Dune Complex Research Articles

Unveiling buried aeolian landscapes: reconstructing a late Holocene dune environment using 3D ground‐penetrating radar

ABSTRACTAcross the UK, sandy beaches and dunes protect coastal infrastructure from waves and extreme water levels during large‐scale storms, while providing important habitats and recreational opportunities. Understanding their long‐term evolution is vital in managing their condition in a changing climate. Recently, ground‐penetrating radar (GPR) methods have grown in popularity in geomorphological applications, yielding centimetre‐scale resolution images of near‐surface stratigraphy and structure, thus allowing landscape evolution to be reconstructed. Additionally, abrupt changes in palaeo‐environments can be visualized in three dimensions. Although often complemented by core data, GPR allows interpretations to be extended into areas with minimal ground‐truth control. Nonetheless, GPR data interpretation can be non‐intuitive and ambiguous, and radargrams may not initially resemble the expected subsurface geometry. Interpretation can be made yet more onerous when handling the large 3D data volumes that are facilitated with modern GPR technology. Here we describe the development of novel semi‐automated GPR feature‐extraction tools, based on ‘edge detection’ and ‘thresholding’ methods, which detect regions of increased GPR reflectivity which can be applied to aid in the reconstruction of a range Quaternary landscapes. Since reflectivity can be related to lithological and/or pore fluid changes, the 3D architecture of the palaeo‐landscape can be reconstructed from the features extracted from a geophysical dataset. We present 500 MHz GPR data collected over a buried Holocene coastal dune system in North Wales, UK, now reclaimed for use as an airfield. Core data from the site, reaching a maximum depth 2 m, suggest rapid vertical changes from sand to silty‐organic units, and GPR profiles suggest similar lateral complexity. By applying thresholding methods to GPR depth slices, these lateral complexities are effectively and automatically mapped. Furthermore, automatic extraction of the local reflection power yields a strong correlation with the depth variation of organic content, suggesting it is a cause of reflectivity contrast. GPR‐interpolated analyses away from core control thus offer a powerful proxy for parameters derived from invasive core logging. The GPR data collected at Llanbedr airfield highlight a complex dune system to a depth of 2.8 m, probably deposited in several phases over ~700 years, similar to elsewhere in North Wales.

Evaluation of various image transformation techniques for the delineation of coastal sand dune features in Tamil Nadu, South India

Image transformation techniques such as Principal Component Analysis, Minimum Noise Fraction and Independent Component Analysis were used for extracting information from the satellite image in various fields, but its application in landform mapping seems to be very less. The objective of the study is to demonstrate the viability of less explored image transformation techniques for delineating coastal dune complex and associated features using European satellite Sentinel 2 multispectral data. Based on the difference in lithology and vegetation cover the study sites has been chosen to extract coastal dune complex features such as dune ridges, dune with or without vegetation, swale with or without vegetation and water. Overall results of ICA shows enhanced visualization followed by PCA in bringing up the fine variations, identifying micro landforms within the dune complex from the optimum band combinations. Thus, sentinel data coupled with advanced image processing technique like ICA could identify maximum information about the boundaries and micro landform within the coastal sand dune complex in a cost-effective manner. However, in areas with dense vegetation cover none of these techniques has given good results in identifying the boundary or in identifying the micro landforms.

Alkaline soil pH affects bulk soil, rhizosphere and root endosphere microbiomes of plants growing in a Sandhills ecosystem.

Soil pH is a major factor shaping bulk soil microbial communities. However, it is unclear whether the belowground microbial habitats shaped by plants (e.g. rhizosphere and root endosphere) are also affected by soil pH. We investigated this question by comparing the microbial communities associated with plants growing in neutral and strongly alkaline soils in the Sandhills, which is the largest sand dune complex in the northern hemisphere. Bulk soil, rhizosphere and root endosphere DNA were extracted from multiple plant species and analyzed using 16S rRNA amplicon sequencing. Results showed that rhizosphere, root endosphere and bulk soil microbiomes were different in the contrasting soil pH ranges. The strongest impact of plant species on the belowground microbiomes was in alkaline soils, suggesting a greater selective effect under alkali stress. Evaluation of soil chemical components showed that in addition to soil pH, cation exchange capacity also had a strong impact on shaping bulk soil microbial communities. This study extends our knowledge regarding the importance of pH to microbial ecology showing that root endosphere and rhizosphere microbial communities were also influenced by this soil component, and highlights the important role that plants play particularly in shaping the belowground microbiomes in alkaline soils.

