Louisiana Wetlands Research Articles

Extracting Wetlands in Coastal Louisiana from the Operational VIIRS and GOES-R Flood Products

Visible Infrared Imaging Radiometer Suite (VIIRS) and Advanced Baseline Imager (GOES-R ABI) flood products have been widely used by the National Weather Service (NWS) for river flood monitoring, and by the Federal Emergency Management Agency (FEMA) for rescue and relief efforts. Some water bodies, like wetlands, are detected as water but not marked as permanent or normal water, which may result in their misclassification as floodwaters by VIIRS and GOES-R flood products. These water bodies generally do not cause significant property damage or fatalities, but they can complicate the identification of truly hazardous floods. This study utilizes the severe Louisiana flood event caused by Hurricane Ida to demonstrate how to differentiate wetlands from real-hazard flooding. Since Hurricane Ida made landfall in 2021, and there was no major flood event in 2022, VIIRS and ABI flood data from 2021 and 2022 were selected. The difference in annual total flooding days between 2021 and 2022 was calculated and combined with long-time flood frequency to distinguish non-hazard floodwaters due to wetlands identified from real-hazard floods caused by the hurricane. The results were compared with the wetlands from the change detection analysis. The confusion matrix analysis indicated an accuracy of 91.58%, precision of 89.97%, and F1-score of 76.63% for the VIIRS flood products. For the GOES-R ABI flood products, the confusion matrix analysis yielded an accuracy of 86.88%, precision of 97.49%, and F1-score of 75.21%. The accuracy and F1-score values for the GOES-R ABI flood products are slightly lower than those for the VIIRS flood products, possibly due to their lower spatial resolution, but still within a feasible range.

Integrating NDVI-Based Within-Wetland Vegetation Classification in a Land Surface Model Improves Methane Emission Estimations

Earth system models (ESMs) are a common tool for estimating local and global greenhouse gas emissions under current and projected future conditions. Efforts are underway to expand the representation of wetlands in the Energy Exascale Earth System Model (E3SM) Land Model (ELM) by resolving the simultaneous contributions to greenhouse gas fluxes from multiple, different, sub-grid-scale patch-types, representing different eco-hydrological patches within a wetland. However, for this effort to be effective, it should be coupled with the detection and mapping of within-wetland eco-hydrological patches in real-world wetlands, providing models with corresponding information about vegetation cover. In this short communication, we describe the application of a recently developed NDVI-based method for within-wetland vegetation classification on a coastal wetland in Louisiana and the use of the resulting yearly vegetation cover as input for ELM simulations. Processed Harmonized Landsat and Sentinel-2 (HLS) datasets were used to drive the sub-grid composition of simulated wetland vegetation each year, thus tracking the spatial heterogeneity of wetlands at sufficient spatial and temporal resolutions and providing necessary input for improving the estimation of methane emissions from wetlands. Our results show that including NDVI-based classification in an ELM reduced the uncertainty in predicted methane flux by decreasing the model’s RMSE when compared to Eddy Covariance measurements, while a minimal bias was introduced due to the resampling technique involved in processing HLS data. Our study shows promising results in integrating the remote sensing-based classification of within-wetland vegetation cover into earth system models, while improving their performances toward more accurate predictions of important greenhouse gas emissions.

An integrated methodology for assessing ecosystem response to environmental stressors under changing climatic conditions in coastal wetlands

