Barrier Dune Research Articles

Morphological characteristics and dynamic changes of typical climbing dunes on the Qinghai-Tibet Plateau

Climbing dunes are a form of topographic barrier dunes that feature in the aeolian landforms on the Qinghai-Tibetan Plateau. Topography fundamentally influences the spatial distribution and morphological characteristics of climbing dunes by modifying the near-surface airflow and creating space for sediment deposition. Previous studies have considered several aspects of the influence of topography on aeolian landforms. However, morphological differences between climbing dunes in different geomorphic contexts and dynamic changes in the area have received little attention. Therefore, topographic measurements, near-surface flow field measurements, dune morphology analysis, and remote sensing image analysis were combined to explore relationships between dune morphology and topography. Topographic obstacles can accelerate the near-surface airflow, particularly with a 25–35° slope gradient, which is beneficial for sand transport and deposition. Suitable accommodation space (concave slope morphology) and abundant sediment comprise the primary factors that control the scale and morphological diversity of climbing dunes, which are also influenced by a variable wind direction. In general, the morphology of the climbing dunes becomes progressively more complicated from the bottom to the middle of the windward slope, and the sand ridge lines of the dunes are perpendicular to the prevailing wind direction. Based on the influence of climate and human activities, the total area of climbing dunes in this region has decreased over the past 30 years. Despite general evidence of enhanced human-induced desertification in semi-arid and sub-humid regions, warming has not led to the rapid expansion of climbing dunes in these arid locations. This research offers new insights into the relationship between the terrain and dune morphology, enriching the theoretical basis for the plateau aeolian geomorphology. Furthermore, it allows us to consider the dynamic changes in climbing dunes area in the context of global warming.

Wind–Wave Conditions and Change in Coastal Landforms at the Beach–Dune Barrier of Cesine Lagoon (South Italy)

Several coastal barriers experienced significant erosion and change in shape throughout the Mediterranean coasts over the past decades, and the issue has become of increasing concern for scientists and policymakers. With reference to a case study and by meteorological and geomorphological investigations, this note aims to define the wind–wave conditions, infer the net longshore transport, and detect the geomorphological processes that shape the landforms of the Cesine Lagoon barrier (South Italy). Despite the importance of the site in coastal defense and environmental conservation, there are still no specific studies. A challenge for this research was to obtain significant results from publicly available sources and simple and inexpensive methods. Geomorphological changes, such as the retreat of dune toes, accretion of washover fans, and formation of gravel beaches, are related to the analyzed wind–wave conditions. The net longshore transport is found in accordance with the direction of the more intense winds. The role of extreme events in the shaping of coastal landforms is yet to be established, even if they greatly increase the vulnerability to flooding of the study area. The results achieved so far are starting points for further data collection and analysis in the perspective of assessing the impact of climate changes and the threatening hazards on the lagoon barrier.

Development and preservation of transgressive sandy versus rocky shorelines: Observations from the SE African shelf

Relict rocky shorelines are seemingly rarely preserved in the geological record, often underrepresented in the literature and the reasons for their scarcity, as well as the conditions needed for preservation are not well understood. On the “Wild Coast” shelf along the subtropical east coast of South Africa a series of submerged shorelines are present. High-resolution multibeam bathymetry, side scan sonar, ultra-high-resolution seismic profiling and legacy seismic reflection data show several fluvial channels incised into the shelf, associated with the Last Glacial Maximum (LGM) lowstand. Palaeo-shorelines are preserved at −85, −75, −60 and −40 m. The −85 and −75 m shorelines reflect sediment abundance and depositional features preserved as lagoonal depressions, lithified barrier-spits and coastal barrier dunes with limited bedrock influence. The shallower shorelines at −60 and −40 m occur on a steeper shelf gradient and reflect the development of rocky headlands, palaeo-cliffs and rock shore platforms. Their occurrence implies increasing bedrock control, erosion and sediment bypass during transgression.The preservation of rocky shoreline signatures on the inner shelf is aided by competency of the bedrock lithologies, in addition to their depth relative to sea-level stillstands and rapid rises in sea level associated with meltwater pulses (MWPs) (notably the −60 m shorelines and MWP1B). MWPs may have helped facilitate the overstepping and eventual preservation of these shoreline landforms on the seabed. Preservation of the −40 m shoreline is considered to correlate with accelerated rates in sea- level rise prior to MWP1C. The preservation of the −85 and −75 m aeolianite shorelines are not linked to meltwater pulses, however, their substantial sediment volume precluded total loss through transgressive erosion and this, coupled with early cementation, promoted their partial preservation. Such deposits rarely survive subaerial exposure but could be preserved if covered by marine sediments. Conversely, the existence of well-preserved, Pleistocene-age rocky shorelines on the shelf points to their high potential for inclusion into the longer-term geological record under subsequent high or low sedimentation. The formation of distinctive rocky shorelines, however, may reflect alternating slow and fast rates of sea-level rise.

