Atchafalaya Basin Research Articles

Why Is Reducing the Dead Zone in the Gulf of Mexico Such a Complex Goal? Understanding the Structure That Drives Hypoxic Zone Formation via System Dynamics

The Northern Gulf of Mexico hosts a severe dead zone, an oxygen-depleted area spanning 1,618,000 hectares, threatening over 40% of the U.S. fishing industry and causing annual losses of USD 82 million. Using a System Dynamics (SD) approach, this study examined the Mississippi–Atchafalaya River Basin (MARB), a major contributor to hypoxia in the Gulf. A dynamic model, developed with Vensim software version 10.2.1 andexisting data, represented the physical, biological, and chemical processes leading to eutrophication and simulated dead zone formation over time. Various policies were assessed, considering natural system variability. The findings showed that focusing solely on nitrogen control reduced the dead zone but required greater intensity or managing other inputs to meet environmental goals. Runoff control policies delayed nutrient discharge but did not significantly alter long-term outcomes. Extreme condition tests highlighted the critical role of runoff dynamics, dependent on nitrogen load relative to flow volume from upstream. The model suggests interventions should not just reduce eutrophication inputs but enhance factors slowing down the process, allowing natural denitrification to override anthropogenic nitrification.

Riverine nitrogen footprint of agriculture in the Mississippi–Atchafalaya River Basin: do we trade water quality for crop production?

Increasing food and biofuel demands have led to the cascading effects from cropland expansions, raised fertilizer use, to increased riverine nitrogen (N) loads. However, little is known about the current trade-off between riverine N pollution and crop production due to the lack of predictive understanding of ecological processes across the land-aquatic continuum. Here, we propose a riverine N footprint (RNF) concept to quantify how N loads change along with per unit crop production gain. Using data synthesis and a well-calibrated hydro-ecological model, we find that the RNF within the Mississippi–Atchafalaya River Basin peaked at 1.95 g N kg−1 grain during the 1990s, and then shifted from an increasing to a decreasing trend, reaching 0.65 g N kg−1 grain in the 2010s. This implies decoupled responses of crop production and N loads to key agricultural activities approximately after 2000, but this pattern varies considerably among sub-basins. Our study highlights the importance of developing a food–energy–water nexus indicator to examine the region-specific trade-offs between crop production and land-to-aquatic N loads for achieving nutrient mitigation goals while sustaining economic gains.

Spatial and temporal variations of seabed sediment characteristics in the inner Louisiana shelf

Although many studies have been performed in the northern Gulf of Mexico, there have been a paucity of high-resolution sediment data collected from seabed. New multicores were collected repeatedly at 4 fixed stations in the inner Louisiana shelf on March 12, 2021, July 7, 2021, November 20, 2021, and March 5, 2022, respectively, to study detailed spatial and temporal variations of surficial sediment. Being a very high sediment accumulation zone, Raccoon Island dredge pit and its nearby shelf were selected as our study area and additional six vibracores were collected inside and outside the pit for comparison. This study area is about 140 km west of the modern Mississippi Delta and 70 km southeast of the Atchafalaya Delta. A total of 624 samples from both vibracores and multicores were analyzed for this study. Spatially, our results show that sediment near Ship Shoal was the coarsest and sediment deposited in the pit was the finest. The organic matter was highest inside the pit and lowest near Ship Shoal. The carbonate content was the lowest near Ship Shoal. Temporally, surficial sediments were generally coarser in July and November of 2021 and finer in March of 2021 and March of 2022. Although the Mississippi and Atchafalaya Rivers supply a large amount of sediment during spring season, it takes time for the river-derived sediment to be delivered into the study area. Hurricanes Delta, Zeta and Ida passed this area and greatly impacted sediment transport in the years 2021 and 2022. The comparatively coarser sediment in July and November of 2021 were likely related to the resuspension of some coarse sediment by these hurricane events. Besides the river supply, Ship Shoal and barrier islands are nearby localized sandy sources and inner Louisiana shelf is a widespread mud source. This spatial heterogeneity of surficial sediment interplays with the timing of Mississippi and Atchafalaya River flood season and hurricanes and together dictates the sediment texture. This research on a filled-up dredge pit can benefit future evaluation of the safety of existing oil infrastructure and the feasibility of building new pipelines and platforms after dredging activities. Our results also shed light on the study of river- and hurricane-impacted sediment transport in muddy and mixed-texture passive continental margins around the world.

