Dune Blowouts Research Articles

Dune Blowouts as Microbial Hotspots and the Changes of Overall Microbial Activity and Photosynthetic Biomass Along with Succession of Biological Soil Crusts

Biological soil crust (BSC) constitutes a consortium of cyanobacteria, algae, lichen, mosses, and heterotrophic microorganisms, forming a miniature ecosystem within the uppermost soil layer. The biomass of different organisms forming BSC and their activity changes along with succession. Previous studies focused primarily on BSC in hyper-arid/arid regions, whereas the ecophysiology of BSC in temperate climates is still not well recognized. In order to determine changes in overall microbial activity and photosynthetic biomass in BSC at different stages of the succession of inland sandy grasslands, we analyzed dehydrogenase activity and determined the content of photosynthetic pigments. We also compared these parameters between BSC developed on the dune ridges and aeolian blowouts in the initial stage of succession. Our study revealed a significant increase in both photosynthetic biomass and overall microbial activity in BSC as the succession of inland shifting sands progresses. We found that chl a concentration in BSC could be considered a useful quantitative indicator of both the presence of photoautotrophs and the degree of soil crust development in warm-summer humid continental climates. The photosynthetic biomass was closely related to increased microbial activity in BSC, which suggests that photoautotrophs constitute a major BSC component. Dune blowouts constitute environmental niches facilitating the development of BSC, compared to dune ridges. High biomass of microorganisms in the dune blowouts may be associated with a high amount of organic material and more favorable moisture conditions. We conclude that deflation fields are key places for keeping a mosaic of habitats in the area of shifting sands and can be a reservoir of microorganisms supporting further settlement of dune slopes by BSC.

Dune toe dynamics along the urbanised macro‐tidal coast of Belgium

AbstractThe dynamics of the dune toe along the urbanised 65 km macro‐tidal coast of Belgium has been examined based on (bi‐)annual cross‐shore profiles derived from airborne LiDAR surveys conducted between 2000 and 2019. Results indicate that the average dune toe level is located at +5.9 m Tweede Algemene Waterpassing (TAW, Belgian Ordnance Datum), which is 1 m lower than the conventional dune toe level. However, this level is not static but rather increasing over time with an average rate of 2.3 cm/year, making it comparable with coastal areas along western Europe. Both landward retreat and seaward progradation of the dune toes are observed, with rates up to 2 m/year. The analysis revealed that dune growth is primarily facilitated by the development of incipient or embryonic dunes, new foredunes and modifications to the stoss slope of the original dune profile. Half of the sea‐fronting dunes were observed to be developed by brushwood fences, which had a positive effect on dune growth. At some locations, incipient dune development and shoreline progradation were observed seaward of old foredunes. Other dune regions were characterised by natural dune blowouts and management activities for recreational purposes. Dune toe reinforcements were implemented in the west to stabilise the dune toe and prevent erosion by waves. However, it was noted that if the adjacent beach accreted because of natural growth or periodic nourishment, incipient dunes could form in front of the reinforcement.

Phylogeographic structure of the dunes sagebrush lizard, an endemic habitat specialist.

Phylogeographic divergence and population genetic diversity within species reflect the impacts of habitat connectivity, demographics, and landscape level processes in both the recent and distant past. Characterizing patterns of differentiation across the geographic range of a species provides insight on the roles of organismal and environmental traits in evolutionary divergence and future population persistence. This is particularly true of habitat specialists where habitat availability and resource dependence may result in pronounced genetic structure as well as increased population vulnerability. We use DNA sequence data as well as microsatellite genotypes to estimate range-wide phylogeographic divergence, historical population connectivity, and historical demographics in an endemic habitat specialist, the dunes sagebrush lizard (Sceloporus arenicolus). This species is found exclusively in dune blowouts and patches of open sand within the shinnery oak-sand dune ecosystem of southeastern New Mexico and adjacent Texas. We find evidence of phylogeographic structure consistent with breaks and constrictions in suitable habitat at the range-wide scale. In addition, we find support for a dynamic and variable evolutionary history across the range of S. arenicolus. Populations in the Monahans Sandhills have deeply divergent lineages consistent with long-term demographic stability. In contrast, populations in the Mescalero Sands are not highly differentiated, though we do find evidence of demographic expansion in some regions and relative demographic stability in others. Phylogeographic history and population genetic differentiation in this species has been shaped by the configuration of habitat patches within a geologically complex and historically dynamic landscape. Our findings identify regions as genetically distinctive conservation units as well as underscore the genetic and demographic history of different lineages of S. arenicolus.

