The Mississippi River delta front (MRDF) is an excellent natural laboratory for studying seafloor instability and evaluating the preconditioning factors and triggering mechanisms that lead to ...seafloor failures. The occurrence of seafloor landslides on the MRDF has been recognized since the 1950s, but the bulk of research on the topic was conducted in the 1970s-80s after seafloor landslides triggered by Hurricane Camille damaged offshore infrastructure. Through these efforts, it was recognized that seafloor instability features are present across the entire delta front, that rapid sediment delivery from the Mississippi River is a primary preconditioning factor for failures, and that cyclic loading from hurricane waves is the main triggering mechanism for deep-seated catastrophic events. However, mounting evidence shows that MRDF seafloor motion occurs even during periods of no hurricane activity, which could be attributed to creep-like motion of underconsolidated sediment, or smaller episodic flows triggered by winter storms or Mississippi River floods. Given the extensive spatial distribution of instabilities on the MRDF, the multiple mechanisms of failure and variety of resulting morphology, and the range of potential triggering mechanisms with short recurrence, the MRDF is an exceptional location to assess the complex problem of seafloor landslides. An improved understanding of seafloor landslides is crucial for understanding global sediment budgets and associated biogeochemical cycling, as they can evacuate large volumes of sediment into deep water over short time periods. Additionally, seafloor landslides pose a hazard to offshore infrastructure and to coastal communities through possible tsunami inundation, and advancing research on preconditioning factors and triggering mechanisms would improve hazard assessments. This paper presents a review and synthesis of geological and geotechnical research on the MRDF, particularly with respect to seafloor landslides: their occurrence, geological and geotechnical controls, triggering mechanisms, and knowledge gaps related thereto. This synthesis is conducted at times of rapidly developing technologies for studying seafloor instability, and as the MRDF enters a stage of degradation characterized by reduced sediment delivery and accumulation.
Rationale
Pyrrolidone‐based drugs find widespread use in treating conditions such as epilepsy and Alzheimer's disease, and in various other medical applications. Brivaracetam, the latest generation ...of pyrrolidone drugs, has exhibited significant promise owing to chemical structure modifications. Its affinity to the SV2A receptor is double that of the previous‐generation drug, levetiracetam. Consequently, brivaracetam holds substantial potential for diverse applications. As a novel drug not yet included in the pharmacopeias of developed nations, comprehensive analysis and research are necessary to guarantee its safe utilization in clinical settings.
Methods
A liquid chromatography quadrupole time‐of‐flight tandem mass spectrometry (LC/QTOFMS) method has been developed to effectively separate, identify and characterize both the degradation products and process‐related substances of brivaracetam. Stress testing of the sample was carried out following the guidelines outlined in ICH Q1A(R2). The structures of these impurities were identified through positive electrospray ionization QTOF high‐resolution MS and NMR spectroscopy. Additionally, the formation mechanism of each degradation product is thoroughly discussed.
Results
Under the analytical conditions outlined in this paper, brivaracetam and its degradation products were effectively separated. Thirteen degradation products were detected and characterized, shedding light on their origins and degradation pathways. Among these, three degradation products align with previously reported impurities, and two unreported degradation products were synthesized and confirmed through NMR spectroscopy. The stress testing results revealed the instability of brivaracetam under acidic, alkaline, oxidative and thermal stress conditions, while it exhibited relative stability under photolytic stress conditions.
Conclusion
The study developed an analytical method for brivaracetam that enabled the effective detection and separation of brivaracetam and its 13 degradation products. This method addresses a gap in both current domestic and foreign drug standards. The structures of all the major degradation products were characterized by high‐resolution LC/QTOFMS, which is essential for quality control during the drug production process, stability evaluation and the establishment of proper storage conditions.
The use of dredged material from continental shelves and estuaries for degraded barrier islands has become a common practice worldwide. South Pelto block on eastern Ship Shoal (SS) off the coast of ...Louisiana has been dredged for high-quality sand resources, including Caminada Dredge Pit (CDP) and multiple pits in East Timbalier borrow areas (ET) adjacent to CDP. To understand how these dredge pits change and sediments infill over time, multiple surveys were conducted, including bathymetry, sidescan sonar, subbottom CHIRP, and sediment samples were collected for grain size analysis.