Eustatic, Climatic and Tectonic Controls on the Evolution of a Middle to Late Holocene Coastal Dune System in Shimokita, Northeast Japan

The Pacific coast of the Shimokita Peninsula, Northeast Japan, is occupied by one of the larger dune complexes in Japan. This coastal aeolian dune complex developed during the Holocene in a monsoon-influenced temperate climatic belt. The stratigraphic and sedimentological characteristics of outcrops, exposures and cores indicate that four generation of aeolian dunes are presented. These dunes developed during eustatic regression following the post-glacial sea-level highstand. Seaward shoreline movement, combined with strong winds from the Pacific Ocean, enhanced aeolian grain transport on the beach, resulting in the onset of dune growth and the consequent shrinkage of the coastal forest. Northeast Japan is located in a transitional zone affected largely by monsoonal circulation from Siberia and Southeast Asia. Thus, the regional climate is responsible for atmospheric changes on a hemispheric scale. Intensified monsoons contributed to flooding produced by rains and snow-melt. Steep increases in annual precipitation at 7200–6300, 4700–3600, 3050–2500, 1850–1100, and 550–200 calendar years before present (cal. yr. BP) increased the amount of surface erosion, causing a large volume of sediment discharge toward the coast. Shimokita has experienced frequent earthquakes and tsunamis, which have reduced dune landform relief by sediment displacement.

The Orphan Tsunami of 1524 on the Konkan Coast, Western India, and Its Implications

In comparison to the east coast, the tsunami hazard for the west coast of India remains under-recognized, despite the impact in 1945 following a Mw 8.1 earthquake in the Makran subduction zone in the northern Arabian Sea. The previous occurrences of tsunamis in the Arabian Sea that would have a bearing on the west coast of India are being debated, including the question whether the Makran region has the potential to generate greater-magnitude earthquakes. With this in the backdrop, we present here the historical and geological evidence of a tsunami impact zone from a site on the Konkan Coast of western India. Located in the village of Kelshi, the impact zone is preserved within a coastal dune complex that also reveals occupation layers. This laterally extending 30–40-cm-thick zone, coinciding with a habitation level, displays varied sedimentary structures including scour-fill features, and is inter-layered with shells, at a height of ~ 3 m from the high-tide level. We attribute these sedimentary features to a tsunami flooding event that was contemporaneous with the transportation of shells, dated at 1508–1681 CE. The geological inference matches with the description by the Portuguese fleets of a sea disturbance in 1524 CE, reported from Dabhol, not far from Kelshi, and also from the Gulf of Cambay, located about 500 km to the north. Precluding submarine landslide scenarios, the modeling results suggest that the high impact in Kelshi could have been generated by a Mw ≥ 9 earthquake sourced in the Makran subduction zone. It is, however, intriguing how a Mw ≥ 9 earthquake in the Makran region finds no mention in the historical documentation. We underscore the need for fresh efforts along the Makran coast to reconstruct the tsunami recurrence history that would generate required validating constraints on the 1524 event, if it was indeed generated by a massive earthquake among other mechanisms.

