Dune Ridges Research Articles

Mapping marine litter on coastal dunes with unmanned aerial systems: A showcase on the Atlantic Coast

Marine litter pollution on coastal dunes has received limited scientific attention when compared with sandy shores. This paper proposes a new framework based on the combined use of Unmanned Aerial Systems (UAS) and a mobile application to map and quantify marine macro-litter (>2.5 cm) accumulation on coastal dunes. The first application on a dune area of 200 m × 80 m at the north-east Atlantic Portuguese coast is shown.Nine different marine litter categories were found, with styrofoam fragments (23% of the total amount) and plastic bottles (20%) being the most abundant items. Plastic was the most common material (76%). The highest number of items (272) was found on the backdune, mostly related with fishing activities (octopus pots and Styrofoam fragments). In contrast, the highest density (0.031 items/m2) was found on the foredune, with the most abundant items associated with human recreational activities (for example, plastic bottles, bags, papers and napkins). Three major marine litter hotspots (~0.1 items/m2) were identified in correspondence of dune blowouts. The recognition of the primary marine litter pathways highlighted the main role that wind and overwash events play on dune contamination, and suggests that the dune ridge restoration can act as a mitigation measure for preventing marine litter accumulation on the backdune.This study shows how UAS offer the possibility of a detailed non-intrusive survey, and gives a new impulse to coastal dune litter monitoring, where the long residence time of marine debris may threaten the bio-ecological equilibrium of these ecosystems.

Geological development of the Limpopo Shelf (southern Mozambique) during the last sealevel cycle

Paleo-shorelines on continental shelves give insights into the complex development of coastlines during sealevel cycles. This study investigates the geologic development of the Limpopo Shelf during the last sealevel cycle using multichannel seismic and acoustic datasets acquired on the shelf in front of the Limpopo River mouth. A detailed investigation of seismic facies, shelf bathymetry, and a correlation to sea level revealed the presence of numerous submerged shorelines on the shelf. These shorelines are characterized by distinct topographic ridges and are interpreted as coastal dune ridges that formed in periods of intermittent sealevel still-/slowstand during transgression. The shorelines are preserved due to periods of rapid sealevel rise (melt water pulses) that led to the overstepping of the dune ridges as well as due to early cementation of accumulated sediments that increased the erosive resistance of the ridges. The high along-shelf variability of the submerged dune ridges is interpreted as a result of pre-existing topography affecting shoreline positions during transgression. The pre-existing topography is controlled by the underlying sedimentary deposits that are linked to varying fluvial sediment input at different points on the shelf. The numerous prominent submerged dune ridges form barriers for the modern fluvial sediment from the Limpopo River and dam sediment on the inner shelf. They may also facilitate along-shelf current-induced sediment transport.

Contributions to the Knowledge of Sandy Soils from Oltenia Plain

Highlighting the sandy soil of Oltenia Plain calls for a better knowledge of their variability their correlation with major natural factors from each physical geography. Pedogenetic processes specific sandy soils are strongly influenced by nature parent material. This leads, on the one hand, climate aridity of the soil due to strong heating and accumulation of small water reserves, consequences emphasizing the moisture deficit in the development of the vegetation and favoring weak deflation, and on the other hand, an increase in mineralization organic matter. Relief under wind characteristic sandy land, soil formation and distribution has some particularly of flat land with the land formed on the loess. The dune ridges are less evolved soils, profile underdeveloped and poorly supplied with nutrients compared to those on the slopes of the dunes and the interdune, whose physical and chemical properties are more favorable to plant growth.Both Romanati Plain and the Blahnita (Mehedinti) Plain and Bailesti Plain, sand wind shaped covering a finer material, loamy sand and even loess (containing up to 26% clay), also rippled with negative effects in terms of overall drainage. Depending on the pedogenetic physical and geographical factors that have contributed to soil cover, in the researched were identified following classes of soils: protisols, cernisols, cambisols, luvisols, hidrisols and antrosols.Obtaining appropriate agricultural production requires some land improvement works (especially fitting for irrigation) and agropedoameliorative works. Particular attention should be paid to preventing and combating wind erosion.

