Coastal Louisiana Research Articles

Vegetation Loss Following Vertical Drowning of Mississippi River Deltaic Wetlands Leads to Faster Microbial Decomposition and Decreases in Soil Carbon

AbstractWetland ecosystems hold nearly a third of the global soil carbon pool, but as wetlands rapidly disappear the fate of this stored soil carbon is unclear. The aim of this study was to quantify and then link potential rates of microbial decomposition after vertical drowning of vegetated tidal marshes in coastal Louisiana to known drivers of anaerobic decomposition altered by vegetation loss. Profiles of potential CH4 and CO2 production (surface to 60 cm deep) were measured during anaerobic incubations, organic matter chemistry was assessed with infrared spectroscopy, and soil porewater nutrients and redox potentials were measured in the field along a chronosequence of wetland loss. After vertical drowning, pond soils had lower redox potentials, higher pH values, lower soil carbon and nitrogen concentrations, lower lignin: polysaccharide ratios, more NH4+ and PO43−, and higher rates of potential CO2 release than vegetated marsh soils. Potential CH4 production was similar in vegetated marshes and open water ponds, with depth‐dependent decreases in CH4 production as soil carbon concentrations increased. In these anoxic soils, vegetation loss exerts a primary control on decomposition rates because flooding drives sustained increases in porewater nutrient availability (NH4+ and PO43, dissolved organic carbon) and decreases in redox potential (from −150 to −500 mV) that lead to higher potential CO2 fluxes within a few years. Without new carbon inputs following wetland loss, the sustained decomposition in open water ponds may lead to losses of stored soil carbon and could influence global carbon budgets.

Ten years later: An update on the status of collections of endemic Gulf of Mexico fishes put at risk by the 2010 Oil Spill.

The 2010 Gulf of Mexico Deepwater Horizon was the largest oil spill in human history that occurred during a 12-week period in a region less than 100 km from the coast of Louisiana; however, after more than a decade of post-spill research, few definitives can be said to be known about the long-term impacts on the development and distribution of fishes in and around the region of the disaster. Here, we examine endemic Gulf of Mexico fish species that may have been most impacted by noting their past distributions in the region of the spill and examining data of known collecting events and observations over the last twenty years (ten years prior to the spill, ten years post-spill). Five years post-spill, it was reported that 48 of the Gulf's endemic fish species had not been collected and, with expanded methods, we now report that 29 (of the 78 endemic species) have not been reported in collections since 2010 (five of these are only known from observations post-spill). Although the good news that some previously 'missing' species have been found may be cause to celebrate, the lack of information for many species remains a cause for concern given focused sampling efforts post-spill.

Satellite NO2 Trends and Hotspots Over Offshore Oil and Gas Operations in the Gulf of Mexico

AbstractThe Outer Continental Shelf of the Gulf of Mexico (GOM) is populated with numerous oil and natural gas (ONG) platforms which produce NOx (NOx = NO + NO2), a major component of air pollution. The Bureau of Ocean Energy Management (BOEM) is mandated to ensure that the air quality of coastal states is not degraded by these emissions. As part of a NASA‐BOEM collaboration, we conducted a satellite data‐based analysis of nitrogen dioxide (NO2) patterns and trends in the GOM. Data from the OMI and TROPOMI sensors were used to obtain 18+ year records of tropospheric column (TrC) NO2 in three GOM regions: (a) Houston urban area, (b) near shore area off the Louisiana coast, and a (c) deepwater area off the Louisiana coast. The 2004–2022 time series show a decreasing trend for the urban (−0.027 DU/decade) and near shore (−0.0022 DU/decade) areas, and an increasing trend (0.0019 DU/decade) for the deepwater area. MERRA‐2 wind and TROPOMI NO2 data were used to reveal several NO2 hotspots (up to 25% above background values) under calm wind conditions near individual platforms. The NO2 signals from these deepwater platforms and the high density of shallow water platforms closer to shore were confirmed by TrC NO2 anomalies of up to 10%, taking into account the monthly TrC NO2 climatology over the GOM. The results presented in this study establish a baseline for future estimates of emissions from the ONG hotspots and provide a methodology for analyzing NO2 measurements from the new geostationary TEMPO instrument.