Three cores were taken along the salinity gradient (n-s) in the coastal wetlands of Louisiana; an intermediate marsh, a brackish marsh, and a mangrove swamp. The cores display remarkable stratigraphic and chronologic correlations, representing six successive ecosystems and environments, namely: interdistributary bay, freshwater marsh/swamp, deltaic lake, freshwater marsh/swamp, intermediate marsh, and brackish/saline. Sedimentary, geochemical, and palynological data were used to reconstruct the paleoenvironments, including ambient environment and ecosystem types. Concentrations of Ba and Br, along with six elemental ratios (Ca/Rb, Zr/Rb, Ti/Rb, K/Ti, Mn/Rb, S/Rb), were employed to infer proxies for a range of environmental conditions (waterlogging, redox levels), depositional processes (fluvial vs marine or in situ), and sediment characteristics (grain size). Correlating the identification of environment types, inferred depositional processes, and the known history of the Mississippi delta cycle with the ecosystem reconstruction provides insight into ecosystem response to a variety of stresses, which information can be used to better understand and predict present and future responses to the ongoing stresses. Additionally, a simple elemental ratio (Zr/Rb) was used to produce a continuous (2 cm resolution) estimate of grain size along the length of the cores. The close correlation between the estimated grain size and measured samples shows that this ratio is a valid method for quickly assessing rough grain size, and is especially useful for identifying sedimentary inflection points.

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.

Biological control of invasive floating fern leads to rapid recovery of ecological functions in coastal fresh water wetlands in Louisiana

Biological control of invasive floating fern leads to rapid recovery of ecological functions in coastal fresh water wetlands in Louisiana

Indigenous Removal and (Un)Recognition in the Plantationocene: Documenting Louisiana's Rising Waters

ABSTRACT: In the 2012 documentary, My Louisiana Love , United Houma Nation (UHN) artist and activist Monique Verdin shares maps that display how her tribe was forced into the wetlands of south Louisiana by settler colonialism (5:40-6:00). In Can't Stop the Water (2014), a documentary about the Isle de Jean Charles Band of Biloxi-Chitimacha-Choctaw (BCC), the tribe dubbed America's "first climate refugees" by The New York Times , Chief Albert Naquin describes his community as made up of "refugees from the Trail of Tears" (4:29-4:35). The issues of subsidence, seawater intrusion from canals dug by gas and oil companies, and rising waters impact all of south Louisiana's residents, yet the state's coastal Indigenous peoples whose cultures and economies are directly tied to the diminishing land are most immediately affected. My Louisiana Love and Can't Stop the Water address these issues within the Indigenous communities at the center of their narratives, communities with a legacy of displacement directly resulting from Plantationocene practices who are forced to consider relocation again in the near future. These documentaries unblinkingly indict the petroleum industry, underscoring the ways it has participated in the destruction of the Gulf Coast with little involvement in its restoration. This article analyzes the efficacy of the films in portraying the challenges faced by their communities and the activism each work depicts and engenders, as well as illuminates the role that southeastern Indigenous Louisianans have played and continue to play in the Plantationocene.

Indigenous Removal and (Un)Recognition in the Plantationocene: Documenting Louisiana's Rising Waters

ABSTRACT: In the 2012 documentary, My Louisiana Love , United Houma Nation (UHN) artist and activist Monique Verdin shares maps that display how her tribe was forced into the wetlands of south Louisiana by settler colonialism (5:40-6:00). In Can't Stop the Water (2014), a documentary about the Isle de Jean Charles Band of Biloxi-Chitimacha-Choctaw (BCC), the tribe dubbed America's "first climate refugees" by The New York Times , Chief Albert Naquin describes his community as made up of "refugees from the Trail of Tears" (4:29-4:35). The issues of subsidence, seawater intrusion from canals dug by gas and oil companies, and rising waters impact all of south Louisiana's residents, yet the state's coastal Indigenous peoples whose cultures and economies are directly tied to the diminishing land are most immediately affected. My Louisiana Love and Can't Stop the Water address these issues within the Indigenous communities at the center of their narratives, communities with a legacy of displacement directly resulting from Plantationocene practices who are forced to consider relocation again in the near future. These documentaries unblinkingly indict the petroleum industry, underscoring the ways it has participated in the destruction of the Gulf Coast with little involvement in its restoration. This article analyzes the efficacy of the films in portraying the challenges faced by their communities and the activism each work depicts and engenders, as well as illuminates the role that southeastern Indigenous Louisianans have played and continue to play in the Plantationocene.

