Naturally vegetated areas converted to urban uses increases impervious surfaces in a watershed with corresponding increases in nutrient, sediment, and metal loadings to downstream ecosystems. Wetlands mitigate detrimental impacts by transforming or retaining pollutants. Current and historic sedimentation and metal retention rates were measured in an urban, depressional wetland in Baton Rouge, Louisiana to evaluate landscape position and watershed development on these processes. Sedimentation disks, feldspar marker horizons, and Cs137 analyses were used in three distinct landscape positions. Inflow channels had the highest elevation and water velocity while the interior was located in the lowest elevations with the longest hydroperiod. An intermediate elevation between the channel and interior was designated as the transitional landscape position. Sedimentation disks yielded significant differences (p = 0.009) in sedimentation rates between the channel (23.8 ± 5.43 g/m2/d) and transitional (37.1 ± 5.09 g/m2/d) landscapes. The interior (27.9 ± 4.65 g/m2/d) position was not significantly different. Feldspar data yielded comparable values for the transitional (29.6 ± 2.57 g/m2/d) and interior (27.2 ± 3.64 g/m2/d) locations, which were not significantly different (p = 0.35). A historic sedimentation rate of 0.49 cm/yr ± 0.11 cm/yr, calculated from Cs137 analysis, was significantly lower than the current rate of 2.95 ± 1.10 (p = 0.010). Lead, Cd, Cu, Zn, Ni, and P sediment concentrations were significantly greater (p < 0.05) in the interior than the transition based on sedimentation disks. Sediment metal concentrations were normalized with Al to compensate for increases in metal concentration with increasing clay content. Significantly higher Al content in the interior resulted in either no differences between the interior and transitional locations or significantly lower concentrations in the interior after Al-normalization. Historic metal retention rates (background concentrations) were calculated for depths below the 1963 Cs137 peak. Metal/Al ratios from soil cores yielded significantly higher Cd, Cr, Cu, Zn, Ni, and P concentrations in sediments deposited since 1963. These higher concentrations correspond with a seven percent increase in developed area surrounding Bluebonnet Swamp from 1963 to 2000. This urban wetland functions as an important sediment and pollutant sink, and protects downstream aquatic ecosystems.

Wetland environments have been impacted by the activities of man over the past several hundred years in North America. Industrialization into wetland areas has brought with it anthropogenic compounds that have been released into soils and groundwater. The use of phytoremediation to detoxify soil and groundwater began in the mid 1990's and has become a popular remediation technology. In 1994, a feasibility study for using phytoremediation in such an industrialized wetland area was conducted at a petrochemical facility at BASF Corporation, located about 20 kilometers south of Baton Rouge, Louisiana in Ascension Parish. The test site consisted of low level concentrations of the herbicide bentazon in the shallow soil and groundwater. In 1996, two test plots of 438 and 1000 black willow saplings were planted over the two shallow groundwater plumes of bentazon contamination. Groundwater monitoring, which began five years prior to plantings, was continued for five additional years after plantings. An effectiveness study was concluded in 2001. This research included measuring plant water use, soil conditions, evapotranspiration rates. Groundwater and statistical modeling were used to evaluate phytoremediation effectiveness. Data support that phytoremediation at the test site was successful at reducing the concentration of bentazon from the shallow groundwater. Modeling studies demonstrated that effective remediation will continue to occur as the trees continue to grow. It is predicted that remediation will be completed within 22 years. This research demonstrates the first comprehensive phytoremediation approach to remove the herbicide bentazon from shallow groundwater.

