Pore geometry and topology are important determinants of sediment physical properties, such as porosity and permeability. They also influence processes that occur in the sediment, such as acoustic propagation, attenuation, and dispersion, single- and multi-phase fluid flow, and hydrodynamic dispersion. This study uses images to evaluate pore geometry and topology of ooid (subspherical particles) and siliclastic (angular quartz) sand that was collected from the marine environment south of Bimni Bahamas and Ft. Walton Beach, FL, respectively. Image analysis techniques and predictive tools enable insight into the relationships among sediment pore geometry, topology, and physical properties for these differently shaped sands. High frequency acoustics utilize short wavelength signals to evaluate sediments. Correspondingly short length scales are then needed for sedimentary property predictions, which is possible with planar and volumetric image analysis of sand. This data was compared to data obtained by direct large scale measurements (e.g., water weight loss, constant head permeability) were made. Mean porosity differed by as much as 0.04 and mean permeability showed good agreement and differed by a factor of 2. Given that the image analysis predictions were made from much smaller samples (~equivalent to the length scale of the high acoustic frequencies used) than the bulk samples, a sediment characterization at acoustically relevant length scales is possible. It was also demonstrated that for these homogeneous sands (i.e., ooids and quartz) two-dimensional pore geometry and topology are quite similar to three-dimensional pore geometry and topology (i.e., pore connectivity). Additionally it was determined that pore network models typically overestimate the topology and therefore, in order to match image and bulk predictions of sediment properties, these models must underestimate the conductance of individual pore throats (i.e., conductive element in sand). Typically pore throats are depicted as straight cylinders. Image data suggests that pore throats are better represented by biconical shapes where conductance is as much as 3 times higher than conductance within the straight cylinders. These findings indicate that increased realism in pore throat shape (higher conductivity) and in topology (fewer pore throats) may significantly influence network model evaluations of fluid flow or acoustic propagation in marine sand.

The Barataria-Terrebonne estuary has been eroding at a rate of up to 103.6 km2 yr-1 for several decades. If the current rate of loss is not reduced, an additional 2,550 km2 of coastal wetlands will be lost by the year 2050. Currently, stormwater in Terrebonne Parish is pumped into canals, ultimately discharging into the Gulf of Mexico. An opportunity exists to use this stormwater for wetland restoration; however, the ecological impacts of stormwater diversions on wetlands are unknown. The objectives of this project were to 1) to investigate the seed banks of a degraded marsh to determine if a viable seed source exists, 2) to gather baseline soil chemistry of a degraded marsh prior to receiving stormwater input, and 3) to compare the soil P chemistry, metal concentrations and accumulation rates, and sedimentation rates for different wetlands receiving stormwater input. An existing degraded marsh that is scheduled to receive stormwater input in the fall of 2004 was selected for the baseline study. These results will be compared to conditions after a new stormwater pump becomes operational. Coastal wetlands that have been receiving stormwater for <10 years and 30 years were selected to carry out the sediment chemistry study. A total of 370 stems germinated from the seed banks from the vegetated areas and a total of 2 stems were counted in the seed banks from the mudflat. These results suggest that replanting will be necessary for establishment of vegetation in the mudflat areas. There was a significant increase (p<0.05) in P concentrations in soil that had been receiving stormwater for 30 years when compared to soil that had been receiving for stormwater for <10 years, which may lead to alteration of plant communities as seen in the Everglades. Sediment profiles indicated a significant difference in Fe, Al, Zn, and Pb concentrations when comparing the age of the pump (P<0.05). However, soil metal concentrations were found below EPA toxicity thresholds even in coastal wetlands receiving stormwater input for 30 years. The results from this study will be used as a foundation for future studies of stormwater input to coastal Louisiana wetlands.

