Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Publication Year
- Publication Type
Articles 1 - 16 of 16
Full-Text Articles in Physical Sciences and Mathematics
Effects Of Hypoxia And High Temperature On Eastern Oysters: Investigating Differential Tolerance In Populations And Ploidies, Nicholas C. Coxe
Effects Of Hypoxia And High Temperature On Eastern Oysters: Investigating Differential Tolerance In Populations And Ploidies, Nicholas C. Coxe
LSU Master's Theses
Increasing prevalence of hypoxia in estuarine waters can pose a serious threat to eastern oysters (Crassostrea virginica). While oysters are considered more tolerant to hypoxia than many other bivalves, their tolerance at temperatures of 28 °C and above, typical in northern Gulf of Mexico estuaries in the summer, is not well characterized. Moreover, it is unknown whether differences in hypoxia tolerance exist among oyster populations or between diploid and triploid oysters. To investigate population differences, wild oysters were collected from four estuaries in the northern and northwestern Gulf of Mexico and spawned. In a series of studies, the …
Breaking Coastal Hypoxia: Destratification Of Gulf Of Mexico Deadzone To Encourage Oxygen Transport Downwards To Maintain Marine Fauna, Veda Thipparthi
Breaking Coastal Hypoxia: Destratification Of Gulf Of Mexico Deadzone To Encourage Oxygen Transport Downwards To Maintain Marine Fauna, Veda Thipparthi
LSU Master's Theses
As a consequence of seasonal eutrophication and human input, a vast hypoxic area termed The Dead Zone develops every year in the Gulf of Mexico (GOM) during summer along the Louisiana coastline characterized by vertical seawater density-stratification with oxygen concentrations less than 2 mg.l-1 at the seafloor. It poses a threat to bottom-dwelling faunae and their environment which has negative ecological and economic consequences. This project aims to mitigate hypoxia by employing mechanical impellers placed at strategic water depths and locations in the Gulf. Enhanced transport of oxygen results by mixing oxygen-enriched seawater at the surface, downward into the …
Dinoflagellate Cysts Track Eutrophication In The Northern Gulf Of Mexico, Andrea M. Price, Melissa M. Baustian, R. Eugene Turner, Nancy N. Rabalais, Gail L. Chmura
Dinoflagellate Cysts Track Eutrophication In The Northern Gulf Of Mexico, Andrea M. Price, Melissa M. Baustian, R. Eugene Turner, Nancy N. Rabalais, Gail L. Chmura
Faculty Publications
We examined organic-walled dinoflagellate cysts from one 210Pb-dated sediment core and 39 surface sediment samples from the northern Gulf of Mexico to determine the relationship between nutrient enrichment and cyst assemblages in this region characterized by oxygen deficiency. The core spans from 1962 to 1997 and its sampling location is directly influenced by the Mississippi River plume. Surface sediments were collected in 2006, 2007, 2008, and 2014 and represent approximately 1 to 4 years of accumulation. A total of 57 cyst taxa were recorded, and four heterotrophic taxa in particular were found to increase in the top section (1986–1997) of …
Fishes Associated With Oil And Gas Platforms In Louisiana's River-Influenced Nearshore Waters, Ryan Thomas Munnelly
Fishes Associated With Oil And Gas Platforms In Louisiana's River-Influenced Nearshore Waters, Ryan Thomas Munnelly
LSU Master's Theses
A distinctive feature of coastal Louisiana is the unrivaled network of oil and gas installations (platforms) extending from inshore waters to the deep Gulf of Mexico. Since 2007 there has been a 38% reduction in platform numbers with the highest removal rates occurring in shallow (< 18 m) nearshore waters. Many fishes and invertebrates are attracted to platforms, presenting a unique opportunity to study detailed species-specific responses to the river-influenced hydrographic characteristics of Louisiana’s nearshore zone (5–25 km water depth). Prior studies of fishes around platforms focused on a few relatively large platforms in water depths ≥ 18 m. However, about one-third of all platforms are small, unmanned and non-drilling platforms located in waters < 18 m depth. Paired video and hydrographic data were collected at 150 small platforms in < 18 m water depth during the summers of 