A comparison of high-end methods for topographic modelling of a coastal dune complex

In recent years, increasing tourism and development in the coastal dune area of the South East of Ireland have resulted in greater pressure on the environment, resulting in issues including soil erosion, flooding and habitat loss. Topographic mapping across a dune field is important for the development of targeted land management actions that maintain biodiversity and ecological functions. Developments in surveying technology, including LiDAR, terrestrial laser scanners (TLS) and aerial surveying from Remotely Piloted Aircraft Systems (RPAS), have enabled high-resolution and high-accuracy spatial data to be gathered quickly and relatively easily for 3D topographic modelling of a coastal dune complex. To-date, however, the relative efficacies of these three modelling methods, in the context of coastal dune modelling, has not been explored. This paper compares high-end methods based on LiDAR, TLS and RPAS technologies, for the topographic modelling of coastal dune complexes with particular reference to the Brittas-Buckroney dune complex in the South East of Ireland. The results identify the advantages and disadvantages of the respective technologies and highlight the efficacy of RPAS, in particular, for topographic modelling of coastal dune complexes. These results can provide reference information for others when selecting suitable methods for topographic modelling of similar environments.

Current state and historical notes on sand dune flora of the Bulgarian Black Sea Coast

This study is the first overview of the floristic diversity of Bulgarian coastal dunes in terms of the presence of typical psammophytic or non-psammophytic plant species. It also aims to reveal changes in sand dune flora over time, based on own samples and existing data from previous studies. Our original floristic data was extracted from 154 phytosociological plots sampled in 12 large dune systems during 2017. All available literature sources were compiled to derive a list of vascular plants recorded for Bulgarian coastal dunes between 1905 and 2016. Due to the different scientific approaches applied in previous publications we split the studies into three periods over time: (I period: 1905 1950; II period: 1951–1990; III period: 1991–2016), and separate lists were also prepared for each. All vascular plants were assigned to one of five groups, according to their general habitat preference: 1) psammophytes, 2) weeds and ruderals, 3) grass- and shrubland plants, 4) forests plants and 5) alien (including invasive) species. The full species list comprises 501 taxa, and the highest number of species was compiled from publications after 1990. Across all periods and studied dune complexes, grass- and shrubland plants were most abundant, while other non-psammophyte species groups showed low presence. A comparison of data from 2003 and 2015 showed that species richness of psammophytes decreased over time, which is in contrast to the average number of weeds and ruderals, and particularly to species richness of grass- and shrubland species. Our results show that a core group of characteristic psammophytes remains constant through all study periods. Alien (including invasive) species still are limited in abundance but there is an alarming recent increase in their numbers. We believe that our synthesis will be of use for further floristic inventories of Pontic sand dunes.

Holocene, silty-sand loess downwind of dunes in Northern Michigan, USA

ABSTRACT In Michigan’s Upper Peninsula, sand dunes are widespread on the sandy floor of former Glacial Lake Algonquin, and many of the nearby uplands also have thin mantles of loess. Previous work concluded that these dunes formed during the early Holocene, long after the lake had drained. Where these dunes have migrated against bedrock uplands, many have accreted into larger dune complexes. South and east of these complexes, uplands are mantled with well-sorted sediment, comparatively rich in finer sands and much like the thin, locally sourced loess deposits in Wisconsin and Michigan. Near the dunes, this loess is typically 50–75 cm thick, and rich in very fine sands; presumably much of this sand was deposited as short-range “blow-over” while the dunes were forming. The loess thins to ≈45 cm and becomes siltier on sites farther downwind, to the southeast. Because the dune complexes contain almost no silt, the silt in the loess was likely generated by deflation of saltating sands on the lake plain, transported in suspension, and deposited generally uniformly across the forested uplands, as indicated by spatial trends in silt contents. Periodic Holocene drought may have thinned the forest and helped to intermittently facilitate this type of eolian activity.