Although there is no nearby muddy sediment, sidescan and grain size data both show low-reflectivity areas inside CDP became larger over time, indicating continual supply from suspended mud. Subbottom data show decreasing pit wall slopes over time and degassing over patchy low reflectivity areas on the pit bottom. Arc-chord rugosity analysis was performed with emphasis applied to ET to examine the difference between cutter and hopper dredge techniques. It was revealed that dredging from the hopper created a higher rugosity value than the cutter, leading to a shorter recovery time for the benthic environment. Bathymetric results reveal approximately 20 m to 60 m of horizontal outward pit wall migrations over 3–5 years. Hurricanes Marco, Zeta, and Ida as well as Tropical Storm Claudette passed the study site (within 50 Km) during the study period which increased wind-wave energies sufficiently to develop new sand ripples discovered on sidescan sonar data near ET and CDP. By integrating various datasets and investigating the effects of tropical cyclones on a dredged area in SS, this study contributes valuable insights that fill existing knowledge gaps and enhance decision-making for future management strategies.
•CHIRP shows pit wall migration significantly less than buffer federally required.•Analysis shows hopper dredge increases overall rugosity compared to cutter dredge.•Tropical cyclones increased energies such that sand ripples formed on Ship Shoal.
Sediment transport over Sandy Point dredge pit in the northern Gulf of Mexico during a cold front event in November 2014 was examined using a finely resolved numerical model. The Delft3D model was ...used to perform numerical experiments that simulate the effect of wind-generated waves, wind-driven currents, river discharge, and tides on sediment dynamics in Sandy Point dredge pit. The hydrodynamics and sediment models were validated and calibrated using field data of current, wave, water level, and suspended sediment concentration. Two potential sources of sediment were examined: fluvial sediment from the Mississippi River and resuspended sediments from the seabed. Results showed that during a cold front, shear stress from wave motions played a significant role in the resuspension of sediments in Sandy Point dredge pit. The maximum cold front-related wave impact on sediment resuspension could increase near-bed sediment concentration in Sandy Point dredge pit by 20–50 times. In addition, the results suggest that the primary source of sediment for Sandy Point dredge pit during a cold front was resuspension from the ambient seabed due to increased bottom shear stress by wind-induced waves and strong southward wind-driven currents. Currents dispersed sediments from the Mississippi River passes and inhibited riverine sediment supply from Sandy Point dredge pit. Results also showed that cold fronts contribute 16%–24% of the annual sedimentation in Sandy Point dredge pit.
•A coupled wave-current-sediment model was used to study the sandy dredged pit.•The combined effect of waves and currents on sedimentation was assessed.•The reverse bottom current inside the pit was identified.•Bottom boundary layer was significantly affected by waves.•Sediment accumulation occurs mostly on the north of the pit.
A three-dimensional numerical model was applied to the Barataria Estuary in the Northern Gulf of Mexico to study its salinity variations as well as the impacts from the Mississippi River discharges ...and proposed river diversions. Model-observation comparison showed that the model was able to reproduce the hydrodynamic fields on subtidal to seasonal time scales. Salinity in the Barataria Estuary was high in fall and low in summer, with a greater variability in the lower estuary than the upper estuary. While salinity in the upper estuary was controlled by discharges from a local freshwater diversion, salinity in the lower estuary was mostly affected by the mixed Mississippi River water transported via the tidal inlets in the south. The correlation between Mississippi River discharge and estuarine salinity indicated that low salinity Mississippi River water could intrude into the estuary through the middle and east tidal inlets. Sensitivity tests were performed to assess the impacts from the Mississippi River discharges and proposed mid-Barataria Estuary sediment diversion. Model results illustrated that salinity in the estuary was more sensitive to an increase of Mississippi River discharge than a decrease. The proposed mid-Barataria sediment diversion was likely to induce a dramatic decrease of salinity in the lower estuary. The ecosystem consequences of the fluctuation of Mississippi River discharge as well as that of the proposed river diversions need further investigations.
