This project examined the economically and ecologically valuable eastern oyster (Crassostrea virginica) in the Northern Gulf of Mexico using field and laboratory experiments. Specifically, this project focused on natural rates of settlement, growth, and mortality in a variety of temperature and salinity regimes within Breton Sound, LA. Seed and market sized oysters in cages resting on the bottom, as well as settlement tiles, were monitored at four sites in Breton Sound, LA, along what is typically a salinity gradient ranging from ~5 to ~20. In April 2010, the Caernarvon Freshwater Diversion was fully opened with the goal of minimizing the impacts of the Deepwater Horizon oil spill on wetlands, resulting in extreme low salinity (< 2) at all sites through August 2010. High seed and market-sized mortality and reduced condition were observed in oysters at all sites. Perkinsus marinus infection prevalence in surviving market oysters was low at all sites and all infection intensities were light. Settlement only occurred at the highest salinity site. In May 2011, the Mississippi River flooded to record levels, resulting in low salinity (<10) at all sites through June 2011. This short period of low salinity minimized disease infection intensity and settlement at all sites. Oysters at the lowest salinity site experienced high mortality and low growth. Oysters at higher salinity sites experienced limited mortality, mostly from predation, along with higher growth and condition. While low salinity may be beneficial to oyster populations by reducing P. marinus infection levels, prolonged extreme low salinity through spring and summer appears to cause heavy mortality and negatively impact recruitment in the short term. While not only is it clear that the timing and duration of freshwater inputs will significantly affect the impacts on oyster resources, it is likely that large scale global climate patterns (including El Niño and La Niña events) will also modify how and to what extent freshwater events may affect Breton Sound. This project highlights the importance of understanding the timing and duration of low salinity events and their impacts on oyster life history stages.

Timber harvesting can degrade the quality of adjacent water bodies, an important concern for Louisiana, nearly 50% of which is forested, and in which the forest industry is the second-largest manufacturing employer. To protect valuable freshwater resources in Louisiana, a manual of best management practices (BMPs) was published in 2000 describing techniques for limiting forestry-caused water quality degradation. While these BMPs are widely implemented, their effectiveness in protecting water quality is largely unknown. To determine the effectiveness of these BMPs, this thesis research conducted three studies to address timber harvest BMP effectiveness on protection of stream dissolved oxygen, metabolism, and carbon, nitrogen, and phosphorus runoff in a low-gradient watershed, Flat Creek, in north-central Louisiana, USA. The first two studies were carried out on a 2nd-order stream adjacent to a loblolly pine stand from 2006 to 2010 that was harvested in the summer of 2007. Dissolved oxygen (DO), water temperature, and stream depth were recorded at 15-minute intervals at a reference site upstream and a site downstream of the harvested area. Using diurnal DO change and an open-system, single-station method at each site, we quantified rates of net productivity (NP), gross primary productivity (GPP), community respiration (CR), and GPP/CR ratios. The third study was conducted at nine sites across the Flat Creek watershed, from 1st-order to 3rd-order streams, for analyses of immediate downstream and watershed-scale changes to stream carbon, nitrogen, and phosphorus concentrations from three timber harvests conducted in 2007. There were no statistically significant changes to any measured carbon, nitrogen, or phosphorus species at either the forest stand scale, or at the watershed scale. Overall, results from this research suggest that Louisianas current BMPs were effective at limiting water quality degradation.

Changing hydrology and climate have significantly altered ecologically significant cypress-tupelo forests in the deltaic plain of the Mississippi River. Though local responses of these swamps to hydrology are relatively well understood, broad-scale evaluation of ecological response differences of deltaic wetland forests has been limited by the lack of site-specific coupled hydrologic and ecological data. Baldcypress tree-rings from twenty-two sites were used to examine the responses of coastal swamp forests throughout the deltaic plain to environmental variables. The responses of these forests to environmental variables varied spatially; however, broad-scale measures of deltaic hydrology were more correlated with tree radial growth than were climatic variables. A strong relationship between coastal water levels and river stage suggests that river stage often controls coastal water levels near the coast, so that even sites not locally hydrologically connected to the river experience broad-scale effects of annual variability in Mississippi river stage. Thus, even though the river is leveed, river stage appears to have significant impacts on forest productivity through linkages with coastal water levels.