2013–2014. Fifty-four species of fishes were associated with small platforms. The assemblage(s) included juveniles of 29 species, indicating the importance of nearshore platforms as diverse nursery habitat. The coastal zone was divided into three regions based on broad-scale interactions between freshwater input and bathymetry driving major distinctions in interregional hydrography and fish assemblages. Co-occurring within this expansive artificial reef network is the second largest hypoxic area (dissolved oxygen (DO) < 2.0 mg l−1) on Earth. Platforms offer reef-like habitat features in the upper water column that may offer refugia for some reef-associated species during hypoxic events. Significant intraregional differences in physicochemical features were related to the presence of hypoxia (defined as DO < 50% saturation), as well as the distribution of sandy shoals. Eleven species accounted for most of the assemblage dissimilarities, composing ~93% of fishes observed. Habitat suitability indices for these 11 species provided information about habitat selection across horizontal and vertical physicochemical gradients throughout the coastal zone, and within hypoxic and well-oxygenated stratified water columns. East Bay, near the outlet of the Mississippi River, exhibited less hypoxia and a distinct fauna that included four adult goliath grouper (Epinephelus itajara). This endangered fish was observed during spawning season (summer), suggesting that East Bay might support a spawning aggregation.
Oil And Gas Platforms On Ship Shoal, Northern Gulf Of Mexico As Habitat For Reef-Associated Organisms, David Bradley Reeves
Oil And Gas Platforms On Ship Shoal, Northern Gulf Of Mexico As Habitat For Reef-Associated Organisms, David Bradley Reeves
LSU Master's Theses
Nearshore Louisiana has experienced substantial changes within the last half-century, including the annual formation of the world’s second largest hypoxic zone and the construction of thousands of oil and gas platforms (rigs). Ship Shoal and its rigs may provide important substrate in nearshore Louisiana because rigs act as de facto artificial reefs and the shoal’s bottom waters were well oxygenated on 43% of days when surrounding areas were hypoxic. From July to September of 2014, fish assemblages and hydrography were compared at shoal rigs, rigs inshore of the shoal, and rigs offshore of the shoal, and stone crab populations were …
Polonium-210 Dynamics In The Northern Gulf Of Mexico, Patrick Robert Jones
Polonium-210 Dynamics In The Northern Gulf Of Mexico, Patrick Robert Jones
LSU Master's Theses
Polonium-210 (t1/2=138 d) is the most common among the 33 known radioisotopes of Polonium found in the natural environment. It is produced by the radioactive decay of its long-lived grandparent Lead-210(t1/2=22.3 d) via Bismuth-210 (t1/2=5.012 d) and forms as part of the natural Uranium-238 decay series. The primary hazard associated with Polonium-210 is its radioactivity, as an alpha particle emitter. Marine organisms receive their maximum radioactive dose in the natural environment from Polonium-210. Polonium has been known to bioaccumulate in the marine food web and can be potentially harmful to humans via the intake of certain marine organisms. Thus it …
Numerical Experiments Of Hurricane Impact On Vertical Mixing And De-Stratification Of The Louisiana Shelf Waters, Mohammadnabi Allahdadi
Numerical Experiments Of Hurricane Impact On Vertical Mixing And De-Stratification Of The Louisiana Shelf Waters, Mohammadnabi Allahdadi
LSU Doctoral Dissertations
The numerical model FVCOM (Finite Volume Community Ocean Model) was applied to study the effects of Hurricane Katrina on the vertical mixing over the Louisiana shelf and the process of post-storm re-stratification. Wind field from Hurricane Katrina was generated using a single vortex analytical model and was evaluated using available wind measurements over the shelf. Simulations of shelf circulation under Hurricane Katrina were done through several numerical tests to find the best approach for treating vertical eddy viscosity. Model results for the shelf during Katrina demonstrated opposite currents between surface and bottom for most of the shelf area. Results also …
