou. Thermodynamic equilibrium modeling estimated organically complexed mercury species in estuarine water using the conditional stability constants of mercury-organic complexes and the concentrations of organic ligands determined by CLE-SSE. Two competing ligands, chloride and thiosalicylic acid (TSA), were used for CLE-SSE. Chloride ion competition determined conditional stability constants for 1 : 1 mercury-ligand complexes ranging from ~1023 to ~1024 with concentrations of organic ligands at low nM levels. TSA competition determined stronger mercury-binding ligands by manipulating the TSA concentration such that a higher binding strength was achieved than that for the mercury-chloride complex. TSA competition determined conditional stability constants for 1 : 1 mercury-ligand complexes ranging from ~1027 to ~1029, with ligand concentrations ranging from 10 to 100 pM. Mercury-organic binding strengths in these ranges are consistent with bidentate mercury complexation by low molecular weight organic thiols. A linear relationship was observed between log stability constants for the mercury-ligand complex and log ligand concentrations, supporting the hypothesis that there is a continuum of mercury binding site strengths associated with dissolved organic matter. In Galveston Bay, organically complexed mercury accounted for > 95 % of the total dissolved mercury in surface water. Organic complexation of mercury coupled with mercury dissolution from particulate phases controls the filter-passing mercury distribution in surface waters of Galveston Bay. The estuarine distributional features of mercury-complexing organic ligands were similar to those of glutathione, supporting mercury complexation by a thiol binding group. In Offatts Bayou, a seasonally anoxic bayou on Galveston Bay, thermodynamic equilibrium modeling suggests that the speciation of dissolved mercury in anoxic systems is dominated by sulfide complexation rather than organic complexation.Item Sonar imaging of bay bottom sediments and anthropogenic impacts in Galveston Bay, Texas(Texas A&M University, 2007-04-25) Maddox, Donald SheaKnowledge of surface sediment distribution in Galveston Bay is important because it allows us to better understand how the bay works and how human activities impact the bay and its ecosystems. In this project, six areas of bay bottom were surveyed using acoustic techniques to make maps of bay bottom types and to investigate the types and extent of anthropogenic impacts. A total of 31 km2 was surveyed in six areas, one in Bolivar Roads (6.1 km2), one near Redfish Bar (3.1 km2), two in East Bay (12 km2), one southeast of the Clear Lake entrance (5.3 km2), and one in Trinity Bay (4.3 km2). Sidescan sonars (100 kHz and 600 kHz) were used to image the bay bottom, and a chirp sonar (2-12 kHz) was used to image subsurface sediment layers and bottom topography. In the side-scan records, objects as small as a few meters in extent were visible, whereas the chirp sonar records show a vertical resolution of a few tens of centimeters. The sidescan images display strong backscatter in some areas due to coarse sediments in addition to weak backscatter in areas of fine sediment. The bay bottom was classified using three levels of sonar backscatter ranging from high to low. Areas of differing sonar backscatter intensity were sampled with cores and grab-samples. High backscatter corresponded to coarse shell debris and oyster reefs, medium backscatter corresponded to a sand-silt-shell mixture, and low backscatter corresponded to silty loam. Chirp sonar records were classified as one of nine different bottom reflection types based on changes in amplitude and stratigraphy. Parallel, layered sediments are seen filling the bay valley and resting atop a sharp contact at which the acoustic signal fades out. Along the flanks of the valley fill the acoustic response revealed an absent or weakly laminated stratigraphy, whereas areas of high oyster productivity produced mounds, strong surface returns, and strong, shallow subsurface reflectors surrounding current oyster reefs. Anthropogenic features imaged with the sonar included sediment disruptions, such as the ship channels, dredge holes, gouges, and trawl marks, as well as debris, such as submerged boats, pipes, and unidentified objects.Item Spatial and temporal patterns of Lycium carolinianum Walt., the Carolina Wolfberry, in the salt marshes of Aransas National Wildlife Refuge, Texas(Texas A&M University, 2006-08-16) Butzler, Rachel ElizabethUnderstanding the salt marsh ecosystem in the Guadalupe Estuary is needed because wetlands in this system support the endangered whooping crane (Grus americana). The marsh plant research and monitoring described herein were based in the salt marshes at Aransas National Wildlife Refuge (ANWR), which are utilized by the cranes each winter. Past research indicates that the Carolina wolfberry (Lycium carolinianum) contributes 21-52% of crane energy intake early in the wintering period (Chavez 1996). Beginning in Fall 2003, vegetation transects were sampled along an estuarine gradient at ANWR. Species diversity and composition was similar at the three sites, with all sites containing the same 6-7 common species. While Spartina alterniflora is only a minor part of this vegetation community, it dominates the few low inter-tidal, fringe areas present. Species composition exhibited little variability from Year 1 to Year 2 of the study. Densities and biomass of L. carolinianum were not significantly different between sites or years. L. carolinianum, while important to salt marsh ecology, accounts for only a small portion of the overall productivity. Based on correlation coefficients, L. carolinianum was found in association with some of the common species in the vegetation community, indicating that its growth and survival requirements are typical to the salt marshes at ANWR. Also beginning in Fall 2003, I repeatedly sampled L. carolinianum in permanent plots along the estuarine gradient. L. carolinianum exhibits strong temporal patterns. Leaf production peaked in early spring and again just prior to peak berry abundance. Flowering of L. carolinianum occurred in October and November. Peak berry abundance coincided with the cranes?? arrival in late October and early November. Berry production occurred in October, November, and December; berries were virtually non-existent in the marshes for the remainder of the year. Stepwise regression showed stem diameter alone was a good estimator of aboveground biomass of this species in ANWR marshes, accounting for 94% of the variability (p<0.001). Changes in aboveground biomass followed no distinct patterns in the year of monitoring, perhaps due to the woody stem of the plant. Spatial patterns in L. carolinianum were not explained by water quality parameters alone; it is suggested that soil properties may help to account for the spatial variability.