Cold fronts play important roles in flushing water out of the Louisiana estuaries. This study is aimed at examining the impact of cold front passages on the hydrodynamics in autumn-winter-spring of 2006-2007, and tries to determine the geographic difference, correlation and relative importance of winds, tides, and river discharge on water level variability and flow field. The amplitude spectra of water level reveal that diurnal tides dominate most stations. Areas west of 91°W have relatively high semidiurnal tides. The subtidal fluctuations are mainly wind-driven. Only the station in the Atchafalaya River shows obvious response to the spring flood of the Mississippi/Atchafalaya Rivers. Coastal bays have different water exchange rates depending on their water body area and geomorphology. Five largest flushing events correspond to migrating extratropical cyclones with frontal orientation perpendicular to the coastline, suggesting that wind direction is one of the controlling factors in the flushing rate and total transport. Both alongshore and cross-shore winds may effectively induce bay-shelf exchange. Northwest/north winds appear to be the most effective wind forcing in driving water movement from bay to shelf. Strong cold fronts may flush more than 40% of the bay waters onto the shelf within a period less than 40 hours. The near-surface current on the Louisiana inner shelf is mainly wind-driven, but tidal forcing becomes more important in the sub-surface layers or in the vicinity of the coastline of shallow waters. A prevailing down-coast flow occurs 81% and 70% of the time at CSI-6 and CSI-3, respectively. Strong cold front events may disturb this down-coast flow system by inducing a 1- to 3-day up-coast flow. At CSI-6, the Mississippi river discharge has little influence in non-flood seasons. During the period of spring flood, however, the large amount of freshwater exerts significant barotropic and baroclinic forcings on the current field and reinforces the down-coast flow. The analytical model reveals that the amplitudes of water level variations induced by alongshore and cross-shore wind forcings have the same order of magnitude (i.e., 10-1 m), indicating that they play almost equally important roles in driving the subtidal water level variability inside the bays.

The calanoid copepod Calanus finmarchicus is broadly distributed in the North Atlantic, where it dominates the spring zooplankton biomass of shelf ecosystems. Calanus finmarchicus diapauses in the deep basins of the Gulf of Maine (GOM) during late-summer through early-winter. During diapause, predators that co-occur in regions of high copepod abundance may reduce survivorship through predation. Consequently it is important to measure the distribution patterns of C. finmarchicus and its predators. Two cruises were carried out during December of 1998 and 1999 in the GOM. Video Plankton Recorder (VPR) data collected in Wilkinson, Jordan and Georges Basins were used to describe the fine- to basin-scale distributions of C. finmarchicus and its predators. The locations of individual zooplanktors were mapped by towyoing a Video Plankton Recorder (VPR), mounted on the towed-body BIOMAPER-II, across the basins. Volumetric distribution patterns were estimated by interpolated abundance data using 3D Kriging. The abundance of C. finmarchicus was lower in December 1998 than in December 1999. This difference is discussed in terms of the spatial distributions and abundances of cnidarian, ctenophore, and crustacean predators. Gelatinous plankton were more abundant during December 1998 than in December 1999. Gelatinous plankton (siphonophores, ctenophores and medusae) were identified as the most aggressive taxa preying on C. finmarchicus. An inverse spatial pattern between C. finmarchicus and predators was observed in all three deep basins during December 1998, suggesting depletion of C. finmarchicus through predation. Water temperatures were generally cooler and fresher during December 1998 and warmer and saltier during December 1999. This hydrological regime changes caused by the shift between the Labrador Subarctic Slope Water and the Slope Water, respectively, seemed to affect both, C. finmarchicus and its invertebrate predators. During December 1998, C. finmarchicus was broadly distributed (0-200 m) in the water column probably due to broader distribution of cooler temperatures. During December 1999 C. finmarchicus was found below 150 m, where cooler temperatures dominated. The low C. finmarchicus abundances observed during December 1998 were possibly caused by the combined action of predation and advection losses since diapausing populations above sill depth (~200 m) are likely advected out of the system.