Sand dunes and valley fills from Preboreal glacial‐lake outburst floods in south‐eastern Norway – beyond the aeolian paradigm

AbstractA major glacial‐lake outburst flood in the Glomma valley, south‐eastern Norway, took place during the final decay of the Scandinavian Ice Sheet. A combined morphological, geophysical and sedimentological study provides new insight into the variety of processes and deposits of the flood. The studied succession, some tens of metres in thickness, comprises the fill of a major flood basin that developed during hydraulic ponding. Large‐scale sand dunes and bars accumulated downstream of locations with expanding flow. Most notable are 10 m high, concentric dune ridges that accumulated downstream of a topographical constriction hosting a high‐velocity flow. Flow expansion at the outlet generated intense turbulence and scouring. The sand‐loaded eddies helped feeding the semi‐stationary dune ridges that grew vertically and downflow under high aggradation rates. Internal structures vary but reflect an overall shift in sedimentation from prevailing supercritical flow to overall subcritical flow conditions at high flood levels. Loading by water and sediment caused large‐scale, synsedimentary deformation, increasing local accommodation space. Fast‐falling flood levels caused stronger flow locally, while mud and fine sand settled in stagnant pools. The fall caused a significant drop in hydrostatic pressure. This triggered a release of excess pore pressure causing massive dewatering and fluidisation. Water‐escape structures include numerous (sub)vertical pipes. The present study shows that outburst flood‐generated, large‐scale dunes can develop in well‐sorted, fine sand and are thereby easily confused with aeolian deposits. Several dune fields in south‐eastern Norway are here reinterpreted as the product of at least two major flood events. Sandy dune fields with similar characteristics elsewhere in Scandinavia should likely also be reinterpreted, and the role of outburst floods during the final deglaciation of Scandinavia has seemingly been underestimated. The study emphasises the importance of ponding, flow expansion, sorting, rapidly changing pressure conditions and deformation for outburst flood‐related sedimentation.

Ecological and geochemical evaluation of ecosystems of the Curonian Spit (Russia)

ABSTRACT This paper presents the results of the quantitative content of metals (Cu, Zn, Pb, Mn, Sr, Ni, Ca, Fe, Br, Rb) in the leaves of the flora dominants of the main ecosystems of the Curonian Spit (foredune, palve area, large dune ridge). The heavy metal content in the upper layer of sandy soils, forest ecosystems (palve area) and large dune ridge was analysed. In the accumulative horizon of soils, the heavy metal content did not exceed the sanitary standards (MAC (maximum allowable concentration)/TAC (tentative allowable concentration)), and their concentration was significantly lower than the similar level in urbanised territories which allows for taking their contents into account as a baseline for the Kaliningrad region. From the ecological and physiological points of view, the content of heavy metals in the studied plants is not toxic, and is typical of the accumulation features in plants.

Multiproxy record of late Holocene climatic changes and natural hazards from paleolake deposits of Urup Island (Kuril Islands, North-Western Pacific)

The evolution of the late Holocene environments has been reconstructed on the basis of multiproxy studies of peat sequences. The vegetation response to short-period climate fluctuations has been traced. Early in the late Holocene there were birch forests with oak and other broadleaf trees; vast areas were occupied by forb meadows. Under cooling (3250 yr BP) the shrub pine (Pinus pumila) became the landscape-forming species, and since 2490 yr BP Selaginella selaginoides appeared in abundance. The Little Ice Age was marked by the disappearance of broadleaf trees and widely spread heath land communities. The higher stands of the lake level were related to warmings (3660–3590; 3450–3180; 2960–2840; 2410–2260 cal yr BP). Shallowing coincided with short-term coolings (3590–3450; 3180–2960; 2840–2410; 2260–2150 cal yr BP) marked by reduced precipitations. The dune ridge formation began during the longest cooling accompanied by a minor regression. The dunes were stabilized and a paleosol developed ~2340–2260 yr BP. A younger generation of eolian sands developed during the Little Ice Age. An ecological effect of volcanic ashfalls has been estimated. The local biotic components seem to have been most afflicted by the eruption in the north of Iturup in ~2100–2300 cal yr BP, when CKr tephra up to 30 cm thick was deposited. The ages of 4 strongest tsunamis that occurred over the last 3660 years were determined. They appeared to be related to the earthquakes with focuses close to Urup Island or south of it. The lake microflora shows ecological effect of the marine water invasions.

