One of the proposed methods for restoring the disappearing Mississippi Delta is sediment diversion which uses channels and structures to divert water and sediment from the Mississippi and Atchafalaya ...Rivers into adjacent basins. This study presents a comprehensive review of geological and physical aspects of sediment dynamics in the Mississippi River Deltaic Plain (MRDP), with special reference to diversion studies over the past two decades. We synthesize these studies, present the current understanding of sediment diversions in the context of sediment dynamics, identify multiple key knowledge gaps, and make recommendations for future studies.
To maximize net land building in the MRDP, management strategies should be focused on (a) enhancing river sediment delivery (both mud and sand), (b) increasing sediment retention in receiving basins and (c) minimizing erosion in bays and estuaries. Compared with extensive studies of land building, there have been relatively fewer studies of erosional processes. A heterogeneous coastal geological framework, cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the MRDP. Sediment retention rates are highly sensitive to spatial and temporal scales, types of sediments and delivery season. Sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes. Structures and devices that improve sediment retention, trap sediments, dissipate waves, and build living shorelines should be explored and cost-to-benefit analysis is needed. Long-term planning should consider more landward diversions, strategic community relocation, and nonlinear response of the complex sedimentary system of the MRDP.
•A review and synthesis of diversion studies and sediment dynamics in the Mississippi River Deltaic Plain.•Explore the methods to maximize land building by enhancing sediment delivery, increasing retention, and minimizing erosion.•Present current understanding, identify knowledge gaps and recommend future work for sediment diversions.
Sediment is needed for coastal restoration in Louisiana and is often excavated offshore from mud-capped and sandy dredge pits. To better understand the post-dredging effects on hydrodynamics, ...sediment transport, and water quality, two tripods were deployed at sandy Caminada pit and mud-capped Sandy Point pit in summer 2018 and 2019, respectively, and profiling data were collected during a total of 34 casts in 2018 and 2019. The results reveal similarities and differences between pit and adjacent waters and are used to compare two pits. Tropical storm events were observed during each deployment which provided insight concerning the effects these storms have on dredge pits. Water masses inside Caminada pit were relatively stable and sluggish which resulted from the pit's deep depth and location. Sandy Point dredge pit was highly impacted by the Mississippi River plume due to its proximity, which effectively stratified the water column in summer 2019, affecting ventilation near the seabed. Strong winds, taller waves, higher shear stresses, elevated turbidity and increased dissolved oxygen were generally found during the passages of tropical storms over both pits. Comparing with outside tripod station, the inside station of Caminada pit experienced a longer duration of low dissolved oxygen in bottom waters. Water mass movements and oxygen consumption from resuspension of pit bottom are likely key mechanisms driving oxygen dynamics. Our results provide observational data for future studies on post-dredging morphologic change, marine communities, and oxygen dynamics of dredge pits on the Louisiana shelf and other coastal dredge areas worldwide.
•Tripod time series analysis of dredge pits in Gulf of Mexico.•Less variable bottom water masses in a dredge pit compared to adjacent seafloor.•Bottom DO conditions are complex, controlled by physical, biogeochemical processes.•Dredge pit location impacts variability of water column.
While many sediment transport studies have been performed on mud capped dredge pits (MCDP), there is a paucity of sediment infilling data for sand dominated dredge pits (SDDP) in the Northern Gulf of ...Mexico (NGoM). In this study, bathymetry, sidescan, and subbottom data were collected in 2018, 2019, and 2020 and sediment cores were collected between the 2019 and 2020 surveys at Block 88: a dredge pit sitting on the sand-dominated Ship Shoal of Louisiana's inner shelf. The crest of Ship Shoal was 5 m below mean sea level before dredging and was excavated to a depth of 10 m below mean sea level after the dredging of 8.4 million m3 of sediment. Two years after dredging, the northern end of the eastern pit wall accumulated ∼0.09 million tons (approximately 500 m long × 50 m wide × 2.5 m deep) of sediment, driven by westward longshore sediment transport and the deposition of bed load on the shoal crest. Sediment accumulation on the pit bottom was mainly driven by suspended load at a rate of ∼0.1 m yr−1 from 2018 to 2019 and ∼0.2 m yr−1 from 2019 to 2020. Thus, the sediment infilling in Block 88 was from both bed- and suspended-loads from contrasting sources. These pit-bottom sediment accumulation rates are approximately one order of magnitude lower than the predicted rate from a previous empirical modeling study conducted on Ship Shoal and lower than the rates (0.5–2 m yr−1) of three other MCDPs on the inner Louisiana shelf. The infilling sediment was patchy and predominantly silt and clay, with lower sidescan reflectivity. The slopes of Block 88's pit walls decreased from ∼20° in 2018 to ∼8° in 2020. These values were smaller than the values of pit wall slopes in MCDPs at a similar stage (i.e., 2–3 years after dredging). Our results indicate that the highest sediment accumulation rates occur immediately adjacent to the eastern pit wall of Block 88, which is down-current of the longshore transport direction. This study helps sand resource managers and policymakers to better plan and design future sediment dredging projects on sandy shoals. This study concludes that the longest axis of a dredge pit should be aligned perpendicular to the longshore transport direction to trap the most sediments for possible reuse. Additionally, both bed load and suspended load should be considered in future modeling to better predict sediment infilling.