Red Swamp Crayfish Procambarus Clarkii In The Atchafalaya River Basin: Biotic And Abiotic Effects On Population Dynamics And Physiological Biomarkers Of Hypoxic Stress, Christopher Paul Bonvillain
Red Swamp Crayfish Procambarus Clarkii In The Atchafalaya River Basin: Biotic And Abiotic Effects On Population Dynamics And Physiological Biomarkers Of Hypoxic Stress, Christopher Paul Bonvillain
LSU Doctoral Dissertations
Crayfish harvested from the Atchafalaya River Basin (ARB) represent the majority of Louisiana wild crayfish landings. However, excluding water level influences, it is difficult to elucidate inter-annual harvest differences and intra-annual population variability among habitats. This research investigated ecological influences on population characteristics of red swamp crayfish Procambarus clarkii in the southeastern ARB as well as physiological biomarkers of hypoxic stress in P. clarkii. Biotic and abiotic effects on P. clarkii populations were examined throughout the 2008 and 2009 commercial crayfish seasons. P. clarkii catch per unit effort (CPUE) at sampling locations increased nearly 600% between sample years despite similar …
Factors Affecting Short-Term Oxygen Variability In The Northern Gulf Of Mexico Hypoxic Zone, Brenda Leroux Babin
Factors Affecting Short-Term Oxygen Variability In The Northern Gulf Of Mexico Hypoxic Zone, Brenda Leroux Babin
LSU Doctoral Dissertations
Open-water continuous monitoring of DO concentrations at a single station (C6) in the Gulf of Mexico from 1989 to 2008 afforded an excellent opportunity to characterize short-term oxygen variability and to estimate the relative importance of key physical and biological factors controlling the development, persistence, and dissipation of hypoxia. I investigated temporal trends in three aspects of short-term DO variability: respiration rates (i.e., how quickly bottom waters become hypoxic), persistence of hypoxia, and the dissipation of hypoxia (i.e., re-aeration events). I identified the range of respiration rates present at the study site, and showed how these rates vary throughout the …
Modeling The Population Effects Of Hypoxia On Atlantic Croaker (Micropogonias Undulatus) In The Northwestern Gulf Of Mexico, Sean Brandon Creekmore
Modeling The Population Effects Of Hypoxia On Atlantic Croaker (Micropogonias Undulatus) In The Northwestern Gulf Of Mexico, Sean Brandon Creekmore
LSU Master's Theses
The northwestern Gulf of Mexico currently experiences a large hypoxic area (“dead zone”) during the summer. While the local effects of hypoxia on organisms have been documented, the population-level effects are largely unknown. I developed a spatially-explicit, individual-based model to analyze how hypoxia effects on Atlantic croaker reproduction, growth, and mortality in the northwestern Gulf of Mexico could lead to population-level responses. The model follows the hourly growth, mortality, reproduction, and movement of individuals on a 300 x 800 spatial grid of 1 km2 cells for 100 years. Chlorophyll-a concentration, water temperature, and dissolved oxygen were specified daily for each …
Microphytobenthos Of The Northern Gulf Of Mexico Hypoxic Area And Their Role In Oxygen Dynamics, Melissa Millman Baustian
Microphytobenthos Of The Northern Gulf Of Mexico Hypoxic Area And Their Role In Oxygen Dynamics, Melissa Millman Baustian
LSU Doctoral Dissertations
The presence or absence of microphytobenthos on the seafloor provides clues about whether benthic oxygen evolution contributes significantly to the oxygen budget of the hypoxic area in the northern Gulf of Mexico. Hypoxia (oxygen < 2 mg l-1) creates inadequate concentrations of dissolved oxygen to support most organisms, such as fish, shrimp and crabs, and occurs over large areas of the Louisiana continental shelf from spring through summer in most years. Oxygen production by benthic autotrophs may offset a decline in oxygen concentrations if there is a functioning community and sufficient light. I sampled three stations (14, 20 and 23 m depths) ~ 100 km west of the Mississippi River over three hypoxic annual cycles (2006 – 2008), and 11 stations along a 14 - 20 m contour on the shelf in late-July in 2006, 2007 and 2008. I used microscopy and high-performance liquid chromatography to estimate the biomass and composition