Morphometric characterization of foredunes along the coast of northern Spain

Foredunes are defined as the first shore-parallel dune ridges adjacent to stable and prograding beaches, formed on the backshore by aeolian sand deposition influenced by vegetation. Foredunes have the important functions for mitigating impacts caused by extreme events, providing sediment to the beaches during storm and accumulating sediment again under fair weather wave conditions. Mainly for this reason, there is currently great interest in preserving, building or recovering foredunes. On a long-term timescale (decades), foredunes are recognized as exhibiting possible equilibrium conditions. The identification of this condition is of interest to projects involving the recovery and creation of foredune/beach systems. Therefore, the main objective of this work is to identify the morphometric characteristics of equilibrium foredunes and the interrelations between the morphometric parameters of height, width, volume and maximum slope (allometric relationships). To reach this objective, 193 foredune/subaerial beach profiles from along the northern coast of Spain that have characteristics close to equilibrium conditions were evaluated. The results indicate that foredune size can vary significantly; however, strong correlations between morphometric parameters have been verified and allometric relationships between foredune volume, height, width and maximum slope are proposed.

Geological inheritance and its role in the geomorphological and sedimentological evolution of bedrock-hosted incised valleys, lake St Lucia, South Africa

The morphology of Lake St Lucia, Africa's largest estuary, has been strongly influenced by antecedent topography throughout its Quaternary evolution. The 5 × 20 km southern basin is bounded to landward by a 50 m-high Early/Mid-Pleistocene dune ridge and to seaward by a 100 m-high Late Pleistocene/Holocene dune barrier. Nine seismic units (A-I) are identified in the enclosed basin, along with two regionally developed sequence boundaries (SB1 and SB2) and two tidal ravinement surfaces (tRS1 and tRS2). The lowermost sequence boundary (SB1) is related to regional late-Pliocene hinterland uplift. SB2 is related to the last glacial maximum (LGM) when sea levels fell ∼130 m below present. Lowstand fluvial sediments occupy the base of both SB1 and SB2 incisions. Thick central basin deposits dominate the valley fills, more so in the Pliocene age valleys, the occurrence and thickness of which is attributed to sheltering by a seaward barrier-dune system as well as to the low gradient settings. Prograding tidal bedforms occupy the minor incisions formed within the tidal ravinement surfaces, marking the onset of lagoonal conditions in the area. The system is capped by lagoonal deposits, deposited above tidal flats. A series of prograding spits mark the early stages of lagoonal segmentation in the Holocene. The preservation of only one incision and fill sequence prior to the development of an LGM-aged valley succession is attributed to geological inheritance whereby older valleys were repeatedly re-incised by younger valleys throughout the Pleistocene, causing partial preservation of Pleistocene fills up to the most recent cycle. The older fill remnant relates to a larger magnitude base level fall prior to the Quaternary, which survived erosion during subsequent sea-level falls. Adjacent topography in the form of rocky cliffs and the seaward fronting barrier limit the accommodation space in which infilling material can be hosted outside the major valley network. The competent basement rock into which these valleys have incised protected lowstand fluvial sediments from subsequent tidal ravinement.