•8.4 million m3 of sediments were excavated from Block 88 in 2018; it is the second largest dredge pit in Louisiana.•∼102,500 m3 of sandy sediment (∼0.15 million tons) have accumulated along the pit wall since the completion of Block 88.•Sediment delivery to the pit bottom occurs at a rate of ∼0.2–0.25 m yr−1 and is likely punctuated.•The Block 88 dredge pit has migrated minimally since excavation was completed.
Accelerating sea-level rise and decreasing riverine sediment supply are widely considered to lead to global losses of deltaic marshes and their valuable ecosystem services. However, little is known ...about the degree to which the related erosion of the seaward delta front can provide sediments to sustain salt marshes. Here, we present data from the mesomacrotidal Yangtze Delta demonstrating that marshes have continued to accrete vertically and laterally, despite rapid relative sea-level rise (10 mm yr−1) and a > 70% decrease in the Yangtze River sediment supply. Marsh progradation has decelerated at a lower rate than fluvial sediment reduction, suggesting an additional source of sediment. We find that under favorable conditions (e.g., a mesomacrotidal range, strong tidal flow, flood dominance, sedimentary settling lag/scour lag effects, and increasing high-tide level), delta-front erosion can actually supply sediment to marshes, thereby maintaining marsh accretion rates in balance with relative sea-level rise. Comparison of global deltas illustrates that the ability of sediment remobilization to sustain marshes depends on coastal processes and varies by more than an order of magnitude among the world’s major deltas.
The Mississippi River Deltaic Plain experiences high relative sea level rise, limited sediment supply, and high marsh edge erosion, leading to the substantial coastal wetland and stored soil organic ...matter (SOM) loss. The objective of this study was to understand the SOM accumulation rates over the past 1000 years related to the changes in the depositional environment in these highly eroding coastal wetlands. Soil cores (2 m) were collected from four sites in Barataria Basin, LA and analyzed for proportion of organic and mineral matter, total C, N, P, particle size, and stable isotopic composition (δ13C and δ15N), as well as 14C and 137Cs dating. The soil carbon stock in the 2 m depth (62.4 ± 2 kg m−2) was approximately 88% greater than the carbon stock in just the 1 m depth (33.1 ± 0.6 kg m−2) indicating a need for considering deeper soil profiles (up to 2 m) to estimate blue carbon stock in deltaic environments. The average vertical accretion rate for Barataria Basin was 8.1 ± 0.6 mm year−1 over 50 years. The long‐term (1000‐year time scale) C accumulation rate (39 g C m−2 year−1) was ∼14% of the short‐term accumulation rate (254 ± 19 g C m−2 year−1). Wetlands in Barataria Basin started as fresh marsh and transitioned over time to intermediate to brackish. These marshes were able to maintain relative elevation through the accumulation of organic matter and mud despite high relative rates of sea‐level rise. However, the high rates of edge erosion may limit these marshes to continue to sequester atmospheric carbon under accelerating sea level in the absence of restoration efforts.
Core Ideas
The carbon accumulation rate in Barataria Basin, Louisiana was 254 ± 19 g C m−2 year−1.
The long‐term (1000 years) carbon accumulation rate was ∼14% of the short‐term (50 years) accumulation rate.
Soil C stock in 2 m depth (62.4 ± 8 kg m−2) was ∼88.5% greater than the C stock in 1 m depth (33.1 ± 0.6 kg m−2).
