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 (C6B) where summer hypoxia occurs consistently. The mean abundance of the benthic infauna in the three summer areas were not significantly different indicating similar prey abundances found in the study area. Diverse infaunal communities exist offshore of the hypoxic zone with similar species composition compared to the inshore but different compared to the hypoxic area. An abundance of benthos at the surface was not found at the summer 2003 hypoxic stations; therefore there was not an abundance of available prey at the surface. However, benthos migrated toward the surface at station C6B in June and July 2004 during hypoxia, providing an increase of prey at the surface compared to other months. During the spring months, the infaunal community was more diverse and abundant compared to the post hypoxic months (August, September, and October), which suggests fewer and less diverse potential prey in the fall for demersal predators. The most abundant prey items for demersal fish in the study area were polychaetes and secondarily molluscs. The benthic community abundances during the summer 2003 and 2004 were not expected and may be due to the storm events in summer 2003 and shorter duration of hypoxia in summer 2004.

Ecosystem response, stakeholder interactions, and the policy implications to a wetland assimilation project are reported here for the City of Mandeville, St. Tammany Parish, Louisiana. Between September 1998 and October 2004, input of secondarily treated wastewater effluent was found to have a net positive effect on the downstream wetland receiving basin. The major hydrologic inputs to the system are the effluent, precipitation, and back water flooding from Lake Pontchartrain. Nutrient levels were generally low except in the immediate vicinity of the outfall and removal efficiencies of N and P ranged from 44% to 87% and 25% to 93%, respectively. On average, TN and TP removal efficiencies were 59% and 69%, respectively, for the study period. Aboveground net primary production of the freshwater forest system was high downstream of the effluent discharge. Also downstream of the outfall, accretion rates were double the rate of relative sea level rise in the area. Re-direction of nutrient-enhanced effluents from open water bodies to wetland ecosystems may maintain plant productivity, sequester carbon, maintain coastal wetland elevations in response to sea-level rise in addition to improving overall surface water quality, reducing energy use, and increasing financial savings. Stakeholder interactions can often be as difficult to resolve as scientific questions. Further progress to improve water quality and regulate point source pollution often requires adjustment in policy strategies to enhance society's capacity to deal with more problematic issues of non-point source pollution. High cost and economic impacts on communities will propel the search for cost-effective water quality management. In addition, cooperation between the public and private sectors can build trust, consensus, and the ability to implement coastal resource projects. In this Mandeville, Louisiana, case, the use of science-driven solutions in natural resource management was successful in developing cost savings and coastal wetland preservation from the renewable ecological engineering technology of wetland wastewater assimilation. Integration of a national carbon and wetland policy may stimulate investments in energy efficiency and wetland enhancement. The next step must be the development of an annual revenue source to encourage state and private landowners to work together by providing incentive to promote wetland enhancement.

Studies in belowground dynamics are limited mainly due to the difficulty of studying roots despite wide recognition of its importance. This dissertation focused on methods for analyzing mangrove roots, root responses to phosphorus and flooding, and variation in root production between forest types. Techniques to separate live and dead roots such as colorimetric, fluorescence, buoyancy, and visual assessment were compared. The traditional method of visual assessment combined with root buoyancy was accurate, fast, and applicable to larger samples. Additionally, techniques such as rhizotrons, root ingrowth cores, and root image analysis were useful to study mangrove roots. Root and litter production, and hydro-edaphic conditions were determined seasonally for one year at eight sites (fringe, basin, and scrub forest types) in Southwest Florida. Root production was equal or greater than litter production showing spatial variation, especially in biomass allocation. Correlations with soil variables indicated that above and belowground processes respond differently to environmental conditions. The combined root+litter production was a good predictor of flooding and nutrient stress. Mangrove root production and morphology responded to nutrient enrichment (additions of nitrogen or phosphorus) depending upon forest type and stress factors interacting with resource acquisition. Root production increased with low nutrient availability and high flooding, and decreased with high salinity and nutrient availability. Nutrient enrichment increased the specific root length and surface area at the basin-monospecific site, and decreased the specific surface area at the scrub forest. Greenhouse experiments were conducted to study root dynamics of Rhizophora mangle and Avicennia germinans seedlings in response to phosphorus availability and flooding regimes. Mangrove species differed in their tolerance of flooding, and their plasticity to nutrients availability. The more flood tolerant species, R. mangle, was slower growing. The faster-growing species, A. germinans, exhibited limitations to flooding and changes in root morphology that altered the surface area for absorption of nutrients. These results indicate a trade-off between root strategies to tolerate flooding and to acquire nutrients. This study contributes to a better understanding of how mangrove ecosystems function. Additional work in other geographic areas and sedimentary settings is needed to provide a broader perspective on belowground processes in mangrove systems.