of phytoplankton and microphytobenthos. The potential seasonal oxygen production was estimated in 2007 and 2008 by incubating coupled light/dark sediment cores and bottom water from two stations. The sediment community (cells > 3 um) differed from those in the water column and were frequently benthic pennate diatoms and filamentous cyanobacteria (58-88% seasonally and 1-99% in mid-summer). The concentration of microphytobenthic biomass was usually < 2.0 ug g dry sed-1, and various biotic parameters were influenced by light at the seafloor. Declines in dissolved oxygen over a seasonal cycle in 2007 and 2008 were affected more by the initial dissolved oxygen concentration than by the presence of microphytobenthos that could generate oxygen. The sediment (1.2 - 27.3 mmol O2 m-2 d-1, n = 97) and bottom-water (1.1 - 17.5 mmol m-2 d-1, n = 23) oxygen consumption rates were within the range of the few previously-reported data. This work adds to these data and also provides the only sediment oxygen consumption rates at fixed sites over seasonal time scales. These results provide critical input to three-dimensional, physical-biological models of oxygen dynamics for this hypoxic area.
Modeling The Impacts Of Pulsed Riverine Inflows On Hydrodynamics And Water Quality In The Barataria Bay Estuary, Anindita Das
Modeling The Impacts Of Pulsed Riverine Inflows On Hydrodynamics And Water Quality In The Barataria Bay Estuary, Anindita Das
LSU Doctoral Dissertations
Eutrophication and coastal wetland loss are the major environmental problems affecting estuaries around the world. In Louisiana, controlled diversions of the Mississippi River water back into coastal wetlands are thought to be an important engineering solution that could reverse coastal land loss. There are concerns, however, that freshwater diversions may increase nutrient inputs and create severe eutrophication problems in estuaries and wetlands adjacent to the diversion sites. My dissertation research concerns modeling the effects of the observed and hypothetical freshwater diversion discharges on the hydrodynamics, salinity and water quality in the Barataria estuary, a deltaic estuary in south Louisiana. This …
Assessment Of Oxygen Sources And Sinks In The Northern Gulf Of Mexico Using Stable Oxygen Isotopes, Zoraida Jazmin Quinones-Rivera
Assessment Of Oxygen Sources And Sinks In The Northern Gulf Of Mexico Using Stable Oxygen Isotopes, Zoraida Jazmin Quinones-Rivera
LSU Doctoral Dissertations
Coastal hypoxia (< 2 mg O2L-1) represents a global problem that continues to worsen as nutrient fluxes to these areas increase. The second largest zone of human-induced hypoxia is located on the Louisiana continental shelf where hypoxic bottom waters commonly occur during summertime. This region is strongly impacted by the large flux of freshwater and nutrients from the Mississippi River, which influences both biological and physical processes that control oxygen dynamics. Yet, based on oxygen concentration measurements alone, it is difficult to separate the effects of biological factors from physical factors. To address this problem, I used a dual budget approach to assess the importance of oxygen sources and sinks on the Louisiana continental shelf. The dual budget was based on using stable oxygen isotopes (ä18O) in combination with conventional oxygen concentration measurements. To analyze temporal trends, surface and bottom water samples were collected monthly between July 2001 and July 2003 along an onshore-offshore transect. For better spatial resolution, shelfwide sampling was conducted extending from the Mississippi River Delta to the Louisiana-Texas border in the month of July of 2001, 2002, and 2003. Oxygen saturations values ranged between 180% at the surface and almost 0% close to the bottom with a corresponding range of ä18O values from 15‰ to 50‰. Biological parameters were important during all seasons for surface oxygen dynamics. The effects of physical factors were less apparent, except during severe physical disturbances. Bottom water oxygen dynamics showed clear seasonal signals of high oxygen depletion and larger contributions of benthic respiration during the summer, which corresponded to the strong stratification of the water column. In bottom