Image-based machine learning for monitoring the dynamics of deltaic islands in the Atchafalaya River Delta Complex between 1991 and 2019

Deltaic islands are distinct hydro-environmental zones with global significance in food security, biodiversity conservation, and fishery industry. These islands are the fundamental building blocks of many river deltas. However, deltaic islands are facing severe challenges due to intensive anthropogenic activities, sea level rise, and climate change. In this study, dynamic changes of deltaic islands in Wax Lake Delta (WLD) and Atchafalaya Delta (AD), part of the Atchafalaya River Delta Complex (ARDC) in Louisiana, USA, were quantified based on remote sensing images from 1991 to 2019 through a machine learning method. Results indicate a significant increase in deltaic islands area for the whole ARDC at a rate of 1.29 km2/yr, with local expansion rates of 0.60 km2/yr for WLD and 0.69 km2/yr for AD. All three parts of the WLD naturally prograded seaward, with the western part (WP) and central part (CP) expanding southwestward to the sea, while the eastern part (EP) prograding southeastwards. Differently from WLD, the three parts of AD irregularly expanded seaward under the impacts of anthropogenic activities. The WP and CP of the AD expanded respectively northwestwards and southwestwards, while the EP remained stable. Different drivers dominate the growth of deltaic islands in the WLD and AD. Specifically, fluvial suspended sediment discharge and peak flow events were responsible for the shift in the spatial evolution of WLD, while dredging and sediment disposal contributed to the expansion of AD. Tropical storms with different intensity and landing locations caused short-term deltaic island erosion or expansion. Tropical storms mainly generated erosion on the deltaic islands of the WLD, while causing transient erosion or siltation on the deltaic islands of the AD. In addition, high-intensity hurricanes that made landfall east of the deltas caused more erosion in the AD. Finally, sea level rise, at the current rate of 8.17 mm/yr, will not pose a threat to the deltaic island of WLD, while the eastern part of AD may be at risk of drowning. This study recognizes the complexity of factors influencing the growth of deltaic islands, suggesting that quantitative studies on the deltaic island extent are of critical for the restoration and sustainable management of the Mississippi River Delta and other deltas around the world.

Managed diversion lead time effects on flood response in a tidal freshwater river

AbstractRiver diversions are a commonly used water management tool throughout the world. Low‐gradient coastal rivers exhibit complex floodplain interactions and are subject to multiple uncertain drivers of future flood risk. The interacting factors make quantification of downstream diversion effects on ambient flood hazards in coastal riverine ecosystems challenging. This article analyzes the effects of a managed ecological diversion (MED) on downstream flood hazards in the flood‐prone tidal freshwater Vermilion River system situated within the Atchafalaya Basin region of Louisiana, USA. A flexible and efficient hydraulic and hydrologic (H&H) modeling setup and counterfactual approach is utilized to develop and analyze 60 simulation scenarios aimed at quantifying the effects of an existing baseflow augmentation program on downstream flood hazards under uncertain future conditions. The analysis demonstrated the significance of preemptive diversion closure on the downstream flood levels in downstream rivers. The role of wetland topography and residual floodplain storage on MED‐induced flood response was also highlighted. A variety of uncertain parameter/forcing scenarios were also evaluated to establish robustness of the findings and to extend the results to more general settings. The study provides insights on downstream flood response induced by MEDs, which are expected to become more prevalent in the future.