Sand dunes and ventifacts on the coast of South Africa

Abstract The Indian Ocean coast of South Africa is characterized by strong seasonal alongshore winds and high sediment availability, resulting in formation of different types of active and vegetated sand dunes landward of sandy beaches. This study considers the dynamics of windblown sand systems along part of this coastal stretch by presenting geomorphological evidence from ventifacts and sand dunes, which can inform on integrated sand transport and depositional system dynamics, respectively. Crestline positions of supratidal translational dunes were mapped from aerial images (2003–2018); results show a range of responses over different time windows, including systematic migration in particular to the northeast, and crestline rotation. Changes in dune geometry are linked closely to changes in synoptic climate patterns, determining seasonal wind regimes. Exceptionally well developed ventifacts are present on clasts within deflation lags located between translational dune ridges. Based on morphological analysis of ventifacts (n = 49), the dominant geomorphically-effective wind direction is from west or northwest, oblique to regional prevailing winds. An important conclusion of this study is that, although both ventifacts and dunes at this site reflect the same wind forcing, they show quite different morphological responses and dynamical behaviours. A reason for such differences may be the role of microtopographic effects on near-surface wind patterns. This means that neither dunes nor ventifacts alone can be used as unambiguous indicators of wind regime, and instead should be viewed as integrated elements of coastal sediment systems.

Dune ridge progradation resulting from updrift coastal reconfiguration and increased littoral drift

Coastal dune ridges are prominent morphological features of many barrier islands. To investigate the environmental controls on coastal dune ridge formation 38 samples from prominent coastal dune ridges on the barrier island of Fanø in the Wadden Sea were dated by the optically stimulated luminescence (OSL) technique. Multiple samples were recovered from each dune ridge to test the internal consistency of the ages and to establish the last time the ridges were active. The OSL ages range from 4 ± 1 yr to 318 ± 27 yr and the average age of the dune ridges from 255 ± 30 to 6 ± 2 yr. The results show that Fanø prograded between 1000 and 1500 m in the last 250 to 300 years with an average long-term progradation rate of 4 to 5 m yr−1. We argue that dune ridge formation was favoured by normal regressive conditions resulting from increased sediment supply after an extreme storm surge event in 1634, induced by a combination of regional-scale morphological changes in the updrift coastal configuration and erosion and deposition resulting from reorientation of the barrier shoreline. Increased storminess during the Little Ice Age does not appear to be directly responsible for dune building at Fanø or in the Danish Wadden Sea but may have contributed to an overall increased sediment supply along the coast. In a regional context, dune ridge building was controlled by the inherited morphology of the shoreline that forms a large-scale embayment favouring sediment surplus and regressive conditions in the inner part to the embayment and sediment deficit and transgressive conditions along protruding parts of the embayment. It is further argued that increased marine sediment supply due to changes in local to regional scale coastal morphology and changes in climatic drivers can be equally important controlling dune ridge formation.