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems

AbstractCoastal dunes provide essential protection for infrastructure in developed regions, acting as the first line of defence against ocean‐side flooding. Quantifying dune erosion, growth and recovery from storms is critical from management, resiliency and engineering with nature perspectives. This study utilizes 22 months of high‐resolution terrestrial LiDAR (Riegl VZ‐2000) observations to investigate the impact of management, anthropogenic modifications and four named storms on dune morphological evolution along ~100 m of an open‐coast, recently nourished beach in Nags Head, NC. The influences of specific management strategies – such as fencing and plantings – were evaluated by comparing these to the morphologic response at an unmanaged control site at the USACE Field Research Facility (FRF) in Duck, NC (33 km to the north), which experienced similar environmental forcings. Various beach‐dune morphological parameters were extracted (e.g. backshore‐dune volume) and compared with aeolian and hydrodynamic forcing metrics between each survey interval.The results show that LiDAR is a useful tool for quantifying complex dune evolution over fine spatial and temporal scales. Under similar forcings, the managed dune grew 1.7 times faster than the unmanaged dune, due to a larger sediment supply and enhanced capture through fencing, plantings and walkovers. These factors at the managed site contributed to the welding of the incipient dune to the primary foredune over a short period of less than a year, which has been observed to take up to decades in natural systems. Storm events caused alongshore variable dune erosion primarily to the incipient dune, yet also caused significant accretion, particularly along the crest at the managed site, resulting in net dune growth. Traditional empirical Bagnold equations correlated with observed trends of backshore‐dune growth but overpredicted magnitudes. This is likely because these formulations do not encompass supply‐limiting factors and erosional processes. © 2019 John Wiley & Sons, Ltd.

Architecture of a sandstone uranium reservoir and the spatial distribution of its internal carbonaceous debris: A case study of the Zhiluo Formation, eastern Ordos Basin, northern China

The sandstone of the Middle Jurassic Zhiluo Formation, in the eastern Ordos Basin, provides the opportunity for conducting a critical case-study of the architecture and internal carbonaceous debris (CD) distribution of a sandstone uranium reservoir located in a field outcrop in Shiwan. The 16–24 m thick outcrop section is a sandstone-dominated subaqueous distributary channel succession, in which six lithofacies types (Se, St, Sm, Sp, Sh, and Fl) occur in a predictable order of repeated fining-upward cycles. These facies emphasize that the dominant structures had been deposited under lower flow regime conditions. Various groups of associated facies have been identified as six distinct architectural elements (intrachannel units, longitudinal bar, transverse bar, diagonal bar, dune complex, and abandoned channel deposits) within a framework of five orders of bounding surfaces. These elements, with specific lithofacies associations and spatial relationships, indicate that the subaqueous distributary channel had involved in four stages of formation: channel-occurring, channel-flooding, channel-waning, and channel-abandonment. Moreover, as one of the most significant reductants in the sandstone succession, the CD occurs in the form of channel lags and is concentrated in the middle and lower parts of the lag deposit zones. The spatial distribution of CD within the studied succession is controlled by the sandstone architecture and the CD-rich zones are preserved exclusively upon the basal surfaces of intrachannel units, longitudinal and transverse bars. This study can be helpful for exploring the distribution of metallogenic flow field as well as the restriction of the reductants on interlayer oxidation.

Distribution, abundance, and ecology of the threatened Gibson’s Big Sand Tiger Beetle (Cicindela formosa gibsoni Brown) in the Elbow Sand Hills of Saskatchewan

Gibson’s Big Sand tiger beetle, Cicindela formosa gibsoni Brown, occurs primarily in the Saskatchewan sand hills and was recently listed as threatened in Canada due to habitat loss caused by dune stabilization. Herein, we report on a 3-year population study initiated in 2016 to better understand the distribution, abundance, and ecology of C. f. gibsoni in the Elbow Sand Hills, a large active dune complex in southern Saskatchewan. Estimated adult population size for the dune complex varied from a low of 1106 (95% confidence interval (CI) 975–1237) to a high of 1474 (CI 1350–1598), possibly due to inter-annual variation in May–June rainfall. Adult abundance varied substantially between interdunal swales (0–137 individuals), with the highest numbers occurring in sparsely-vegetated habitats on the stoss side of the dune complex where the rate of encroachment by vegetation is highest. Approximately a third of the total population is concentrated within a relatively small area (~ 6 ha) in the northwestern region of the dune complex, although the specific cause for this localized distribution is not clear. Our findings suggest that the distribution of C. f. gibsoni within the dune complex is not limited by prey availability or larval habitat quality but is instead related to the amount of sparsely-vegetated habitat. We hypothesize that sparsely-vegetated areas allow beetles to shuttle between exposed and shaded microhabitats, thereby assisting in thermoregulation and maintenance of high body temperatures that are optimal for foraging.