Machine Learning Predictions of Vertical Accretion in the Mississippi River Deltaic Plain

AbstractDeltaic landscapes consist of vast wetland systems that rely on sedimentation to maintain their elevation and ecological communities against relative sea‐level rise. In the Mississippi River Deltaic plain, rising relative sea level and anthropogenic activities are causing land loss that will continue unless vertical accretion of sediment on the wetland surface is enough to fill the accommodation space. Even though the fate of the Mississippi Deltaic plain is tied directly to vertical accretion, there is not yet a clear understanding of the system‐wide controls on this process. Here, we investigate vertical accretion in coastal Louisiana using a data set of 266 stations from the Coastwide Reference Monitoring System (CRMS). Using linear regression models, we analyze vertical accretion in freshwater‐intermediate, brackish, and saline marsh communities. Integrating results from these models into a Gaussian Process regression model, we predict controls on vertical accretion rates across the deltaic plain. Consistent with previous studies, our results suggest that tidal amplitude and flood depth are critical controls on vertical accretion. These effects are additive and marshes with high tidal amplitudes and flood depths experience the most vertical accretion. Interestingly, the normalized difference vegetation index is found to be important for predicting vertical accretion, but not because of an increase in biomass production, but because it records unique marsh communities and flooding regimes. This study emphasizes the importance of incorporating marsh specific information into predictive models for the vertical accretion of coastal wetlands and that better predictions of wetland accretion probably require denser observational data.

A Neopragmatic Perspective on the Processual Nature of Landscape—Coastal Land Loss in Louisiana in the Context of Scientific Findings, Social Patterns of Interpretation, and Individual Experience

The changes on the Louisiana coast due to land loss can be understood as a process, and the social construction of these processes is highly complex. Due to this complexity, we will examine these social patterns of interpretation as well as individual experiences of coastal land loss in Louisiana within a neopragmatic meta-theoretical framework using several methods, data, researcher perspectives, forms of representation, and theories, with a special focus on the construction of coastal land loss by the media. For this purpose, comments below a YouTube video on a hurricane event on Grand Isle, Louisiana, as well as on-site interviews with people affected by coastal land loss, were qualitatively analyzed. The results were interpreted with the help of various theories such as the theory of three landscapes, Dahrendorf’s conflict theory, Bourdieu’s theory of social capital, and Luhmann’s autopoietic systems theory. The research reveals patterns of interpretation, categorization, and evaluation of processes from an internal and external perspective that are highly morally charged.

Managing retreat? An empirical reflection on adopting relocation initiatives as adaptation policy in Louisiana

ABSTRACT Coastal Louisiana is experiencing climate-related impacts at rates substantially higher than other areas worldwide. Unique coastal communities face imminent impacts requiring adaptation and possible relocation. As such, Louisiana's strategies for ecosystem-scale flood management and ecological restoration are relevant globally. In this paper, we trace the idea of managed retreat as a nonstructural adaptation mechanism through the analysis of Louisiana's Coastal Master Plan and LA SAFE documents, and interviews with residents and planning professionals. Although Louisiana's plans and policies increasingly recognise increasing risk, and relocation as a necessary adaptation strategy, planning goals for relocation have weakened over time. Our analysis found two reasons for this. First, professionals and residents view risk and relocation differently. Low- and moderate-income residents had varied claims and constraints that influenced the adoption of relocation programmes and highlighted the need for community-driven initiatives. Second, no social infrastructure was implemented with the technical capacity or financial resources to work with communities to develop and implement relocation initiatives. As climate impacts increase, policies facilitating managed retreat will also need to expand. This work provides insights into the evolution of large-scale relocation planning, and a better understanding of the challenges facing states and communities as these efforts are expanded.