A suitable foraging habitat model based on prey density, biomass, and energy values in varying hydrologic conditions can provide an objective quantifiable method to assess habitat conditions for the Whooping Crane (<i>Grus americana</i>). Nekton and macroinvertebrates are considered the important prey sources in Whooping Crane's diet at different times. This study focuses on the understanding of habitat relationships of nekton and macroinvertebrate assemblage in the Chenier Plain to provide a foundation for the development for foraging suitability models for the reintroduced Whooping Crane. In this dissertation, in a laboratory study I experimentally examined the effect of salinity on the survival of dominant macroinvertebrates in freshwater marsh (i.e., <i>Procambarus clarkii</i> Girard, <i>Cambarellus puer</i> Hobbs, Libellulidae, Dytiscidae). In addition, I compared nekton and aquatic macroinvertebrate assemblages in freshwater, brackish and saline marshes of the Chenier Plain. In the laboratory experiment, to determine survival rate, a series of 45 cm x 30 cm x 15 cm plastic trays were filled with water of six salinities (i.e., 0.6, 7.2, 13.5, 19.4, 25.1, and 30.7 g/lTDS) both with and without prey for 28 days. At the lower threshold, low salinities (i.e.,¡Ü 0.6 g/lTDS) allowed species to survive even without food. Above the upper threshold, however, high salinities (i.e.,¡Ý 25.1g/lTDS) killed species whether they had food or not. Survival of all species was affected by salinity but upper and lower thresholds existed for each species. In the field studies, I measured the effects of hydrologic connectivity on several environmental variables and their combined effect on several nekton community metrics. I collected 31,011nekton of 42 taxa from 540 seasonal samples with a throw trap and minnow traps. Nekton density of brackish ponds was higher than saline ponds but freshwater ponds did not statistically differ from brackish and saline ponds. However, nekton biomass of brackish and saline ponds was greater than freshwater ponds. Nekton community diversity of freshwater ponds had the highest diversity. Nekton community composition appeared to be structured by individual species responses to the salinity gradient as well as pond habitat attributes (submerged aquatic vegetation coverage, dissolved oxygen, hydrologic connectivity). To determine the effects of hydrologic connectivity and environmental variables on aquatic macroinvertebrate community metrics, I collected 32,130 aquatic macroinvertebrates from 52 taxa from 252 monthly sweep net samples. A total of 50 taxa were identified in freshwater marsh, 20 in brackish marsh, and 12 in saline marsh. Freshwater marsh had 32 exclusive taxa but brackish and saline did not have any exclusive taxa. Furthermore, density, biomass, and diversity of aquatic macroinvertebrates in freshwater ponds were higher than in brackish and saline ponds. Variation in life history traits of macroinvertebrates and responses to environmental conditions (water depth, salinity) seem to be influenced macroinvertebrate assemblages across multiple marsh types.

Harvest of the eastern oyster (Crassostrea virginica) is a primary contributor to oyster reef habitat disturbance in the northern Gulf of Mexico. The impacts of oyster dredging on reef substrate and resident fauna have not been thoroughly examined on the extensive sub-tidal oyster reefs of Louisiana. Several reef structure and resident community metrics were compared on unharvested and harvested reefs during the spring, summer, and fall of 2010. Unharvested reefs had higher amounts of oyster clusters, solid reef substrate, and more large oysters, while harvested reefs had higher amounts of loose shell, mixed shell/mud substrate, and elevated chlorophyll-a levels. Overall, faunal densities did not differ with harvest status and dominant species were similar, although greater invertebrate diversity was found on harvested reefs. Several resident species were found to primarily associate with live oysters [freckled blenny (Hypsoblennius ionthas) and skilletfish (Gobiesox strumosus)] and chlorophyll-a levels [Harris mud crab (Rhithropanopeus harrisii) and snapping shrimp (Alpheus sp.)], indicating the importance of live oysters in determining reef microhabitat preferences by regulating types of available food sources. Condition (weight:length ratio) of naked gobies (Gobiosoma bosc) was greater on unharvested reefs, while other common fish species showed no difference. Large interstitial spaces associated with oyster clusters appear to enable several fish species to reach larger sizes at unharvested reefs and promote retention of age = 0 G. bosc. Stable isotope values (del 13C and del 15N) of dominant species and basal food sources were used to compare food web characteristics between sites. Non-pelagic source contributions and trophic positions of dominant species were elevated at harvested sites. Trophic order did not differ suggesting that no major shifts in feeding behavior occur at harvested reefs with the exception of zooplankton (trophic position increased substantially at harvested sites). While not changing total refuge capacity, oyster harvest appears to decrease the number of large oysters and also fragment solid reef area, resulting in elevated phytoplankton abundance, decreased benthopelagic coupling, and increased habitat heterogeneity. A larger forage base in the water column and mixed shell/mud substrate could account for increased invertebrate diversity and trophic position elevations on harvested oyster reefs.

