Sandy Surfaces Research Articles

Remote-sensing-based analysis of landscape change in the desiccated seabed of the Aral Sea—a potential tool for assessing the hazard degree of dust and salt storms

With the recession of the Aral Sea in Central Asia, once the world's fourth largest lake, a huge new saline desert emerged which is nowadays called the Aralkum. Saline soils in the Aralkum are a major source for dust and salt storms in the region. The aim of this study was to analyze the spatio-temporal land cover change dynamics in the Aralkum and discuss potential implications for the recent and future dust and salt storm activity in the region. MODIS satellite time series were classified from 2000-2008 and change of land cover was quantified. The Aral Sea desiccation accelerated between 2004 and 2008. The area of sandy surfaces and salt soils, which bear the greatest dust and salt storm generation potential increased by more than 36%. In parts of the Aralkum desalinization of soils was found to take place within 4-8years. The implication of the ongoing regression of the Aral Sea is that the expansion of saline surfaces will continue. Knowing the spatio-temporal dynamics of both the location and the surface characteristics of the source areas for dust and salt storms allows drawing conclusions about the potential hazard degree of the dust load. The remote-sensing-based land cover assessment presented in this study could be coupled with existing knowledge on the location of source areas for an early estimation of trends in shifting dust composition. Opportunities, limits, and requirements of satellite-based land cover classification and change detection in the Aralkum are discussed.

Aeolian vertical mass flux profiles above dry and moist sandy beach surfaces

The vertical distribution of aeolian mass flux was investigated in a natural beach environment. Field experiments conducted on the beach of the Łeba Barrier, southern Baltic coast, Poland, measured the sand transport rate and the vertical mass flux distribution above dry rippled sand and a moist flat sandy surface. The experiments were intended to show the changes in the vertical distribution of sand with changing wind speed. All the data represent saturated flux conditions. Sand transport was measured using 0.5m-high vertically segmented passive sand traps, while the wind speed and direction were monitored at 1m elevation. The obtained dataset comprises 65 measurements on dry surfaces and 51 measurements on moist sandy surfaces. The sand transport rate above the moist surface was up to 90% higher than above the dry surface for wind speeds of 7–11m/s, but higher velocities gave smaller differences between the surfaces. The saltation layer was thicker above the moist surface than above the dry surface. All the vertical sand flux profiles are best described by exponential decay functions. Analysis of the normalised flux profiles grouped by wind velocity shows that the fitted curves are less inclined for moist surfaces than dry surfaces. Moreover, the regression coefficients depict a marked trend in which the intercept decreases and the slope increases with increasing wind speed; this indicates that more sand is transported at higher elevations above the bed and less at lower elevations. The proportion of total transport seems to be independent of wind speed at elevations of approximately 35mm and 50mm above the dry and moist surfaces, respectively. Differences between the measured- and exponential-fit values of mass flux are particularly distinct close to the bed, where the exponential fit either over- or under-predicts the measured values. Over-predictions occur in weaker winds (up to 6–7m/s), whereas under-predictions become more pronounced as the wind becomes stronger and when the layer in which the under-prediction occurs thickens. The under-predictions are particularly obvious above the moist surface; it is not clear whether this phenomenon is due to technique measurement error or to another source. The proportion of creep is often considered to be responsible for the difference from the exponential fit which represents the saltation mode of aeolian transport. This proportion is difficult to determine because the mass flux measured by the lowermost chamber of the sand trap used in the experiments represents sand transported in both saltation and creep or/and reptation.