Flocculation characteristics of suspended Mississippi River mud under variable turbulence, water and salt sources, and salinity: a laboratory study

Muddy sediment constitutes a major fraction of the suspended sediment mass carried by the Mississippi River. Thus, adequate knowledge of the transport dynamics of suspended mud in this region is critical in devising efficient management plans for coastal Louisiana. We conducted laboratory tank experiments on the sediment suspended in the lower reaches of the Mississippi River to provide insight into the flocculation behavior of the mud. In particular, we measure how the floc size distribution responds to changing environmental factors of turbulent energy, sediment concentration, and changes in base water composition and salinity during summer and winter. We also compare observations from the tank experiments to in situ observations. Turbulence shear rate, a measure of river hydrodynamic energy, was found to be the most influential factor in determining mud floc size. All flocs produced at a given shear rate could be kept in suspension down to shear rates of approximately 20 s−1. At this shear rate, flocs on the order of 150–200 μm and larger can settle out. Equilibrium floc size was not found to depend on sediment concentration; flocs larger than 100 μm formed in sediment concentrations as low as 20 mgL−1. An increase in salinity generated by adding salts to river water suspensions did not increase the flocculation rate or equilibrium size. However, the addition of water collected from the Gulf of Mexico to river-water suspensions did enhance the flocculation rate and the equilibrium sizes. We speculate that the effects of Gulf of Mexico water originate from its biomatter content rather than its ion composition. Floc sizes in the mixing tanks were comparable to those from the field for similar estimated turbulent energy. Flocs were found to break within minutes under increased turbulence but can take hours to grow under conditions of reduced shear in freshwater settings. Growth was faster with the addition of Gulf of Mexico water. Overall, the experiments provide information on how suspended mud in the lower reaches of the Mississippi might respond to changes in turbulence and salinity moving from the fluvial to marine setting through natural distributary channels or man-made diversions.

Scales of Diversity Affecting Ecosystem Function across Agricultural and Forest Landscapes in Louisiana

Current land use and extensive modifications of natural ecosystems across the state of Louisiana are generally similar to those across the southeastern USA where rainfall supports forest ecosystems. Both intentional and unintentional consequences of ecosystem modifications from the scales of water and sediment movement across a field edge to state-wide loss of functional grasslands are legacies from previous development across the state. While major investments and large-scale, long-term plans are aspects of some continuing ecological issues across the state, small-scale, volunteer-led restoration of native grassland plant communities in the Louisiana Coastal Prairie illustrates the value associated with the restoration of natural ecosystem function in drastically disturbed environments. As is now becoming increasingly recognized, Louisiana grasslands represent less obvious components of forest, woodland, and wetland landscapes across the state, where they have contributed essential wildlife habitat, and ecosystem functions. These are now largely missing from many landscapes across the state and region. The strategic restoration of grassland functions combining novel native grass pastures and fully functional native grassland plant communities as landscape components could provide both economic and ecosystem benefits. Specific native grassland seed resources are needed for various restoration activities to enhance ecosystem function at a range of scales across the state and region.

Variations in Subsidence Patterns in the Gulf of Mexico Passive Margin From Airborne‐LiDAR Data and Time Series InSAR: Baton Rouge Case Study

AbstractThe Coast of Louisiana is affected by accelerating sea level rise compounded by land subsidence, leading to land loss. Vertical crustal motions in the region are caused by natural and anthropogenic processes that vary temporally and spatially across the Gulf of Mexico. We investigate the role of growth faulting contributions to subsidence in a case study of Baton Rouge, where two E‐W striking, down‐to‐the‐south normal faults, the Denham Springs and Baton Rouge faults, cut compacted Pleistocene strata, and where sediment compaction should be minimal. We used InSAR time series and LiDAR differencing data spanning 1999–2020 to quantify modern vertical and horizontal displacements. After calibration with GNSS data, both methods reveal similar spatial patterns in ground motion, with the faults delimiting areas with different absolute rates. On average the area north of the Baton Rouge fault is subsiding faster than the south, opposite to the long‐term sense of fault slip. LiDAR mean vertical rates range between −5 to −11 mm/y and −2.4 to −7 mm/y. InSAR time‐series mean rates in the LOS direction range between −10.9 to −13.6 mm/y and −8 to −10.6 mm/y, respectively, for the north and south areas. Subsidence in the northern area likely is controlled by groundwater level changes caused by pumping as indicated by groundwater extraction models. The southern area average is likely influenced by the injection of fluids. Our results suggest volumetric changes caused by fluid extraction and injection in regions separated by growth faults that are creeping to accommodate the spatial variations in subsidence.