ESR dating of optically bleached quartz grains from Plio-Pleistocene to Holocene coastal dune deposits (Wilderness-Knysna area, South Africa): a comparison with luminescence

Five Plio-Pleistocene to Holocene aeolian quartz samples from the coastal dune deposits of the Wilderness-Knysna area (South Africa) previously dated by OSL were selected for ESR dating. Samples were processed following the Multiple Centre approach and using the Multiple Aliquot Additive dose method. Aluminium (Al) and Titanium (Ti) signals were systematically measured in all samples. Our study shows that ESR results obtained for Middle Pleistocene to Holocene samples may be strongly impacted by (i) the presence of a significant high frequency noise in the ESR spectra acquired for the Ti signals and (ii) the choice of the fitting function employed. In particular, if not taken into account, very noisy spectra can lead to a significant overestimation of the true ESR intensity measured for the Ti–H signal. These sources of uncertainty are however not sufficient to remove the ESR age overestimations. Consequently, our results indicate that the Al and Ti ESR signals of these quartz samples have not been fully reset during their aeolian transport. While this work contributes to improve our understanding of the ESR method applied to quartz grains, and especially of the potential and limitations of the Ti signals, it also provides additional baseline data to illustrate the existing variability among quartz samples of different origins or sedimentary context. Our results are consistent with previous studies by confirming that the Ti–H signal shows the best potential for the evaluation of low dose values (<100 Gy for these samples), whereas it becomes inappropriate for the higher dose range, and the Ti–Li–H (option D sensu Duval and Guilarte, 2015) should be used instead. Beyond the methodological outcome, this ESR dating study also provides a useful addition to the existing chronology of the aeolian deposits in this region. In particular, new (and possibly) finite numerical age results were obtained for the two oldest samples, constraining the aeolianite landward barrier dune and the coversand formations to the MIS 10-8 and Pliocene, respectively.

A chemical and isotopic approach to investigate groundwater dynamics in a coastal aquifer

The hydrogeological processes in two different zones of a sandy coastal aquifer of the province of Buenos Aires, Argentina, have been assessed on the basis of hydrochemical tools and environmental isotopes (2H and 18O). In general, groundwater in the sand dune barrier is either a Ca-HCO3 or a Na-HCO3 type, whereas in the coastal plain it is a NaCl type. In general terms, the isotopic composition of groundwater matches the average isotopic composition of the rainfall, which would indicate that there is no significant fractionation during the recharge process. However, the interpretation of data allowed the detection of different processes— rapid infiltration, selective infiltration, evaporation, mineral dissolution and mixing—in certain locations. The last process mentioned includes both natural lateral and vertical interface mixing, as well as the one generated by anthropogenic action (saline intrusion). There is a relationship between the variability of the isotopic contents and the thickness of the unsaturated zone. In the northern zone, its lesser thickness causes greater variability in isotopic contents, whereas in the southern zone a greater thickness is suggested by more homogeneous, clustered values. In both zones, selective infiltration was observed; they were represented by both highly depleted and highly enriched isotopic contents, as well as evaporation processes occurring prior to infiltration. Besides, in both zones it was possible to recognise the effects of the displacement of the freshwater–saltwater interface towards the continent as a consequence of intensive groundwater exploitation. The mixing percentage of salt water is about 51% for both conservative elements oxygen-18 and chloride. The importance of the association of hydrochemical and isotopic methodologies stands out as a tool in the sustainable management of groundwater resources in coastal sand-dune regions.