Storm surge is an abnormal rise of the sea surface caused by atmospheric forcing, including the wind stress and atmospheric pressure associated with extra-tropical and tropical cyclones. Hurricanes and typhoons have a great impact on coastal regions, and can cause severe loss of lives and great damages. A systematic investigation of storm surge impact to the coasts of Louisiana and Texas, where the continental shelf reaches up to 200 km in width, is conducted here using the hydrodynamics Finite-Volume Coastal Ocean Model, FVCOM (Chen et al., 2003). The model is applied to the northern Gulf of Mexico to simulate the storm surges caused by Hurricanes Rita (September 2005) and Ike (September 2008), and allows the resolution of the flooding along the Louisiana and Texas coasts. Observations of inland flooding from USGS are used to validate the model with satisfactory results. Various idealized scenarios are also simulated using FVCOM, to gain insight into specific surge mechanisms. This study focuses on the following topics: 1) The roles of shelf geometry and tides in a hurricane surge are explored in a set of experiments where the nonlinear interaction between tide and surge is investigated and found to be important, relative to the tidal amplitude; 2) The receding flow of Hurricane Ritas surge waters back to the Gulf of Mexico and the different dynamics that produce the remarkably different flooding (~0.5 days) and return (>7 days) periods are explained; 3) The effect of the often overlooked forward speed of a hurricane, which was found to have an unexpected and significant impact on coastal surges, in that faster storms produce higher coastal peak surges but smaller overall inland flooding (vice-versa for slower storms); and 4) The importance of Galveston Bays barrier islands on the propagation of Hurricane Ikes surge, where results suggested that under a realistic erosion scenario for Bolivar Peninsulas, the bay is exposed to dangerously high water levels almost as much as if the Peninsula was leveled to about Mean Sea Level, underlining the non-linear nature of this bay-barrier system.

Sediments from the Gulf of Papua were examined to estimate particle flux and sediment mass accumulation rates on multiple timescales. Patterns of sediment mass accumulation and inventory-derived 210Pb fluxes display regional variations, decreasing seaward, and along isobaths seaward from the northeastern shelf edge. The amount of terrigenous sediment load being discharged annually from the shelf and accumulating in Pandora Trough is approximately 7-14×106 tonnes. The existence of possible turbidity-current transport and deposition have been documented in deeper parts of the Gulf of Papua. High excess 210Pb fluxes estimated from seabed inventories at the shelf edge and upper slope are consistent with the combined effects of sediment focusing and boundary scavenging of oceanic water masses. Sediments may be transported from inner-shelf depocenters by oceanic processes, focused in depocenters near the northeastern Gulf of Papua shelf edge, and distributed downslope through a combination of nepheloid-layer flow and possible turbidity-currents. For the cores located between shelf edge and lower slope, biodiffusion coefficients and mixing depths exhibit a decreasing trend with increasing water depth. Using a two-layer model, biodiffusion coefficients in these cores are in the range of 0.007-60 cm2 y-1 for the upper layer and 0.002-2.9 cm2 y-1 for the bottom layer. Sediment mass accumulation rates without the influence of physical mixing are probably overestimated by a factor of ~1.4. Jumbo piston cores taken from the shelf edge and upper and middle slope in the northern Pandora Trough suggest variation in sediment mass accumulation rates during post-Last Glacial Maximum (LGM) sea level rise. Upper 12 m of the sediment on the northeastern shelf edge has deposited in < 12 ky BP after post-LGM sea level rise. The bulk of this mud deposit, with mass accumulation rates as high as 3900 g cm-2 ky-1, is constrained between the time of Last Glacial Maximun and Younger Dryas. The findings from this study suggest that physical processes building the mud wedge on the northeastern Gulf of Papua shelf were similar to the physical processes acting today building the clinoform in the western Gulf of Papua shelf.

The gag grouper (Mycteroperca microlepis) population in the Gulf of Mexico supports both a commercial and recreational fishery but has experienced a decrease in the male to female sex ratio over the past thirty years. Protogynous fish populations naturally have a smaller male to female ratio than gonochoristic fish populations; however the decline in the gag population is such that sperm limitation may be occurring. In an effort to correct the decline in sex ratio, fishery managers have recently implemented two marine reserves designed specifically to protect gag spawning aggregations. Results from two population models (an age-structured model and an individual based model) suggest that utilizing marine reserves in the management of gag (a female-first protogynous grouper) may be an effective method to increase the male to female sex ratio in the population. Both models show that marine reserves can have a positive impact on sex ratio, but the effectiveness of marine reserves is a function of the magnitude and pattern of fishing effort. The inclusion of density-dependence to the sex change function of the models, in an effort to model socially-induced sex change, showed that the mechanism controlling sex change in the population will impact the population response to fishing. Socially-induced sex change may act as a buffer to high fishing mortality and increase the expected benefits of marine reserves. Both models successfully simulated a protogynous fish population and these methods may improve upon existing stock assessment models.