Assessing impacts of climate change on selected foundation species and ecosystem services in the South‐Central USA

AbstractClimate change, interacting with and exacerbating anthropogenic modifications to the landscape, is altering ecosystem structure and function, biodiversity, and species distributions. Among the most visible short‐term impacts are the altered ecological roles of foundation species—those species, native or non‐native—that create locally stable environmental conditions and strongly influence ecosystem services. Understanding the future of these species is crucial for projecting impacts on ecosystem services at both local and regional scales. Here we present foundation species by ecoregion study cases across the US South‐Central Region (Louisiana, New Mexico, Oklahoma, and Texas), including C4grasses, mesquite, and northern bobwhite in the Southern Great Plains, mangroves and nutria in coastal Louisiana wetlands, tiger salamanders and sandhill cranes in wetlands of the Southern Great Plains, and post and blackjack oaks and eastern redcedar in the Cross Timbers ecoregion. These case studies explore the impacts of climate change on foundation species and the consequences for ecosystem services, the outlook for climate adaptation efforts, and the sustainability of restoration in these systems. We underscore risks and vulnerabilities that stakeholders should consider when managing or restoring natural resources and conserving ecosystem services in an increasingly extreme and variable climate. We show that past management, through a lack of understanding or implementation of actions, has exacerbated shifts in invasive species, resulting in significant changes in ecosystem structure and function. These changes, interacting with landscape fragmentation and shifting land use and exacerbated by climate change, can result in critical losses of biodiversity. Unfortunately, lack of public understanding may hinder political support for restoration efforts and climate adaptation strategies crucial for the continued supply of traditional ecosystem services. Furthermore, the resulting invaded systems may provide opportunities for income via new ecosystem services valued by society that may reduce support for restoration to historical baselines, thus further shifting management priorities. These priorities should be informed by an understanding of past and ongoing ecological trends in region‐specific situations, such as those we present, to highlight the immediacy of climate change impacts on the environment and society and provide evidence for the critical nature of informed management decisions.

Disturbance legacies and shifting trajectories: Marsh soil strength and shoreline erosion a decade after the Deepwater Horizon oil spill

Marsh resilience post disturbance is strongly dependent on the belowground dynamics affecting the emergent plants aboveground. We investigated the long-term impacts at the marsh-water interface in coastal wetlands of south Louisiana after the 2010 Deepwater Horizon oil spill with a combination of fieldwork (2010–2018) and spatial analysis (1998–2021). Data were collected on shoreline erosion rates, marsh platform elevation heights and cantilever overhang widths, and soil strength up to 1 m depth. Oil concentration in the top 5 cm of the marsh soil were determined using gas chromatography/mass spectrometry and were 1000 times higher than before the spill and remained 10 times higher eight years post-oiling. The oiling initially caused the marsh edge to subside, and chronic effects lowered soil strength, creating a faster erosion rate and deeper water within 150 cm of the shoreline. Soil strength declined by 50% throughout the 1 m soil profile after oiling and has not recovered. The mean erosion rate for 11 years post-spill was double that before oiling and there was an additive impact on erosion rates after Hurricane Isaac. Erosion appeared to have recovered to pre-spill rates by 2019, however from 2019 to 2021, the rate increased by 118% above the pre-spill rate. The continuing loss of soil strength indicates that the belowground biomass was seriously compromised by oiling. The perpetuation of oil in the remaining marsh may have set a new baseline for soil strength and subsequent storm induced erosional events. The remaining marsh soils retain chronic physical and biological legacies compromising recovery for more than a decade that may be evident in other marsh habitats subject to oiling and other stressors.

Restoration otherwise: Towards alternative coastal ecologies

This article considers how to rethink ecological restoration as a process tethered to ongoing formulations of racial and environmental justice. It is situated in the context of coastal Louisiana's wetland loss crisis and the state's unprecedented investment in large-scale wetland restoration projects as a technoscientific fix that comes at the expense of several small, Black and Indigenous bayou communities. Critical of approaching restoration as a practice predicated on loss and return, this article builds upon scholarship in Black and Indigenous ecologies and ethnographic fieldwork among Black coastal communities in southeast Louisiana to reimagine restoration as an intergenerational, socioecological set of practices grounded in cultivating cultural continuity and community care across time and space. Working with the Black feminist geographic concepts of the plot and the shoal, the article develops the notion alternative restorations—or restoration otherwise—around three reformulations of restoration: As a practice of cultural continuity, as a mode of cultivating self-reliance, and as a scientific practice of integrity and humility. It concludes by reflecting the ways Black ecological practices and values can shift the course of restoration science toward sustaining Black life in the era of climate change.