Near shore atmospheric acoustic transmission loss: Numerical predictions

This work presents advances in the development of a numerical model of atmospheric acoustic propagation designed for a littoral or riverine environment with a near-shore acoustic source and on-shore receivers. A parallel experimental effort uses a measurement system that records concurrent atmospheric and acoustic transmission loss data. The numerical model uses a generalized terrain parabolic equation method to account for sea surface roughness and ground topography along the propagation path. The model accounts for vertical temperature and wind speed profiles as well as surface impedance at the shore. For the comparison with experimental data, wind speed is used to predict the sea state. The propagation range consists of three segments: over water, over swash and sandy shore, and over complex dune with highly varied vegetation of up to 2 m height. Surface impedance estimates for the sandy shore are made based on grain size distribution and impedance tube measurements of excised samples. Existing models for surface impedance of vegetation were used for the dune portion of the propagation range.This work presents advances in the development of a numerical model of atmospheric acoustic propagation designed for a littoral or riverine environment with a near-shore acoustic source and on-shore receivers. A parallel experimental effort uses a measurement system that records concurrent atmospheric and acoustic transmission loss data. The numerical model uses a generalized terrain parabolic equation method to account for sea surface roughness and ground topography along the propagation path. The model accounts for vertical temperature and wind speed profiles as well as surface impedance at the shore. For the comparison with experimental data, wind speed is used to predict the sea state. The propagation range consists of three segments: over water, over swash and sandy shore, and over complex dune with highly varied vegetation of up to 2 m height. Surface impedance estimates for the sandy shore are made based on grain size distribution and impedance tube measurements of excised samples. Existing models ...

A very-high resolution (20m) measurement-based dust emissions and dispersion modeling approach for the Oceano Dunes, California

This study shows the results from very high-resolution (20 m) dust emissions and transport simulations for the Oceano Dunes State Vehicular Recreation Area (ODSVRA), a coastal sand dune complex located in San Luis Obispo County, California. Field data from an enhanced observation period carried out in May–July 2013 helped estimate the emissions and flow conditions over the dune field. Emissions are based on a comprehensive emissions grid developed from in-situ measurements using the Portable In-Situ Wind ERosion Lab (PI-SWERL). PI-SWERL estimates the potential for a soil surface to produce PM10 dust emissions for a range of wind speeds. This approach provided a well-determined PM10 emissions field as a function of time and space. Wind and turbulence fields were estimated using the CALMET diagnostic meteorological model constrained with surface stations, upper air soundings, buoys, and the North American Reanalysis data. Hourly, three-dimensional wind flow and instability objective analysis fields were developed at 20 m resolution in order to consider the complex flow over realistic dune morphology, land use/land cover and terrain characteristics over and around the Oceano Dunes. The dust dispersion simulations were performed using a computationally efficient and vectorized Lagrangian Stochastic Particle Dispersion Model driven by the CALMET output and the PI-SWERL time-space variable emissions. The dispersion model is based on the Langevin formulation and includes the turbulent diffusion and stochastic particle motion (of millions of particles) in the inertial sub-range, and assuming particles as discrete units neglecting deposition. The model estimates diffusion of particles from an initial particle releases that scale according to the PI-SWERL time-variable emissions estimates. Results were then tested at two independent-downwind locations, with positive correlations for flow conditions (R2 = 0.89) and similar receptor PM10 concentrations (R2 = 0.85). Evaluations against those observations during mean flow conditions as well as for elevated dust events suggest that the model framework can capture the spatial and temporal characteristics of mean day-to-day and diurnal PM10 variability. In this study we describe the details of the model framework and its performance as well as its implementation to locate the dust sources that have the strongest impact in the receptor sites and to evaluate the impact of different dust reduction strategies used at the ODSVRA to mitigate PM10 at downwind receptors.