Latitudinal pattern of the thermal sensitivity of running speed in the endemic lizard Liolaemus multimaculatus.

Physiological performance in lizards may be affected by climate across latitudinal or altitudinal gradients. In the coastal dune barriers in central-eastern Argentina, the annual maximum environmental temperature decreases up to 2°C from low to high latitudes, while the mean relative humidity of the air decreases from 50% to 25%. Liolaemus multimaculatus, a lizard in the family Liolaemidae, is restricted to these coastal dunes. We investigated the locomotor performance of the species at 6 different sites distributed throughout its range in these dune barriers. We inquired whether locomotor performance metrics were sensitive to the thermal regime attributable to latitude. The thermal performance breadth increased from 7% to 82% with latitude, due to a decrease in its critical thermal minimum of up to 5°C at higher latitudes. Lizards from high latitude sites showed a thermal optimum, that is, the body temperature at which maximum speed is achieved, up to 4°C lower than that of lizards from the low latitude. At relatively low temperatures, the maximum running speed of high-latitude individuals was faster than that of low-latitude ones. Thermal parameters of locomotor performance were labile, decreasing as a function of latitude. These results show populations of L. multimaculatus adjust thermal physiology to cope with local climatic variations. This suggests that thermal sensitivity responds to the magnitude of latitudinal fluctuations in environmental temperature.

State changes: insights from the U.S. Long Term Ecological Research Network

AbstractUnderstanding the complex and unpredictable ways ecosystems are changing and predicting the state of ecosystems and the services they will provide in the future requires coordinated, long‐term research. This paper is a product of a U.S. National Science Foundation funded Long Term Ecological Research (LTER) network synthesis effort that addressed anticipated changes in future populations and communities. Each LTER site described what their site would look like in 50 or 100 yr based on long‐term patterns and responses to global change drivers in each ecosystem. Common themes emerged and predictions were grouped into state change, connectivity, resilience, time lags, and cascading effects. Here, we report on the “state change” theme, which includes examples from the Georgia Coastal (coastal marsh), Konza Prairie (mesic grassland), Luquillo (tropical forest), Sevilleta (arid grassland), and Virginia Coastal (coastal grassland) sites. Ecological thresholds (the point at which small changes in an environmental driver can produce an abrupt and persistent state change in an ecosystem quality, property, or phenomenon) were most commonly predicted. For example, in coastal ecosystems, sea‐level rise and climate change could convert salt marsh to mangroves and coastal barrier dunes to shrub thicket. Reduced fire frequency has converted grassland to shrubland in mesic prairie, whereas overgrazing combined with drought drive shrub encroachment in arid grasslands. Lastly, tropical cloud forests are susceptible to climate‐induced changes in cloud base altitude leading to shifts in species distributions. Overall, these examples reveal that state change is a likely outcome of global environmental change across a diverse range of ecosystems and highlight the need for long‐term studies to sort out the causes and consequences of state change. The diversity of sites within the LTER network facilitates the emergence of overarching concepts about state changes as an important driver of ecosystem structure, function, services, and futures.

Variability of 222Rn in the sandy aquifer of Buenos Aires coast

222Rn is widely used as a tracer to detect and calculate submarine groundwater discharge in coastal zones, rivers and lakes. Relatively few investigations, however, have used this element for other applications in hydrogeology. We analyze the relationship between 222Rn activity in groundwater and variations in the water cycle in the sandy aquifer of Buenos Aires coast, Argentina. Groundwater levels, electrical conductivity and 222Rn activity were measured in situ in wells in March 2016 and November 2018, representing two different hydrological conditions. Groundwater flow maps were drawn, hydrological gradients and flux velocities were calculated. An inverse correlation between 222Rn activity and recharge conditions was found. Lower water surplus shows higher 222Rn activity and vice versa, potentially due to dilution of high 222Rn activity water with ‘newer’ lower activity recent recharge. A variability in 222Rn spatial distribution was identified along the sand dune barrier. A correlation between 222Rn and groundwater electrical conductivity was not observed.