Future Wetland Loss in Louisiana Threatens the Carbon Sequestration Potential of the Coastal Habitats

Photo 1. Scientists collecting aboveground biomass in a saline wetland (light green is smooth cordgrass, Spartina alterniflora and dark green are black mangroves, Avicennia germinans) located in coastal Louisiana. Aboveground net primary productivity, soil carbon accumulation rates, and greenhouse gas emissions can be used to estimate the net ecosystem carbon balance of coastal habitats like this saline wetland. Our estimates suggest that existing saline wetland habitats are a net sink of greenhouse gases. Photo credit: The Water Institute of the Gulf. Photo 2. Saline wetland habitat (dominated by black mangroves, Avicennia germinans) and saline open water habitat in coastal area of Louisiana. The 2017 Coastal Master Plan model output projects that at year 2050, the highest area of habitat will be the saline open water. Photo credit: The Water Institute of the Gulf. Photo 3. Fresh forested wetlands (dominated by cypress trees, Taxodium distichum) are commonly observed in the Atchafalaya Basin in the Louisiana coast area. Our net ecosystem carbon balance estimates suggest that existing fresh forested wetland habitats are a net sink of greenhouse gases. Photo credit: The Water Institute of the Gulf. These photographs illustrate the article “Climate Change Mitigation Potential of Louisiana's Coastal Area: Current Estimates and Future Projections” by Baustian, Melissa M, Bingqing Liu, Leland Moss, Alyssa Dausman, and James W. Pahl published in Ecological Applications. https://doi.org/10.1002/eap.2847

Sustainable Crawfish Farming in Louisiana: Strategies to Promote Crawfish Production

This study is used to describe sustainable crawfish farming in the state of Louisiana, and to also suggest some key strategies to help the state of Louisiana to promote crawfish production. It is an undeniable fact that the Louisiana Crawfish production over the years has been produced from wild habitats, mainly from the Atchafalaya River basin, which seems to be a factor of seasonality. Following the statistics of the total Crawfish production by Louisiana Crawfish Promotion and Research Board, it was underscored that more than 100 million pounds of crawfishes were produced. Out of the 100 million capacity of crawfishes produced annually, approximately 82 million pounds of crawfishes were obtained from regular crawfish farms and more than 18 million pounds of crawfishes were harvested from natural habitats by the activities of approximately 1,600 fishermen. Surprisingly, the crawfish industry employs about 7,000 people directly or indirectly and injects $300 million into the state's economy each year. Therefore, the sustainability of this industry will continue to generate sustainable employment, and reliable revenue to support the state’s project. The study adopted a cross-sectional data collection procedure to sample 250 crawfish farmers in the State of Louisiana with the help of Cluster random sampling technique. The study was modeled after Ranganathan et al. (2017) and Robinson (2018) analysis and interpretation of Logistic regression model to estimate the strategic determinants of sustainable crawfish production in Louisiana. The study revealed that the engagement/involvement of crawfish farmers' in the productive and efficient system of production in the State of Louisiana (such as productive cage system) will remain an important driver of sustainable crawfish growth. The study further revealed the following fishing production strategies as sustainable for the crawfish growth based on the farmers perception and understanding: crawfish health management, genetically improved crawfish strains, more affordable quality feeds, human capacity development and extension services, as well as policy and public investment support for crawfish production. The study recommended that the Louisiana State government and the other key stakeholders should continuously invest in technology and transfers that will aid in sustainable crawfish production, and to also focus beyond the farm by strengthening the implementation of policy and public investment support for crawfish farming. These strategies will go a long way to generate more sustainable employment, and revenue to ensure growth in Louisiana. Keywords : Sustainability, Strategies, Production, Natural and Wild-Habitats, Employment, Logistic Regression, Revenue, Crawfish, Seafood, Aquaculture, and Fishing DOI: 10.7176/PPAR/13-2-02 Publication date: March 31 st 2023