The western Louisiana inner shelf along the Chenier Plain coast has experienced fluid mud deposition in response to increased fine sediment supplied by the Atchafalaya River since ~1950s. The goal of this project is to assess the characteristics comprising the sedimentary strata and stratigraphic architecture that result from mud deposition on the inner shelf. Recent time-series cores collected from the inner shelf along the Chenier plain coast show the region is subject to transient fluid mud deposition, leading to high long-term accumulation rates. Sediment cores were collected in May 2001, March and May 2002 from the inner shelf landward of the 10 m isobath, 100 km west of Atchafalaya Bay. Porosity, granulometry, X-radiography, and 7Be, 210Pb and 137Cs geochronology indicate the presence of high-porosity event layers 2-25 cm thick composed of clay with basal silt laminations. These event layers appear to concentrate around a depocenter located 95-110 km west of the Atchafalaya River, landward of the 7 m isobath, but can be ephemeral features on a seasonal time scale. The combination of high-energy benthic hydrodynamics and sufficient fine sediment can result in cross-shelf gravity-driven flows (on very low slopes) that can blanket hundreds of square kilometers to thicknesses exceeding 10 cm. The sedimentary fabric that results from gravity-driven flows consists of a stacked pattern of predominantly fine-grained, fining upward packages. The resulting morphology of the shelf may be a clinoform, with maximum deposition occurring on the foreset (convex upward) region. The observations from the western Louisiana inner shelf (mud/silt couplets that comprise the fine-scale stratigraphy of the region, ephemeral 7Be deposits, and clinoform morphology exhibiting erosional features in sidescan and chirp data) are consistent with the wave-enhanced gravity-driven flow model. These results indicate that wave-enhanced gravity driven flows may be an important component in the dispersal of Atchafalaya River sediment.

Knowledge of mangrove litter dynamics is crucial to an understanding of the energetic links between mangrove ecosystems and nearby estuaries and coastal waters. Previous research into the role played by macrodetritivores in Neotropical mangrove litter processing has been contradictory. This study used leaf tethering to examine the effects of macrodetritivores on initial rates of mangrove litter degradation in South Florida, USA. Leaf litter dynamics experiments were run in both natural and restored mangrove forests to assess functionality of the restoration projects. Although less important than in some other parts of the world (e.g., the Indo-Pacific), macrodetritivores played a significant role in increasing in situ leaf degradation within mangrove forests on both east and west coasts of Florida. In contrast to Indo-Pacific forests, gastropods were the primary macrodetritivores usually observed feeding on abscised mangrove leaves in South Florida. During leaf tethering trials, macrodetritivores (the gastropod Melampus coffeus and grapsid crabs) attacked between 1.7 and 29.6% of deployed leaves at different sites and accounted for 24.0% more leaf mass loss compared to non-attacked leaves. Macrodetritivores increased leaf litter degradation in several different mangrove forest types and under different environmental conditions within this study. In addition, macrodetritivore degradation rates varied among site histories (natural versus restored) and macrodetritivore characteristics. Although macrodetritivore community populations were greater in restored forests, litter cycling processes were similar to nearby reference forests. Litter and environmental characteristics were also examined to help understand macrodetritivore impacts on litter cycling. Litter fall rates varied from 0.4 ± 0.1 to 3.2 ± 0.3 g m-2 d-1 at the several sites. Standing stocks of litter on the forest floor varied widely within and among sites and ranged from 29 g m-2 to 559 g m-2 with an overall mean of 269 g m-2. Differences in litter fall and litter standing crop across sites and seasons were partly attributable to environmental variables (i.e., temperature, porewater salinity, forest structure, and light). The restored mangrove forests observed during this study appear to have gained some natural functionality of leaf litter dynamics as compared to nearby reference forests.