Petroleum platforms number greater than 4,200 in the Gulf of Mexico and Caranx crysos (blue runner) is one of the most abundant fish species around these platforms. Forty-six blue runner were tagged with acoustical transmitters in August 2005, though the study was terminated prematurely due to the impending arrival of Hurricane Katrina. Nineteen blue runner were tagged in September 2006 and tracked for up to two months. Blue runner exhibited limited site fidelity around the platforms in 2005. The home range of twenty-three blue runner was calculated in 2005. A significant difference was found between the fork length of the fish and their overall 50% range, but their overall 95% range. The reverse was true when comparing mean daily ranges and fork length. The daytime core ranges were generally larger than the nighttime core ranges, though not significantly so. In 2006 tagged fish were released at unmanned platforms and all but one returned to the main complex and remained there over the course of the study period. The size of blue runner schools was estimated to be 36m. They were found to school more during the day than at night and moved between schools showing no preference for schooling with a particular fish. The blue runner showed a distinct diel vertical migration pattern with a marked descent to about 25m at night and ascent to the surface in the morning. The rate of ascent was significantly greater than the rate of descent. There was no relationship between these rates, the amplitude of migrations and maximum nightly depths with the lunar periodicity. There was a significant difference between the nighttime distribution of blue runner at the unmanned platforms and the manned platforms with fish at the unmanned platforms having a greater mean depth. The swimming speeds of tagged blue runner were greater during the day than at night and were indicative of passive foraging behavior. The lighted manned platforms appear to allow for greater foraging opportunities at night than the unmanned platforms.

Seafloor instability along the Mississippi River Delta Front (MRDF) gained renewed attention with the landfall of Hurricanes Ivan (2004) and Katrina (2005). Traditional root causes for MRDF shelf failure were exacerbated by sea-state conditions associated with these severe tropical cyclones and their interaction with the seafloor. These conditions were characterized by large waves, long wave periods and wave-induced turbulence in the bottom boundary layer and throughout the water column. An evaluation of local and regional MRDF bathymetry data revealed substantial changes in seafloor elevation and the immediate subsurface sediment profile, hypothesized as the end result of cyclic wave-seafloor interaction, seafloor scour and failure, and the re-initiation of antecedent seafloor slides and subsequent sediment re-deposition. Observed bulk wave and bottom layer conditions during Hurricanes Ivan and Katrina, during which significant wave height and wave period exceeded 15 m and 12 sec, respectively, were used to calibrate a series of MIKE 21 numerical wave models. Once calibrated, hindcasts were generated for earlier MRDF hurricanes dating from 1965. Spectral frequency data indicated long-period, often bimodal MRDF wave effects up to 48 hours prior to storm arrival. Lithologic and geotechnical parameters indicate widely varying shear strengths and safety factors, with higher shear stresses coincident with the 25-m isobath. Safety factors decreased in tandem with hurricane approach both prior to and after peak conditions. One-dimensional sediment failure modeling, calibrated to past seafloor failures, indicated variable ranges of mudslide length, ranging up to several kilometers. A composite risk framework was constructed that employed various triggering, revealing and predisposition danger factors, a statistical analysis of elements at risk, and a vulnerability assessment to identify likely scenarios for future hurricane-initiated seafloor failure. A top tier of historical storms, including Hurricanes Ivan, Camille and the 1856 Last Island Hurricane, was risked as most prone to failure; a secondary tier included Hurricanes Katrina, Opal, Carmen and the 1915 New Orleans Hurricane. Five hypothetical future hurricanes of varying intensity were then used to help characterize potential MRDF seafloor response. Areas at highest risk included those characterized by steep slopes, rapid sedimentation rates, and lengthened temporal exposure to severe hurricane conditions.

<P>The marshland upwelling system (MUS) was designed to treat domestic wastewater from coastal dwellings where conventional methods are inadequate due to high water tables, poor hydraulic soil conditions, anaerobic soils, and saline groundwater. Currently there is no adequate treatment system available and coastal dwellings are contributing to water quality problems. This study focused on determining the treatment effectiveness of the MUS for organic matter and understanding the specific processes involved in nitrogen treatment.</P> <P>The treatment of organic matter, measured as five-day carbonaceous biological oxygen demand (CBOD₅), was effective in field tests for both saltwater and intermediate marshes. Global removal efficiencies were 95 and 99% and first-order removal constants were 0.80 and 1.30 m^-1 for saltwater and intermediate marshes, respectively. A laboratory study confirmed effective treatment of organic matter. Wastewater nitrogen present as nitrate was removed very effectively (> 99%) during a laboratory simulation study. Ammonium removal was not as effective and dropped to 20% by the conclusion of this study. Removal of ammonium was dependent upon the sorption capacity of the soil under reducing conditions. While a field site would offer a much greater soil treatment volume and longer effective retention, ammonium would eventually saturate the soil sorption capacity which will be important in determining MUS longevity. As nitrogen is primarily present as ammonium in the wastewater, conversion of ammonium to nitrate, via nitrification, prior to injection would improve performance. A preliminary oxidation study yielded a 20% conversion of ammonium to nitrate. Further research should focus on improving nitrification rates prior to injection.</P> <P>Additionally, a higher salinity (20, relative to 2) was found to have an initial, significantly negative impact on treatment of carbon, sorption of ammonium, and denitrification. Therefore, the impact of the native salinity should be considered in any future design modifications to the MUS.</P> <P>In conclusion, the MUS has demonstrated great effectiveness in treating wastewater carbon and nitrate. This research showed additional work is required to enhance nitrification rates prior to injection to improve ammonium treatment. Thus, with modifications, the MUS stands to become the first, long-term, effective treatment system for coastal dwelling wastewater.</P>