Autonomous anchoring for robotic construction

Advances in construction automation have tended to focus on either automating conventional earthmoving equipment or on the discrete assembly of superstructure elements. Neither paradigm has addressed anchoring introduced material into soil, a critical task for virtually all useful structures. Simple anchoring can be achieved by driving posts (discrete linear elements) or sheet piles (interlocking profiles) into the ground, serving as a foundation for a later superstructure. In this paper we present Romu, a wheeled robot that uses a combination of a vibratory hammer and its own body mass to drive both posts and piles into the ground. We report on the effects of hardware parameters on pile driving performance, and demonstrate operation in both controlled and natural environments. Romu is first configured to drive interlocking sheet piles. In addition to their utility as foundations, such walls could be useful directly as check dams, interventions used to prevent erosion and promote groundwater recharge in arid regions. We use simulations based on real-world terrains to explore the potential impact of a fleet of such robots deployed over a large watershed region, using a simple reactive approach to dynamically determine dam placement. Romu is then configured to drive a range of readily available building materials that commonly serve as posts. These include wooden slats that can be used for sand fencing, an intervention used to collect wind-blown sand to build barrier dunes. Post driving performance is characterized for a range of materials, and finally the use case of sand fencing is evaluated using physical tests at 1:10 scale in order to predict its potential impact. To broaden the utility of such robots in field settings, directions for future work include refinement of the hardware for improved operation in more terrains, increased capabilities for fuller autonomy, and integration with other construction tasks for more complex projects.

Landscape Change and Associated Increase in Habitat Fragmentation During the Last 30 Years in Coastal Sand Dunes of Buenos Aires Province, Argentina

The Eastern Barrier of Dunes (EBD) and Southern Barrier of Dunes (SBD) extend along the coast of Buenos Aires province, Argentina. These regions have been severely altered by anthropic activities for years, mainly through the development of cities and afforestation with exotic species. We quantified the effect of anthropic activities on the landscape of coastal dunes, evaluating its temporal evolution during the last 30 years. Using Landsat satellite images from 1985, 1996, 2005, and 2015, we performed supervised classifications and obtained thematic maps for coastal dune barriers. Over these maps, we quantified the main classes of natural habitats and anthropic environments and analyzed changes in their extent and arrangement over time. Temporal analyses showed a gradual replacement of anthropic environments over natural habitats. During the last 30 years, the area impacted by anthropic activities went from 13 to 31.7% on the EBD and from 3.6 to 5.9% on the SBD. In the SBD, fragmentation along the main natural habitats increased over the years, whereas fragmentation along the EBD, although higher than that in SBD, remained constant through time. Drastic reductions of the extent of natural habitats were recorded at or near areas where anthropic environments developed. Both coastal dune barriers showed a clear advance of anthropic fragmentation over coastal dune habitats, with EBD being the most impacted by human activities.

Exploring Sea Country through high-resolution 3D seismic imaging of Australia’s NW shelf: Resolving early coastal landscapes and preservation of underwater cultural heritage

Almost 2 million square km of Australia’s continental shelf was flooded following the termination of the last glacial maximum, and with it the cultural heritage of the first arrival and coastal occupation of Australia beginning some 65,000 years ago. In order to prospect for this missing cultural record, we must first identify submerged coastal landscapes and landforms that likely provided favourable environments for occupation and resource use. However, this task is challenged by the sheer size of the Australian continental margin. To help address this, we use industry 3D seismic datasets, that cover vast areas of Australia’s continental shelf, to map seafloor bathymetry at high resolution (10–25 m). Our study focuses an area of 6500 square km on the mid/outer shelf regions proximal to Barrow Island. The 3D seismic bathymetry revealed a highly complex and geomorphically mature coastal landscape preserved at depths of 70–75 m below sea level, including coastal barrier dunes, lagoonal systems, tidal flats and estuarine channels. Based on the depth of the submerged shorelines and reconstructed sea level curves, the age range of these coastal landforms is constrained to Marine Isotope Stage 3 (57–29 ka), which overlaps with the known onset of occupation at Barrow Island and the wider Carnarvon bioregion and the adjacent Pilbara. Such feature preservation has significant geoheritage value, but also allows for human behavioural ecology modelling and provides targets for future dating and site survey.