Anatomy of a late Quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI

The data set of the island of West Caicos consists of a combination of high-resolution lidar and digital imagery, radiometric data, and amino acid racemization (AAR) D/L values as well as extraordinary preservation of sedimentary and bio-constructed deposits on the island. Together with a well-established regional stratigraphic framework from the neighboring Bahamian island chain and detailed field mapping, the West Caicos data set provides an opportunity to advance our understanding of the link between carbonate stratigraphy and the controlling parameters of sea level, sediment supply, tectonics, and climate. The exceptionally well-preserved stratigraphic record of the mid–late Pleistocene from West Caicos allows recognition of marine isotope stages (MIS) 9/11, 5e, and Holocene. The west coast of the island provides a continuous 8.4 km exposure of the MIS 5e record that enhances our understanding of the intra-MIS 5e bipartite succession in this region and supports a sea-level lowering that occurred during the last interglacial (LIG).West Caicos accreted as a series of eolian, foreshore–shoreface, barrier-reef, and fringing-reef facies. Shoreline positions for all but the MIS 7 and MIS 5a/c deposits are now captured in the sub-meter geodetic-quality topobathy lidar survey. The Star Town unit of MIS 9/11 age forms the southern margin of the island as well as the central karst-modified spine, with uranium–thorium (UTh) coral ages of between 368 and 365 thousand years ago (ka) and a D/L Glu average of >0.60. Early MIS 5e strata include the Railroad Ridge unit in the center of the island, which was previously identified as one of the older units. The Railroad Ridge unit is a north–south linear dune ridge that has a D/L Glu average of 0.52 and indicates the onset of sediment sources from the east associated with a flooded central Caicos Platform. Approximately synchronously, the early MIS 5e South Reef unit (+3.75–4 m sea-level elevation) nucleated on the western coast of West Caicos, attached to the middle Pleistocene Star Town unit. The South Reef corals yield an average coral UTh age of 126.5 ka, with an average D/L Glu from skeletal matrix of 0.46. This transitional barrier/fringing reef is unconformably overlain by the late MIS 5e Boat Cove unit. Corals in the basal transgressive phase of this upper MIS 5e Boat Cove unit yield an average 120.6 ka UTh and average D/L Glu of 0.45. Shallow-marine, foreshore, and eolian facies of the late MIS 5e rest on a wave-cut terrace that cuts the early MIS 5e South Reef unit by as much as 3 m down to a +0.5 m above present sea-level elevation. The upper MIS 5e Boat Cove unit displays a maximum of +4.5 m elevation above present-day sea level, measured from the middle of the foreshore. This estimate may be a minimum value as the exposures on the west coast are part of a forced regressive foreshore sequence. Last stages of the upper MIS 5e deposition are seen in a series of regressive dune-beach ridge deposits referred to as the Northeast Ridges unit, with sea-level positions ranging from +4.5 m early in the central part of West Caicos, to +0.5 m on the far northeast coast, eventually building down below present-day sea level. This sea-level history fits well with previously documented records in the Bahamas and globally, and the extensive erosion supports a short-lived (between 126 and 120 ka) intra-MIS 5e relative-sea-level fall. Holocene deposition on West Caicos is restricted to northern and eastern margins of the island as a combination of strandplain and dune ridge mixed skeletal–oolitic units.Using the high-resolution digital elevation model (DEM) and linked digital geologic map makes it possible to compare areas of the different Pleistocene and Holocene units quantitatively and to constrain volumetric assessments and accumulation rates on the island for different units. The peak sediment volume production/accumulation rate—between 6.5 and 8 × 106 m3 or between 2.2 and 2.7 × 106 m3 per ka—is observed in the upper MIS 5e unit. This rate is 5 times greater than the 0.5 × 106 m3 per ka estimated for the Holocene ooid dune-ridge/strandplain complex, suggesting that the combination of higher sea level, greater wave and wind energy, and warmer ocean temperatures may have fostered the higher rate of chemically precipitated sediment supply.

Long-Term GIS Analysis of Seaside Impacts Associated to Infrastructures and Urbanization and Spatial Correlation with Coastal Vulnerability in a Mediterranean Area

The relationship between the impacts of coastal perimeter transformations derived from human activity and coastal vulnerability is not easy to assess. The impacts associated with coastal dynamics are phenomena that usually develop very extensively over a considerable time. These are transformations that cause significant environmental damage in vulnerable coastal areas, but whose results are very often not really visible until 10, 20, or even 40 years have elapsed. In addition, the analysis and quantification of the current context in complex territories is particularly difficult, since the spatial feedback of various issues and its consequences can generate an uncertain scenario with many interrelated variables. In this field, the use of GIS tools can be of great help to objectively analyze the relationship between coastal anthropization and its impact on its vulnerability in order to correct wrong inertias in vulnerable coastal areas. To this end, a long-term GIS analysis has been carried out of the impacts from urbanization and seaside infrastructures suffered by a complex Mediterranean coastal area in Spain. This territory, with singular elements such as dune ridges, beaches located in protected areas, and a coastal lagoon, will be evaluated using GIS spatio-temporal indicators over the last 90 years and geostatistical correlation methods. This approach will allow us to better understand the relationship between territorial transformations on the coast and the current coastal vulnerability of this area.