In this study, I quantified freshwater and nutrient inputs in the Breton Sound estuary which is receiving freshwater reintroduction in an effort to restore deteriorating wetlands. Almost all wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. This has altered water and nutrient budgets and is a primary cause of the massive wetland loss in the delta. Maintenance of the delta depends on a healthy, functioning ecosystem which includes riverine input. The Breton Sound estuary is located southeast of New Orleans and until recently was hydrologically isolated from direct riverine input. In 1992, a freshwater diversion became operational at Caernarvon, LA that re-introduces freshwater, nutrients, and sediments from the Mississippi River into the estuary. Several inputs and losses were calculated for three annual (2000, 2001, and 2002) water budgets including precipitation (PPN), potential evapotranspiration (PET), the diversion, stormwater pumps, and groundwater. The inputs of ammonium (NH₄-N), nitrate (NO₃-N), total nitrogen (TN) and total phosphorus (TP) were determined for each of the water sources. There was a different precipitation pattern for each of the years for which water and nutrient budgets were calculated. Precipitation contributed 48-57% of freshwater input while the diversion structure accounted for 33-48%. The net input of fresh groundwater was 3 to 4 orders of magnitude less than diversion input and precipitation. Atmospheric deposition was the largest contributor of NH₄-N accounting for 62-72% of the total NH₄ input followed by the diversion (total annual NH₄-N input was 1.39x10⁵ to 1.96x10⁵ kg). NO₃-N input to the estuary was an order of magnitude greater than NH₄-N input. The diversion was the greatest source of nitrate to the study area (7.78x10⁵ to 1.64x10⁶ kg) contributing 77-88% of total nitrate input. The diversion contributed 1.26x10⁶ to 2.10x10⁶ kg of TN, representing 77-79% of TN input. The diversion contributed 81-98% of TP input and was an order of magnitude greater than precipitation and stormwater pumps combined. Annual loading rates of NH₄-N and NO₃-N were 0.16-0.22 and 1.6-2.2 gNm^-2y^-1, respectively. TN ranged from 1.9-3.2 gNm^-2y^-1 and TP ranged from 0.17-0.29 gPm^-2y^-1.

Wetlands improve water quality through sedimentation and the uptake of excess nutrients. As human population increases in the coastal zone, wetlands receive greater nutrient inputs. These additional nutrients may accelerate microbial activity, leading to faster decomposition rates. This decomposition could exceed belowground organic matter production, resulting in a net reduction in soil organic matter accumulation and vertical marsh accretion. The effects of nutrient enrichment on belowground organic matter decomposition in subtropical marshes have received little attention. As such, this research examined the effects of four levels of nitrogen combined with two levels of phosphorus enrichment on belowground decomposition through the use of cotton strip and litter bag assays in a Sagittaria lancifolia dominated marsh in Madisonville, Louisiana. Litter bags contained S. lancifolia root or shoot tissues; roots were of uniform tissue quality while shoots were from unenriched or enriched soils. Soil nitrogen and phosphorus applications both significantly increased belowground decomposition rates of cotton strips. The effect of tissue quality on shoot decomposition was dependent on nitrogen soil enrichment level. At low nitrogen enrichment levels, low quality shoot tissues decomposed more slowly than high quality tissues; this relationship was reversed at high nitrogen soil enrichments. Also, the effect of phosphorus enrichment on shoot decomposition was dependent on the level of nitrogen enrichment. Phosphorus soil enrichment only increased decomposition at the high nitrogen levels. Similarly, phosphorus enrichment combined with moderate nitrogen enrichments raised the decomposition rate of labile root tissue components. However, neither nitrogen nor phosphorus enrichments affected the decomposition rate of recalcitrant root components. Cellulose decomposition was positively correlated with interstitial pH. Shoot decomposition and the recalcitrant root decomposition rate also positively correlated with interstitial pH. This research demonstrated that nitrogen and phosphorus soil enrichments affect the decomposition of roots, shoots, and cotton strips, though in different ways. Variations in the nutrient and carbon quality of the individual tissues, as well as abiotic factors such as pH, modify the effects of soil nutrient enrichments on the decomposition of different tissues in the study marsh.

