Physical Sciences and Mathematics Commons^™

Running Out Of Oxygen: Revealing The Interannual And Intra-Annual Dynamics Of Bottom Water Hypoxia In A Great Lakes Estuary Using Time-Series Observations, Experiments, And Analyses, Nate M. Dugener

Masters Theses

Bottom water hypoxia, a condition of low dissolved oxygen in the bottom waters, negatively effects lakes and freshwater and marine coastal estuaries globally. As climate change shifts climatological and ecological patterns, hypoxia continues to shift in duration and severity. In Muskegon Lake, Michigan, hypoxia occurs annually, restricting fish habitat, increasing cyanobacteria blooms, and disrupting ecological and socioeconomic prosperity. In the current study, we examined the duration and severity of hypoxia over a 11 years (2011-2021) utilizing data from the Muskegon Lake Observatory buoy (MLO, https://www.gvsu.edu/wri/buoy/). During 2021, we analyzed the dissolved oxygen (DO) concentrations observed by the MLO, conducted biweekly …

The Effects Of Temperature And Oxygen Availability On Aerobic Performance In Three Coastal Shark Species; Squalus Acanthias, Carcharhinus Limbatus, And Carcharhinus Leucas, Alyssa M. Andres

USF Tampa Graduate Theses and Dissertations

Anthropogenically driven climate changes are altering marine habitats globally. Rising sea surface temperatures and coastal eutrophication, arising from global warming and coastal nutrient loading, have resulted in progressive ocean deoxygenation. This may restrict available habitat of marine organisms as studies suggest that the balance between metabolic oxygen demand and environmental supply plays an important role in limiting viable habitat and species fitness. As ectothermic predators, with temperature-dependent metabolism and high metabolic demands, coastal shark species may be susceptible to shifts in ocean temperature and oxygen. Such environmental changes may alter metabolic performance and ultimately success and survival within shark habitat. …

Algal Coverage Detection And Classification Using Envi: Correlation With Dissolved Oxygen Levels In Elkhorn Slough, Ca, Jason Dawson

All HCAS Student Capstones, Theses, and Dissertations

Estuaries are exposed to varying stressors, whether they be physical, chemical, or environmental. The most notable of stressors is eutrophication of coastal and inland ecosystems. This is a result of increased supply of nutrients fueling production within the system. One outcome of this increased nutrient load to the system is that of algal blooms. These blooms can impact the aesthetic appearance and degrade the quality of health of the system. Many of these coastal zones and waterways are critical habitats for many biological (some endangered) species and serve as recreational areas for human populations. Elkhorn Slough, California is one of …

Character And Water Quality Of Sandpiper Pond: A Coastal Pond Assessment, Fifteen Years After Restoration, Nicholas E. Workman

Honors Theses

Sandpiper Pond is a coastal pond at Huntington Beach State Park, South Carolina. Originally a tidal inlet surrounded by marshland, it was isolated in 1989 and rechanneled in 2004-2005 under a community-based wetland restoration project. The project was designed to restore the pond to a tidal inlet to improve water quality and biodiversity. Since then, the tidal connection with the ocean has been severed once more and the main influx of seawater occurs from the marsh during spring high tides. In this three-month study, the current state of Sandpiper Pond is evaluated using fundamental biogeochemical indicators that are indicative of …

Influence Of Natural And Anthropogenic Environmental Variability On Larval Fish Diet, Growth, And Condition In The Northcentral Gulf Of Mexico, Angie Hoover

Master's Theses

The northern Gulf of Mexico experiences high levels of freshwater runoff annually from various sources including the Mississippi River and Mobile Bay, among other sources. Early life history stages of fishes are especially vulnerable to environmental variability created by freshwater discharge. The objectives of this study were to describe the available prey field, diet, growth and condition of larval fishes with respect to various effects of freshwater discharge in the northern Gulf. The first chapter compared these parameters in larval Gulf Menhaden (Brevoortia patronus) collected from three different water masses characterized by physical and biological parameters after the …

Geotraces And Beyond: Studies Of Trace Elements In Coastal And Open Ocean Waters With An Emphasis On The Effects Of Oxygen Depletion And Hydrothermal Plumes, Peng Ho

Dissertations

We investigated various dissolved trace element (dTE) distributions in two distinct areas: the coastal northern Gulf of Mexico and the eastern tropical Pacific Ocean.