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.

Rainfall and grazing: not the only barriers to arid-zone conifer recruitment

An understanding of the drivers of infrequent recruitment is fundamental in managing for species persistence. Callitris glaucophylla Joy Thomps. & L.A.S. Johnson (white cypress-pine) is a slow-growing, long-lived conifer, with a distribution that extends across arid Australia. Arid populations of C. glaucophylla are endangered in New South Wales, and are characterised by infrequent recruitment. We examined recruitment patterns of C. glaucophylla in differential grazing exclosures (excluding rabbits, excluding large herbivores or excluding both) and in unfenced areas. More recruitment occurred in rabbit-proof exclosures, compared with nearby large herbivore and control exclosures, although some rabbit-proof exclosures recorded no recruitment. Increases in recruitment at several long-term exclosures were associated with wet periods, as was recruitment at some unfenced sites. Apart from grazing and rainfall, recruitment was related to mature tree size and stand density (probably because of their influence on seed availability). These endangered arid C. glaucophylla woodlands are all that remains of a once extensive distribution, and are habitat for a suite of threatened species. Reduction in grazing pressure, particularly from rabbits, is clearly critical to maintain recruitment in these remnant populations. Chances of recruitment appear to be enhanced in low-density stands, around large trees, and in dune blow outs – fencing should focus on these areas.

Disassembly of a dune‐dwelling lizard community due to landscape fragmentation

Landscape fragmentation alters patterns of landscape structure that affect quality and configuration of habitats, and disrupts population dynamics and persistence of species. Community disassembly, a process of community change due to nonrandom species losses and declines, is occurring worldwide as a result of landscape fragmentation, habitat loss, and habitat degradation. We carried out a comparative study at 27 trapping sites designed to characterize how fragmentation affects community structure in a dune‐dwelling lizard community. Lizard communities in non‐fragmented sites demonstrated nested community structure. Conversely, lizard communities at sites fragmented by roads and well pads from oil and gas development had consistently lower abundance of two species, and demonstrated random community structure. Species loss and lower abundance of species at fragmented sites suggested a pattern of community disassembly. The dunes sagebrush lizard (Sceloporus arenicolus), an ecological specialist, and the lesser earless lizard (Holbrookia maculata) were present on most non‐fragmented sites. However, neither species was present on more than half of the fragmented sites, and their abundances were much lower than on non‐fragmented sites. We attributed reduced species diversity on fragmented sites to quantitative differences in landscape configuration compared to non‐fragmented sites. Specifically, both size and shape of sand dune blowouts differed between non‐fragmented and fragmented sites. Fragmented sites possess more large patches of open sand and barren ground and fewer, smaller, and more dispersed shinnery dune blowouts. Patterns of occurrence and relative abundance suggest S. arenicolus and H. maculata were sensitive to these patch‐scale attributes. In this ecosystem, landscape‐scale fragmentation appears to influence landscape configuration and community disassembly at the patch‐scale. Our findings allow us to disentangle drivers of species loss and enhance our understanding of the processes of community disassembly in fragmented landscapes.

The twentieth-century migration of parabolic dunes and wetland formation at Cape Cod National Sea Shore, Massachusetts, USA: landscape response to a legacy of environmental disturbance

Cape Cod, an early North American colony, was covered by mature forest prior to European contact but, with settlement in the late seventeenth century, aeolian processes dominated into the twenty-first century. An aerial photographic time series from AD 1938 to 2003 quantifies dune movement that reflects processes over centuries and documents accelerated parabolic dune movement at ~4 m/yr from 1938 to 1977 during a drier interval. In contrast, dune movement between 1987 and 2003 slowed to ~1 m/yr with wetter conditions. Wetlands expand post dune movement often forming in dune blowouts with seasonally wet conditions. Stratigraphic studies, coupled with optically stimulated luminescence ages, place erosion and burial of the pre-settlement forest soil by migrating dunes at AD 1690 ± 40 yr, with aeolian deposition continuing into the nineteenth and twentieth centuries, consistent with the historic record of land surface conditions. A threshold of landscape stability was exceeded in the late seventeenth to early eighteenth centuries, indicated by dune formation in response to human-induced land-cover changes, concomitant severe droughts and exposure to tropical storm/hurricane windfield. Dune orientation indicates preferential movement during winter with winds dominantly from the W—NW and with reduced vegetation cover. The present high biodiversity in interdunal wetlands is a legacy of aeolian processes from landscape disturbance initiated by European settlers in the seventeenth century.