Coastal Dune Vegetation Mapping Using a Multispectral Sensor Mounted on an UAS

Vegetation mapping, identifying the type and distribution of plant species, is important for analysing vegetation dynamics, quantifying spatial patterns of vegetation evolution, analysing the effects of environmental changes and predicting spatial patterns of species diversity. Such analysis can contribute to the development of targeted land management actions that maintain biodiversity and ecological functions. This paper presents a methodology for 3D vegetation mapping of a coastal dune complex using a multispectral camera mounted on an unmanned aerial system with particular reference to the Buckroney dune complex in Co. Wicklow, Ireland. Unmanned aerial systems (UAS), also known as unmanned aerial vehicles (UAV) or drones, have enabled high-resolution and high-accuracy ground-based data to be gathered quickly and easily on-site. The Sequoia multispectral sensor used in this study has green, red, red edge and near-infrared wavebands, and a regular camer with red, green and blue wavebands (RGB camera), to capture both visible and near-infrared (NIR) imagery of the land surface. The workflow of 3D vegetation mapping of the study site included establishing coordinated ground control points, planning the flight mission and camera parameters, acquiring the imagery, processing the image data and performing features classification. The data processing outcomes included an orthomosaic model, a 3D surface model and multispectral imagery of the study site, in the Irish Transverse Mercator (ITM) coordinate system. The planimetric resolution of the RGB sensor-based outcomes was 0.024 m while multispectral sensor-based outcomes had a planimetric resolution of 0.096 m. High-resolution vegetation mapping was successfully generated from these data processing outcomes. There were 235 sample areas (1 m × 1 m) used for the accuracy assessment of the classification of the vegetation mapping. Feature classification was conducted using nine different classification strategies to examine the efficiency of multispectral sensor data for vegetation and contiguous land cover mapping. The nine classification strategies included combinations of spectral bands and vegetation indices. Results show classification accuracies, based on the nine different classification strategies, ranging from 52% to 75%.

Nuevos datos sobre la distribución de mamíferos (Mammalia) en las dunas de Erg Chebbi (Marruecos)

El progresivo aumento del turismo de aventura en el entorno de las dunas de Erg Chebbi, amenaza, desde hace casi dos décadas, la conservación del único complejo dunar (Erg) de todo Marruecos. Con el propósito de valorar algunos de los efectos de esta actividad sobre la comunidad de mamíferos locales, entre marzo y abril de 2018 se llevó a cabo un muestreo intensivo utilizando 5 métodos de detección distintos. El objeto principal era evaluar la presencia y distribución actual de las especies de mamíferos presentes, teniendo como referencia las citadas en la zona desde 1900 (Aulagnier et al., 2017). De las 16 especies históricamente citadas, 9 han sido detectadas en el presente trabajo, lo que representa un 56.2%. Resulta de interés la ausencia total de datos sobre 5 de las especies potencialmente más abundantes como son: Gerbillus amoenus (de Winton, 1902), Gerbillus gerbillus Olivier, 1801, Gerbillus tarabuli (Thomas, 1902), Pachyuromis duprasi Lataste, 1880 y Psammomys obesus Cretzschmar, 1828. Algunos datos apuntan a la drástica reducción de los recursos hídricos experimentada en los últimos años, como una de las causas de la aparente reducción de sus poblaciones. Al mismo tiempo, otras especies de requerimiento hídricos menores, tales como: Meriones libycus Lichtenstein, 1823 o Jaculus jaculus Linnaeus, 1758, presentan un aparente buen estado de conservación. Se confirma la presencia de Poecilictis libyca Hemprich & Ehrenberg, 1833, tras 32 años de ausencia de datos.

UAVs for Structure-From-Motion Coastal Monitoring: A Case Study to Assess the Evolution of Embryo Dunes over a Two-Year Time Frame in the Po River Delta, Italy.

