Search Results (11)

Coastal Louisiana continues to experience rapid wetland loss, increasing the exposure of marsh-creation containment dikes to storm-driven waves, erosion, and sediment loss. This study evaluated offshore-to-nearshore wave transformation, erosion risk reduction, wave runup, and hydrodynamic loading at a representative marsh-creation site in Plaquemines Parish, Louisiana. A 25-year return-period offshore wave condition was derived from long-term Wave Information Study hindcast data and propagated using the SWAN spectral wave model. Two idealized foreshore conditions were examined: a bare-bed case and a marsh-roughened shallow water case represented through enhanced bottom friction. Web Soil Survey data were used to characterize the local soil context of the containment-dike zone. The results show strong wave attenuation across the inner shelf and marsh platform. Relative to the bare-bed case, marsh roughness reduced dike toe significant wave height by 16.1–27.4% and decreased the Hs²-based erosion exposure proxy by 29.6–47.4% across three still-water levels. These reductions produced 15.4–26.4% lower 2% exceedance runup and 28.5–45.8% lower quasi-hydrostatic loading on the containment dike. The results indicate that marsh-induced dissipation can help reduce erosion potential and support sustainable coastal restoration infrastructure management. Full article

Coastal tidal flat soil organic carbon (SOC) is significantly affected by reclamation activities. However, the limited availability of historical SOC data constrains the reconstruction of past SOC. SOC data were integrated in current time-point and remote sensing data during the last two decades by applying machine learning (ML) methods such as random forest (RF), boosted regression trees (BRT), and extreme gradient boosting (XGBoost) to map the spatiotemporal distribution of tidal flat reclamation and the spatial distribution of SOC content in the western coastal region of the Bohai Rim over the last two decades and to explore how the period and type of reclamation affect SOC content. The results show that: (1) The area of tidal flats decreased by 61.92% from 2000 to 2020 due to reclamation activities. (2) Among the ML methods, the XGBoost model demonstrated the best performance (R² = 0.71, MAE = 0.93 g/kg, RMSE = 1.32 g/kg, d-Willmott = 0.98), with the modified normalized difference water index (MNDWI) being the most important predictor variable. (3) The SOC content of tidal flats decreased from 4.11 g/kg in 2000 to 3.33 g/kg in 2020, a reduction of 18.98%. (4) The reclamation of tidal flats into marshes, forest lands, grasslands, farmlands, and bare lands led to an increasing trend in SOC content, with the greatest increase observed in regions converted to farmlands. This study provides data support for the control of reclamation activities, creation of tidal flat conservation policies, and strategic decision-making for climate change mitigation. Full article

In Louisiana’s marsh creation projects designed to mitigate wetland loss, riverine sediments are hydraulically dredged and transported through pipelines. These dredged materials are extremely soft, with moisture contents well above 100%, resulting in significant consolidation settlements even under minimal self-weight loads. Conventional one-dimensional (1-D) oedometer consolidation tests are commonly used to assess consolidation behavior; however, they are limited to soils with much lower moisture contents. At higher moisture levels, the soft slurry tends to overflow due to the weight of the standard stainless-steel dial cap and porous stone, which together apply a seating pressure of 1.07 kPa (0.01 TSF). This study presents a modified oedometer setup utilizing 3D-printed dial caps made from lightweight materials such as polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS), reducing the seating pressure to 0.21 kPa (0.002 TSF). This modification enables the testing of dredged soils with moisture contents up to 100% without overflow. Settling column tests were also integrated with the modified oedometer tests, allowing for the development of void ratio–effective stress relationships spanning from 0.02 kPa (0.0002 TSF) to 107.25 kPa (1 TSF). The results demonstrate that combining settling column and modified oedometer tests provides an effective approach for evaluating the consolidation behavior of high-moisture slurry soils. Full article

This research focused on studying the soil improvement ability provided by the roots of smooth cordgrass, Spartina alterniflora, flourishing in the dredged soil of the Sabine Refuge Marsh Creation Project in the coastal area of Louisiana, USA. Vane shear tests were conducted in the created marshland to obtain the in situ undrained shear strength of the soil vegetated with Spartina alterniflora. Direct shear tests were performed on undisturbed rooted soil samples to investigate the overall effect of the roots on soil shear strength. Laboratory tensile tests were conducted on the roots of Spartina alterniflora to estimate their tensile strength. In this research, the W&W model and the fiber bundle model (FBM), were adopted, and modified ones were proposed to study the correlation between root-enhanced soil cohesion and the nominal tensile strength of the roots. The model outcomes were compared with field and laboratory measurements. The research results showed that the roots of Spartina alterniflora significantly increased soil shear strength, with an increase in cohesion of up to 130% at one location. The increases varied at different locations depending on the root area ratio (RAR), soil sample depth, and root tensile strength. Full article