How bottom-up and top-down controls shape dune topographic variability along the U.S. Virginia barrier island coast and the inference of dune dynamical properties

When topography is incorporated into models of barrier dune dynamical states, how it is represented determines the dynamical properties inferred. Bottom-up representations rely on elevation and localized biogeomorphic modification. Top-down representations incorporate constraints imposed by the spatial patterns of topography. These spatial patterns emerge from island morphological context and the extent localized biogeomorphic processes can expand and structure the larger landscape. We compared topographies across 30 sites among seven barrier islands of the Virginia (U.S.A) coast to gauge the importance of elevation, the bottom-up variable often weighted most in dune biogeomorphic models, relative to top-down patch and continuous surface landscape representations of topography. LiDAR-derived digital elevation models of each site were characterized with non-metric multidimensional scaling to assess how these bottom-up and top-down metrics structured dune topographic variability. Multiple response permutation procedures gauged the strength of topographic differences among sites grouped according to island morphology versus groupings defined by clustering of topographic metrics. Elevation was the dominant metric structuring topography for these low relief islands. Spatial structure was weakly developed. Topographic differences were more robust when based on clusters defined largely by elevational properties rather than by island or island morphological type. For the Virginia barrier islands, storm inputs may more directly shape topography and override landscape-extent top-down spatial structure. The dominance of elevation suggests that resistance may be the more relevant dynamical property for this coast. Properties like resilience may be greater on higher islands with longer storm-free intervals in which biogeomorphic elements can configure relief and act as recursive top-down controls.

Wetland management: preparing for climate and coastal change using adaptation pathways

Freshwater ecosystems are among the most threatened in the world. The list of threatened species in freshwater ecosystems is greater than that in terrestrial or marine systems and freshwater vertebrates are particularly at risk. Freshwater wetlands have evolved in coastal zones protected from tidal influence by barrier dune systems. Similarly, estuaries have supported zones of low salinity diluted by flows from land, but water resource development has limited these flows and driven ecological change in estuarine systems. These historical uses of river flows, and the impacts of catchment development on water quality and yields, have combined to threaten coastal wetland ecosystems. They are now under increasing threat through climate change driven alterations to hydroclimatic conditions, as well an rising sea levels which risk inundation of low lying coastal regions, including wetlands. Coastal freshwater systems offer considerable ecosystem services to human systems and host significant biodiversity assets. These have been subjected to increased risk through catchment and coastal development, but are now acutely threatened through changed river flows and elevated sea levels that result from climate change. Managing these systems requires an adaptation pathways approach that accommodates human needs, and society’s obligations to global biodiversity.

Multiple Representations of Topographic Pattern and Geographic Context Determine Barrier Dune Resistance, Resilience, and the Overlap of Coastal Biogeomorphic Models

We compared two biogeomorphic models that postulate how vegetation is intertwined in the response and recovery of barrier island dunes. Each model was developed in a separate coastal region using different methods. Both relied on simple elevational representations of topography. By comparing topographies among more islands of these two regions and by linking multiple representations of topographic pattern to resistance and resilience, we provide a synthesis that shows the validity of both models and the consequences of reifying one over the other. Using airborne LiDAR, topographic metrics based on point, patch, and gradient representations of topography were derived for fifty-two sites across eleven islands along the Georgia Bight and Virginia. These seventeen metrics were categorized in terms of resistance and resilience to disturbance from storm-forced high water levels and overwash. Resistance refers to intrinsic properties that directly counter expressions of power from disturbance. Resilience refers to the degrees of freedom to adjust and adapt to disturbance. Using a cross-scale data modeling approach, these data were visualized as topographic state space using multidimensional scaling. In this state space, similarity in topography as well as resistance and resilience were inferred through a site’s position along low-dimension axes representing geomorphic resistance and high-dimension axes representing the spatial landscape properties of biogeomorphic resilience. The two models overlap in how they account for barrier dune resistance and resilience along the U.S. south Atlantic coast. Islands of the Georgia Bight have a propensity for higher resistance and resilience. The Virginia islands have lower resistance and resilience. Key Words: barrier islands, biogeomorphology, cross-scale structure, dunes, resilience.