Floodplains forests are productive and diverse ecosystems characterized by frequent riverine flooding. Levees and dams have eliminated or altered riverine flooding which can potentially affect floodplain tree recruitment and growth. Increased light availability from canopy disturbances may increase photosynthesis given sufficient soil moisture, but information on the combined effect of canopy disturbances and hydrologic modifications on tree recruitment and growth is lacking. I used dendrochronological techniques to reconstruct tree recruitment, growth (Quercus lyrata, Fraxinus pennsylvanica), and canopy disturbance patterns over a 90-year period at several floodplains in the Mississippi River Alluvial Valley, USA: an unleveed site below dams and two sites within a ring levee. At the site below dams, flood frequency increased in the late non-growing season during the post-dam period, but decreased in the late growing season, although stage may have kept water in the root zone. Mean flood duration of pre-dam and post-dam periods was similar. Interannual variability in flooding may have resulted in recruitment of tree species of varying flood tolerances. Recruitment of shade-tolerant species (Celtis laevigata, Ulmus americana) was common during periods of infrequent canopy disturbances, but recruitment and growth of moderately shade-tolerant species such as F. pennsylvanica increased following widespread canopy disturbances. Unlike Q. lyrata, F. pennsylvanica had positive relationships with river stage during the late growing season in the post-dam period, suggesting riverine influence via groundwater links. At sites within a ring levee, flooding was short duration with longer duration flooding at lower elevations due to ponding of precipitation. Recruitment of flood-intolerant species such as C. laevigata expanded after levee construction except at lower elevations where recruitment of flood-tolerant species such as Q. lyrata followed canopy disturbances. In the post-levee period, growth of Q. lyrata and F. pennsylvanica was closely correlated with surface soil moisture and increased following canopy disturbances. Growth maintained strong relationships with spring stage at low elevations despite the elimination of overbank flooding, suggesting riverine influence via groundwater links. Results of my study indicate that broad-scale hydrologic modifications affected floodplain forest recruitment and growth but local-scale factors such as topography, canopy disturbances, surface soil moisture, and groundwater mediated these effects.

The effect of inorganic fillers including precipitated calcium carbonate (PCC), glass fiber (GF), and nano-clay on properties of structured WPCs was investigated. In PCC-bamboo-polymer hybrid composites, tensile and flexural moduli were improved with increasing PCC content. After silane treatment of bamboo, RBF-filled hybrid composites showed better mechanical properties compared to those of GBP-filled hybrid composites. The hybrid composites showed 3-4 times higher modulus than those of PCC-filled composites at high PCC levels. Various property differences were observed between weak- and strong-core coextruded systems with shell composition changes. While the weak-core systems showed improved flexural strengths compared to their core-only control, the strong-core systems had lowered flexural strengths. In both systems, impact strengths increased at low shell filling levels but decreased at high shell filling levels. Impact fracture types varied with core quality and shell filling composition. Coextruded composites with treated PCC-filled shell showed better water absorption (WA) property compared to core-only controls and coextruded composites with high WF-filled shell. Plastic-only shell increased overall coefficient of thermal expansion (CTE) of coextruded composites, but filled shells led to the CTE decreases of coextruded composites. GF in shell behaved as an effective reinforcement for coextruded composites. The comparisons of flexural property among different core systems show that GF reinforcements were optimized at high GF loadings in a shell layer and GF alignments in the shell layer also played an important role. In coextruded composites with different shell thicknesses, the flexural property enhanced with the increase of shell bending modulus and strength at a given shell thickness. When the flexural property of shell was less than that of core, the increase of shell thickness led to reduced flexural property. On the other hand, when the flexural property of shell was higher than that of core, the opposite was true. In sound transmission loss (TL) testing, the stiffness and surface density were major factors influencing the sound insulation property of materials. The experimental TL results showed that the addition of clay or PCC and/or wood fiber (WF) fillers led to the increases of general resonance frequencies and TL in filled composites. However, at high filling levels, composite stiffness decreases led to TL reduction. The experimental TL curves of filled HDPE and WPCs were well approximated with the combined TL predictions from their corresponding stiffness-1 and stiffness-2 TL for S-region and mass law TL for M-region.