Pollination networks along the sea-inland gradient reveal landscape patterns of keystone plant species

Linking the functional role of plants and pollinators in pollination networks to ecosystem functioning and resistance to perturbations can represent a valuable knowledge to implement sound conservation and monitoring programs. The aim of this study was to assess the resistance of pollination networks in coastal dune systems and to test whether pollination interactions have an explicit spatial configuration and whether this affect network resistance. To this aim, we placed six permanent 10 m-wide belt transects. Within each transect we placed five plots of 2 m x 2 m, in order to catch the different plant communities along the dune sequence. We monitored pollination interactions between plants and pollinators every 15 days during the overall flowering season. The resulting networks of pollination interactions showed a relatively low degree of resistance. However, they had a clear spatial configuration, with plant species differently contributing to the resistance of pollination networks occurring non-randomly from the seashore inland. Our results evidenced that beside contributing to the creation and maintenance of dune ridges, thereby protecting inland communities from environmental disturbance, plant species of drift line and shifting dune communities have also a crucial function in conferring resistance to coastal dune pollination networks.

SOIL CONTAMINANT SAMPLING RESULTS FROM LOWER RIO GRANDE VALLEY NATIONAL WILDLIFE REFUGE'S BOCA CHICA TRACT, CAMERON COUNTY, TEXAS

SOIL CONTAMINANT SAMPLING RESULTS FROM LOWER RIO GRANDE VALLEY NATIONAL WILDLIFE REFUGE'S BOCA CHICA TRACT, CAMERON COUNTY, TEXAS

Distribution Pattern of Red Fox (Vulpes vulpes) Dens and Spatial Relationships with Sea Turtle Nests, Recreation, and Environmental Characteristics

Although sea turtles are formidable prey as adults, their nests are highly vulnerable to terrestrial predation. Along the Southeastern coast of the United States, a primary predator of sea turtle nests is the red fox (Vulpes vulpes). Examining the relationship between fox populations and nest predation is often difficult due to coastal development. Masonboro Island, North Carolina is an undeveloped, natural, 13-km-long barrier island complex that is a component of the North Carolina National Estuarine Research Reserve (NERR). Masonboro Island consists of beaches, a dune ridge, back barrier flats, an expansive salt marsh, a lagoon, and spoil islands seaward of the Intracoastal Waterway. A field survey, which was conducted each spring from 2009 through 2012, recorded den entrance coordinates based upon recent use by foxes. Sea turtle nests were located using a similar survey methodology, which identifies viable and predated nests as well as false crawls. A series of spatial-temporal pattern analysis techniques were used to identify trends through time. The results indicated that: (1) fox den entrances and predated sea turtle nests were clustered throughout the island (p = 0.01); (2) den entrances in the northern part of the island were closer to the sea turtle nests than other locations on the island; (3) fox den entrances were positively correlated (p = 0.01) with dune height, (4) fox den entrances were located closer to the island boat access sites than expected (p = 0.01). A variety of spatial sensitivity tests were used to test the validity of the statistically significant cluster analyses. A Geographically Weighted Regression model was created to predict the location of fox dens using dune elevation, the distance to predated sea turtle nests, and the distance to boat access sites. The model accounted for 40% of the variance and had a small residual error, which indicates that the independent variables were statistically valid. Results from this project will be used by the NC NERR staff to develop management plans and to further study fox-related impacts on the island. For example, given the higher density of fox den entrances on the northern part of the island, managers may consider targeted wildlife control measures during the sea turtle nesting season to diminish predation.