Louisiana's deltaic coast is a dynamic sedimentary environment made vulnerable by Mississippi River channelization, which restricts freshwater, sediment, and nutrient inputs to adjacent estuaries. Freshwater diversions now reconnect some estuaries with historic fluvial sources, like Breton Sound basin, which receives Mississippi River suspended loads through the Caernarvon freshwater diversion. The project objectives were to quantify short-term sediment accumulation using sediment traps, evaluate sediment trap effectiveness, and compare long-term deposition using feldspar horizon markers and 210Pb dating to the annual sediment trap deposition. Magnitude and variations of sediment deposition at 14 sites were compared during an 18-month study in the upper 415 km2 of Breton Sound estuary, Louisiana. Short-term dry deposition over sediment traps (t=15d) varied for hydrologic pulsing regimes, averaging 3.143 g/m2/d during non-pulsing periods (<183m3/s) and 4.740 g/m2/d during pulsing periods (¡Ý183m3/s). Deposition was greatest near the diversion and decreased with increasing distance from the diversion. Exterior marsh sites (n=5) received more total and allochthonous sediment than interior marsh sites (n=9). Fluvial pulses are significant sediment delivery mechanisms for interior marshes within close proximity (<6km) to the diversion. Exterior marsh deposition is influenced by both fluvial pulsing and resuspension events. Annual deposition over feldspar markers was highly variable but averaged 3.4 cm/yr. In contrast, long-term deposition measured using 210Pb and 137Cs geochronology revealed sedimentation rates within the last 75 years of about 0.12 cm/yr. Near vertical Pb and Cs activities occur within a distinct clay layer attributed to the 1927 flood, where 210Pb dating confirms its origin as circa 1927. Ephemeral short-term sediment deposition is driven by overland flow and highly variable due to prevailing winds and tides. Long-term deposition includes cumulative effects of internal sediment processes, such as compaction and organic matter decomposition, and is more representative of actual accretion rates (i.e., land-building). Estuarine sediment budgets indicate land-building processes are 66% deficient relative to the combined effects of sea level rise, subsidence, and erosion. A critical issue for managing coastal marshes and addressing land loss is elucidated here. Management efforts may be best directed at optimizing estuarine sediment loading based on peaks in river sediment discharge.

Estuaries are often the receiving basins for major river systems which makes them vulnerable to anthropogenic influences. I used Ecopath and Ecosim to investigate the structure of the Weeks Bay, Alabama, USA food web, and the responses of the food web to bottom-up perturbations. Four season-specific steady-state Ecopath models were developed and used to compare the production, biomass, consumption, biomass flows, and higher order indices of ecosystem functioning of the Weeks Bay food web under winter, spring, summer, and fall conditions. The season-specific Ecopath snapshots indicated that the structure of the Weeks Bay food web was resilient. Winter had the lowest biomass and production and heavy reliance on detritus, leading to high biomass and production in spring and summer, culminating in the most complex food web in fall. Ecosim simulations were performed that examined the responses of the Weeks Bay food web to single pulses of high and low flow years, more extreme seasonal variation of river flow, and interannual variation in river flow (two high-flow years followed by four low-flow years). Baseline simulations produced cyclic behavior at the lowest trophic levels that was gradually dampened as one moved to higher trophic levels of the food web. Lower trophic level groups showed the largest responses and quickest recovery from single pulses of high flow and low flow, while upper trophic level groups showed generally the smallest responses and longest recovery. More extreme within-year variation in river flow caused exaggeration of the seasonal responses predicted under baseline conditions, with little or no change in the average long-term biomass of groups. Interannual variation in high and low flow was mimicked in the biomasses of lower trophic level groups, with some of the upper trophic level groups responding with small, yet consistent, net changes in their long-term average biomass. Additional simulations showed that net changes in biomass were due to the magnitude, number, and temporal arrangement of high- and low-flow years. Results suggest that changes in nutrient influxes or precipitation patterns can affect the variation and long-term average biomass of key groups of the Weeks Bay food web.

The pattern and process of wetland loss in coastal Louisiana has the potential to influence the distribution and abundance of fishes and macroinvertebrates that utilize inshore estuarine habitat as nurseries during their early life histories. Current management plans designed to stabilize marsh elevations, such as freshwater diversions, may also influence the distribution and abundance of estuarine-dependent nekton. Given the importance of nursery function of inshore estuaries in coastal Louisiana, it is of interest to explore the response of estuarine-dependent organisms to environmental gradients. To this end I examined the ecology of two sympatric tonguefishes, the blackcheek tonguefish (Symphurus plagiusa) and the offshore tonguefish (S. civitatium), in coastal Louisiana. Both species are common transients, occupying estuarine waters from post-settlement to early adulthood. Examination of patterns of resource utilization within the Barataria study area identified significant differences between species with respect to microhabitat selection. Offshore tonguefish were generally more abundant than blackcheek tonguefish in the Barataria study area. Blackcheek tonguefish used lower salinities, higher temperatures, finer substrates, shallower depths, and were found closer to shore than offshore tonguefish. Ontogenetic shifts in resource utilization were also evident for both species; larger individuals typically utilized warmer waters with lower dissolved oxygen concentrations and higher salinities, and were collected farther from shore in deeper water over coarser substrates. Blackcheek tonguefish were abundant along the marsh edge while offshore tonguefish were rare, indicating the apparent avoidance of marsh-edge habitat by offshore tonguefish. In a similar study conducted in the Vermilion system, blackcheek tonguefish were more abundant than offshore tonguefish, indicating that salinity can substantially alter the distribution and abundance of these tonguefishes. Examination of growth rates within the Barataria system indicated that offshore tonguefish grew at a significantly higher rate than did blackcheek tonguefish. Growth of both species was significantly affected by various biotic and abiotic factors. Qualitative loop analyses indicate that tonguefish abundances are potentially affected by the input of nutrients, changes in emergent marsh habitat, and alterations in salinity. Environmental changes associated with wetland loss and associated management alternatives have the potential to affect these sympatric tonguefishes as well as other estuarine-dependent species.