Thermodynamic stabilities of apatite phases in a wetland system: Implications for bone diagenesis

Evaluating the fate and stability of apatite minerals, the largest phosphorus (P) reservoir on Earth's surface, has direct consequences for understanding our vertebrate fossil record as well as biogeochemical cycling. Bone (bioapatite) deposited following the death of an animal represents a potential source of phosphorus in terrestrial and aquatic ecosystems for micro and macrofauna. Exposure of bone to ambient geochemical conditions also represents the first step of the fossilization process. However, the thermodynamic stability of bone in these ecosystems, which are frequently phosphorus-limited, is unknown. The goal of this study was to approach questions related to recrystallization, diagenesis, and fossilization from a thermodynamics perspective, focusing on the role of geochemistry on bioapatite (bone) preservation. By developing thermodynamic models, run using PHREEQC, the stabilities of a range of apatite and other phosphorus-bearing phases were considered under physiochemical conditions measured in a Louisiana wetland and an adjacent river. The models integrated variable temperatures (5–40 °C), concentrations of phosphorus ([PO43-] from 0.0006 to 0.0484 mmol/L), and pH (6.5–9.25) from representative waters collected over 3 years at the wetland. In all models, waters are undersaturated with respect to hydroxylapatite, except under the highest temperatures, [PO43-], and pH conditions. In contrast, fluorapatite approached stability under lower pH and temperatures, and carbonated fluorapatite exhibited a broad range of stable conditions. These results suggest that if bioapatite (bone) were deposited under these present-day conditions, solutions are predicted to be undersaturated with respect to many apatite phases, leading to mineral dissolution. However, if bioapatite undergoes substitutions forming a fluorinated and/or carbonated phase, stability may shift towards preservation. These results have implications for identifying potential biases and mechanisms driving bone preservation over geologic time in a wetland system. The modeling results demonstrate that preservation of bone is favored under subsurface (burial) rather than surface conditions, aligning with long-held views on the formation of our vertebrate fossil record.

The effects of external forcing agents on the biodiversity and species richness associated with the environmental history of Louisiana's wetlands over the late Holocene

This study evaluates plant diversity and species richness levels and reconstructs the environmental history of a site near Little Lake in southeast Louisiana, USA over the past 3200 years. Six successive ecosystems occurred as a result of changing environmental conditions, ranging from the local (anthropogenic activities), regional (delta lobe switching), and to global (sea level rise): interdistributary bay (3.2–2.3 cal kyr BP), hydrophytic freshwater marsh (2.3–1.42 cal kyr BP), mesophyte coastal prairie (1.42–0.92 cal kyr BP), Typha marsh (0.92–0.33 cal kyr BP), intermediate marsh (0.33 cal kyr Bp – ad, 1972 CE), brackish marsh (197 CE2-present). Biodiversity was evaluated for each ecosystem, with maximum diversity occurring during the period of maximum delta-growth as the river dynamics increased landscape heterogeneity by creating diverse habitats, including marsh, swamps, oxbow lakes, and natural levees, while the transgressive phase presents the lowest biodiversity due to increasing salinity. Multivariate analysis is used to identify the primary depositional processes for each stage and infer the proximate forcing agents(s). Early ecosystem shifts were controlled by the stages of the delta cycle, while more recent shifts are associated with anthropogenic activities and the effects of global climate change such as sea-level rise, and more intense tropical cyclones.