Influence of River Disconnection on Floodplain Periphyton Assemblages

The Atchafalaya River Basin (ARB) in southcentral Louisiana, USA, is a structurally and biotically diverse floodplain of Atchafalaya River (AR), which is the largest distributary of the Mississippi River. Annual floodplain inundation facilitates the exchange of nutrients and organic material between the AR and its floodplain, giving rise to the high productivity of the river-floodplain system. Production within the ARB is driven by periphytic algae, phytoplankton, and aquatic macrophytes, however, very little is known about periphytic algal assemblages in floodplain systems or how loss of annual flooding impacts these assemblages. In this study, we use artificial substrates to sample periphytic algae bi-weekly (January 2019 – September 2019) from ARB sites with active river connections and from a permanently-isolated floodplain system (Lake Verret). Our results showed that connection to the river caused spatiotemporal shifts in periphytic algal assemblages in the ARB. Overall, ARB sites had a higher density of algal cells compared with non-ARB sites, and for ARB sites with more active river connections, total algal density was greater nearer to river inputs, particularly for cyanobacteria and centric diatoms, with diatoms dominating periphyton assemblages year-round. In contrast, the river-isolated system was dominated largely by chlorophytes. In both isolated and connected systems, sites with heavy macrophyte cover showed increased densities of euglenoids, chrysophytes, and xanthophytes. Shifts in periphytic algal assemblages due to floodplain alterations, such as the disconnection of a floodplain from its river source, could impact higher trophic levels and should be considered in future wetland management decisions.

Hydrologic Connectivity and Residence Time Affect the Sediment Trapping Efficiency and Dissolved Oxygen Concentrations of the Atchafalaya River Basin

AbstractLittle is known about water movement, volume, or residence time (RT), and how those characteristics affect sediment trapping efficiency (TE) and dissolved oxygen concentrations (DO) in the United States' largest remaining bottomland hardwood swamp, the Atchafalaya River Basin. To better understand these dynamics, this study used bathymetry, lidar, and stage records to determine volumes in the Basin's hydrologically distinct water management units (WMUs). Discharge measurements determined flow distribution and RT. Residence time was compared with DO to identify conditions that coincided with DO increases or decreases. Suspended sediment concentrations (SSC) were used to determine TE relative to calculated and measured discharge and RT. Discharge through units (85–2,200 m3/s) and RT (0.37–231 d) depended on connectivity and river stage. At high stages, with water temperatures >20°C, DO in the largest WMU declined by −0.21 mg/l/day. DO trends indicated less well‐connected areas of the WMU contributed hypoxic waters as the flood wave lengthened and stages fell. In the two WMUs examined for TE, TE (−266% to 99% and up to 38 Gg/day) correlated with hydrologic connectivity, SSC, RT, water volume, and, in one WMU, discharge losses. Long RT and high TE indicated a high potential to process nutrients. These relationships varied among WMUs. Large volumes of sediment‐laden water moving over the floodplain combined with long RT, high TE, and hypoxia indicate that this ecosystem has continental‐scale importance in reducing nutrient loads to the northern Gulf of Mexico. Reports from other systems suggest similar processes may be operating on other large river floodplains globally.

Heavy Precipitation Impacts on Nitrogen Loading to the Gulf of Mexico in the 21st Century: Model Projections Under Future Climate Scenarios

AbstractWhile spatial heterogeneity of riverine nitrogen (N) loading is predominantly driven by the magnitude of basin‐wide anthropogenic N input, the temporal dynamics of N loading are closely related to the amount and timing of precipitation. However, existing studies do not disentangle the contributions of heavy precipitation versus non‐heavy precipitation predicted by future climate scenarios. Here, we explore the potential responses of N loading from the Mississippi Atchafalaya River Basin to precipitation changes using a well‐calibrated hydro‐ecological model and Coupled Model Intercomparison Project Phase 5 climate projections under two representative concentration pathway (RCP) scenarios. With present agricultural production and management practices, N loading could increase up to 30% by the end of the 21st century under future climate scenarios, half of which would be driven by heavy precipitation. Particularly, the RCP8.5 scenario, in which heavy precipitation and drought events become more frequent, would increase N loading disproportionately to projected increases in river discharge. N loading in spring would contribute 41% and 51% of annual N loading increase under the RCP4.5 and RCP8.5 scenarios, respectively, most of which is related to higher N yield due to increases in heavy precipitation. Anthropogenic N inputs would be increasingly susceptible to leaching loss in the Midwest and the Mississippi Alluvial Plain regions. Our results imply that future climate change alone, including more frequent and intense precipitation extremes, would increase N loading and intensify the eutrophication of the Gulf of Mexico over this coming century. More effective nutrient management interventions are needed to reverse this trend.