Marshlands in arid and semi-arid areas are considered constantly changing environments due to unsecured water supplies as a result of high evapotranspiration and limited and highly variable rainfall. Classification of marshlands in these regions and mapping of their land cover is not an easy task and maps need to be upgraded frequently. Satellites provide enormous amounts of information and data for the continuous monitoring of changes. The aim of this paper is to introduce an approach using multispectral satellite imagery that was adopted to classify and monitor the Al Hammar Marsh (Iraq) over several years and to suggest a relationship between the Normalized Difference Vegetation Index (NDVI), the Normalized Difference Moisture Index (NDMI), and the Normalized Difference Water Index (NDWI), using Landsat 8 data with a resolution of 30 m × 30 m, validated with Sentinel-2 datasets at 10 m × 10 m. Six land cover classes were used: (1) open water, (2) dry area, (3) dense vegetation, (4) medium-density vegetation, (5) sparse vegetation, and (6) wet soil. Three indices, NDWI, NDMI, and NDVI, were chosen for the automatic classification of each pixel and the creation of a time series of land cover maps. The proposed method can efficiently classify and monitor marshlands and can be used to study different marshlands by adjusting the thresholds for NDVI, NDMI, and NDWI. Overall, the correlation for all classes (R) between Landsat 8 and Sentinel-2 is about 0.78. Thus, this approach will help to preserve marshes through improved water management. Full article

Sea level rise increases the pressure on many coastlines to retreat landwards which will lead to coastlines previously held in position through management, being allowed to retreat where this is no longer affordable or sustainable. Barrier beaches have historically rolled back in response to different hydrodynamic events and sea level rise, but very little is known as to how quickly and how far roll-back is going to occur once management has ceased. Data from more than 40 topographical surveys collected over 7 years along the 1.5 km long, almost swash-aligned shingle barrier at Medmerry (southern England) are used together with hydrodynamic data in a wide-ranging assessment of barrier roll-back. This study shows that roll-back is progressing through time along the barrier in downdrift direction in response to a gradual reduction in cross-sectional area through longshore transport. The Barrier Inertia concept provides a practical means to assess stability/instability for events experienced, but also a tool to assess the short- to medium term risk to the coast downdrift of the immediate study area where flood risk still needs to be managed. Roll-back is influenced particularly by the creation of an artificial tidal breach and removal of its sediment, the elevation of the underlying marsh and clay sediments, the number and severity of storms experienced and the presence of legacy groynes; roll-back has exceeded modelled predictions and expert judgement by an order of magnitude. Full article

Here we review an extensive series of studies of Barataria Basin, an economically and ecologically important coastal basin of the Mississippi Delta. Human activity has greatly altered the hydrology of the basin by decreasing riverine inflows from leveeing of the river and its distributaries, increasing runoff with high nutrient concentrations from agricultural fields, and channelization of wetlands of the basin interior that has altered flow paths to often bypass wetlands. This has resulted in degraded water quality in the upper basin and wetland loss in the lower basin. Trophic state analysis found the upper basin to be eutrophic and the lower basin to be mesotrophic. Gross aquatic primary production (GAPP) was highest in the upper basin, lowest in the mid basin, and intermediate in the lower basin. Forested wetlands in the upper basin have degraded over the past several decades due to increased periods of flooding, while there has been massive loss of emergent wetlands in the lower basin due to increasing water levels and pervasive alteration of hydrology. Restoration will entail reconnection of waterways with surrounding wetlands in the upper basin, and implementation of river sediment diversions, marsh creation using dredged sediments and barrier island restoration. Findings from this review are discussed in terms of the functioning of deltas globally. Full article