•Estuary salinity is highly impacted by mixed Mississippi River water from the tidal inlets.•Estuary salinity is more sensitive to a increased Mississippi discharge than an decreased one.•Proposed river diversion is likely to introduce a dramatic decrease of salinity in the lower estuary.
Along much of the world's coastline, coastal barriers serve as the first line of defense against oceanic and meteorological forces. Extreme storms cause large morphological changes on coastal ...barriers through high sediment transport rates, which may degrade their defensive capabilities. The understanding of morphological impacts is therefore important for coastal resiliency, but is often challenged by site-specific characteristics, such as land cover and sediment availability, and their poorly understood impacts on the governing physical processes. The Caminada Headlands, Louisiana, USA presents unique considerations for morphodynamic modeling with regard to its low-lying topography, variable land cover, nearshore muddy substrate and sand deficiency. This study investigates the effects of land cover and limited sediment supply on low-lying barrier island morphology under storm conditions by using physics-based numerical models. A high-resolution, local-scale sediment transport/morphodynamic model (XBeach) of the Caminada Headlands is verified for Hurricane Gustav's (2008) impact using pre- and post-storm LIDAR surveys. When accurate input data are used to create physics-based numerical models these tools are robust in hindcasting storm impacts and provide a wealth of information as to the governing processes, which is otherwise difficult to obtain observationally. The simulation results show that a short-duration overwash regime dominates the morphological change in this low-lying barrier and is influenced by backbarrier wetland deterioration. The morphological response to overwash is modulated by backbarrier land cover and topography, as reduced accommodation space limits landward transport during the subsequent inundation regime. An intact backbarrier marsh reduces landward washover sediment transport distances and promotes deposition at supratidal elevations. In light of these findings, simultaneous restoration/creation of backbarrier wetlands in conjunction with subaerial beach renourishment may be an effective form of increasing the resiliency of low-lying barriers subject to frequent overwashing.
•A basin-scale hydrodynamic-wave and local-scale sediment transport model constructed for barrier washover simulations.•A hindcast of Hurricane Gustav's (2008) hydrodynamics and morphological impact to Louisiana verified with multiple data.•A relationship between storm-driven washover sediment transport and backbarrier wetland land cover/topography investigated.•Limited nearshore sand sediment supply influences the accuracy of storm-driven washover sediment transport modeling.
A coupled Flow-Wave-Sediment model was used to study hydrodynamics, sedimentation, and bottom boundary layer (BBL) dynamics over the Sandy Point Dredge Pit (SPDP; a potential sand mining site in the ...Louisiana shelf, northern Gulf of Mexico) during fair weather summer conditions (July and August 2015). The Delft3D modeling system on a curvilinear computational grid with spatial resolution between 10 m and 2.8 km was used. The flow, wave, and sediment transport models were evaluated using water level, current speed, wave parameters, and sediment concentration. During this period, the wind over the Louisiana shelf is characterized as low energy with the prevailing direction from southeast to the southwest, which corresponds to small wave heights (Hs < 1.2 m) and small wave periods (Tm < 4 s). The relatively shorter waves resuspended sediments only in very shallow areas along the Mississippi Birdfoot Delta. Simulations with and without the SPDP showed that the presence of the pit could decrease the speed of surface currents by as much as 19%, while its effect on wave characteristics was minor. The northward current produced by the prevailing winds transported the discharged sediments from the Mississippi River contributed 60% of the sedimentation over the SPDP. Sediment re-suspension inside the BBL of the SPDP occurred during the days that more energetic waves propagated over the shelf. As a result, sediments from the Mississippi River significantly increased the sediment concentration near the bottom of and throughout the water column above the SPDP.