Agricultural development in the Mississippi River Basin has contributed to an 3-fold increase in NO3 loading of the river. Increased NO3 loading is a primary cause of eutrophication in the northern Gulf of Mexico. Identification of best management practices (BMPs) to reduce NO3 loss and wetlands restoration to remove NO3 through denitrification are critically needed. The objectives of this research were to determine factors controlling denitrification potential of different landscape units in an agricultural watershed and quantify the effects of BMPs and organic C amendments on denitrification rates of cultivated lands and restored forested wetlands. N2O, CH4 and CO2 emissions from restored and natural forested wetlands were measured to determine if restoration for NO3 removal will increase greenhouse gas emissions, thereby contributing to global warming and compromising the water quality benefits of restoration. Low-elevation, wetland clay soils exhibited 6.3 and 2.5 times greater denitrification potential than the high-elevation silt-loam and low-elevation clay soils under cultivation, respectively. Denitrification potentials of vegetated ditches were 1.3 to 4.2 times greater than the unvegetated ditches and cultivated soils, respectively. Soil cores collected from forested wetlands displayed 2.0 - 6.6 times greater denitrification rates than cultivated soils when incubated at 70 to 100% water-filled pore space (WFPS). Significantly lower N2O:N2 emission ratios were observed from wetlands than from cultivated soils. Denitrification rates in the cultivated and restored forested wetland soils increased 200% and 42%, respectively, when amended with cotton gin trash (CGT). BMPs increased denitrification rates of restored wetlands. Nitrate addition to forested wetlands led to a 48% increase in N2O emissions. Forested wetlands exhibited net CH4 sink of 438-1050 g CH4 ha-1 y-1. CO2 emission decreased as WFPS increased from 40 to100% in forested wetlands. Low-elevation clay soils in agricultural watersheds are the best candidates for wetland restoration for water quality improvement. CGT amendment of cultivated and restored soils in conjunction with BMPs can help reduce on-site NO3 loss. Wetland restoration in the Lower Mississippi valley will not significantly affect the global greenhouse gas emissions budget; however, increased N2O emissions due to NO3 additions merit consideration when establishing CO2 storage credits on restored wetlands.

As biological invasions have become a common phenomenon throughout the world, ecologists have intensified efforts to understand why natural communities are susceptible to invasion. Invading species can cause shifts in community structure that result in irreversible changes to ecosystem function. Phragmites australis has rapidly spread in North American coastal wetlands during the past 50 years and has become a dominant feature in Northern Gulf of Mexico brackish marshes. The rate at which Phragmites is spreading or the mechanisms controlling its establishment in these marshes is unknown. My research objectives were to: (1) determine the spatial and temporal patterns of Phragmites invasion and expansion; (2) evaluate how disturbance and nutrient enrichment controls brackish marsh invasibility and Phragmites establishment, and (3) identify the ecosystem impacts occurring within a brackish marsh during Phragmites invasion. I found substantial increases in the abundance and size of clones of Phragmites during the past 75 years. Annual increases of 11-23% occurred in area covered by clones, which had intrinsic rates of increase in size of 0.07 - 0.23 yr-1. To test marsh invasibility, I manipulated both nutrient levels and disturbance regimes in conjunction with purposeful introductions of Phragmites seed and rhizome material. Phragmites demonstrated the potential for active growth and spread when rhizomes were introduced into brackish marsh. To examine the ecosystem impacts of Phragmites invasion, I located three isolated Phragmites invasions and identified four distinct community types along a transect from the center of each invasion to adjacent un-invaded marsh. My results demonstrate for the first time that Phragmites increases marsh surface elevation relative to un-invaded marsh. Phragmites invasion resulted greater aboveground biomass, increased organic matter accumulation and peat development and lower cellulose decomposition rates relative to un-invaded marsh. The numbers and sizes of Phragmites invasions are increasing without apparent restriction in this Louisiana brackish marsh. These communities remain vulnerable to future Phragmites invasions if rhizomes are transported to new locations. Furthermore, Phragmites has an obvious affect as an ecosystem engineer and may allow invaded marshes to better tolerate increasing water levels due to sea-level rise/land subsidence than native short-stature graminoids.