Coupling numerical models of deltaic wetlands with AirSWOT, UAVSAR, and AVIRIS-NG remote sensing data

Abstract. Coastal marsh survival relies on the ability to increase elevation and offset sea level rise. It is therefore important to realistically model sediment fluxes between marshes, tidal channels, and bays as sediment availability controls accretion. Traditionally, numerical models have been calibrated and validated using in situ measurements at a few locations within the domain of interest. These datasets typically provide temporal information but lack spatial variability. This paper explores the potential of coupling numerical models with high-resolution remote sensing imagery. Products from three sensors from the NASA Delta-X airborne mission are used. Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) provides vertical water level change on the marshland and was used to adjust the bathymetry and calibrate water fluxes over the marsh. AirSWOT yields water surface elevation within bays, lakes, and channels, and was used to calibrate the Chezy bottom friction coefficient. Finally, imagery from AVIRIS-NG provides maps of total suspended solids (TSS) concentration that were used to calibrate sediment parameters of settling velocity and critical shear stress for erosion. Three numerical models were developed at different locations along coastal Louisiana using Delft3D. The coupling enabled a spatial evaluation of model performance that was not possible using simple point measurements. Overall, the study shows that calibration of numerical models and their general performance will greatly benefit from remote sensing.

Eroding Landscapes, Emerging Carescapes: How Migrants from Coastal Louisiana Experience Disasters and Care from Afar

Eroding Landscapes, Emerging Carescapes: How Migrants from Coastal Louisiana Experience Disasters and Care from Afar

A hyperspectral view of the nearshore Mississippi River Delta: Characterizing suspended particles in coastal wetlands using imaging spectroscopy

Suspended particle concentration (Total Suspended Solids or TSS) determines sediment availability for deposition, whereas particle physico-chemical properties (e.g. composition and size) can influence sediment transport and accretion. These variables are critical to modeling and understanding nearshore sediment dynamics and coastal soil accretion and erosion. Upcoming satellite imaging spectrometers (e.g., GLIMR, SBG) have the potential to improve the detailed mapping and characterization of suspended particles in nearshore areas. Here, we conducted a detailed feasibility study assessing the capacity of imaging spectroscopy to accurately map suspended particle concentrations and physico-chemical properties in the Mississippi River Deltaic Plain (Louisiana, USA), a nearshore system with extreme coastline vulnerability. To that end, a large dataset of in situ TSS, Particulate Organic Carbon (POC) concentration, particle size, inherent optical properties (IOPs), and hyperspectral remote sensing reflectance (Rrs) was collected during the 2021 NASA Delta-X field campaigns in coastal Louisiana. Analyses of the data revealed that the enhanced spectral information provided by imaging spectroscopy (hyperspectral Rrs) improved the retrieval of TSS and POC/TSS (% organic carbon content), but highlighted the challenge of retrieving particle size in this system. Partial-least-squares-regression (PLSR) algorithms for TSS performed better than existing state-of-the-art algorithms and confirmed the importance of using local measurements and near-infrared Rrs. Implementation on Airborne Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) imagery generated high-resolution (< 5 m), high-quality maps of TSS and POC/TSS in contrasted areas with a wide range of TSS concentrations from (0.1 to 100 mg L−1), and demonstrated the enhanced potential of upcoming missions such as SBG and GLIMR to inform studies of nearshore sediment dynamics and coastal vulnerability/resilience.

