Mississippi River Delta Research Articles

Coastal wetland area change for two freshwater diversions in the Mississippi River Delta

Coastal systems around the globe are being re-integrated with adjacent river systems to restore the natural hydrologic connection to riparian wetlands. The Mississippi River sediment diversions or river reconnections are one such tool to combat high rates of wetland loss in coastal Louisiana, USA by providing freshwater, sediment, and nutrients. There has been some disagreement in the published literature whether re-establishing river reconnection is slowing or contributing to coastal wetland loss. This issue is due to the difficulties in the application of remote sensing in low-relief environments where water level changes could indicate either land loss or simply temporary submergence. We analyzed land change at the receiving areas of two existing freshwater river diversions, Davis Pond and Caernarvon, which have been intermittently receiving river water for up to 2+ decades. This study provides a robust analysis of wetland land change rates in proximity these river diversions including years before river reconnection. Our analyses indicate a net land gain since river reconnection operations began at Davis Pond Diversion (+3.42 km2; range: +2.02–4.81 km2) and no statistically significant change at the Caernarvon Diversion. The Davis Pond wetland results are corroborated with data from a decadal field study documenting increased inorganic sedimentation in the soil. It is clear from this study and others, that river reconnection can increase or, in the case of Caernarvon, have no statistical effect on the land change in these systems due to differences in vegetation, hydroperiod, sediment delivery and external factors including hurricane impacts. Our remote sensing analysis was compared with a global water area change analysis mapping tool which also supported our findings.

Pre‐instrumental perspectives on Arkansas River cross‐watershed flow variability

AbstractWe present four reconstruction estimates of Arkansas River baseflow and streamflow using a total of 78 tree‐ring chronologies for three streamflow gages, geographically spanning the headwaters in Colorado to near the confluence of the Arkansas‐Mississippi rivers. The estimates represent different seasonal windows, which are dictated by the shared limiting forcing of precipitation on seasonal tree growth and soil moisture—and subsequently on the variability of Arkansas River discharge. Flow extremes that were higher and lower than what has been observed in the instrumental era are recorded in each of the four reconstructions. Years of concurrent, cross‐basin (all sites) low flow appear more frequently during the 20th and 21st Centuries compared to any period since 1600 A.D., however, no significant trend in cross‐basin low flow is observed. As the most downstream major tributary of the Mississippi River, the Arkansas River directly influences flood risk in the Lower Mississippi River Valley. Estimates of extreme high flow in downstream reconstructions coincide with specific years of historic flooding documented in New Orleans, Louisiana, just upstream of the Mississippi River Delta. By deduction, Mississippi River flooding in years of low Arkansas River flow imply exceptional flooding contributions from the Upper Mississippi River catchments.

Competing effects of vegetation density on sedimentation in deltaic marshes

Marsh vegetation, a definitive component of delta ecosystems, has a strong effect on sediment retention and land-building, controlling both how much sediment can be delivered to and how much is retained by the marsh. An understanding of how vegetation influences these processes would improve the restoration and management of marshes. We use a random displacement model to simulate sediment transport, deposition, and resuspension within a marsh. As vegetation density increases, velocity declines, which reduces sediment supply to the marsh, but also reduces resuspension, which enhances sediment retention within the marsh. The competing trends of supply and retention produce a nonlinear relationship between sedimentation and vegetation density, such that an intermediate density yields the maximum sedimentation. Two patterns of sedimentation spatial distribution emerge in the simulation, and the exponential distribution only occurs when resuspension is absent. With resuspension, sediment is delivered farther into the marsh and in a uniform distribution. The model was validated with field observations of sedimentation response to seasonal variation in vegetation density observed in a marsh within the Mississippi River Delta.