The scale of genetic differentiation in the Dunes Sagebrush-Lizard (Sceloporus arenicolus), an endemic habitat specialist

The Dunes Sagebrush-Lizard (Sceloporus arenicolus) is a North American species endemic to sand-shinnery oak habitats of the Mescalero and Monahans sand dunes in eastern New Mexico and western Texas. This lizard is listed as Endangered in New Mexico and exhibits habitat specificity at several geographic scales. Dunes Sagebrush-Lizards are only found in topographically complex shinnery oak (Quercus havardii) dominated landscapes within their small geographic distribution and are not found in surrounding human-altered landscapes. Within suitable sand-shinnery oak habitat, individuals predominantly occupy non-vegetated sand dune blowouts and utilize blowouts with particular physical characteristics due to thermoregulatory, reproduction, and foraging requirements. Here, we examined historical and contemporary patterns of genetic differentiation with respect to the current distribution of suitable habitat at multiple spatial scales using mitochondrial DNA sequences and microsatellite data from individuals throughout the entire range. We found three genetic clusters of individuals generally concordant with geographic regions and low sequence divergence at mitochondrial loci suggesting a recent origin of these populations. We also found high levels of genetic structure at microsatellite loci among populations within each of these groups indicating restricted gene flow at intermediate scales. Despite high habitat specificity, we did not detect genetic structure among sand blowouts at finer spatial scales. Within each population, matrices comprised of both sand blowouts and vegetated shinnery oak patches are necessary for genetic connectivity, but the fine scale spatial arrangement of blowouts may not be as critical. We discuss our results with respect to the scale of landscape heterogeneity and habitat connectivity and consider the conservation implications for this threatened taxon.

A Conservation Evaluation of Smooth Goosefoot, Chenopodium subglabrum (Chenopodiaceae), in Canada

Smooth Goosefoot (Chenopodium subglabrum) is restricted to North America and reaches its northern distribution limit in Alberta, Saskatchewan and Manitoba. The habitat of Chenopodium subglabrum contains some element of active sand. It is commonly found on the stabilizing edges of active dunes as well as dune blowouts, and occasionally on bare or recently disturbed sand plains. Chenopodium subglabrum is a sexually reproducing annual species with seeds that may remain in the seed bank for several years, waiting for the conditions it favours for germination. Germination of this species is erratic, possibly in response to moisture, making the overall population trend difficult to determine. The estimated population in Canada is likely between 5000 and 10000 individuals. There has been considerable loss of habitat as dunes become vegetated. The processes of dune stabilization and fire control threaten survival of this species.

The effect of gap dynamics on the size and spatial structure of Solidago sempervirens on primary coastal dunes

Abstract. The role of gap dynamics in shaping the spatial and size distributions of the gap specialist Solidago sempervirens (seaside goldenrod) were examined on the primary dune grassland (Ammophila breviligulata, American beachgrass) of an Atlantic barrier island. Results suggest that coastal dune blowouts are patchy disturbances that allow S. sempervirens to temporarily establish and disperse seed. Natural measurements and clipping experiments demonstrated that A. breviligulata competitively dominated S. sempervirens in undisturbed grasslands. Coastal dune blow‐outs reversed this dominance by temporarily burying A. breviligulata and increasing densities and above‐ground biomass of S. sempervirens. Examination of size/density distributions of S. sempervirens suggested that blow‐outs were seed sources but not regeneration sites. Regeneration was found primarily in neighboring transition and undisturbed grassland areas. Comparison of lateral growth by A. breviligulata on blow‐out margins suggested that disturbances were closed by lateral encroachment from gap edges. After blow‐out recovery, greater densities and skewed size distributions of S. sempervirens could still be detected for a number of years after blow‐out recovery.