Barataria Bay is a receiving basin for a large Mid-Barataria Sediment Diversion scheme in Louisiana, USA. In this region, data on sediment transport and hydrodynamics are scarce but essential for the ...design and planning of future sediment diversion and marsh creation. Four months of bottom boundary layer observations were conducted to study winter and spring hydrodynamics and sediment dynamics in this coastal bay. Hourly waves, tides, currents, and bottom suspended sediment concentrations were measured using multiple optical and acoustic sensors attached to two tripod platforms. High temporal resolution data indicated that the salinity in the northern bay was mainly controlled by northerly winds, and tidal currents kept the salinity high in the southern bay during the winter cold front season. In spring, frequent, pervasive southerly winds and the westward shelf transport of less saline water emerging from the Mississippi River Delta lowered the salinity in the southern bay. Spectral analysis showed that wave-current combined shear stress played the most critical role in triggering sediment resuspension. The Style-Glenn 1-D bottom boundary layer model was applied in sediment flux calculations, and showed that net sediment transport mainly occurred during cold front passages. During two 3-day cold-front events, southward sediment fluxes accounted for 56% of the total sediment flux during the 35-day winter period, revealing their nonlinear, event-driven, and episodic nature. The direction of the sediment transport generally rotated, and its magnitude changed considerably, when southeasterly winds shifted to intensified northwesterly winds. Long-duration southerly pre-frontal winds facilitated wetland sedimentation by transporting sediment to the northern bay during high water level conditions impacted by flooding spring tides or southerly winds. Conversely, northerly winds during cold fronts dominated bidirectional tidal currents and led to southward net sediment transport and possible escape of sediment from the bay. The timing of diversion openings, the orientation of receiving basins, and dominant wind directions in relation to fetch, as well as the dynamic water levels should be considered in the planning and management of future diversion operations in coastal areas.
•First long-term time-series BBL observational research conducted in Barataria Bay, Louisiana, USA.•Rotational sediment transport was captured in 2019 spring observational period.•Sediment transport mainly occurred with cold front passage.•Special morphology, such as tidal channel, can strengthen tidal impacts on sediment dynamics in microtidal area.
Cbf-14 (RLLRKFFRKLKKSV), a designed antimicrobial peptide derived from the cathelicidin family, is effective against drug-resistant bacteria. Structurally related peptide impurities in peptide ...medicines probably have side effects or even toxicity, thus impurity profiling research during the entire production process is indispensable. In this study, a simple liquid chromatography–high-resolution mass spectrometry (LC-HRMS) method using a quadrupole time-of-flight (Q-TOF) mass spectrometer was developed for separation, identification, and characterization of structurally related peptide impurities in Cbf-14. A total of one process-related impurity and thirty-two degradation products were identified, and seven of them have been synthesized and confirmed. These impurities have not been declared in custom synthetic peptides. The degradation products were divided into five categories: fifteen Cbf-14 hydrolysates, five Cbf-14 isomers, four acetyl-Cbf-14 isomers, two aldimine derivatives, and six oxidized impurities. Combined with the peptide synthesis and the stress-testing studies, the origins and the formation mechanisms of these impurities were elucidated, which provides a unique insight for the follow-up quality study of Cbf-14 and other peptide products.
Graphical abstract
To mitigate land losses in the Mississippi River Delta, sediment diversions are being employed to enable the flow of river water and sediments into wetlands experiencing degradation. A ...two-dimensional coupled flow-wave Delft3D model was used in this study to explore the hydrodynamics and sediment transport in Fourleague Bay (FLB), Louisiana, USA, which has been considered an analog site for studying the efficiency of sediment diversion projects. In-situ measurements of sediment accretion and hydrodynamic characteristics from 2015 to 2016 were utilized to calibrate and validate the morphodynamic model. The validated model was then applied to quantify sediment transport in FLB and surrounding marshes between May 2015 and May 2016. The results show that more sediment could be deposited to the surrounding marshes with high river discharges and strong winds. Thus, by strategically aligning the timing of pulses of river water from the diversion with the seasonal intensification of atmospheric forcing, it is possible to sustain and promote the growth of the surrounding wetlands. Moreover, we found that multiple sediment transport processes occurred during the entire study period, including the deposition of riverine sediment into the bay floor, direct deposition of riverine sediment in the surrounding marshes, resuspension of bay floor sediment, and redistribution of resuspended sediment to adjacent marshes and the Gulf of Mexico (GoM). The results indicate that the riverine sediment tended to be directly deposited in the marshes when the river discharge was high. During calm weather conditions and normal river discharge, FLB acted as a reservoir, storing sediment from the upper river, and later acted as a sediment source to the nearby wetlands and the GoM during energetic atmospheric conditions. This suggests that using the bay floor as a reservoir can extend the distance over which wetlands can benefit from the sediment diversions, as the supply of sediment to the wetlands becomes a multi-step process. Thus, it is important to retain sediments from river diversions in shallow bays and allow storms to redistribute them to adjacent wetlands.