J.W. Day, H.C. Clark & R.G. Hunter (eds.) Energy production in the Mississippi River Delta: implications on coastal ecosystems and pathways to restoration. Springer Nature Switzerland AG

J.W. Day, H.C. Clark & R.G. Hunter (eds.) Energy production in the Mississippi River Delta: implications on coastal ecosystems and pathways to restoration. Springer Nature Switzerland AG

Multidecade Trends of Sea Surface Temperature, Chlorophyll-a Concentration, and Ocean Eddies in the Gulf of Mexico

This study characterizes the spatial patterns of the overall and monthly trends in sea surface temperature (SST) and chlorophyll-a (Chl-a) of the Gulf of Mexico (GoM) to investigate the seasonal variations in oceanic climate trends. We also investigate the trends in mesoscale eddies using three parameters to identify ocean-eddy-related energetic features in their area, strength, and intensity. Multidecadal remote-sensing-based observations of monthly SST, Chl-a, and sea surface height are used to detect trends at both basin and grid scales. Prominent warming trends are found in most regions of the GoM in all months, with the largest trends in the northern GoM. Winter cooling trends are also detected along the Texas and Florida coast. The overall summer warming trend (~0.22 °C/decade) is larger than the winter trend (~0.05 °C/decade), suggesting seasonal variations of increase in SST with warming. Chl-a trends and variations are confined on the continental shelf and slope in the northern GoM. The largest increase trends are found near the Mississippi River Delta. No obvious Chl-a trend is detected in the deepwater of the GoM, consistent with previous studies. Small but significant changes are found in eddy characteristics, indicating the eddy activities might be slowly affected by climate change in the GoM. The detailed monthly trends at per-grid scale are valuable for regional resource management, environmental protection, and policy making in the GoM.

Temporal and Spatial Relationships of Yellowfin Tuna to Deepwater Petroleum Platforms in the Northern Gulf of Mexico

AbstractIn 2006–2007, 110 Yellowfin Tuna Thunnus albacares were tagged with acoustic transmitters near deepwater oil platforms and one drillship in the northern Gulf of Mexico off the Mississippi River delta to determine the extent to which platforms act as fish aggregating devices (FADs). Vemco acoustic receivers were installed on six deepwater platforms to detect the presence of tagged individuals. Five of 12 Yellowfin Tuna captured in 2006 were detected in 2007, demonstrating multi‐year presence in the region. Ninety Yellowfin Tuna were detected in 2007, resulting in 221 platform residencies and 32 single detections. Duration of residence at a platform was positively correlated with the platform's depth, and the number of transitions decreased with platform‐to‐platform distance. In total, 109 movements between platforms by 46 (51%) different individuals were detected, traveling distances of up to 98.2 km. Yellowfin Tuna displayed interactions with deepwater platforms in the northern Gulf of Mexico similar to their interactions with FADs and other studied geological features, by way of aggregating or using them as meeting points, landmarks, and stopovers within a movement corridor. The large number of oil and gas platforms located in the northern Gulf of Mexico may have a significant effect on distribution, retention, and migration of Yellowfin Tuna populations in this area of the gulf.

FEASIBILITY OF SHORT STORY CLUBS IN A HEMATOLOGY/ONCOLOGY PROGRAM

Background The death rate from colorectal cancer is high and affects poor and medically underserved populations disproportionately. In the United States, health disparities are particularly acute in the Lower Mississippi River Delta region. Because many in the region have limited access to basic health care resources, they are not screened for cancer, even though screening is one of the most effective strategies to prevent colorectal cancer. Community-based participatory research is a promising approach to prevent colorectal cancer in this population. Community Context The Empowering Communities for Life program was implemented in 2 underserved counties in the Arkansas Lower Mississippi River Delta. The program arose from a 9-year partnership between the University of Arkansas for Medical Sciences and 9 cancer councils across Arkansas. Methods Empowering Communities for Life is a community-based participatory intervention designed to increase colorectal cancer screening in rural, un...