Hydrologic modification and channel evolution degrades connectivity on the Atchafalaya River floodplain

AbstractThe Atchafalaya River Basin is the largest remaining forested wetland in the contiguous United States. Since 1960, dredging and channel erosion in the Basin have resulted in changes to the hydrologic connectivity that have not been quantified. Analyses were conducted to determine the hydraulic and geomorphic factors that have changed since discharge became controlled that may have decreased river/floodplain connectivity. We examined: (1) stage/discharge relationships from 1960 to 2014; (2) hydroperiods across the floodplain; (3) discharge distribution to the floodplain by comparing discharge measurements from 1959–1968 to 2005–2012; and (4) channel cross‐sections and floodplain elevations. Our results indicate that much of the floodplain no longer receives headwater discharge (upstream to downstream, > 200 km2) or receives too little discharge to alleviate stagnancy and hypoxia in the forested wetland at lower stages. Large portions of the Basin (400 km2) have low water levels controlled by channel geomorphology and sea‐level rise that inundate the forested floodplain for more than 50% of the calendar year. This extended duration of inundation contributes to hypoxia and likely reduces nutrient retention. The confinement of discharge to a large efficient channel compromises the ability of this system to respond to sea‐level rise and subsidence. This study provides insight to the effects of flood management projects along Coastal Plain rivers and deltas.

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.

Nonstationary streamflow effects on backwater flood management of the Atchafalaya Basin, USA

A non-stationary increasing streamflow trend has been observed on the Mississippi River and other major river basins around the world. The current study analyzed the non-stationary streamflow effects (NSFEs) on flood management in backwater areas adjacent to the Atchafalaya Basin floodway in Louisiana, USA. A continuous simulation hydrology model coupled with a quasi-two-dimensional hydrodynamic model of the basin floodway and surrounding regions was used to develop over 180 simulation scenarios by superimposing local flood events (early summer 2014 and late summer 2016) against 90-years’ worth of daily Atchafalaya River streamflow hydrographs. The NSFE on the Atchafalaya River induced substantial reductions in the performance of major flood regulating structures with seasonal effects based on the annual flood cycle. Capacity reductions at the structures were demonstrated to trigger a cascade of effects in ostensibly protected backwater areas including amplification of erosion potential near the levee and within tidal passes during early summer floods. Increases in mean and peak flood levels on the order of 15–20 cm during local storm events were shown to extend as far as 20 km away from the floodway protection levee during both early and late summer local flooding scenarios. Low-lying areas closest to the levee were adversely affected during both the high (early summer) and low flow (late summer) periods of the annual discharge cycle. The approach and findings of this study are relevant for risk management in river basins around the world affected by NSFEs.

Four-decades of bed elevation changes in the heavily regulated upper Atchafalaya River, Louisiana, USA