Improving Channel Hydrological Connectivity in Coastal Hydrodynamic Models With Remotely Sensed Channel Networks

AbstractCoastal wetlands are nourished by rivers and periodical tidal flows through complex, interconnected channels. However, in hydrodynamic models, channel dimensions with respect to model grid size and uncertainties in topography preclude the correct propagation of tidal and riverine signals. It is therefore crucial to enhance channel geomorphic connectivity and simplify sub‐channel features based on remotely sensed networks for practical computational applications. Here, we utilize channel networks derived from diverse remote sensing imagery as a baseline to build a ∼10 m resolution hydrodynamic model that covers the Wax Lake Delta and adjacent wetlands (∼360 km2) in coastal Louisiana, USA. In this richly gauged system, intensive calibrations are conducted with 18 synchronous field‐observations of water levels taken in 2016, and discharge data taken in 2021. We modify channel geometry, targeting realism in channel connectivity. The results show that a minimum channel depth of 2 m and a width of four grid elements (approximatively 40 m) are required to enable a realistic tidal propagation in wetland channels. The optimal depth for tidal propagation can be determined by a simplified cost function method that evaluates the competition between flow travel time and alteration of the volume of the channels. The integration of high spatial‐resolution models and remote sensing imagery provides a general framework to improve models performance in salt marshes, mangroves, deltaic wetlands, and tidal flats.

Strategic approaches to sediment management for restoration of a deltaic plain

Sediment resources are essential to fulfill the State of Louisiana’s commitment to implement a Coastal Master Plan (CMP) to mitigate its chronic land loss, protect more than 2 million people who live in the coastal zone, and to save Louisiana’s rapidly disappearing complex and fragile ecosystem. With increasing rates of sea level rise and increased storm intensities along with continuing subsidence, the future quantity of sediment needed for ecosystem restoration will significantly increase, and at the same time, the accessibility to the sediment resources will become much more technologically challenging and cost prohibitive. These devastating environmental circumstances will compound the complexities of a sustainable ecosystem restoration in coastal Louisiana. Restoration projects must be robust enough (using adequate compatible sediment) to survive future environmental scenarios while the quantity of actively captured sediment resources available for critical restoration projects is likely to decrease, rendering the dredging and transporting of these sediment resources increasingly difficult and costly. These challenges will be an opportunity for Louisiana to utilize more sustainable, passively captured sediment (i.e. using large sediment diversions from the Mississippi River) to help offset limitations concerning actively harvesting sediment and to build and sustain wetlands in coastal Louisiana. Although any large-scale and meaningful restoration of the Louisiana coastal plain must involve sediments from the Mississippi River, the scope of this paper is restricted to offshore sediment resources. A strategic approach to optimize utilization of sediment resources includes minimizing handling and transport costs by first locating potential sediment sources and then identifying the most cost-effective way of using that sediment resource for restoration. The project cost and its success are defined by the sediment selection process. Thus, it is suggested that improvements in planning and management of multiple-use conflicts be based on regional understandings of sediment resources for an approach that maximizes benefits. The Louisiana Sediment Management Plan (LASMP) was conceptualized and formulated to improve planning and coordination of sediment utilization in Louisiana. This plan has evolved and has been adaptively managed in the absence of any prototype. Restoration activities are further complicated by competing interests and multiple uses of limited sediment resources. To maximize the availability of offshore sediment, the state is collaborating with the Bureau of Ocean Energy Management (BOEM) and engaging with other stakeholders in deciding the fate of decommissioned pipelines and to strategically plan the installation of new pipelines in offshore areas identified as significant sediment resources with the intent of protecting identified sediment resources for future use. Future offshore wind-farms may pose new challenges but simultaneously offer opportunities for conflict resolution via stakeholder engagement. For the past two decades the State of Louisiana/Coastal Protection and Restoration Authority (CPRA) of Louisiana has developed a considerable institutional knowledge base and expertise and improved the art and science of sediment management. A robust process has been adaptively developed with interagency collaboration and coordination to resolve conflicts/issues concerning obstacles to resource access. LASMP is not only a template for sediment management for coastal restoration, but also provides guidance for stakeholder engagement and conflict resolution for competing needs of seafloor resources especially in Northern Gulf of Mexico (NGOM).