Recent research suggests that oyster reefs provide unique three-dimensional hard bottom habitat for many fish species. Along the northern shore of the Gulf of Mexico, oyster shell bottoms are predominantly flat, subtidal and cultched, lacking the vertical relief and spatial heterogeneity provided by natural reefs. This study compared finfish assemblages, gut contents, and macroinvertebrate assemblages at subtidal oyster shell (cultched oyster lease) and mud bottoms in Barataria Bay, Louisiana. Three mud and three shell sites were sampled on seven dates from October 2001 to October 2002, using gill nets and substrate trays. Data from the gill nets were used to compare fish assemblages, as well as to document feeding habits through gut content analysis. Data from the substrate trays were used to document benthic fish and invertebrate communities associated with the two bottom types. Finfish abundance was greater at shell (N = 234) than mud (N = 179) bottoms. Substrate trays collected significantly greater numbers of benthic fishes (p = 0.001) and decapod crustaceans (p = 0.001) at shell bottoms. Gut contents showed predation on fishes, bivalves, and decapod crustaceans. These results show that cultched shell bottoms support a more abundant finfish assemblage than mud bottoms, and provide a potentially important food source for transient fishes due to abundant benthic fishes and decapod crustaceans.

Adenosine triphosphate (ATP) is a unique biochemical indicator of active microbial biomass and its relationship to environmental conditions. Its assay in sediments is complicated, however, by adsorptive loss to the sediment matrix and subsequent interferences in the luciferin-luciferase assay by compounds released during the extraction process. Corrections must be applied to correct for these losses and we describe a novel approach using radioactive ATP to correct for ATP adsorption. The sediment matrix also plays a significant role in determining both the magnitude of the ATP pool and the extent of the ATP adsorptive loss. Coarser sediments were found to have greater ATP levels and little adsorption, whereas silts and clays had significantly lower ATP levels and up to 95% adsorptive loss. Application of the ATP assay to very fine-grained marine sediments in off shore oil producing areas revealed a sedimentary ATP biomass of approximately 40ngg^-1 prior to oil development but after drilling the ATP level dropped 10 to 15 fold to 2 to 3 ngg^-1. Post-drill sediments contained high levels of barium which is associated with drilling fluids, and had no detectable oxygen at a depth of 3mm, and the mean grain size decreased indicating the bottom was being coated over by the drill spoils.

Short-term, wave induced erosion along bay beaches in the northern Gulf of Mexico has been linked to the postfrontal phase of cold front passages. Not until recently has consideration been given to the importance of wave erosion on marshes fringing large bays during the entire cold front event. Two WAVCIS (Wave-Current-Surge-Information System) stations were established on the north and south flank of a small marsh island in Terrebonne Bay, Louisiana, to measure and elucidate the hydrodynamic response to these events. Data from WAVCIS stations, which includes wind speed and direction, air temperature, significant wave height and water level, were collected between June 1999 and January 2002. These data were coupled to measured shoreline change data obtained from a series of north/south repetitious profiles along the length of the island. Four high-resolution topographic surveys were conducted between April and June 1999 and a fifth in December 1999. These surveys were complimented by annual surveys conducted in spring from 2000 on with an additional survey in October 2003. Data obtained from this effort allows the conclusion that low-energy fringing marshes undergo substantial geomorphological change from locally generated high-frequency waves developed by strong winds (12.99-14.14 m/s maximum wind speed) associated with cold fronts. On marsh islands, 80% to 90% percent of erosion occurs during the winter causing the island to thin in space 2.5 m/yr. Erosional patterns observed on the marsh edge include 1) neck and cleft formation, 2) neck cut off and 3) undercutting and marsh toppling. When compared to tropical storms, erosion associated with a season of cold fronts is equal to erosion from one tropical storm. This work underscores the significance of locally generated waves in marsh loss of coastal Louisiana over short time scales (years).