Previous studies have established that under natural conditions, alluvial river confluence zones experience channel scour followed by mid-channel bar development. Less attention is given to bed evolution downstream of large alluvial river confluences under engineered conditions, such as discharge regulation and levee confinement. Here we present four decades of morphologic changes along the 69-km uppermost Atchafalaya River, a downstream distributary of the confluence of the Mississippi River Outflow channel and the Red River. We aim to find the answer to one critical question: how does the channel bed downstream of an engineering-controlled confluence respond to regulated flow? We utilize single-beam bathymetry data collected in 1967, 1977, 1989, 1998, and 2006 to quantify riverbed deformation of the reach after the flow regulation began in 1963. Suspended sediment load and stream power during the four decadal periods are calculated. Results show that between 1967 and 2006, extensive bed degradation occurred and the average bed elevation reduced by 3.8 m. A total volume of 105 ± 26 × 106 m3 sediment was scoured from the uppermost Atchafalaya riverbed over this 40-year period, implying that channel erosion in this river reach has contributed to downstream coarse sediment delivery and associated deltaic growth in the Atchafalaya Bay. Bed aggradation only occurred during 1989–1998 in response to excess sediment input from the Mississippi River, likely attributable to the 1993 long-lasting Mississippi River flood. But the same amount of riverbed deposit eroded in the following eight years, demonstrating how quickly a large regulated river can diminish a perturbation owing to excess sediment input. These findings not only reveal the complexity of morphologic adjustments of a river channel in response to intensive engineering disturbances but also provide useful information for future modeling studies and management plans for the Atchafalaya and other large, engineered alluvial river confluences.

Decreasing land growth and unique seasonal area fluctuations of two newborn Mississippi subdeltas

A total of 491 Landsat satellite images from 1973 to 2017 were used to study the evolution of two newborn subdeltas of the Mississippi-Atchafalaya system, the Wax Lake Delta (WLD) and the Atchafalaya Delta (AD). The exposed delta areas derived from the satellite images using an unsupervised classification method were applied to evaluate the long-term land growth and seasonal area variations in the WLD and AD, as well as their main influencing factors. The results show that the land growth rate of the WLD decreased relative to the mean sea level from 1.67 km2/year to 0.35 km2/year from 1983–1999 to 1999–2017, and the growth rate of the AD decreased from 1.51 km2/year to 0.80 km2/year from 1973–1999 to 1999–2017. The land building of the two subdeltas during the 1980s to 1999 was more efficient than that from 1999 to 2017. The significant decreases in the land growth rate and land building efficiency are attributed both to the increased impact from relative sea level rise and to the decrease in river sediment discharge, and the extension of the distributary channels, as well. The satellite-derived exposed areas of the WLD and AD show unique seasonal loops affected by the growth of vegetation during the warmer weather from April to June and the decay of vegetation mainly due to the cold fronts in December, which is different from the monotonic changes in the areas of other deltas, mainly driven by the rise and fall of water levels. A new method based on the correction between the exposed areas and water levels from December to April was used to estimate the vertical growth rates of the WLD and AD. After deducting the relative sea level rise rate, the net sediment deposition rates of the WLD and AD were estimated to be 20.8 and 24.2 mm/year, respectively. Approximately 72% and 62% of the sediments deposited in the WLD and AD were used to offset the effects of relative sea level rise when building deltaic lands from 1999 to 2017. This study not only improves our understanding of the growth of newborn subdeltas but also aids in assessing whether river course shifts and sediment diversions can restore deltas or deltaic wetlands that are at risk of drowning.

A Numerical Investigation of Wave‐Supported Gravity Flow During Cold Fronts Over the Atchafalaya Shelf