The "Impassable Morass" in Translation: Louisiana's Wetlands, Chateaubriand's Atala, and the Aesthetics of Colonial Ambivalence

In 1682, La Salle claimed for France all the countries watered by the Mississippi and named them Louisiana. Over the next century, as published accounts of this territory proliferated in the Atlantic world, it was described simultaneously as a "New Eden" and an "impassable morass," while colonial observers also speculated about its potential as a pastoral middle ground. Freely adapting such accounts into his own prose, Chateaubriand composed in Atala, ou les amours de deux savages dans le désert (1801) a likewise ambivalent picture of the region. This essay locates the novella at a narrative intersection of several of these descriptive accounts and argues that it provides a literary node for examining the hemispheric text-network that documented and translated Louisiana's settlement within an uneasy, yet increasingly coherent wetlands discourse. This process of translation is linguistic, as English and Spanish editions of Atala began circulating soon after its publication, but it is also the founding matter of the novella. While a landmark of French fiction, Atala's aesthetic appeal cannot be uncoupled from the environmental and topographical specificity of its source material, and in this light the novella is also an early American text in translation, one that is itself a melancholy document of the colonial project.

Temporal variability in the relative strength of external drivers controlling ecosystem succession in a coastal wetland near Bayou Lafourche, southeast Louisiana, USA

The coastal wetlands of Louisiana are extremely dynamic due to their location on the edge of the continent, the heavy but spatially and temporally variable influence of the discharge of the Mississippi River, and the effects of both chronic (sea-level rise, coastal retreat) and abrupt (hurricanes, lobe switching) stressors. In these coastal wetlands the timing and mode of ecological succession can result from a variety of external factors and vary from sudden to gradual. This paper uses a palynology-based multi-proxy analysis of sediment cores retrieved from a small pond on a mangrove-dominated island in Bay Champagne near Port Fourchon, Louisiana to describe and date the successive ecosystems that have covered this site since 4000 BP and applies a PCA-based interpretation to infer the drivers responsible for each shift. During the late Holocene, the most important controlling agents have been the Mississippi River delta development, sea-level rise, climatic variability, shoreline retreat, tropical cyclones, and, more recently, anthropogenic effects. These processes have progressively transformed the site from a freshwater to a saline environment, consisting of four distinct ecosystems: a Taxodium-Nyssa freshwater forest (4.0–1.3 cal yr BP), a Typha-Bacopa freshwater deltaic-lake (1.3–0.7 cal yr BP), an intermediate and brackish marsh (0.7–0.2 cal yr BP), a Spartina-dominated saline marsh (since 0.2 cal yr BP), and a short-stature Avicennia forest since the early 1900s. The Mississippi River delta cycle (lobe switching) was the dominant driver of ecosystem changes early in the site's history, while relative sea-level rise, shoreline retreat, tropical cyclones, climate, and anthropogenic effects have been the main drivers since the 19th century.

Using rapid repeat SAR interferometry to improve hydrodynamic models of flood propagation in coastal wetlands

The propagation of tides and riverine floodwater in coastal wetlands is controlled by subtle topographic differences and a thick vegetation canopy. High-resolution numerical models have been used in recent years to simulate fluxes across wetlands. However, these models are based on sparse field data that can lead to unreliable results. Here, we utilize high spatial-resolution, rapid repeat interferometric data from the Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) to provide a synoptic measurement of sub-canopy water-level change resulting from tide propagation into wetlands. These data are used to constrain crucial model parameters and improve the performance and realism of simulations of the Wax Lake wetlands in coastal Louisiana (USA). A sensitivity analysis shows that the boundary condition of river discharge should be calibrated first, followed by iterative correction of terrain elevation specified originally by a Digital Terrain Model derived from LiDAR measurements. The calibration of bed friction becomes important only with the boundary and topography calibrated. With the model parameters calibrated, the overall Nash-Sutcliffe model efficiency for water-level change increases from 0.15 to 0.53 with the RMSE reduced by 26%. In areas with dense wetland grasses, the LiDAR signal is unable to reach the soil surface, but the L-band UAVSAR instrument detects changes in water levels that can be used to infer the true ground elevation. The high spatial resolution and repeat-acquisition frequency (minutes to hours) observations provided by UAVSAR represent a groundbreaking opportunity for a deeper understanding of the complex hydrodynamics of coastal wetlands.