A multi-year (2007‒2011) chemical time series of eight stations in the western Mississippi Sound (MS) and northwestern Mississippi Bight (MB) was undertaken to examine the factors affecting chemical distributions in this dynamic region. Key findings include the frequent development of bottom water hypoxia in MB during late spring-summer, the likely contribution of submarine groundwater discharge (SGD) to the material flows, and observation of effects of episodic events including tropical storms and the opening of the Bonnet …

Ecophysiology Of Oxygen Supply In Cephalopods, Matthew A. Birk

USF Tampa Graduate Theses and Dissertations

Cephalopods are an important component of many marine ecosystems and support large fisheries. Their active lifestyles and complex behaviors are thought to be driven in large part by competition with fishes. Although cephalopods appear to compete successfully with fishes, a number of their important physiological traits are arguably inferior, such as an inefficient mode of locomotion via jet propulsion and a phylogenetically limited means of blood-borne gas transport. In active shallow-water cephalopods, these traits result in an interesting combination of very high oxygen demand and limited oxygen supply. The ability to maintain active lifestyles despite these metabolic constraints makes cephalopods …

A Multi-Faceted Biogeochemical Approach To Analyzing Hypoxia In Green Bay, Lake Michigan, Shelby Labuhn

Theses and Dissertations

Green Bay, Lake Michigan is a large freshwater estuary that has experienced seasonal hypoxia for decades. Hypoxia, or dissolved oxygen concentrations less than 2 mg L-1, is a problem in coastal ecosystems around the world because it has a negative impact on ecosystem health by decreasing biodiversity and fisheries. In order to create adequate management policies for hypoxia, it is important to understand the sources and sinks of oxygen within Green Bay. This study utilizes a number of traditional and novel field methods to measure the production and respiration of oxygen within lower Green Bay, defined as south of Chambers …

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.

A Statistical Model For The Prediction Of Dissolved Oxygen Dynamics And The Potential For Hypoxia In The Mississippi Sound And Bight, Andreas Moshogianis

Master's Theses

Hypoxia events occur when dissolved oxygen concentrations fall below the minimum threshold (dissolved oxygen concentrations < 2 mg O₂ L^-1) necessary to avoid respiratory distress among aquatic organisms. In the Mississippi Sound and Bight, hypoxia is most prevalent from late-spring through late summer. Since hypoxia events can have dramatic effects on coastal fisheries, the spatial and temporal magnitude of hypoxia presents a clear threat to the productive fisheries in the northern Gulf of Mexico. Long-term hydrographic data were collected from eight sampling stations on a monthly basis from January 2009 to December 2011 along a cross-shelf transect from the mouth of …

Macrobenthic Communities In The Northern Gulf Of Mexico Hypoxic Zone: Testing The Pearson-Rosenberg Model, Shivakumar Shivarudrappa

Dissertations

The Pearson and Rosenberg (P-R) conceptual model of macrobenthic succession was used to assess the impact of hypoxia (dissolved oxygen [DO] ≤ 2 mg/L) on the macrobenthic community on the continental shelf of northern Gulf of Mexico for the first time. The model uses a stress-response relationship between environmental parameters and the macrobenthic community to determine the ecological condition of the benthic habitat. The ecological significance of dissolved oxygen in a benthic habitat is well understood. In addition, the annual recurrence of bottom-water hypoxia on the Louisiana/Texas shelf during summer months is well documented.

The P-R model illustrates the decreasing …

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 …

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 …

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 …

Geochemical Tracers Linking Submarine Groundwater Discharge To Hypoxia Formation In Long Bay, South Carolina, Usa, Sarah Lynn Chappell

Electronic Theses and Dissertations

Long Bay, South Carolina has experienced hypoxic conditions (<2mg/L dissolved oxygen) in the nearshore environment, not fully attributed to traditional formation mechanisms. Past research suggested physical, biological, and/or anthropogenic influences on low dissolved oxygen levels. This project aimed to determine the contribution of submarine groundwater discharge (SGD) to hypoxia formation. We measured activities of 222Rnxs, 224Raxs, 223Ra, 228Ra, and 226Ra (3.8d, 3.6d, 11.5d, 5.8yr, 1600yr half-lives, respectively) in nearshore bottom waters from April 2012 through April 2013. Radium activities observed during a hypoxic event on 16-Aug-2012 were up to an order of magnitude higher than those seen during oxic conditions and the highest ever observed in the open ocean, to our knowledge. We determined that a hypoxic water mass, comprised heavily of offshore anoxic SGD, migrated inshore due to physical conditions constraining mixing over a two week time period. High groundwater content suggests that observed hypoxic conditions in nearshore Long Bay may be independent of biological influence once offshore SGD occurs.

The Effects Of Significant Rainfall Events On Surface Dissolved Oxygen Concentrations Off The Coast Of Long Bay In South Carolina, Kelsey M. Couch

Honors Theses

Long Bay in South Carolina is currently facing recurrent hypoxic conditions ("South Carolina Coastal Hypoxia"). Therefore the purpose of this study was to examine the effect of eight significant rainfall events on the surface dissolved oxygen content of the bay. Differences in theoretical values of average monthly dissolved oxygen content and actual values of average monthly dissolved oxygen were observed. When analyzed, the data from the eight-month study showed no strong correlation between significant rainfall events and changes in surface dissolved oxygen content. Phytoplankton blooms, phytoplankton productivity and seasonal stratifications could be causing these fluctuations (Lomas et al. 2009).

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

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

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

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

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

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 …

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 …