MANAGEMENT OF AEOLIAN SAND TRANSPORT ON A DIKE, DUNKIRK SEAPORT, FRANCE

The shoreline of Dunkirk Seaport partly consists of a macrotidal beach oriented WSW-ENE backed by a 6 km long coated dike called “digue du Braek”. Aeolian sand transport was estimated on asphalt by means of sand traps. Also, time-averaged wind speed profiles were measured using cup anemometers under various wind velocities and directions along a transversal profile on the dike and the upper beach. High rates of sand transport enabled the setup of different kinds of experimental windbreaks on asphalt, in order to test potential dune formation on this kind of substrate. Under oblique onshore winds, it was regularly observed that amounts of sand captured in the traps placed on the dike were more important than those in traps placed on the upper beach. These results were related to sand sources: windblown sand captured on the dike originated from the coastal dunes developed at the dike toe, while sand trapped on the upper beach came from the tidal zone were aeolian transport is limited by complex intertidal bar-trough topography. It also appeared from the topographic surveys carried out on the windbreaks that although their location seemed to play a major role on the amount of sand captured, fences and synthetic fabrics deployed on sandy surfaces were also able to trap windblown sand on the seaport dike.

Determination of aeolian transport rates of volcanic soils in Iceland

Sandy deserts cover >20000km2 in Iceland, consisting primarily of volcanic materials with basaltic volcanic glass being the main constituent. Wind erosion is severe in the country, causing dust pollution with widespread aeolian redistribution affecting most Icelandic ecosystems and sand movement over vegetated areas in the form of advancing sand fronts. We quantified wind erosion, using BSNE field samplers and automated sensors over several years at two sites with contrasting environments. The study sites are Holsfjöll with andic soil materials in the arid northeast highlands (<400mm annual precipitation) and Geitasandur on sandy surfaces in the humid south lowlands (>1200mm). Both areas show similar annual aeolian transport of 120–>670kgm−1yr−1. Aeolian flux in storms at the NE site was 3–43kgm−1h−1 on average with up to >200kgm−1h−1 during gusts. Multiple regression shows potential flux of >200kgm−1h−1 during intense storms of >20ms−1 (at 2m height). The research shows major aeolian activity in the humid South Iceland. Height distribution curves indicate considerable transport high above the surface at both sites (>60cm). Stable height distribution curves for each location allow for measurements using single dust trap over long periods. The research explains the intense activity of advancing sand fronts in Iceland and the significance of continuously recharged sand sources for maintaining severe wind erosion in humid areas of Iceland.

Herpetological assemblages of the Pilbara biogeographic region, Western Australia: ecological associations, biogeographic patterns and conservation

The Pilbara region has one of the most diverse reptile assemblages in the world and includes many typical arid zone species as well as many saxicoline endemics. We present the results of a four-year survey of the region during which pitfall trap lines were used to sample 297 quadrats for a total of two weeks in spring and in autumn. The quadrats were located across the region and were chosen to sample the main substrate types. Environmental variables were measured to characterise the soil as well as the geomorphic, vegetative and climatic setting of each quadrat. We used the program PATN to expose patterns in species composition among quadrats, and in relation to the environmental variables. A strong signal for community structure emerged that was linked to surface type. Broad rock, clay, sand and loam categorisations seemed to explain most assemblage composition, with climatic variables showing only weak influence. However, many taxa occurred across several surface types, reflecting the close juxtaposition of habitats within the region, wide dispersion of some taxa, and perhaps the influence of recent environmental history including anthropogenic changes. Examination of biogeographic characteristics of the species groups indicated strong endemism for taxa that preferred rocky substrates. In addition, many saxicoline Pilbara taxa have ranges that extend south into rocky areas of the Gascoyne, western Murchison and adjacent areas. Sandy habitats similar to those found in the Pilbara are widespread across Australia's arid zone, and accordingly few endemic taxa showed a preference for sandy surface types, and taxa with such preferences have distributions extending far beyond the Pilbara. The sandy areas of the coastal plain in the Roebourne subregion contained many taxa from Dampierland and the Great Sandy Desert to the north and north-east, as well as some taxa from the rich sand-adapted fauna of the Carnarvon region to the south. Some endemic taxa are associated with clay in the region, although clay surfaces were not as extensive as the rocky, loamy and sandy surfaces. Species associated with the fine-textured soils of the mulga woodlands in the southern part of the region appear to be an extension of herpetofaunal communities of regions to the south. Herpetofauna composition at the regional scale appears to have persisted, and patterns discerned in our analysis appear robust, despite the changes that have accompanied European colonisation in the Pilbara, including pastoralism, changed fire regimes, weeds, introduced animals, mining and infrastructure. However, the existing reserve system does not adequately capture the region's herpetofaunal diversity, especially the endemic taxa in the Fortescue and Roebourne subregions, and there are likely to have been changes in community composition at the local level.