Biogeochemical and Hydrological Variables Synergistically Influence Nitrate Variability in Coastal Deltaic Wetlands

AbstractCoastal river deltas are centers of surface water nitrate processing, yet the mechanisms controlling spatio‐temporal patterns in nutrient variability are still little understood. Nitrate fluctuations in these systems are controlled by complex interactions between hydrological and biogeochemical drivers, which act together to transport and transform inorganic nutrients. Distinguishing the contributions of these drivers and identifying wetland zones where nitrate processing is occurring can be difficult, yet is critical to make assessments of nutrient removal capacity in deltaic wetlands. To address these issues, we analyze relationships among regional “external” (river discharge, tides, wind) and local “internal” (water level, temperature, turbidity, and nitrate) variables in a deltaic wetland in coastal Louisiana by coupling a process connectivity framework with information theory measures. We classify variable interactions according to whether they work uniquely, redundantly, or synergistically to influence nitrate dynamics and identify timescales of interaction. We find that external drivers work together to influence nitrate transport. Patterns of hydrological and sediment connectivity change over time due to tidal flushing and discharge variation. This connectivity influences the emergence of functional zones where local nitrate fluctuations and temperature and water level process couplings are strong controls on nitrate variability. High vegetation density decreases hydrological process connectivity, even during periods of high river discharge, but it also increases biogeochemical process connections, due to the lengthening of the hydraulic residence time. Based on these results we make recommendations for monitoring nitrate in a wetland.

Hydrologic Restoration of the Lac des Allemands Swamp, Barataria, Louisiana

Most of the forested wetlands of coastal Louisiana are in decline, primarily due to impoundment and increased flood duration. The Lac des Allemands swamp of Barataria Basin was a prime example of prolonged inundation prior to hydrologic restoration completed in February of 2018; the swamp had been impounded for over 60 years. To characterize restoration benefits, eight paired 625 m2 permanent sites were established close to and halfway between eight 30 m × 122 m gaps cut into the spoil bank of Bayou Chevreuil. During 2018, canopy closure increased by 20%. In addition, aboveground production of wood and leaves increased over 2017 from 2018–2020. Furthermore, natural regeneration has occurred annually and many of the seedlings are now approximately 1 m tall. In conclusion, hydrologic restoration of impounded wetlands in coastal Louisiana is an extremely cost-effective landscape restoration method.

Holocene environmental history of a freshwater wetland in southern Louisiana: a sedimentary record of delta development, coastal evolution and human activity

AbstractThe world's most extensive and active deltas, Louisiana's wetlands, are deteriorating rapidly due to multiple stressors. Their ecological and anthropogenic histories on a multimillennial timescale have not been thoroughly documented. This study investigates hydrological and anthropogenic impacts on southern Louisiana wetlands to guide future efforts toward environmental restoration. A 3.6 m sediment core (JOYWMA) extracted from a freshwater wetland adjacent to Lake Pontchartrain yielded a 5000‐year record. Multiproxy data indicate four distinct stages, with the earliest period representing an oyster reef (~4.5 cal yr bp) marked by elevated Ca and Sr concentrations. Evolution to a freshwater marsh occurred 4.5–4.0 cal yr bp during the St. Bernard delta progradation, marked by increased Zr and Br concentrations. The site transitioned to a lake due to the isolation from the St. Bernard delta and local subsidence (4.0–2.0 cal yr bp), marked by increased Ti, Fe, Mn and K concentrations. The site altered to a cypress swamp after 2.0 cal yr bp due to increased sediment supply during the St. Bernard subdelta progradation. Both natural (delta progradation and subsidence) and anthropogenic (fire, deforestation) stressors have impacted the site over the last 4500 years. Delta‐switching of the Mississippi River caused the significant geomorphological and ecological changes.