Meta-Analysis and Spatial Distribution of Ecosystem Services in Louisiana's Coastal Zone: Implications for Coastal Restoration

Meta-Analysis and Spatial Distribution of Ecosystem Services in Louisiana's Coastal Zone: Implications for Coastal Restoration

The Future of Cyanobacteria Toxicity in Estuaries Undergoing Pulsed Nutrient Inputs: A Case Study from Coastal Louisiana

Harmful cyanobacteria blooms (cyanoHABs) are a global phenomenon, especially in calm, warm, and nutrient-rich freshwater and estuarine systems. These blooms can produce various potent toxins responsible for animal poisoning and human health problems. Nutrient-rich freshwater pulsed into estuaries affects turbidity, water temperature, salinity, and nutrient concentrations and ratios at irregular intervals, creating a highly dynamic habitat. However, the underlying processes that lead to the selective development of cyanoHABs for certain species and the fate of their toxins are still uncertain. This paper draws upon the rich body of research available for one such system, the Lake Pontchartrain Estuary, Louisiana, to generate insights about future research directions in pulsed-nutrient-delivery estuaries. Toxin-producing cyanobacteria blooms in river-dominated Louisiana coastal ecosystems have already been documented at high concentrations, presenting a potential risk to human health as $2.4 billion worth of Louisiana’s fish and shellfish are consumed by millions of people throughout the US every year. Recent studies have shown that the Lake Pontchartrain Estuary, just north of New Orleans, Louisiana has been experiencing cyanoHABs, likely connected to combinations of (a) high interannual variability in nutrient loading associated with seasonal and episodic rainfall, (b) the timing, duration, and magnitude of the flood-stage Mississippi River water diverted into the Lake Pontchartrain Estuary, and (c) saltwater inputs from tropical storms. It is expected that cyanoHABs will become more frequent in Louisiana with a warming climate and changes to the timing and magnitude of river water diverted into the Lake Pontchartrain Estuary, which will play a dominant role in the development of blooms in this region. More studies are needed to focus on the environmental conditions that control the succession or/and co-existence of different cyanobacteria species and their toxins, optimally culminating in a near-term forecasting tool since this information is critical for health agencies to mitigate or to provide early warnings. Toxin forecasts for pulsed-nutrient estuaries, including Lake Pontchartrain, could directly inform state and municipal health agencies on human exposure risks to upcoming cyanobacteria toxicity events by predicting cyanobacteria species shifts, potency, and toxin modality along the freshwater-to-marine continuum while also informing a longer-term projection on how the changing climate will impact the frequency and potency of such blooms.

Watershed-Scale Evaluation of Flood Mitigation Benefits from Surface Water Diversion and Subsurface Injection in Coastal Louisiana

Watershed-Scale Evaluation of Flood Mitigation Benefits from Surface Water Diversion and Subsurface Injection in Coastal Louisiana

Heat, hurricanes, and health: Effects of natural disturbances on angling effort.

Recreational angling is a very popular outdoor activity that is weather-dependent, although investigations of this relationship are rare. This study used weekly fishing effort (2015-2021) estimates throughout coastal Louisiana to understand how effort changed in response to weather conditions. Although we found evidence for some effect of all the weather variables, temperature reported the greatest number of monthly effects, along with an overall declining effect throughout the year. We also examined how tropical storms and hurricanes reduce fishing effort, but that effort recovers rapidly after the storm. Finally, we examined fishing effort during the first year of the pandemic (2020) compared to previous years and found some monthly increases exceeding 100% of normal effort. Understanding angler motivations remains an important part of fishery management, and in a future with changes to weather, hurricanes, and global health crises, we can now know more about how environmental factors change angling effort.

ANALYZING THE IMPACT OF SEA LEVEL RISE ON COASTAL FLOODING AND SHORELINE CHANGES ALONG THE COAST OF LOUISIANA USING REMOTE SENSORY IMAGERY