Wind velocity and algal crusts in dune blowouts

In two saucer-shaped blowouts wind velocity was measured at 0.18 m height and compared to the wind velocity data from the nearest standard meteorological station at Valkenburg about 3.5 km to the northeast. In blowout 1 relative velocities are highest when the wind blows from directions between E and SSE. In blowout 2 winds blowing from directions between S and WSW are relatively stronger. In general the wind speed increases as its moves along the surface inside the blowout, because the aerodynamic roughness of the blowout surface is less than that of the surrounding area. Less important are the influence of the configuration of the terrain surrounding the blowout and the influence of the slopes within the blowout. The frequency distribution of the general wind at Valkenburg is analysed and combined with the horizontal wind velocity pattern within blowouts. A simulation model, producing the spatial distribution of the wind power shows that the prevalence of algal crusts at the SW side of blowouts agrees well with the location which reaches the lowest wind power values. In other parts of the blowouts algal crusts are damaged by moving sand at times of high wind velocity.

Topographic changes associated with coastal dune blowouts at island beach state park, New Jersey

AbstractTopographic changes in two blowouts located in Island Beach State Park, New Jersey, USA were monitored over the winter of 1981‐1982. Elevation changes were measured with erosion pins, and sediment traps placed at comparable locations in each blowout monitored the amount of sand moved by the wind. Discrete wind events were identified from regional data, and morphological data for the intervals with the highest onshore and offshore wind speeds are examined in detail.Vegetation is the primary influence on the development of the two blowouts. Blowout A is characterized by eroding sidewalls, a stable base, and an accreting blowout rim. High rates of sediment transport occur through the blowout throat which results in accretion on the vegetated rim. This blowout is an active sediment transfer system. Vegetation causes a large amount of deposition in the throat of blowout B. As vegetation was buried over the winter, the area of deposition migrated inland. Sidewall erosion also occurred in blowout B. Little change was recorded on the blowout rim. Blowout B is a recovering system where sediment is delivered to the blowout floor from the beach by onshore winds and from the blowout rim by offshore winds where it is stabilized by vegetation.The development of foredune blowouts is governed largely by vegetation cover on the dune crest and by sidewall erosion during offshore and onshore winds. Blowout recovery depends on vegetation growth and sediment deposition in the throat, and on the role of the sidewalls as sources of sediment which is deposited elsewhere within the system. Foredune blowouts are dynamic systems in which positive feedbacks in sediment availability and vegetation growth lead to a cycle of development and closure.

Spatial patterns in algae colonization of dune blowouts

Shape characteristics of blowouts were found to have a significant influence on the spatial extent of algal crusts in blowouts. The colonization of algae is caused either by expansion of an existing crust or by algae growth on sand containing organic material mainly brought into the blowout by rain slpash or surface runoff. Moreover, the geomorphological situation of the blowouts causes differences of surface dynamics (mean rate and frequency of change in surface level) and consequently determine whether the algal layer initial formed, is able to grow or is eroded. As a result of the balance between algae colonization and erosion of algae, most algae are found in small blowouts where they prevent the blowout from further growth. In large blowouts, algae are a periodical phenomenon and are found mainly on gently sloping inner flanks at the upwind side.

The development of dune blowouts, as measured with erosion pins and sequential air photos

The development of blowouts in dune terrains where no stabilization measures are taken requires constant watch to detect unwanted developments at an early stage. Two methods for investigating blowout development are in use. Since 1983, blowouts in a 40 ha section of Meijendel, a coastal dune area near The Hague have been twice yearly measured with erosion pins. Most of the 32 to 35 blowouts grew in length against the prevailing SW wind. The total blowout deflation area increased from 2.8 to 3.3% of the terrain in 4 years time. Air photos of 1958, 1967, 1977, 1984 and 1986 were used to study blowouts in a nearby area, De Blink north of Noordwijk, one of the most severely eroded dune terrains along the Dutch mainland coast. Total deflation area here increased from 0.8% in 1958 to 3.7% in 1986. There is a definite modal length class but the size is site-specific: 25 to 30 m in Meijendel, 15 to 20 m in De Blink. Many blowouts disappear shortly after they are formed. From the results it appears that the processes involved in the formation of blowouts can best be investigated with erosion pins whereas aerial photographs are preferable when changes in the spatial and temporal pattern of blowouts and the contributing factors are of interest.

The role of algae in the stabilization of coastal dune blowouts

AbstractA number of mechanisms prevent blowouts in the dunes along the Dutch‐coast from growing beyond a certain length. Plants play an important role in the stabilization process. Algae are the first plants to colonize the blowouts. Their filaments are surrounded by mucilaginous sheaths which adhere to the sand grains and increase the resistance of the sand to entrainment by wind. This suggests that artificially induced algal growths might be used in cheap, and ecologically justifiable, stabilization measures.