The effect of bottomset on fluviodeltaic land‐building process: Numerical modelling and physical experiment

AbstractThe loss of land in coastal regions is an emerging topic across the scientific community, as many countries struggle to minimize the consequences of an accelerating relative sea‐level rise. Various methods have been attempted to mitigate land loss, and river diversion for the Mississippi River Delta, which makes use of the natural river delta‐building process, has been proposed and significantly examined. Prior delta‐building models predicted possible ranges of new delta‐building rates and verified the feasibility of reduction in land loss on the Louisiana coast by river diversion by only considering the delta topset and foreset deposition without incorporating the muddy bottomsets because sand was regarded as the main delta‐building sediment, and mud was treated as washload. Since sand flux is significantly smaller than mud flux in most coastal rivers and muddy bottomsets are common in most deltas, it is critical to understand the depositional processes of mud in deltas. Here, we present the results of a coupled numerical modelling and flume experiment that includes a moving boundary at the foreset‐bottomset break in addition to the shoreline. We find that bottomset aggradation can accelerate the shoreline progradation by decreasing the foreset length (i.e., depth at the delta front). We also apply our model to a field scale based on parameters taken from the Wax Lake Delta. When 10%–50% of the mud supplied to the delta is retained in the bottomset, the subaerial delta area increases by 4.4%–25.4% compared to that in a delta with no bottomset accumulation. Therefore, considering the bottomset in land‐building modelling can provide more accurate predictions for a new land‐building area by river diversion.

The Estuarine Ecological Knowledge Network Makes Progress: International Project Sites and Potential Ways Forward

Abstract The Estuarine Ecological Knowledge Network (EEKN) brings together scientists and coastal fishing communities in seeking new ways forward for Earth's major river deltas and estuaries, including the Mississippi (United States), Rio Grande (United States), Danube (Romania/Ukraine), Ganges (India/Bangladesh), Niger (Nigeria), and Mekong (Vietnam) river deltas, and the Patos Lagoon (Brazil). Such environments are universally understood as crucial for the biological productivity of oceans and they are home to hundreds of millions of human inhabitants, many of whom directly depend on that marine richness in terms of the operation of their socioeconomic systems. As human-induced climate change and its consequences for Earth's oceans and coastlines increases, estuarine ecosystems are particularly threatened by problems such as sea-level rise, coastal erosion, saltwater intrusion, and increased impacts from tropical storms. These problems are often amplified by human dynamics of environmental degradation, including overfishing, pollution, and large-scale landscape modification projects. The EEKN is designed to enhance communication and cooperation between fishing communities, scientists, and policy makers in learning about the complexity of both ecological and socioeconomic systems in estuaries and deltas, and in developing more effective policy for managing fisheries, protecting and restoring coastlines, and increasing the resilience of coastal communities.

Mangrove expansion at poleward range limits in North and South America: Late-Holocene climate variability or anthropocene global warming?

Mangroves are expanding poleward in North and South America, but it is unclear whether such ecotonal-shift is an Industrial-Era phenomenon, or a recurring occurrence tied to Holocene climate variability. Our multi-proxy and remote sensing data from the U.S. Gulf Coast and southeastern Brazil suggest that the Industrial Era is the first time throughout the Holocene when mangroves were able to extend their distributions to the current boreal and austral range limits. A mangrove expansion of ∼1.3 ha (from 0.002 to 1.33 ha), 103 ha (from 23 to 126 ha), and 1.42 ha (from 0.39 to 1.81 ha) are documented at Bolivar Flats (Texas, U.S.A.), Mississippi River Delta (Louisiana, U.S.A.), and Apalachicola (Florida, U.S.A.), respectively, since the early 2000s, suggesting that mangrove expansion in North America is a 21st -century phenomenon and likely governed by warming winters. In contrast, the relatively slow mangrove expansion (from 96.1 to 106 ha between 2003 and 2019) at the austral range limit is controlled primarily by available habitats with suitable salinity and sediment substrate.