•A morphodynamic model was developed to understand the fine sediment dispersal process from a river to coastal wetlands.•The model was calibrated and validated using unique measurements of hydrodynamics and sediment accretion rates.•More sediment could be deposited to the surrounding marshes with high river discharges and strong winds.•Sediment deposited on the surrounding marshes was primarily from the river and bay floor.•Riverine sediment tends to be directly deposited onto the marshes during high discharge stages.
The Mississippi River Delta consists of six major passes and numerous small crevasses through which water and sediments are transported to the continental shelf of northern Gulf of Mexico. The water ...and sediment fluxes through individual passes are not routinely monitored due to the complex morphology and challenging environment. However, they are critical factors in determining the highly nonlinear near-field characteristics of freshwater plumes, fronts, possible internal hydraulic jumps, nutrient dispersal and rapid initial deposition of fine sand and mud. The flux partitioning and flow/sediment dispersal characteristics near the modern Mississippi River Delta were investigated using a high-resolution (~ 100 m horizontally) unstructured-grid, three-dimensional coupled hydrodynamic-wave-sediment numerical model. Model result analysis for the period of April–June 2010 revealed that Southwest Pass is the main conduit among the six major passes, through which 64% and 32% of the Mississippi River water and sediment, respectively, are transported to the coastal ocean. In contrast, South Pass has the lowest water and sediment fluxes among the tri-furcation channels downstream of the Head of Passes. Due to the more energetic flow at Southwest Pass compared to other passes, an elongated freshwater/sediment jet is typically present in the near-field. The average width of the plume originating from Southwest Pass, 5 km away from the mouth, is approximately 8 km, while the high sediment concentration within the plume (SSC > 10−2 kg/m3) is maintained in the upper 4 m of the water column for more than 8 km. The pattern of the plume in the far-field varies with wind direction, and the buoyant plume bends towards the coast/mid-shelf in response to downwelling/upwelling favorable winds.
•Water & sediment budgets through the Mississippi Birdfoot Delta passes are modeled.•About 64%/32% of the water/sediment flux passes through the Southwest Pass.•South Pass has the least water/sediment flux among the passes below Head of Passes.•The high SSC from the Southwest Pass is maintained for more than 8 km.•Wind direction and the buoyant plume govern the far-field Mississippi River plume.
To restore degraded barrier shorelines of the Mississippi River Deltaic Plain of Louisiana, sand is dredged from borrow areas in estuaries and continental shelves. The dredge pit in South Pelto ...Blocks 12 & 13 on eastern Ship Shoal used for Caminada-Moreau Headland restoration project is one of several sand dredge pits for barrier island restoration in Louisiana. Ship Shoal Sand Complex is in a sand-dominated, energetic, continental shelf environment. During energetic events, transient mud can blanket Ship Shoal, and then bypasses the shoal and deposits in deeper water. In this study, we collected and interpreted a suite of geophysical data from South Pelto Dredge Pit which is located in water depths of ∼9 m on eastern Ship Shoal. Repeat bathymetric survey data show that South Pelto Dredge Pit is presently infilling at an average rate of approximately 27,480 m3/year, which is slower than the predicted rate presented by an earlier numerical model. Side-scan mosaic maps indicate low-backscatter (muddy) sediments were transported into this pit and deposited in many patches within two years after dredging. The seabed inside this pit became smoother over time and the slope of the pit walls became gentler. Infilling of the South Pelto Dredge Pit seem to be controlled by sediment availability, which is volumetrically dominated by (a) far-field fluvial suspended sediment, (b) the adjacent seabed sediment resuspended by tides, waves, and currents, but presumably less impacted by (c) hurricanes or tropical storms during our study period of 2017–2018. The South Pelto Dredge Pit thus displays a unique mixing and redistribution of cohesive mud and non-cohesive sand. Initial spatial control on sediment infilling appears to be dictated by micro-bathymetry on the pit bottom created by the dredging activities. Bathymetric, side scan and grain-size data all indicate that mud was prone to deposit in the troughs.
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