Effects of checkerboard barriers on the distribution of aeolian sandy soil particles and soil organic carbon

Sand-barrier setup is an important measure to protect the topsoil against wind erosion. Salix psammophila checkerboard barriers are used widely in the Mu Us Sandy Land in order to ensure the safety of life and agricultural production. To measure variations in soil structure and quality caused by barriers with different duration (7 years and 2 years), the composition of aeolian sandy soil particles and the soil organic carbon (SOC) distributions are studied; the dunes with no barrier are used as controls (CK). Analyzed by multi-fractal parameters, the topsoil samples are collected in the field and tested in the laboratory.The predominant soil particles are fine sand, medium coarse sand and clay, and the contents of silt and very fine sand increase with extending barrier duration, which shows a wider distribution range, greater dispersion degree and larger soil particle heterogeneity. The aeolian sandy particles, particularly fine granular grains, are deposited and accumulate at the bottom and top of dunes because of the barrier blocking effect.The particle size distribution (PSD) heterogeneity is the highest in 7-year barrier dunes and the lowest in the no barrier dunes. The mean values of D0 (Capacity dimension) of 7-year barrier dunes, D1 (entropy dimension) of the no barrier dunes and D1/D0 of 2-year barrier dunes are maxima. In addition, the PSD range and distribution increased with prolonged dune barrier duration, as well as the changes of Δf(∂) (shape of the multi-fractal spectrum) and Δ∂ (width of multi-fractal spectrum).SOC content increased with increasing barrier duration and decreasing D1/D0. The average SOC contents of 7-year barrier dunes were the maximum and one of no barrier dunes had the minimum SOC content, and their difference was significant (P < 0.05). In both the PSD and SOC distribution, the 7-year barrier showed better results on the topsoil than that of 2-year and no barrier situation.Correlations between the SOC content and the PSD multi-fractal parameters of both 7-year and 2-year barrier dunes are significantly different (P < 0.01). The multi-fractal parameters can be used to indicate soil nutrient contents, which provide fundamental knowledge for evaluating the effectiveness of ecological engineering to restore soil quality and structure to sandy ecosystems. Salix psammophila checkerboard sand barriers play a role in increasing the fine particles and soil organic carbon in surface dune soil, which is helpful in restoring the Mu Us sand ecosystem. The early use of sand barriers is therefore recommended.

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.

Transport of Radium and Nutrients Through Eastern South African Beaches

AbstractSubmarine groundwater discharge (SGD) plays a critical role in coastal and ocean biogeochemistry. Elucidating spatially and temporally heterogeneous SGD fluxes is difficult. Here we use radium isotopes to explore the external sources and mixing regime along the eastern coast of South Africa. We demonstrate that the long‐lived radium isotope compositions are controlled by low inputs of low‐ and high‐salinity terrestrial groundwater. While activities of 228Ra and 226Ra in beach porewaters are similar to coastal waters, 224Ra is enriched by inputs of 228Th from coastal seawater. Porewater ages, based on the production of 224Ra from 228Th, range from 0.3 to 2.3 days, indicating rapid flushing of the beach system. Unlike radium, however, nutrients follow a more complex pathway. We hypothesize that high total dissolved nitrogen (TDN) and phosphorus concentrations in beach porewaters (TDN ranges from 1 to &gt;700 μM) and the coastal ocean (TDN ranges from 1 to &gt;40 μM) are derived from a source not enriched in radium. We speculate that this source is terrestrial water flowing below the dune barrier at depths exceeding our beach sampling depths. This water likely flows upward through breaches in the confining layer into the beach or enters the ocean directly through paleochannels. The presence of high nutrient concentrations in the coastal ocean unaccompanied by high 228Ra activities leads to the hypothesis of this additional nutrient source. These combined inputs may be of considerable importance to the coastal ecology of southeastern Africa, an oligotrophic ecosystem dominated by the nutrient‐poor Agulhas Current.