A Model of the Spatiotemporal Dynamics of Soil Carbon Following Coastal Wetland Loss Applied to a Louisiana Salt Marsh in the Mississippi River Deltaic Plain

AbstractThe potential for carbon sequestration in coastal wetlands is high due to protection of carbon (C) in flooded soils. However, excessive flooding can result in the conversion of the vegetated wetland to open water. This transition results in the loss of wetland habitat in addition to the potential loss of soil carbon. Thus, in areas experiencing rapid wetland submergence, such as the Mississippi River Delta, coastal wetlands could become a significant source of carbon emissions if land loss is not mitigated. To accurately assess the capacity of wetlands to store (or emit) carbon in dynamic environments, it is critical to understand the fate of soil carbon following the transition from vegetated wetland to open water. We developed a simple soil carbon model representing soil depths to 1 m using the data collected from a Louisiana coastal salt marsh in the Mississippi River Deltaic Plain to predict soil carbon density and stock following the transition from a vegetated salt marsh to an open water pond. While immediate effects of ponding on the distribution of carbon within the 1‐m soil profile were apparent, there were no effects of ponding on the overall, integrated, carbon stocks 14 years, following wetland submergence. Rather, the model predicts that soil carbon losses in the first meter will be realized over long periods of time (∼200 years) due to changes in the source of carbon (biomass vs. mineral sediment) with minimal losses through mineralization.

Nature versus Humans in Coastal Environmental Change: Assessing the Impacts of Hurricanes Zeta and Ida in the Context of Beach Nourishment Projects in the Mississippi River Delta

Hurricanes are one of the most devastating earth surface processes. In 2020 and 2021, Hurricanes Zeta and Ida pounded the Mississippi River Delta in two consecutive years, devastated South Louisiana, and raised tremendous concerns for scientists and stakeholders around the world. This study presents a high-resolution spatial-temporal analysis incorporating planialtimetric data acquired via LIDAR, drone, and satellite to investigate the shoreline dynamics near Port Fourchon, Louisiana, the eye of Ida at landfall, before and after the beach nourishment project and recent hurricane landfalls. The remote sensing analysis shows that the volume of the ~2 km studied beachfront was reduced by 240,858 m3 after consecutive landfalls of Hurricanes Zeta and Ida in 2020 and 2021, while 82,915 m3 of overwash fans were transported to the backbarrier areas. Overall, the studied beach front lost almost 40% of its volume in 2019, while the average dune crest height was reduced by over 1 m and the shoreline retreated ~60 m after the two hurricane strikes. Our spatial-temporal dataset suggests that the Louisiana Coastal Protection and Restoration Authority’s (CPRA’s) beach nourishment effort successfully stabilized the beach barrier at Port Fourchon during the hurricane-quiescent years but was not adequate to protect the shoreline at the Mississippi River Delta from intense hurricane landfalls. Our study supports the conclusion that, in the absence of further human intervention, Bay Champagne will likely disappear completely into the Gulf of Mexico within the next 40 years.

A multi-criteria CCUS screening evaluation of the Gulf of Mexico, USA

Continued research into reservoir characterization along with offshore carbon dioxide (CO2) transportation and infrastructure assets is needed to facilitate development of safe and successful carbon capture, utilization, and storage (CCUS) projects. This paper outlines a multi-criteria evaluation methodology that incorporates disparate sets of quantitative, spatially variable data into a decision-making framework for screening the Gulf of Mexico (GOM) outer continental shelf (OCS) for potentially viable CO2 storage and enhanced oil recovery (EOR) sites. Criteria categories include favorable geologic characteristics, logistics, and potential risks. Data compiled for 14 criteria from several publicly available geographic information system (GIS) layers was aggregated over 2559 spatially balanced points across the study area using the National Energy Technology Laboratory (NETL)-developed Cumulative Spatial Impact Layers™ (CSIL) GIS tool. Criteria are weighted by qualitative expert opinion relative to their perceived importance to given scenarios— the output of combined criteria values and weights enables regional CO2 storage suitability differentiation. The methodology considers both technical and non-technical factors impacting CCUS decision-making. The flexible methodology enables a systematic approach to regional ranking at high spatial resolution over a large study domain. Additionally, the framework enables high-grading of priority sites that warrant further characterization and follow-on analysis. Areas along the Louisiana coast and Mississippi River Delta consistently rank high for all scenarios largely a result of the favorable geology with the potential for stacked storage, as well as the density of existing pipelines and platforms, and proximity to several onshore CO2 sources. High-graded regions for the CO2 EOR-related scenarios are typically located further offshore towards the middle and edge of the OCS compared to higher priority regions for the geologic storage scenarios which fall closer to the Louisiana coastline.