Insights into barrier-island stability derived from transgressive/regressive state changes of Parramore Island, Virginia

Barrier islands and their associated backbarrier ecosystems front much of the U.S. Atlantic and Gulf coasts, yet threshold conditions associated with their relative stability (i.e., state changes between progradation, erosion, and landward migration) in the face of sea-level rise remain poorly understood. The barrier islands along Virginia's Eastern Shore are among the largest undeveloped barrier systems in the U.S., providing an ideal natural laboratory to explore the sensitivity of barrier islands to environmental change. Details about the developmental history of Parramore Island, one of the longest (12 km) and widest (1.0–1.9 km) of these islands, provide insight into the timescales and processes of barrier-island formation and evolution along this mixed-energy coast. Synthesis of new stratigraphic (vibra-, auger, and direct-push cores), geospatial (historical maps, aerial imagery, t-sheets, LiDAR), and chronologic (optically stimulated luminescence, radiocarbon) analyses reveals that Parramore has alternated between periods of landward migration/erosion and seaward progradation during the past several thousand years. New chronology from backbarrier and barrier-island facies reveals that Parramore Island has existed in some form for nearly 5000 years. Following a period of rapid overwash-driven retrogradation, and coinciding with a period of slow relative sea-level rise (~1 mm/ yr), Parramore stabilized ~1000 years ago in partial response to pinning by and sediment delivery from erosion of a Pleistocene-aged antecedent high. Following pinning, Parramore built seaward through development of successive progradational beach and dune ridges. Morphological and historical evidence suggests that these processes were interrupted by inlet formation—possibly associated with an interval of enhanced storminess—at least three times during this period. Following inlet closure in the early 1800s, island progradation was rapid, with Parramore Island reaching its maximum width ca. 150 years ago. It has since switched states again, undergoing accelerating erosion (~12 m/ yr since 1980). The relative youth of Parramore Island is in contrast to many East Coast barrier islands, which generally reached their present positions about 3500–2000 years ago. Moreover, these results demonstrate that the apparent robustness and stability of Parramore are ephemeral features of an island that has undergone multiple state changes within the last 1000 years. Finally, they refine current knowledge of the roles of antecedent topography, sediment delivery rates, storms, and sea-level rise in barrier-island stability and resilience to future climate change.

Diversity and dominance patterns in Amazon coast dune forest island tree communities

Aiming to better understand richness, dominance, diversity and community changes of coastal vegetation, we studied woody plant communities and soil parameters of equatorial dune forest islands. We investigated four sites isolated by mangroves (Buraco Beach, Bonifacio, Camarauacu, Apeu-Salvador) and compared data to a paleodune forest with higher floristic and structural complexity (Salinas do Roque) for assessment of the regional species pool. We determined grain size distribution and organic matter content at Buraco Beach, Camarauacu and Apeu-Salvador. Grain size distribution was similar among sites but upper soil layers at Camarauacu showed low organic matter contents. We recorded trees and shrubs along several transect plots crossing forested dune ridges and surveyed areas outside of plots for additional species. Richness was lower at Camarauacu (18 species vs. 25, 26 and 28 at Bonifacio, Apeu-Salvador and Buraco Beach, respectively). Fisher’s α ranged between 3.2 and 4.7, Pielou’s J’ between 0.70 and 0.80. Renyi profiles confirmed lower diversity for Camarauacu, dominated by a small group of species with high importance values. Within-site beta diversity was lowest at Buraco Beach. Species were mainly wide-spread generalists. We found low richness compared to the Salinas do Roque reference site; null model tests indicated that the species pool of the dune sites was partly shaped by environmental filtering. We attribute differences in species composition and diversity/dominance patterns among the four dune sites to distance to the mainland and stochastic events with effects on non-standard long distance dispersal.