Geoheritage significance of three Pleistocene formations recording a succession of climates and sea levels on the Yalgorup Plain in southwestern Australia

The Yalgorup Plain of southwestern Australia is underlain by two limestone formations and a linear quartz-sand formation containing limestone lenses. These limestones record carbonate deposition in seagrass banks during the Pleistocene; they are capped either by a prograding beach-ridge system of small cuspate forelands or a quartz-rich shore-parallel coastal barrier. The cuspate forelands formed behind protective offshore limestone reefs within a given Pleistocene wind-and-wave field, while the quartz-rich coastal dune barrier formed under enhanced swell conditions. These formations record three different Pleistocene interglacial depositional events, separated by unconformities, each linked to a distinct climate and mean sea level. Foraminiferal assemblages within the two limestones and within the limestone lenses of the quartz-sand formation faithfully record changes in minimum seawater temperature, reflecting these changes in climate. They indicate a cycle of warm–cool–warm water accumulation of carbonates. Such a record of both climate and sea level history for southwestern Australia is unique, contributing greatly to the Pleistocene coastal sedimentary history of limestones within southwestern Australia. These formations occur within the globally unique setting of Western Australia and are conserved within a National Park and represent an outstanding record of Quaternary coastal geomorphic development in terms of both carbonate and siliciclastic sedimentation linked to both climate and sea level changes. Given their array of lithofacies, environmental setting, sea level and climate changes, as well as their biostratigraphy reflecting these changes, these formations form a sedimentary ‘package’ that is of global geoheritage significance, with many of its inherent geological features also of global to national geoheritage significance.

LAND USE AND MITIGATION EFFECTS ON BARRIER BEACH EROSION IN STORMS: CASE STUDY IN RHODE ISLAND

Sea Level Rise (SLR) and storm intensification lead to re-evaluating inundation assessments along the North Atlantic US shoreline. A particular effort is devoted to assessing coastal community risk to “100-year storm” events in Rhode Island, US, using a chain of state-of-the-art storm surge, wave propagation, and coastal erosion 2D models. Damage risks imposed on infrastructures and services incited US federal and state agencies to come up with innovative engineering solutions to improve coastal resiliency while preserving natural coastal and marine environments. This study critically evaluates available design tools used to assess the performance of two types of Natural and Natural Based Features (NNBFs) for coastal protection: natural vegetated barrier islands and dunes reinforced with Geotextile Sand-filled Containers (GSCs), on urbanized barrier islands. Comparative analyses with field data identifies the capabilities and limitations of phase averaging and phase resolving hydro-morphodynamic models used for simulating bed level changes in dissipative beaches, during 3 Sallenger storm regimes. Recommendations are provided on modeling approaches for simulating effects of vegetation and using GSCs to limit coastal erosion.

Germination responses to abiotic stress shape species distributions on coastal dunes

Plant species occupy distinct zones on coastal dunes, but the mechanisms limiting their distributions have not been fully explained. We combined field surveys of plant distributions and abiotic conditions with controlled germination experiments to assess the contribution of germination requirements to plant zonation. Species presence and abiotic conditions were measured in ten transects across the barrier dune at Waquoit Bay, Massachusetts. Germinating seeds of six species were exposed to four fully crossed treatments: pre-treatment (soaked in fresh water, soaked in salt water, or not soaked), temperature (low, moderate, or high), soil salinity (none, moderate, or high), and light (full light, shade, dark). Species distributions in the field were affected by both distance from the shore and presence of dominant shrubs. Germination tolerance of soil salinity reflected species zonation: species found on the front slope of the dune tolerated salinity, while germination of other species was limited by salinity alone or by salinity in combination with high temperature. Shrubs reduced soil surface temperature and decreased light, but these conditions had limited effects on germination. These results indicate that limitations to germination can contribute to explaining species distributions on coastal dunes.