Decorrelation of L-Band and C-Band Interferometry Over Vegetated Areas in California

Temporal decorrelation is one of the main limitations for recovering interseismic deformation along the San Andreas Fault system using interferometric synthetic aperture radar. To assess the improved correlation properties of L-band with respect to C-band, we analyzed L-band Advanced Land Observation Satellite (ALOS) interferograms with a range of temporal and spatial baselines over three vegetated areas in California and compared them with corresponding C-band European Remote Sensing Satellite (ERS) interferograms. Over the highly vegetated Northern California forests in the Coast Range area, ALOS remains remarkably well correlated over a 2-year period, whereas an ERS interferogram with a similar temporal and spatial baseline lost correlation. In Central California near Parkfield, we found a similar pattern in decorrelation behavior, which enabled the recovery of a fault creep and a local uplifting signal at L-band that was not apparent at C-band. In the Imperial Valley in Southern California, both ALOS and ERS have low correlation over farmlands. ALOS has lower correlation over some sandy surfaces than ERS, probably due to low signal-to-noise ratio. In general, L-band interferograms with similar seasonal acquisitions have higher correlation than those with dissimilar season. For both L- and C-band, correlation over vegetated areas decreases with time for intervals less than 1 year and then remains relatively constant at longer time intervals. The decorrelation time for L-band is more than 2 years in the forest in California whereas that for C-band is less than 6 months. Overall, these results suggest that L-band interferograms will reveal near-fault interseismic deformation once sufficient data become available.

Daily course of the soil temperature in summer in chosen ecosystems of Słowiński National Park, northern Poland

Daily course of the soil temperature in summer in chosen ecosystems of Słowiński National Park, northern Poland Patterns of the daily changes of the soil temperature in summer at three different ecosystems within the Słowiński National Park were analyzed. Strong correlation between the solar radiation and the soil temperature was found, particularly for the bare sandy surfaces, while the plant and humus cover hampers the solar energy flux to the soil. In the same way, correlations between the temperature of soil surface and the air temperature were computed. Finally, logarithmic models for the relationship between the global solar radiation and the soil surface temperature and between the soil surface temperature and the air temperature were constructed.

Relationship between the NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; photolysis frequency and the solar global irradiance

Abstract. Representative values of the atmospheric NO2 photolysis frequency j(NO2) are required for the adequate calculation and interpretation of NO and NO2 concentrations and exchange fluxes near the surface. Direct measurements of j(NO2) at ground level are often not available in field studies. In most cases, modeling approaches involving complex radiative transfer calculations are used to estimate j(NO2) and other photolysis frequencies for air chemistry studies. However, important input parameters for accurate modeling are often missing, most importantly with regard to the radiative effects of clouds. On the other hand, solar global irradiance ("global radiation", G) is nowadays measured as a standard parameter in most field experiments and in many meteorological observation networks around the world. Previous studies mainly reported linear relationships between j(NO2) and G. We have measured j(NO2) using spectro- or filter radiometers and G using pyranometers side-by-side at several field sites. Our results cover a solar zenith angle range of 0–90°, and are based on nine field campaigns in temperate, subtropical and tropical environments during the period 1994–2008. We show that a second-order polynomial function (intercept = 0): j(NO2)=(1+α)× (B1×G+B2×G2), with α defined as the site-dependent UV-A surface albedo and the polynomial coefficients: B1=(1.47± 0.03)×10-5 W−1 m2 s−1 and B2=(-4.84±0.31)×10-9 W−2 m4 s−1 can be used to estimate ground-level j(NO2) directly from G, independent of solar zenith angle under all atmospheric conditions. The absolute j(NO2) residual of the empirical function is ±6×10-4 s−1(2σ). The relationship is valid for sites below 800 m a.s.l. and with low surface albedo (α&lt;0.2). It is not valid in high mountains, above snow or ice and sandy or dry soil surfaces.