Floating marshes are wetlands of emergent vascular vegetation which have a significant mat of live and dead roots, decomposing and dead organic material, and mineral sediments. This mat moves vertically as ambient water levels rise and fall. These marshes have unique hydrology in that overland sheet flow is reduced or eliminated leaving no inorganic sediment input, but there is extensive belowground water exchange. The effect of significant sediment introduction into wetlands with floating marshes is unknown. The purpose of this study was to observe the marsh mat response to Mississippi River sediment addition and measure species composition change and growth response of vegetation. Study sites were Cypress Canal in Barataria Basin and Turtle Bayou in Terrebonne Basin, Louisiana, USA. Both are thin-mat floating marshes dominated by Eleocharis baldwinii. At each site, twenty plots were constructed around a boardwalk built on the marsh. Each 1 m² plot was randomly assigned one of five treatments: low, medium, and high sediment additions, and two controls. With increasing sediment addition, there were significant increases in bulk density and significant decreases in percent organic matter in the top 25 cm of the marsh mat. No significant differences in water level over the mat were found between treatments, indicating that buoyancy was not affected by sediment addition. Vegetation species composition after one growing season was not affected by the addition of sediment to the marsh mat. The number of species present was not affected. Aboveground biomass showed trends of increase with sediment addition, though these trends were not statistically significant. Belowground biomass was not significantly affected by the addition of sediment. Neither plant tissue nutrients nor soil nutrient levels showed much significant change with the addition of sediment to the marsh. Most of the sediment added remained in the top 25 cm of the marsh mat. Results presented suggest that some addition of sediment to the surface of a fresh water thin-mat floating marsh will not negatively affect the buoyancy of the mat. Increased bulk density facilitates increased vegetative growth, as is found in prior studies. Future data must be collected to determine more definite results.

This is the first study to compare nekton use and habitat value among Spartina alterniflora (Spartina), Avicennia germinans (black mangrove), and transition (S. alterniflora and A. germinans) sites within Louisiana's salt marsh-mangrove ecotone. Fishes and crustaceans were collected in Caminada Bay during fall 2003 and spring 2004 using 4 m2, bottomless lift nets. Although analyses were unable to demonstrate significant differences in fish (p=0.0753) and crustacean (p=0.1457) densities and species composition (p=0.8801) across sites, habitat-specific trends in nekton use were evident. Fishes, including gulf killifish and sheepshead minnows, showed affinities for the Spartina site, while crustaceans, especially white shrimp, were more associated with the mangrove site. Total fish biomass (p=0.0396) and gulf killifish biomass (p=0.0223) and densities (p=0.0543) were significantly greater at Spartina than mangrove sites. White shrimp biomass was significantly greater at mangrove than Spartina (p=0.0062) and transition sites (p=0.0143) and gulf stone crab densities were also higher at mangrove than transition sites (p=0.0061). Habitat type, areal stem cover (ASC), turbidity, and temperature explained 52% of the variability in nekton densities. Greater structural complexity (ASC, p<0.0001) at the mangrove site may increase refuge value for crustaceans given that (1) most were juveniles, including white shrimp, brown shrimp, blue crabs, and gulf stone crabs, and (2) white shrimp and brown shrimp were positively associated with ASC. Lower ASC and greater flooding depths (p=0.0318) and durations (p=0.0065) at Spartina than at the higher elevation mangrove site may benefit larger nekton by increasing access to the flooded marsh. The transition site had similar vegetation characteristics as the Spartina site, but flooding depths and durations resembled the mangrove site. Nekton densities were positively related to flooding duration at mangrove (fish, p=0.0031; crustacean, p=0.0040) and transition sites (fish, p=0.0018). Low fish use at mangrove and transition sites during spring 2004 suggests that (1) reduced hydroperiod negatively affects fishes, and (2) Spartina marshes may become especially important when meteorological events reduce access to mangrove and transition habitat types. More research is necessary to determine if these findings are representative of Louisiana's salt marsh-mangrove ecotone statewide, and to understand the fisheries implications of continued mangrove expansions.