The ongoing softwood lumber trade dispute between the United States (U.S.) and Canada is one of the most contentious and largest bilateral trade battles over the recent decades. The bilateral trade debate is mostly because of the different forestland ownership systems in the U.S. and Canada, and the alleged timber subsidies by provincial governments to Canadian lumber producers. The Softwood Lumber Agreement (SLA) 2006 between the U.S. and Canada is the latest transitory solution of this dispute, entailing Canada to impose mandatory export charges on its lumber shipments to the U.S. In order to understand this trade dispute from a strategic policy perspective, this study analyzes SLA 2006 using game-theoretic frameworks. A Cournot-Nash duopoly model is developed to assess the possible effects of the export tax on overall lumber price and production of softwood lumber in both countries. The empirical econometric models are estimated to uncover the findings of the Cournot-Nash duopoly model by employing the historical time-series data of the softwood lumber market. Even though the game-theoretic model suggests that the export tax under SLA 2006 could decrease Canadian lumber exports to the U.S., the empirical estimation reveals that SLA 2006 is quite ineffective in restricting the lumber trade between the two countries. This study also develops a two-country two-stage game, and concludes that the optimum export tax under the framework of SLA 2006 is mainly determined by the level of Canadian lumber production costs and the U.S. lumber production capacity. Unlike the actual export tax of 0-15%, the empirical estimation reveals that the monthly optimal export tax ranges from -23% to 30%. Given that SLA 2006 is scheduled to expire in October 2015 and that both countries already started looking for ways forward, this study provides useful information in country-level bargaining and trade negotiations between the two countries.

Crayfish are important for stability, determining ecosystem structure, and ecosystem functions in freshwater habitats. Louisiana has many endemic species of crayfish, but most are poorly described. This study investigated the populations of some of the lesser known crayfishes in the South Central Plains. Specifically, the goals were to examine movement, movement across anthropogenic barriers, and estimate population size of 10 species reported from the area: Procambarus natchitochae, P. vioscai, P. clarkii, P. acutus, P. zonangulus, P. tulanei, P. kensleyi, Orconectes maletae, O. lancifer, and O. palmeri. In combination with a field team, I sampled twelve wadeable streams with DC backpack electrofishers and traps at least twice at 2-3 month intervals during summer, fall, and winter of 2014. Although all sampled crayfish of sufficient size were double marked, recaptures were minimal, thus, generalized N-mixture models were performed on the three most widely captured species to generate population and transience estimates based on sampling unmarked animals over time. All population estimates were very low and were dependent on river basin, specific conductance, and stream width. Although the relationship among species and river basins has been previously described, relationships with stream size and specific conductance were novel. P. natchitochae and P. vioscai appeared to spatially segregate along a gradient of stream size. Specific conductance, which is an indicator of available calcium, had a positive association with abundance for P. vioscai, P. natchitochae. P. natchitochae and P. vioscai showed the possibility of seasonal transience and potential relationships with dissolved oxygen. These results give conservation scientists and managers more information for conservation of Louisiana crayfishes.

Rates of hybridization between species that do not normally interbreed have increased due to human impacts on natural environments, such as habitat alteration or introductions of non-native species. Human-induced hybridization can be detrimental to wildlife and contribute to species extinctions. In Florida, feral Mallards (Anas platyrhynchos) hybridize with endemic Mottled Ducks (A. fulvigula) at rates close to 9%. However, levels of hybridization between these two species have not been extensively examined in the western Gulf Coast (from Alabama to northern Mexico) despite the potential impact on the Mottled Duck lineage. In this study, I examined the degree of hybridization between Mottled Ducks and Mallards in the western Gulf Coast. In addition, I validated a key developed in Florida to distinguish Mottled Ducks from Mallards and their hybrids for western Gulf Coast Mottled Ducks. Lastly, I examined the genetic structure of Mottled Duck populations and estimated gene flow by determining the number of migrants between regions across the western Gulf Coast. I used 36 microsatellite loci to genotype 405 ducks including putative Mottled Ducks, Mallards, and hybrids. Overall, genetic analyses revealed very low rates of hybridization (5.4%) in the western Gulf Coast. The key to distinguish Florida Mottled Ducks from Mallards and their hybrids proved highly effective (97%) for the western Gulf Coast population. Finally, multiple analyses indicated that Mottled Ducks are a single genetic population across the western Gulf Coast, which may be primarily due to dispersal of juvenile ducks. Currently, hybridization with Mallards is not a threat to western Gulf Coast Mottled Ducks; however, Mottled Duck hybridization should be monitored in the future to ensure that hybridization rates do not increase.