An invasive population of Roseau Cane Scale in the Mississippi River Delta, USA originated from northeastern China

An invasive population of Roseau Cane Scale in the Mississippi River Delta, USA originated from northeastern China

The distribution of manta rays in the western North Atlantic Ocean off the eastern United States

In 2018, the giant manta ray was listed as threatened under the U.S. Endangered Species Act. We integrated decades of sightings and survey effort data from multiple sources in a comprehensive species distribution modeling (SDM) framework to evaluate the distribution of giant manta rays off the eastern United States, including the Gulf of Mexico. Manta rays were most commonly detected at productive nearshore and shelf-edge upwelling zones at surface thermal frontal boundaries within a temperature range of approximately 20–30 °C. SDMs predicted highest nearshore occurrence off northeastern Florida during April, with the distribution extending northward along the shelf-edge as temperatures warm, leading to higher occurrences north of Cape Hatteras, North Carolina from June to October, and then south of Savannah, Georgia from November to March as temperatures cool. In the Gulf of Mexico, the highest nearshore occurrence was predicted around the Mississippi River delta from April to June and again from October to November. SDM predictions will allow resource managers to more effectively protect manta rays from fisheries bycatch, boat strikes, oil and gas activities, contaminants and pollutants, and other threats.

Mobilized shear strengths of Mississippi River Delta Front sediments during submarine landslides

Mobilized shear strengths of Mississippi River Delta Front sediments during submarine landslides

Effect of trophic position on mercury concentrations in bottlenose dolphins (Tursiops truncatus) from the northern Gulf of Mexico

Marine species from the Gulf of Mexico often have higher mercury (Hg) concentrations than conspecifics in the Atlantic Ocean. Spatial differences in Hg sources, environmental conditions, and microbial communities influence both Hg methylation rates and the bioavailability of Hg to organisms at the base of the food web. Mercury bioaccumulates within organisms and biomagnifies in marine food webs, and therefore reaches the greatest concentrations in long-lived marine carnivores, such as dolphins. In this study, we explored whether differences in trophic position and foraging habitat among bottlenose dolphins (Tursiops truncatus) from the northern Gulf of Mexico (nGoM) contributed to the observed variation in skin total Hg (THg) concentrations. Using the δ13C and δ34S values in dolphin skin, we assigned deceased stranded dolphins from Florida (FL; n=29) and Louisiana (LA; n=72) to habitats (estuarine, barrier island, and coastal) east and west of the Mississippi River Delta (MRD). We estimated the mean trophic position of dolphins from each habitat using δ15N values from stranded dolphin skin and tissues of primary consumers taken from the literature following a Bayesian framework. Finally, we compared trophic positions and THg concentrations among dolphins from each habitat, accounting for sex and body length. Estimated marginal mean THg concentrations (μg/g dry weight) were greatest in dolphins assigned to the coastal habitat and estuarine habitats east of the MRD (range: 2.59-4.81), and lowest in dolphins assigned to estuarine and barrier island habitats west of the MRD (range: 0.675-0.993). On average, dolphins from habitats with greater THg concentrations also had higher estimated trophic positions, except for coastal dolphins. Our results suggest that differences in trophic positions and foraging habitats contribute to spatial variability in skin THg concentrations among nGoM bottlenose dolphins, however, the relative influence of these factors on THg concentrations are not easily partitioned.