There are currently over 4000 functioning oil and gas platforms in the northern Gulf of Mexico (Gulf). Platform operations, and their prior drilling operations, produce trace amounts of lead, barium, vanadium, and lanthanum residues that are leached into the surrounding waters and are deposited on the sea floor. These residues have isotopic ratios different from those typical of the Gulf seafloor and can be used as harmless fingerprints if they become incorporated into hard-parts or tissues in fishes associated with oil and gas platforms. From 2002 to 2004, 115 red snapper were collected from oil and gas platforms and artificial reefs off Louisiana and Alabama. Otoliths were removed and analyzed using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The objective of this study was to determine if a trace element isotope ratio fingerprint could be detected and described as unique to red snapper inhabiting the platforms. Stepwise and canonical discriminant function analyses were used to compare red snapper otolith fingerprints from on and off platforms, and from east and west of the Mississippi River. Classification accuracies based on the probability of an individual fish being correctly classified into the habitat from which it was sampled were over 90% for each of the two main comparisons. When comparing the elemental composition of red snapper otoliths from Louisiana oil and gas platforms and Louisiana artificial reefs, the classification accuracy was 93.75%. When comparing the elemental composition of red snapper otoliths from Louisiana artificial reefs and Alabama artificial reefs, the classification accuracy was 91.06%. Vanadium 51, Lead 206, Lead 207, and Lead 208 all appear to be linked with oil and gas platforms or their prior drilling operations, as the concentrations of these four elements or isotopes were significantly higher in otoliths sampled on platforms in Louisiana than in otoliths sampled from artificial reefs in either Louisiana or Alabama. Results from this study indicate that it may be possible in future studies to determine if oil and gas platforms contribute disproportionately to the survival of juvenile and adult red snapper, and as such can be considered viable management tools for stock rebuilding.

The balance between river and marine influences is important in governing landscape sustainability in river deltas. River- and atmospherically driven sea level variability, sediment loading, and estuary-ocean exchange in the Mississippi River delta are examined in this study. Subtidal estuarine sea level variability in the Breton Sound estuary was driven by a combination of remote atmospheric forcing outside the estuary over the continental shelf and controlled river inputs through a gated diversion structure at the estuary head. The highly-frictional deltaic landscape acted as a low-pass filter to coastal fluctuations near the estuary mouth. When substantial quantities river water were discharged into the estuary, upper estuary sea levels responded to a combination of river and atmospheric forcing, while sea levels in the lower estuary responded only to coastal forcing. Annual sediment loading into Breton Sound through a Mississippi River diversion was approximately 1 × 105 metric tons yr-1. Four pulsed, high-discharge diversions were conducted during the study, and sediment loading across each pulse was highly variable and was greatest during rising limbs of Mississippi River floods. Overland flow was induced when diversion discharge exceeded 100 m3 s-1. These results indicate timing and magnitude of diversion events are both important factors governing marsh sediment deposition in river diversion receiving basins. Sediment inputs measured during this study were negligible compared to historical loading through crevasses in the region. An investigation of estuary-shelf exchanges through Barataria Pass revealed that tidal exchange accounted for approximately 80% of the observed flow variability. Two dominant vertical subtidal exchange modes were identified. A barotropic mode, which accounted for most of the flow variance, was most coherent with cross-shelf wind stress. A second mode resembling baroclinic estuarine circulation recurred over fortnightly timescales, apparently in response to variations in tidal stirring. The baroclinic mode also appeared to be modulated by variability in freshwater inputs to the estuary. These findings provide a greater understanding of the physical dynamics that govern landscape sustainability in microtidal river deltas

A number of environmental stressors have been shown to interfere with reproductive and behavioral processes of fish by interfering with endocrine function. Most biomarkers of endocrine disturbance tend to be static measurements from dynamic systems making them difficult to evaluate within the context of an individual, or subtle effects that do not relate well to endpoints of ecological significance. I present an approach that uses a series of models, based on Atlantic croaker, to extrapolate laboratory results to indicators of individual and population health. First, I created a physiologically based model that simulates vitellogenesis in a female fish. The model simulates the major biochemical reactions from the secretion of gonadotropin to the production of vitellogenin. I simulated the effects of three environmental stressors that affect vitellogenin production differently. Model simulations demonstrated that it is possible to relate contaminant-induced changes in biomarkers to vitellogenin production and fecundity. A field application of the vitellogenesis model showed potential utility in interpreting field-measured biomarkers and to infer potential population hazards. Uncertainty analyses identified parameters that contributed most to variability of predictions. Second, I used a statistical model linked to an individual-based model to convert changes in behavior of ocean larvae exposed to two different contaminants to population relevant endpoints. Each contaminant imposed different effects and the effects were largely driven by impaired foraging abilities. Finally, I developed a matrix population model that realistically simulated two distinct populations of Atlantic croaker: Gulf of Mexico and Mid-Atlantic Bight. Simulations incorporated contaminant induced changes that were predicted by the other models, and compared population dynamics for 100 years under baseline conditions and under two separate contaminant scenarios. Predictions generated from the matrix model suggested that contaminant exposures at higher levels than observed in field measurements have the potential to impact populations, and that contaminant residency time within fish and the number of individuals exposed, interact with site-specific factors and life history traits, to determine population effects. The bottom-up approach employed here suggests that it is possible to scale laboratory effects to the population and provides a framework from which to base future model development and testing.