AbstractWave‐supported fluid mud (WSFM) plays an important role in sediment downslope transport on the continental shelves. In this study, we incorporated WSFM processes in the wave boundary layer (WBL) into the Community Sediment Transport Modeling System (CSTMS) on the platform of the Coupled Ocean‐Atmosphere‐Wave‐and‐Sediment Transport modeling system (COAWST). The WSFM module was introduced between the bottommost water layer and top sediment layer, which accounted for the key sediment exchange processes (e.g., resuspension, vertical settling, diffusion, and horizontal advection) at the water‐WBL and WBL‐sediment bed boundaries. To test its robustness, we adapted the updated model (CSTMS + WBL) to the Atchafalaya shelf in the northern Gulf of Mexico and successfully reproduced the sediment dynamics in March 2008, when active WSFM processes were reported. Compared with original CSTMS results, including WSFM module weakened the overall intensity of sediment resuspension, and the CSTMS + WBL model simulated a lutocline between the WBL and overlying water due to the formation of WSFM. Downslope WSFM transport resulted in offshore deposition (>4 cm), which greatly changed the net erosion/deposition pattern on the inner shelf off the Chenier Plain. WSFM flux was comparable with suspended sediment flux (SSF) off the Atchafalaya Bay, and it peaked along the Chenier Plain coast where wave activities were strong and the bathymetric slope was steep. The influence of fluvial sediment supply on sediment dynamics was limited in the Atchafalaya Bay. Sensitivity tests of free settling, flocculation, and hindered settling effects suggested that sediments were transported further offshore due to reduced settling velocity in the WBL once fluid mud was formed. Although sediment concentration in the WBL was sensitive to surface sediment critical shear stress, cohesive bed behavior was less important in WSFM dynamics when compared with strong hydrodynamic during cold fronts.

Monitoring Water Level Change and Seasonal Vegetation Change in the Coastal Wetlands of Louisiana Using L-Band Time-Series

Coastal wetlands are productive ecosystems driven by highly dynamic hydrological processes such as tides and river discharge, which operate at daily to seasonal timescales, respectively. The scientific community has been calling for landscape-scale measurements of hydrological variables that could help understand the flow of water and transport of sediment across coastal wetlands. While in situ water level gauge data have enabled significant advances, they are limited in coverage and largely unavailable in many parts of the world. In preparation for the NISAR mission, we investigate the use of spaceborne Interferometric Synthetic Aperture Radar (InSAR) observations of phase and coherence at L-band for landscape-scale monitoring of water level change and vegetation cover in coastal wetlands across seasons. We use L-band SAR images acquired by ALOS/PALSAR from 2007 to 2011 to study the impact of seasonal changes in vegetation cover on InSAR sensitivity to water level change in the wetlands of the Atchafalaya basin located in coastal Louisiana, USA. Seasonal variations are observed in the interferometric coherence ( γ ) time-series over wetlands, with higher coherence during the winter and lower coherence during the summer. We show with InSAR time-series that coherence is inversely correlated with Normalized Difference Vegetation Index (NDVI). Our analysis of polarimetric scattering mechanisms demonstrates that double-bounce is the dominant mechanism in swamps while its weakness in marshes hinders estimation of water level changes. In swamps, water level change maps derived from InSAR are highly correlated (r2 = 0.83) with in situ data from the Coastwide Reference Monitoring System (CRMS). From October to December, we observed that the water level may be below wetland elevation and thus not inundating wetlands significantly. Our analysis shows that water level can only be retrieved when both images used for InSAR are acquired when wetlands are inundated. The L-band derived-maps of water level change show large scale gradients originating from the Gulf Intracoastal Waterway rather than the main delta trunk channel, confirming its significant role as a source of hydrologic connectivity across these coastal wetlands. These results indicate that NISAR, with its InSAR observations every 12 days, will provide the measurements necessary to reveal large scale hydrodynamic processes that occur in swamps across seasons.

Changes to Subaqueous Delta Bathymetry Following a High River Flow Event, Wax Lake Delta, USA

The construction of the subaqueous delta front is foundational to deltaic land building and field data is needed to validate conceptual models of delta front evolution. The bathymetric change that occurred across the entire delta front (~ 75.9 km2) of the Wax Lake Delta (WLD) in coastal Louisiana was measured between February 2015 and July 2016. Sediment removal (− 9.85 × 106 m3) exceeded sediment accumulation (7.64 × 106 m3), making the delta front net-erosional (− 2.21 × 106 m3) despite the occurrence of a flood. These results factor in an estimated 4.28 cm of subsidence during the survey period. Deposition on the delta front was localized around channels and the northern and eastern flanks of the delta whereas erosion was more spatially uniform. This erosion coincides with an anomalously strong winter storm season that may have exported this sediment offshore and is consistent with a growing body of research that identifies winter storms as a significant mechanism for sediment removal from Atchafalaya Bay. Winter storm erosion is crucial to understanding and predicting volumetric growth of the WLD and has important implications to land building from sediment diversions. Future models of deltaic growth need to account for significant volume export and erosive episodes on the delta front.