Coastal environments are usually characterized by a brittle balance, especially in terms of sediment transportation. The formation of dunes, as well as their sudden destruction as a result of violent storms, affects this balance in a significant way. Moreover, the growth of vegetation on the top of the dunes strongly influences the consequent growth of the dunes themselves. This work presents the results obtained through a long-term monitoring of a complex dune system by the use of Unmanned Aerial Vehicles (UAVs). Six different surveys were carried out between November 2015 and December 2017 in the littoral of Rosolina Mare (Italy). Aerial photogrammetric data were acquired during flight repetitions by using a DJI Phantom 3 Professional with the camera in a nadiral arrangement. The processing of the captured images consisted of the reconstruction of a three-dimensional model using the Structure-from-Motion (SfM). Each model was framed in the European Terrestrial Reference System (ETRS) using GNSS geodetic receivers in Network Real Time Kinematic (NRTK). Specific data management was necessary due to the vegetation by filtering the dense cloud. This task was performed by both performing a slope detection and a removal of the residual outliers. The final products of this approach were thus represented by Digital Elevation Models (DEMs) of the sandy coastal section. In addition, DEMs of Difference (DoD) were also computed for the purpose of monitoring over time and detecting variations. The accuracy assessment of the DEMs was carried out by an elevation comparison through especially GNSS-surveyed points. Relevant cross sections were also extracted and compared. The use of the Structure-from-Motion approach by UAVs finally proved to be both reliable and time-saving thanks to quicker in situ operations for the data acquisition and an accurate reconstruction of high-resolution elevation models. The low cost of the system and its flexibility represent additional strengths, making this technique highly competitive with traditional ones.

WIND TUNNEL TESTS OF HOW COASTAL PLANTS FEEDBACK ON DUNE SHAPE

Theoretical evolution of a coastal dune system starts at the individual plant level with the formation of bedforms, nebkha and shadow dunes, around plants. Over time, these initial bedforms can evolve into a fully developed foredune and eventually a complex dune system capable of buffering upland coastal areas against high tides and storms. Recent studies suggest that dunebuilding plant species may differ in their sand trapping efficiency and they may support different topographies, building dunes morphologically similar to their own stature – i.e. a taller steeper plant would build a taller and steeper dune. We believe that the bedforms created at the onset of dune evolution, i.e. after a storm or at the backbeach, may carry over through the life of the dune, such that understanding how plant morphology and density affects the initial formation stages of dune morphology is key to optimizing dune management, maintenance, and creation. With ERDC and USGS funding, we built a removable bed unilateral flow wind tunnel to test how the morphology among and within dominant US East coast foredune plants feeds back on bedform creation around individual plants at a baseline of zero (i.e. flat back beach or post storm).

The Combined Effect of Sediment Availability and Wind Regime on the Morphology of Aeolian Sand Dunes

AbstractAeolian‐driven sand dune orientation is a key parameter that determines dune morphology. Although wind regime, surface condition, and sediment availability all control sand dune formation, researchers have mostly put emphasis on the wind regime. However, research shows that the formation of dune orientation cannot be explained solely on wind because different dune types can form under the same wind regime in a given area. In this study, we investigate the combined effects of wind regime and sediment availability on dune orientation based on numerical simulations. The model clarifies the extent to which sediment availability influences dune orientation as well as the physical mechanisms that allow for the coexistence of different dune types. We found that linear dunes and barchans can coexist when the sediment availability is less than 10% with a localized sand source, and where barchans are situated at the extremity or on the same flank of the linear dunes. When the angle between two dominant winds is greater than 90° and sediment availability is greater than 10%, oblique dunes may occur, and they can evolve from asymmetric barchans. This study offers insight into the potential relationship between dune‐forming factors related to the wind regime and the available erodible sediment within a dune system, in view of the fact that such a model would be a valuable tool in ascertaining the causes behind complex dune formation processes.