Mapping coastal marshes is an important component in the management of coastal environments. Classification of marshes using remote sensing data has traditionally been performed by employing either parametric supervised classification algorithms or unsupervised classification algorithms. The implementation of these conversional classification methods is based on the underlying distributions concerning the probability density functions (PDF). Neural networks provide a practical approach to this classification because they are essentially non-parametric data transformations that are not restricted by any underlying assumptions. The major objective of this study was to evaluate the ability of neural networks using Moderate Resolution Imaging Spectro-radiometer (MODIS) data to classify coastal marshes based on the phenelogical stages of plants. The first stage of the study was to develop a neural network model. The analysis has shown that six day images with eight input variables each are required to perform the classification. The variables are: MODIS bands - the near infrared and the near infrared composite bands, biophysical variables the leaf area index (LAI) and the fraction of photosynthetically active radiation (fPAR). Other variables are vegetation indices the normalized difference vegetation index (NDVI), the enhanced vegetation index (EVI), and the wetness index (WI), and, the day time land surface temperature. The near infrared and the wetness index were found to be the strongest predictor variables in the classification. Six hidden neurons and one output neuron were required in the neural network model for the output of six classes. The second stage of the dissertation was the model application. Images from four years: 2001, 2002, 2003, and 2004 were classified using the model. Accuracy assessment of the classification indicated that neural network techniques using MODIS data could achieve an accuracy of over 80% (at 0.95 confidence level). Using the classified images change detection was performed to determine the loss and gain of four marsh types; saline marsh, brackish marsh, intermediate marsh, and, fresh water marsh found in the south eastern coastal areas of Louisiana. The greatest gain was in the intermediate marsh, 3.0% of the study area, and the greatest loss was in the saline marsh, 3.8% of the study area.

The Moresby and Pandora Troughs of the northern Coral Sea are components of the deep-sea depositional system that is the ultimate sink for the Source to Sink Papua New Guinea (PNG) Focus Area. Cores collected from the R/V Melville during March-April 2004 reveal marine volcaniclastic and terrigenous turbidites deposited in these troughs during the Quaternary. Constraining the spatial, temporal, and provenance characteristics for these terrigenous sands through mineralogical, chemical, and textural analysis is the primary focus of this study. All cores contain thinly-bedded sandy turbidite packages interlayered with hemipelagic marls and typical centimeter-to-meter-thick turbidite sequences. The Moresby Trough core JPC22 appears to be generally finer-grained then the Pandora trough core JPC 66. Typical QFL percentages from JPC22 are 13:65:23, respectively, and plagioclase/ total feldspar ratios are near 0.90. These basal turbidite sands contain well-preserved rhyolitic pumice fragments and glass shards, with phenocrysts of amphibole, plagioclase, biotite, pyroxene and oxides. Typical QFL percentages from Pandora Trough core JPC66 are 69:14:17, and plagioclase / total feldspar ratios are near 0.47. These basal turbidite sands are predominantly quartzofeldspathic with a significant amount of heavy minerals (zircon, amphibole and oxides). The contrast in submarine sand mineralogy and mineral chemistry between 66JPC and 22JPC reflects distinct sedimentary sources composed of both fluvial and volcaniclastic material. The Moresby Trough has received secondary monomagmatic volcaniclastic turbidite sands derived mostly from volcanic/collision margin highlands of SE PNG, and the Pandora Trough has received quartzo-feldspathic sands from the Fly/Strickland system, more akin to a trailing-edge margin. Mineral textures and chemistry suggests minimal associations between sand bodies, and may represent isolated basins controlled by complex sea-floor bathymetry and episodic turbidity flows from diverse sources. The signature of the adjacent submarine fan deposits may aid the interpretation of continental margin growth as a function of sediment flux, sediment source, and dispersal pathways. These deposits may also give insight into the evolution of volcanic island arcs on longer time scales. This investigation concludes that the Pandora and Moresby trough turbidite sand bodies record varying sediment sources and somewhat isolated volcanic events contributing to the evolution of the southern PNG continental margin.