The upper Breton Sound estuary was hydrologically reconnected to the Mississippi River via the Caernarvon freshwater diversion structure in 1991. The Caernarvon structure can provide controlled freshwater pulses to the upper Breton Sound estuarine ecosystem, replicating historic freshwater pulsed events, although the original authorization was to control salinity isohalines at specific locations in the estuary. However, unlike historic freshwater pulsed events prior to the construction of levees, the current freshwater pulse contains an unprecedented amount of inorganic nitrogen, predominately as nitrate (annual average 71.4 µM NO3-). Denitrification is a microbial process, which can potentially remove excess nitrate entering coastal Louisiana ecosystems due to these riverine pulsed events. This study presents the first 15N isotope pairing technique (IPT) denitrification estimates from coastal sediments in Louisiana, and evaluates the influence water temperature and different habitat types have on denitrification rates. Three IPT assumptions were tested in the current study and were fulfilled; however, the fourth assumption, the influence of annamox, was not evaluated. The three IPT assumptions evaluated were fulfilled in the benthic and marsh habitat sediments. However, the marsh habitat sediments from upper Breton Sound provide a dilemma for the current IPT design; 15NO3- diffusion will not reach deep into the plant rhizosphere where optimal conditions persist for coupled nitrification-denitrification activity. There was a significant interaction between habitat (marsh and benthic) and water temperature (8 and 22 °C) treatments on denitrification rates. Mean total denitrification (direct + coupled denitrification) estimates from a 70 µM 15NO3- incubation concentration were 17.5 (± 3.1) and 5.1 (± 1.5) ìmol N m-2 h-1 for benthic and marsh habitat sediments at 22 °C, and were 7.8 (± 1.9) and 2.1 (± 0.45) ìmol N m-2 h-1 for benthic and marsh habitat sediments at 8 °C, respectively. Overall, total denitrification rates ranged from 0.28 to 284.1 ìmol N m-2 h-1 for both habitats at 22 °C over a 2 to 200 µM 15NO3- incubation concentration range. Coupled denitrification comprised the majority of the total denitrification rate measured. Mean direct denitrification rates did not exceed 2 ìmol N m-2 h-1, and suggests direct denitrification measured by the isotope pairing technique in my study is not a major pathway for NO3- removal in upper Breton Sound benthic and marsh habitats.

Absorption and fluorescence measurements of chromophoric dissolved organic matter (CDOM) were examined along a transect containing 36 sampling stations in the Barataria Basin during high and low conditions to observe seasonal variation in these optical properties. The objectives of this study were (i) to observe CDOM variability in Barataria Basin in variable flow (high and low) conditions, and to characterize the CDOM, (ii) to identify the constituents of CDOM and to model CDOM compositional variability in the Barataria Basin using parallel factor analysis (PARAFAC). CDOMsalinity relationships were non-conservative in lower and upper part of the transect; however a conservative inverse relationship in the middle basin suggest that CDOM could be used as an useful indicator of salinity in the middle Barataria Basin. Larger variations in mean CDOM absorption and fluorescence values have been observed during low flow conditions than that during high flow conditions along the same transect. In general, mean CDOM absorption and fluorescence have shown linear inverse relation with salinity (r2 = 0.5 for high flow; r2 = 0.6 for low flow) and increased upstream along the stations. Using PARAFAC, four components could be identified in the Barataria Basin. Two humic, one non-humic, and one pedogenic component derived from PARAFAC modeling. These components showed the characteristics of the bulk fluorescence properties with an exception of component 3 (non-humic). Component 3 was found similar to autochthonous production of labile organic matter and was supported by elevated levels of chlorophyll-a between stations from 25 to 30. Fluorescence and humification indices along with peak ratios were calculated. In conclusion, CDOM variability in the Barataria Basin was characterized and modeled using the PARAFAC. The results obtained in this study are similar to previously reported results in estuarine environments. This study showed the potential application in characterizing CDOM variability in the Barataria Basin which explained over 99% variability of the water samples consisting of four major constituents. In future studies, water discharges from different water bodies in the Barataria Basin could be traced using CDOM compositional variability observed by EEM-PARAFAC technique.