Sand-grain micromorphology used as a sediment-source indicator for Kharga Depression dunes (Western Desert, S Egypt)

Abstract Roundness and surface-feature characteristics of sand grains collected from two dune ridges in Kharga Depression (southern Egypt) were tested for potential use as source-to-sink indicators of dunes movement. Grain examination was accommodated through Scanning Electron Microscope (SEM) analysis. Five grain types were distinguished: A) fresh; B) sheet precipitated with “raindrop” structures; C) platy precipitated; D) broken; and E) with chemically etched surfaces—each type diagnostic of a specific geomorphic inheritance. Regarding the level of sphericity, these grains were subdivided into nine roundness classes (0.1–0.9), where angular grains are marked by 0.1 and very well-rounded grains by 0.9. Significant roundness and grain-type surface variations are observed both along dune ridges and between them. Poorly and medium-rounded grain populations dominate, along with sheet-precipitated grains. The contribution of well- and very well-rounded grains is low. The northern part of both eastern and western dune ridges is characterized by grains that represent high-energy aqueous environments with well-rounded grains, whereas platy precipitated grains with a lower level of roundness are concentrated in the middle part of the dune ridges. The southern part of the Kharga Depression is again characterized by sheet-precipitated grains. Our results indicate that the northern part of dune ridges in the Kharga Depression is mainly built of sands that originate from beyond the depression ( e.g., Ghard Abu-Maharik) and the weathered deposits of the Nubian and Moghra Sandstones. The dunes in central and southern part of the Kharga Depression also derive sand from a local depression bottom comprised of playa and fluvial deposits. The growing importance of the local sand source may be explained by the lowering of the local groundwater table, which resulted in playa drying. This groundwater loss resulted in the degradation of the vegetation cover, facilitating an increase in wind entrainment of playa sediments.

Special issue – coastal dune slack hydro-ecology

Coastal dune slack wetlands exist at the interface between land and sea. They typically occur in the low-lying areas between dune ridges where the water table remains at or near the ground surface for some or all of the year. Like many wetland habitats, the hydro-ecological conditions provide a niche in which specially adapted species can exist. Notable dune slack species with European protection include the natterjack toad (Bufo calamita) and the fen orchid (Liparis loeselii). Dune systems are amongst the most dynamic of all habitats and dune wetlands can appear or disappear in timescales comparable to human lifespans as coastal processes deposit or erode the substrates upon which they form. It is these dynamic processes that create areas of bare sand suitable for development of early successional stages of dune vegetation whilst elsewhere in the dune system natural succession drives a progression towards more mature vegetation. Over time, anthropogenic pressures including afforestation, abstraction and addition of nutrients have resulted in a decline in the quality and extent of dune habitat such that the majority of humid dune slacks across Europe are now in unfavourable condition. Management to address these pressures and improve dune habitats is underway in many countries however the complex mix of natural and anthropogenic processes that influence dune wetlands is at times difficult to disentangle making it hard to identify the most suitable management practices at particular sites. Up to now effective management of these habitats has not been supported by a coordinated presentation of the relevant research. The establishment of multidisciplinary groups such as the UK Sand Dune and Shingle Network has proved effective in bringing together the range of expertise necessary to affect change. This special issue is the result of the second meeting of the network’s Sand Dune Hydrology Group which was held in Swansea in September 2013 with the intention of supporting effective habitat management through sound science.

A novelty coastal susceptibility assessment method: application to Valdelagrana area (SW Spain)

The main aim of this paper is to present a new methodology to determine coastal susceptibility to erosion and flooding processes by means of an index-based method. The proposed indices take into account physical parameters, such as dune and beach geomorphologic characteristics, shoreline evolution, local significant wave height and relative run-up. The coastal susceptibility has been estimated by elaboration of spatial input data into a GIS environment. The method has been tested in Valdelagrana area, a sandy spit located in SW Spain. The spit includes several morpho-sedimentary environments: sandy beach, discontinuous embryo dunes and foredunes, mud flats and wide areas of vegetated salt marshes. The Northernmost sector is densely urbanized whilst the rest is part of a natural protected area belonging to the Bahia de Cadiz Natural Park. The results obtained showed how the Southern part of the spit presented a high susceptibility due to an elevated erosion rate and the presence of low and discontinuous dune ridges.