Little is known about the morphometrics and the feeding ecology of paddlefish in Louisiana. I examined the morphometrics and feeding ecology of paddlefish from the Mermentau River, Louisiana from March 2002 to February 2003. Paddlefish were examined morphometrically by taking measurements of eye-fork length (EFL), body cavity length (BCL), girth (G), vent girth (VG), mouth vertical (MTB), mouth horizontal (MSS), and mouth gullet bottom (MGB) to determine which parameters would give a better estimate of weight (W). Regression analysis resulted in a morphometric model of the form: logW = 10.10 + 1.52 (logEFL) + 1.21 (logG) + 0.24 (logVG) (r2 = 0.97), though I recommended a more inclusive conservation model of the form: logW = -9.82 + 1.15 (logG) + 1.39 (logEFL) + 0.25 (logVG) + 0.15 (logBCL) (r2 = 0.97). Reanalysis of range wide data revealed reservoir/lake paddlefish were generally heavier than river paddlefish at larger eye-fork lengths. This may reflect denser patches of zooplankton in reservoir/lake systems, which may allow for greater paddlefish foraging success than in rivers. Copepods and cladocerans occurred in 90% and 82% of the stomachs, respectively. Feeding seasonality peaked in summer and winter. Diet appeared to switch from copepods in the summer to cladocerans in the winter. Diatoms dominated most of the full May stomachs. Paddlefish diets were similar between seasons except for the summer and winter seasons. Copepods and cladocerans contributing to most of the similarities and dissimilarities. Paddlefish diets were similar between all stages of sexual maturity with copepods and cladocerans contributing to most of these similarities and dissimilarities. An evaluation of size selectivity using Chessons Alpha indicated non-selective feeding and thus paddlefish may be described as indiscriminate planktonic feeders. Calculations of apparent ingestion time indirectly suggest that paddlefish were able to locate dense patches of zooplankton. This study followed the Mississippi Interstate Cooperative Resource Associations (MICRA) paddlefish studies.

The paucity of research into the environmental requirements, stock membership, abundance and residency patterns of bottlenose dolphins (Tursiops truncatus) in coastal Louisiana creates difficulty in understanding how local ecosystems and threats (such as fishery interactions, habitat degradation and pollution) affect populations. This study combined fine-scale environmental measurements and photo-identification techniques to describe patterns of habitat usage and abundance of bottlenose dolphins in lower Barataria Basin from June 1999 to May 2002. In addition I investigated the validity and limitations of using mark-recapture models to estimate abundance from cetacean photo-identification data. Bottlenose dolphins were present year-round in a wide range of water temperatures (10.9 33.9 ºC), dissolved oxygen levels (3.7 16.6 mg/L), salinities (11.7 31.5 psu), turbidity levels (1.4 34.0 NTU), distances from shore (3 800 m), and water depths (0.4 - 12.5 m). However, feeding activity was concentrated in a narrower range of conditions, 20 24 ºC water temperature, 6 9 mg/L of dissolved oxygen, turbidity values between 20 28 NTU, 200 500 m from shore, and depths of 4 6 m. Spatial mapping showed differences in the seasonal distribution of individuals and a tendency for feeding activity and larger group sizes to be concentrated in passes. Using distinctive natural markings present on dorsal fins, I identified 133 individual dolphins. Closed-population models were improved by inclusion of temporal and individual heterogeneity as sources of sighting variability and produced estimates of between 138 and 238 (95% CL range = 128 297) bottlenose dolphins for the study area. Analysis of Jolly-Seber model assumptions demonstrated the importance of ensuring cetacean surveys accurately represent temporal, geographic and demographic properties of a study population. In addition such factors as non-preferential image acquisition, group size, gender, behavior, stability and distinctiveness of natural markings, weather conditions and boat traffic must be considered. Evidence of a relatively closed Barataria Basin population agrees with current assumptions that bay bottlenose dolphin stocks are distinct from those found in deeper, offshore waters. Furthermore, the characterization of environmental usage patterns for this bay population strengthens adequate description and management of this relatively discrete Gulf of Mexico bottlenose dolphin stock.