Levee construction aboveground and hydrocarbon removal from belowground in coastal wetlands can create hydrologic changes that increase plant stress through flooding. But the significance of the subsidence they cause individually or in combination is contested. This study untangled them to demonstrate elevational limits of salt marshes by studying dredged and natural waterways in two salt marshes in Louisiana, USA. The areas had a homogenous plant cover before drilling for oil and gas extraction peaked in the 1960s, and now are a mixed network of natural waterways and dredged canals used to drill wells with an average drill date of 1965.8 ± 2.7 (µ ± 1 SEM; n = 18) and well depth of 4661.0 m ± 56.6 (µ ± 1 SEM; n = 18). Aerial imagery was used to document how canals widened to become 2 to 4 times larger than their original construction width at the high production site and 50% larger at the low production site, whereas increases at the nearby natural channels were much less. Light detection and ranging (LIDAR) measurements at the high production site from 2002 showed that the marsh surface near wells subsided by 34 cm compared to undredged sites. Elevation in marshes at producing and dry wells were equal at the low production site, but high production well locations were even lower than at dry wells. An elevation vs. percent open water curve developed from these data overlapped with an independent analysis of a brackish marsh. A relative subsidence rate between 7.4 to 10.4 mm y⁻¹ transformed these salt marshes to an open water habitat within a few decades. The local creation of accommodation space through hydrocarbon removal and leveed wetlands is a parsimonious explanation for the spatial and temporal land loss rates on this deltaic coast over the last 80 years of oil and gas exploration. Substantial losses from the accelerating rates of sea level rise are indicated to occur before 2050. Full article

Multi-cohort forest management in northern hardwood stands may well be the best way to successfully regenerate tree species of intermediate shade tolerance, such as yellow birch (Betula alleghaniensis Britt.). The creation of large enough gaps in the canopy favors increased light availability within the opening, while soil scarification provides suitable germination seedbeds. Evidence of these methods’ success nonetheless remains mostly the purview of experimental studies rather than operational tests. In Quebec, Canada, the multi-cohort methods promoted include group selection cutting and patch cutting. The present study tested their implementation at an operational scale and over a large territory in both hardwood-dominated and mixedwood stands. We assessed their efficacy in promoting natural regeneration of commercial hardwood trees, notably yellow birch and sugar maple (Acer saccharum Marsh.). We conducted regeneration surveys at 2, 5, 10, and 15 years after harvest. Overall, group selection and patch cuttings were successful in regenerating the target species. Yellow birch, for instance, showed a mean stocking around 60% and a mean sapling density around 3400 stems ha⁻¹ after 15 years. We compared several variables for measuring regeneration in early years, and found that the relative abundance, the stocking based on one stem per sampling unit, and the mean maximum height were good predictors of the relative presence of yellow birch and sugar maple in 15-year-old canopy openings. Using smaller sampling units (6.25 m² rather than 25 m²) and waiting until year 5 may be more useful for making such predictions. In addition, there was an important turnover in vertical dominance in these openings. Non-commercial woody competitors were frequently dominant in early years but were often replaced by commercial hardwoods, notably yellow birch. We propose certain thresholds for assessing the success of post-harvest regeneration and for evaluating the need for a cleaning treatment. Full article

Cotonou is the largest city and main economic centre of the nation of Benin, Africa. Following independence, the city has experienced major population growth resulting in the extensive development of slums on flood plains and marshes causing the loss of biodiversity of these fragile ecosystems. Infrastructural development, unable to keep pace with informal settlement development, and a cumbersome municipal service system, have led to the illegal dumping of organic and plastic wastes, and extensive land pollution. In addition, due to its primary dune coastal location, Cotonou is facing sea level rise risks demonstrating the urgent need to sustainably address urban development. Through a socio-technical framework, this paper considers the use of transformed plastic wastes as new settlement building blocks to reduce solid waste, create jobs, and develop low-cost housing. This new strategy offers employment empowerment and a strategy to generate an income of US$2,380,000 per annum and the creation of 3200 permanent jobs. Full article

During any marine oil spill, floating oil slicks that reach shorelines threaten a wide array of coastal habitats. To assess the presence of oil near shorelines during the Deepwater Horizon (DWH) oil spill, we scanned the library of Synthetic Aperture Radar (SAR) imagery collected during the event to determine which images intersected shorelines and appeared to contain oil. In total, 715 SAR images taken during the DWH spill were analyzed and processed, with 188 of the images clearly showing oil. Of these, 156 SAR images showed oil within 10 km of the shoreline with appropriate weather conditions for the detection of oil on SAR data. We found detectable oil in SAR images within 10 km of the shoreline from west Louisiana to west Florida, including near beaches, marshes, and islands. The high number of SAR images collected in Barataria Bay, Louisiana in 2010 allowed for the creation of a nearshore oiling persistence map. This analysis shows that, in some areas inside Barataria Bay, floating oil was detected on as many as 29 different days in 2010. The nearshore areas with persistent floating oil corresponded well with areas where ground survey crews discovered heavy shoreline oiling. We conclude that satellite-based SAR imagery can detect oil slicks near shorelines, even in sheltered areas. These data can help assess potential shoreline oil exposure without requiring boats or aircraft. This method can be particularly helpful when shoreline assessment crews are hampered by difficult access or, in the case of DWH, a particularly large spatial and temporal spill extent. Full article