•The Sandy Point Dredge Pit could decrease the speed of surface currents, but the effect on wave characteristics was minor.•The Mississippi River increased the sediment concentration near the bottom of and throughout the water column above the Pit.•The northward current transported the sediments from the Mississippi River contributed 60% of the sedimentation over the Pit.•The average sedimentation rate inside the Sandy Point Dredge Pit was ∼2.5 mm/day.
River-sediment diversions have been recognized as a key strategy for offsetting land loss in coastal Louisiana. Recently, much attention has been focused on sediment capture from the main stem river ...and conveyance of that material through diversion outflows. Yet, the performance and long-term feasibility of diversions as land-building agents also hinges upon the subsurface stratigraphic architecture of receiving basins, a concept that has largely been unexplored. A major core collection and analysis program was undertaken to study the geological properties of substrates in the Middle Barataria Bay and Middle Breton Sound diversion receiving basins, Louisiana, USA. Over a region of ∼200 square kilometers in both basins, 50 vibracores up to 5.5 m in length were collected in spring and summer of 2015. Cores were logged for bulk density and imaged with a Geotek Multi Sensor Core Logger. Split cores were then subsampled for granulometry, organic content, and 14C dating. Both receiving basins are characterized by 1–2 m of organic-rich surficial strata, underlain by > 2 m of mineral-rich sand and silt beds that display a greater bulk density. Additionally, some cores contain deeper peaty strata intercalated within muds and sands. 14C dates of these buried peats range between 1910 and 3203 calendar years before present demonstrating that relatively old deltaic strata exist at shallow depths. Age comparisons of stratigraphically-similar peat beds from this study and previous delta-lobe chronological models indicate that the St. Bernard lobe prograded eastward at a time-averaged rate of 75 m/yr. From a geotechnical standpoint, the surficial, uncompacted (<2 m depth, average 1.15 g/cc bulk density) peaty strata in both basins are likely to erode and/or compact under the influence of diversion flows, but deeper consolidated mineral-rich strata (average 1.85 g/cc bulk density) are likely to be more resistant. Hydrodynamic models that predict the erosion associated with river-sediment diversion outflows in this region would benefit from incorporating a two-layer subsurface configuration, with a weaker, peat-like layer overlying a stronger, mineral-rich layer. The results of our study suggest that regions with an abundance of clastic strata at depth should be sought out when planning coastal restoration methods such as river-sediment diversions.
Mud-capped dredge pits (MCDPs), defined as sand borrow sites from paleo river channels with cohesive sediment-capped walls, are used for northern Gulf of Mexico (NGoM) coastal restoration projects ...due to lower cost than more distal restoration resources. MCDP evolution, including infilling and pit wall slope stability, is poorly understood in relation to sandy borrow areas. We present and interpret bathymetric data from Sandy Point MCDP, which was constructed in 2012 about 20 km northwest of Southwest Pass, the most active Mississippi River distributary, in water depths of ∼11 m. Repeat bathymetric surveys show the pit is infilling ∼54 cm (or volumetrically 200,000 m3) per year, which is on the same order as seasonal-scale and an order of magnitude higher than the decadal-scale vertical accretion rates observed seaward of Southwest Pass. This infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate, sediment-starved settings. MCDP infill is volumetrically dominated by far-field (here defined as river plume or shelf bed resuspension) sediment, with only ∼9% of pit infill from pit wall failure. Geomorphic comparison of Sandy Point MCDP walls with Southwest Pass mudflow gully walls shows that the MCDP is oversteepened relative to natural depression features in this setting; the convergence of MCDP and mudflow gully gradients towards a common value (4–5°) may represent an “angle of repose” in lieu of decadal-scale forcings. Findings from this experiment of opportunity show that MCDPs (1) are effective sediment traps, (2) have steep but relatively laterally stable walls (3) do not represent significant risk to infrastructure in a 3-year time scale, and (4) are predicted to infill within about 2 decades provided a proximal sediment source exists.
•Mud-capped dredge pit infilled 1–5 times the rate of proximal deltaic sediment accumulation.•Pit walls lost steepness at average rate of 1.1°/year during three years post-dredging.•Mud-capped dredge pit evolution is appreciably different from sandy dredge pits.
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