This dissertation focuses on impact on water quality of two freshwater diversions, the Bonnet Carre Spillway and the Caernarvon freshwater diversion, as well as the Atchafalaya River Estuarine Complex. As water passed through the Bonnet Carre Spillway, there were reductions in total suspended sediment concentrations of 82-83%, in nitrite+nitrate of 28-42%, in total nitrogen (TN) of 26-30%, and in total phosphorus (TP) of 50-59%. The Si:N ratio generally increased and the N:P ratio decreased from the river to the plume edge in Lake Pontchartrain. At the Caernarvon diversion, there were reductions in concentrations of dissolved inorganic Si, N, and P of up to 38%, 57% and 23%, respectively. The DSi:DIN ratio rose from 0.9 to 2.6 at the Gulf end member station, while the DIN:DIP ratio fell from 107 to 26. There were decreases in total suspended sediment, large changes in salinity correlated to diversion discharge, and decreased water temperatures associated with riverine discharge. Chlorophyll concentrations near the diversion were low due to light limitation, but increased after suspended sediments decreased below 80 mg L-1, then decreased Gulfward. In the Atchafalaya River estuarine complex, salinity fluctuated seasonally, with the lowest salinities occurring during high river discharge. There was a 41-47% decrease in NO3- concentrations and total suspended sediments decreased as river water flowed through the estuarine complex. In summary, the following conclusions can be made from these studies of the effect on water quality of riverine input into coastal wetlands: (1) riverine input has a pronounced effect on salinity throughout a receiving basin. Whereas nutrients and sediments are actively deposited and/or transformed as riverine derived water passes through an estuarine system, freshwater passes conservatively with no change, diluting higher salinity waters; (2) There is rapid and effective trapping of suspended sediments in estuarine systems due to decreased water velocity and sediment settling; (3) Nitrate concentrations are substantially reduced in the estuarine environment due to the processes of denitrification, assimilation and reduction; (4) dissolved inorganic molar Si:N ratios increase, and N:P ratios decrease as riverine water flows through an estuarine system.

Larval bay anchovy (Anchoa mitchilli) habitat quality in Chesapeake Bay was predicted using an individual-based model applied to spatially-detailed field data from Rilling and Houde (1999). Habitat quality was predicted using the ratio of instantaneous mortality rate to instantaneous growth rate. Model predictions of habitat quality were compared to field estimates of habitat quality derived from the spatially-detailed field data. Three sets of one-day simulations were performed to estimate larval growth and mortality rates throughout Chesapeake Bay during June and during July 1993. Field-based simulations used field data to estimate the model inputs of water temperature, zooplankton densities, and the densities and sizes of bay anchovy larvae and gelatinous predators (Mnemiopsis leidyi and Chrysaora quinquecirrha). Standardized larvae simulations used the same field data, but standardized larval sizes and densities throughout the Bay. A third set of simulations was performed to determine the relative importance of six factors in determining the bay-wide spatial variation in predicted growth and mortality rates. Model predictions from the field-based simulations produced spatial patterns of habitat quality in the Bay that sometimes conflicted with the otolith-based predictions of Rilling and Houde. Field estimates of anchovy egg and larvae abundances were generally high in regions predicted to have low M/G ratios, but low in regions with low otolith-estimated M/G ratios. The standardized larvae simulations generally supported the conclusions of the field-based simulations. The effect of habitat quality on larval production was evaluated using the predicted mortality rates from the two sets of simulations. Initial larval abundances dominated the percent of survivors projected 20-days into the future that a region would produce, but when larvae were standardized across the bay, differences in habitat quality among regions was important in determining the relative contributions of survivors by region. Initial larval length and zooplankton densities were the most important factors determining the spatial variation in growth rate, while predator density was most important for mortality rate. Future research should focus on field and laboratory data collection to resolve the discrepancy between model-predicted and otolith-estimated M/G ratios.