waters, summer oxygen depletion was predominantly due to benthic respiration, accounting for about 73%, 80% and 60% of the total oxygen loss for 2001, 2002 and 2003 respectively. Model estimates of production/respiration (P/R) ratio during the July shelfwide cruises indicated that surface waters were productive with an average calculated P/R above 1. Depth stratified sampling (5 m intervals), which started in July 2002, showed that productivity in the mixed layer (5 to 10 m) was not homogeneous. Calculated P/R exceeded 1 only in the surface layer, while at 5 m P/R was approximately 1 and at a depth of 10 m, P/R was less than 1. Additionally, hypoxic conditions were only detected within 5 m of the bottom sediments. The dual budget approach yielded new estimates of productivity dynamics in surface waters and of sediment oxygen demand in bottom waters. For the first time, this study provided routine insight into productivity and respiration dynamics over large temporal and spatial scales. This could not have been accomplished using traditional methods because they commonly rely on time-consuming incubations. The study has shown that respiration dynamics in bottom waters vary seasonally with higher contribution of benthic respiration during stratified summer conditions and prevalent water column respiration during fall and winter. In contrast, seasonality in surface waters was less pronounced as productivity was more dependent on (salinity-inferred) nutrient supply than climatic forcing.
Predicting Water Quality Effects On Bay Anchovy (Anchoa Mitchilli) Growth And Production In Chesapeake Bay: Linking Water Quality And Individual-Based Fish Models, Aaron Thomas Adamack
Predicting Water Quality Effects On Bay Anchovy (Anchoa Mitchilli) Growth And Production In Chesapeake Bay: Linking Water Quality And Individual-Based Fish Models, Aaron Thomas Adamack
LSU Doctoral Dissertations
Water quality in the Chesapeake Bay and the Patuxent River has decreased since the 1950s due to an increase in nutrient loadings. Increased nutrient loads have caused an increase in the extent and duration of hypoxic conditions. Restoration via large-scale reductions in nutrient loadings is now underway. How reducing nutrient loadings will affect water quality is well predicted; however the effect on fish is generally unknown as most water quality models do not include trophic levels higher than zooplankton. I combined two water quality models with bay anchovy models (Anchoa mitchilli) to examine the effects of changes in nutrient loadings …
The Impact Of Hypoxia On Mercury Methylation In Bottom Sediment Of Northern Gulf Of Mexico, Mei Huey Tan
The Impact Of Hypoxia On Mercury Methylation In Bottom Sediment Of Northern Gulf Of Mexico, Mei Huey Tan
LSU Master's Theses
Widespread concern has developed about high mercury content in fish in the Gulf of Mexico and adjacent estuaries and bays. Among the areas implicated as possible sources of the mercury that moves up the food chain from the methylmercury formed in sediments and anoxic waters is the seasonal hypoxic zone in the northern Gulf. This research was designed to determine if methylmercury formation is stimulated by the anaerobic sediment conditions accompanying the onset of summer hypoxia in the Gulf. Both field and laboratory studies were carried out. For the field study sediment samples were collected at three stations (i.e. C4, …
Benthic Communities In The Northern Gulf Of Mexico Hypoxic Area: Potential Prey For Demersal Fish, Melissa Millman Baustian
Benthic Communities In The Northern Gulf Of Mexico Hypoxic Area: Potential Prey For Demersal Fish, Melissa Millman Baustian
LSU Master's Theses
Bottom-water hypoxia (≤2 mg O2 l-1) usually occurs on an annual basis on the Louisiana/Texas continental shelf from mid-May through mid-September over a large area (up to 20,000 km2 in mid-summer). The effects of hypoxia on the benthic infauna (potential prey) for demersal fish were examined, because changes in optimal diet can lead to negative impacts on growth and reproduction. Benthic samples were taken in three areas (inshore and offshore out of hypoxia and in the hypoxic area) during August 2003. Samples were also taken monthly from September 2003 to October 2004 at a fixed station …