Repackaging Louisiana’s Crawfish Production and Marketing to Generate Revenue and Employment

Louisiana accounts for 90% to 95% of the total U.S. production of Crawfish from year to year, either from wild waters of the state, or on farms. Even though, the commercial sales of crawfish in Louisiana date back to the late 1800s—the state is still actively engaged in crawfish industry to provide millions of pounds harvested from farms and natural waterways in the Bayou State. The harvesting of wild crawfish from natural habitats such as bayous, swamps and marshes provides a significant number of jobs for Louisiana residents. The Atchafalaya Basin is world famous for its crawfish production. More than 800 commercial fishermen harvest crawfish from wetlands, mostly in the Atchafalaya Basin. The governor making an attempt to set the favorable environment and also give incentives to the crawfish farmers may boost its production to add to the GDP of the economy. Because revenue generation and employment diversification are very critical to the state of Louisiana, this particular study is devoted to unearth the numerous repackaging techniques for Louisiana crawfish production and its marketing strategies to assist the state in diversifying or broaden its revenue base and employment avenues to ensure growth and development. As a result the study used 200 sample size of crawfish farmers across the state of Louisiana. To better inform policymakers, the study used binomial logistic regression to analyze the perceived determinants of crawfish production in Louisiana. The study found out that the Louisiana State can diversify its marketing strategies to employ more people to work on the promotion of the crawfish production in the state of Louisiana. The following marketing strategies (deployment, channel management, contact database, email marketing, event triggered actions, lead management, multi-campaign and the use of social media platform) revealed in the study to assist the state of Louisiana to improve upon it employment avenues through sales and also expected to generate more revenue for the state through taxes. The study reveals that crawfish farmers continue to be in business due to the following factors: price/profit, government regulations, transport assistance, and the market trends/demand for the product. The study further revealed that repackaging the Louisiana crawfish farming will lead to revenue generation, employment creation, cultural enrichment & promotion and also improve upon the export earnings associated with crawfish products. Above all, the study strongly recommends that the governors and the federal government should support the repackaging of the old marketing tools used by the farmers to adapt to the modern forms of sales-marketing in order to enhance more jobs creation and also promote the sales of the crawfish products to boost the nation’s GDP and revenue generation. Keywords : Employment, Revenue, Crawfish, Logistic Regression, Regulations, Sales, Cultural, and Transport DOI: 10.7176/JESD/11-12-05 Publication date: June 30th 2020

English

Abstract Anthropogenic modifications to river-floodplain systems can decouple floodplains from mainstem inputs, alter flood pulse dynamics, and disrupt population dynamics and trophic web stability of aquatic biota. The Atchafalaya River Basin (ARB) receives an annual flood pulse from the Mississippi River that contributes to high crayfish abundance. Conversely, reduced crayfish abundance in the Barataria Basin (BB) is attributed to the system no longer receiving an annual flood pulse from the Mississippi River. Therefore, the purpose of this research was to determine if the absence of an annual flood pulse and reduced crayfish abundance influenced the diets of carnivorous fishes by examining stomach contents of fishes from both basins. Stomach contents were grouped as crayfish, fish, non-crayfish invertebrate, and herpetological. Although the percent occurrence of crayfish in fish stomachs differed between floodplain inundation and low-water periods in the ARB, crayfish were still the major diet constituent of ARB fishes during both periods. Non-crayfish invertebrate was the major diet constituent in BB fishes, with crayfish ranking as the second fewest diet constituent present. Our results demonstrate how flood pulse dynamics influence crayfish, and ultimately trophic webs, in large river-floodplain systems.