VEGETATION MAPPING OF A COASTAL DUNE COMPLEX USING MULTISPECTRAL IMAGERY ACQUIRED FROM AN UNMANNED AERIAL SYSTEM

Abstract. Vegetation mapping, identifying the distribution of plant species, is important for analysing vegetation dynamics, quantifying spatial patterns of vegetation evolution, analysing the effects of environment changes on vegetation, and predicting spatial patterns of species diversity. Such analysis can contribute to the development of targeted land management actions that maintain biodiversity and ecological functions. This paper represents a methodology for 3D vegetation mapping of a coastal dune complex using a multispectral camera mounted on an Unmanned Aerial System (UAS) with particular reference to the Buckroney dune complex in Co. Wicklow, Ireland. UAS, also known as Unmanned Aerial Vehicles (UAV’s) or drones, have enabled high-resolution and high-accuracy ground-based data to be gathered quickly and easily on-site. The Sequoia multispectral camera used in this study has green, red, red-edge and near infrared wavebands, and a normal RGB camera, to capture both visible and NIR images of the land surface. The workflow of 3D vegetation mapping of the study site included establishing ground control points, planning the flight mission and camera parameters, acquiring the imagery, processing the image data and performing features classification. The data processing outcomes include an orthomosiac model, a 3D surface model and multispectral images of the study site, in the Irish Transverse Mercator coordinate system, with a planimetric resolution of 0.024 m and a georeferenced Root-Mean-Square (RMS) error of 0.111 m. There were 235 sample area (1 m × 1 m) used for the accuracy assessment of the classification of the vegetation mapping. Feature classification was conducted using three different classification strategies to examine the efficiency of multispectral sensor data for vegetation mapping. Vegetation type classification accuracies ranged from 60 % to 70 %. This research illustrates the efficiency of data collection at Buckroney dune complex and the high-accuracy and high-resolution of the vegetation mapping of the site using a multispectral sensor mounted on UAS.

Spatio-temporal geomorphological and ecological evolution of a transgressive dunefield system, Northern California, USA

Abstract A series of historic aerial photographs in addition to the U.S. Coast Survey 1870 map were used to document evolution of the coastal barrier and transgressive dunefield system at the Lanphere-Ma-le'l Dunes on Humboldt Bay, California, USA, between 1870 and 2016. Geomorphic units (shorelines, foredunes, nebkha, blowouts, parabolic dunes, deflation basins, and dunefields) as well as vegetation alliance were mapped in ArcGIS at approximately decadal intervals and compared among three subareas delineated based on large scale geomorphic differences that coincided with contrasting biological invasion and management histories. Sand inundation events in the 1930s and 1940s led to deterioration of the foredune and burial of deflation basins in the south, with the transgressive dunefield directly abutting the backshore in places. The transgressive dunefield in the north differentiated into parabolic dunes that decoupled from the foredune complex earlier than in the southern subareas, which have retained undifferentiated transgressive dunefields. Shoreline progradation increased dramatically following the historic 1964 flood, but exhibited a north-south gradient consistent with the Mad River to the north acting as the primary source of sediment, and effective north-south littoral drift. Biological invasions of Lupinus arboreus in the north and Ammophila arenaria in the south contributed to stabilization post-1965, but concomitant increases of native vegetation in other areas suggest these biotic processes were subordinate to other forcing factors. A notable switch from an erosional to a depositional system occurred coincident with the Pacific Decadal Oscillation (PDO) shift from a cool to a warm phase in the late 1970s, suggesting climate forcing as a major driver of dune evolution. Changes in the rate of vegetation stabilization per time interval post 1948 are correlated with change in mean monthly PDO index for the same intervals. Alongshore gradients of sediment availability and tectonic subsidence are likely superimposed on climatic controls. Stability of the dune system reached its maximum extent in 2000, despite erosional effects of the 1998–2000 La Nina event and invasive plant removal projects in the 1990s. Increased storminess (2015–2016 El Nino) resulted in decreased shoreline stability in the most recent interval, coincident with sharply declining rates of progradation and a reduction in mean monthly PDO index. This study provides insights into how transgressive dune phases can be formed, sustained and decoupled, as well as how they change their geomorphology over time. The absence of relict foredunes in the study area and elsewhere on the North Spit barrier suggests that the foredune-blowout-parabolic dune complex may build to quite large proportions for some time, and then be destroyed or destabilized to such a degree that the sediments comprising the complex are released to form a new dunefield phase. Ruptures along the Cascadia subduction zone are a likely mechanism for transgressive dunefield initiation, both in the past, and likely in the future.