Abstract. Sea level rise poses risks to coastal areas which is increasingly rendering such areas susceptible to flood and shoreline retreat. Notably, coastal areas like Southern Louisiana located along the Gulf of Mexico has experienced endangering events of land subsidence due to flood inundations resulting from incessant distribution of hurricanes and tropical storms. This research therefore employed remote sensing data to analyze the impacts of sea level rise on coastal flooding and shoreline retreat along the coast of Louisiana. That is, by assessing Sentinel-2 imagery data to evaluate flood prone and flood extent areas particularly during the Louisiana floods and Hurricane Harvey. Based on this, the results show most of the inland parishes in coastal Louisiana such as Assumption, St. James, Livingston, Lafourche and Terrebonne were within high flood risk zones of about 9.3. These parishes also suffered severe damage in terms of affected croplands, potentially flooded areas and affected urban areas. On the other hand, most of the parishes in close proximity to the waterbodies such as the Gulf of Mexico were interestingly within low flood risk zones of about 6.1 suggesting proximity to waterbodies not being the only indicating factor of a flood prone area. This research also highlights that Louisiana's shorelines are rapidly receding at a rate that could result in the loss of one million acres of the state’s land in the next four decades. Hence, the results from this research are anticipated to contribute to sustainable shoreline setback plans and mitigative strategies to protect Louisiana's coast.

MAXIMUM LIKELIHOOD ALGORITHM DETECTS COASTAL WETLAND CHANGES IN TWO CONTRASTING COASTAL WETLANDS IN LOUISIANA

Abstract. Louisiana coastal wetlands contain about 37 percent of the estuarine herbaceous marshes in the conterminous United States. However, the combined effect of sea level rise and other anthropogenic factors have altered land use land cover over the last few years. This is true for two wetlands in coastal Louisiana, Barataria bay and Wax Lake delta. Barataria Bay, Louisiana, USA has experienced significant land loss. Updated information on the dynamics of change in these wetlands is limited and poorly documented. This information is necessary to develop strategies that will contribute to reversing and halting degradation. Thus, this study employed the Maximum Likelihood classifier on Landsat satellite imagery to assess land use and land cover changes in Barataria Bay and Wax Lake Delta, southeastern Louisiana, USA. The analysis revealed notable alterations in the land cover patterns over the study period. In Barataria Bay, there was a decrease in salt marsh areas with a corresponding increase in open water and Built-up area. In contrast, Wax Lake Delta demonstrated substantial land/wetland growth, with significant expansion of vegetation cover. The Maximum Likelihood classifier demonstrated high accuracy in classifying the land cover types, with an overall accuracy of 86% for Barataria Bay and 92% for Wax Lake Delta. These results highlight the effectiveness of the classifier in accurately identifying and mapping land cover changes in coastal environments. The findings contribute valuable insights for understanding the dynamics of coastal ecosystems and can inform decision-making processes for coastal management and conservation efforts.

THE EFFECT OF TROPICAL CYCLONES’ TRANSLATION SPEEDS AND LANDFALL ANGLES ON MAXIMUM SURGE HEIGHTS ALONG IDEALIZED COASTS

Global warming has known to alter the cyclonic translation speed (TS) in the past, for instance, a slowdown trend of TS in the Northwest Pacific region. Thus, the importance of TS along with landfall angle (LA) has been examined over the coast of Louisiana (Rego, 2009). Not only these cyclone’s characteristics but also the geometries that the cyclone is traveling over are found to be crucial to the development of storm surge. Meanwhile, previous studies mainly focus on one or two individual characteristics in specific sites, which made their conclusions limitedly understood. Therefore, this study aims to generalize the synthetic effects of TS, LA, and coastal geometries on a maximum surge height (MSH) along the coast through the numerical simulations of a series of idealized scenarios.

LONG TERM MORPHOLOGIC MODELLING OF DELTA DEVELOPMENT IN BRETON SOUND RESULTING FROM A PROPOSED DIVERSION STRUCTURE

Sediment deprivation, hydrologic alteration, subsidence, sea level rise, and saltwater intrusion have been causing significant land loss in coastal Louisiana. Breton Sound combined with the nearby Barataria Bay, and Mississippi River Delta have lost approximately 1800 square kilometers (or 447,000 acres) of land, representing one of the highest land loss rates in the world since the 1930s when the Mississippi River was leveed. To address this problem, the Coastal Protection and Restoration Authority (CPRA) initiated several sediment diversion projects in the Lower Mississippi River (LMR). The Mid- Breton Sediment Diversion (MBrSD) project is one of the costal restoration projects proposed to restore natural processes in Breton Sound, which can strategically reestablish hydrologic flows, carry land-building sediments, nourish marshes and sustain land.