Storm Surge and Tidal Dissipation in Deltaic Wetlands Bordering a Main Channel

AbstractDeltas are complex systems where tidal and riverine signals interact with each other. In river‐dominated deltas, where river discharge is sufficiently high, tidal amplitude is attenuated and distorted. Here we use wavelet analysis to examine the water level signal in stations located in wetlands adjacent to the main river outlet in the Wax Lake system, part of the Mississippi River Delta in Louisiana, USA. We study the signal attenuation in lateral wetlands at different frequency bands, following the propagation of the water level signal from the Gulf of Mexico to the innermost stations. During high river discharge, the astronomical tide measured inside the wetlands is reduced of 90%–98% in comparison to the tide in Atchafalaya Bay. Storm surge events, largely occurring at lower temporal frequencies, propagate conserving their energy once the signal enters the delta mouth. The river discharge signal, mostly present at frequencies lower than 1.59 μHz, is felt depending on river discharge conditions and the station position within the wetlands. Our results suggest that lateral wetlands in the Wax Lake system act as a low pass filter, attenuating tidal components but not the low frequency components of storm surges.

Spatial–Temporal Land Loss Modeling and Simulation in a Vulnerable Coast: A Case Study in Coastal Louisiana

Coastal areas serve as a vital interface between the land and sea or ocean and host about 40% of the world’s population, providing significant social, economic, and ecological functions. Meanwhile, the sea-level rise caused by climate change, along with coastal erosion and accretion, alters coastal landscapes profoundly, threatening coastal sustainability. For instance, the Mississippi River Delta in Louisiana is one of the most vulnerable coastal areas. It faces severe long-term land loss that has disrupted the regional ecosystem balance during the past few decades. There is an urgent need to understand the land loss mechanism in coastal Louisiana and identify areas prone to land loss in the future. This study modeled the current and predicted the future land loss and identified natural–human variables in the Louisiana Coastal Zone (LCZ) using remote sensing and machine-learning approaches. First, we analyzed the temporal and spatial land loss patterns from 2001 to 2016 in the study area. Second, logistic regression, extreme gradient boosting (XGBoost), and random forest models with 15 human and natural variables were carried out during each five-year and the fifteen-year period to delineate the short- and long-term land loss mechanisms. Finally, we simulated the land-loss probability in 2031 using the optimal model. The results indicate that land loss patterns in different parts change through time at an overall decelerating speed. The oil and gas well density and subsidence rate were the most significant land loss drivers during 2001–2016. The simulation shows that a total area of 180 km2 of land has over a 50% probability of turning to water from 2016 to 2031. This research offers valuable information for decision-makers and local communities to prepare for future land cover changes, reduce potential risks, and efficiently manage the land restoration in coastal Louisiana.

Fetch and distance from the bay control accretion and erosion patterns in Terrebonne marshes (Louisiana, USA)

AbstractWetlands in the Mississippi River Delta are rapidly degrading. Sea level rise and low sediment supply are widely recognized as the two main factors contributing to land‐to‐water conversion. To determine what marsh areas are more resilient, it is fundamental to identify the drivers that regulate marsh accretion and degradation. In this study, a combination of field data and aerial images is used to determine these drivers in Terrebonne Bay, Louisiana, USA. We find that accretion and degradation patterns depend on whether the marsh is located inland in a sheltered area or facing open water. In the first case, the distance to the nearby channel is important, because during flooding of the marsh platform more sediment is deposited in the proximity of channel banks. The accretion rates of marshes facing open water are high and correlate to fetch, a proxy for the ability of waves to resuspend bottom sediment. These areas are more resilient to sea level rise, but waves are also the main mechanism of degradation, as these marshes tend to degrade by edge erosion. Consequently, we propose a bimodal evolution trajectory of the marshes in Terrebonne Bay: marshes close to the bay and facing open water accrete rapidly but are affected by lateral erosion due to waves, whereas sheltered marshes accrete slowly and degrade in large swathes due to insufficient sediment supply.