Leaf gas exchange and water status responses of a native and non-native grass to precipitation across contrasting soil surfaces in the Sonoran Desert

Arid and semi-arid ecosystems of the southwestern US are undergoing changes in vegetation composition and are predicted to experience shifts in climate. To understand implications of these current and predicted changes, we conducted a precipitation manipulation experiment on the Santa Rita Experimental Range in southeastern Arizona. The objectives of our study were to determine how soil surface and seasonal timing of rainfall events mediate the dynamics of leaf-level photosynthesis and plant water status of a native and non-native grass species in response to precipitation pulse events. We followed a simulated precipitation event (pulse) that occurred prior to the onset of the North American monsoon (in June) and at the peak of the monsoon (in August) for 2002 and 2003. We measured responses of pre-dawn water potential, photosynthetic rate, and stomatal conductance of native (Heteropogon contortus) and non-native (Eragrostis lehmanniana) C(4) bunchgrasses on sandy and clay-rich soil surfaces. Soil surface did not always amplify differences in plant response to a pulse event. A June pulse event lead to an increase in plant water status and photosynthesis. Whereas the August pulse did not lead to an increase in plant water status and photosynthesis, due to favorable soil moisture conditions facilitating high plant performance during this period. E. lehmanniana did not demonstrate heightened photosynthetic performance over the native species in response to pulses across both soil surfaces. Overall accumulated leaf-level CO(2) response to a pulse event was dependent on antecedent soil moisture during the August pulse event, but not during the June pulse event. This work highlights the need to understand how desert species respond to pulse events across contrasting soil surfaces in water-limited systems that are predicted to experience changes in climate.

Tensile test of natural microbiotic crust

The mechanical properties of microbiotic crust are important to stabilize sandy surfaces in arid and semi-arid regions. We developed a new experimental approach to perform the tensile test of natural microbiotic crust. The modulus of elasticity, ultimate stress and one-dimensional stress–strain relation was obtained. The microbiotic crust we measured exhibits linear elastic behavior firstly and then breaks. This mechanical character was applied to the study of the rupture of microbiotic crust under the impact of one saltating grain. A very simple dimensionless variable was suggested to quantitatively assess surface stability.

USING REMOTE SENSING DATA TO EVALUATE SURFACE SOIL PROPERTIES IN ALABAMA ULTISOLS

Evaluation of surface soil properties via remote sensing could facilitate soil survey mapping, erosion prediction, and allocation of agrochemicals for precision management. The objective of this study was to evaluate the relationship between soil spectral signature and surface soil properties in conventionally managed row crop systems. High-resolution remote sensing data were acquired over bare fields in the Coastal Plain, Appalachian Plateau, and Ridge and Valley provinces of Alabama using the Airborne Terrestrial Applications Sensor multispectral scanner. Soils ranged from sandy Kandiudults to fine textured Rhodudults. Surface soil samples (0 to 1 cm) were collected from 161 sampling points for gravimetric soil water content, soil organic carbon, particle size distribution, and citrate dithionite extractable iron content. Surface roughness and crusting were also measured during sampling. Two methods of analysis were evaluated: (1)multiple linear regression using common spectral band ratios and (2)partial least-squares regression. Our data show that thermal infrared spectra are highly, linearly related to soil organic carbon, sand and clay content. Soil organic carbon content was the most difficult to quantify in these highly weathered systems, where soil organic carbon was generally <1.2%. Estimates of sand and clay content were best using partial least-squares regression at the Valley site, explaining 42 to 59% of the variability. In the Coastal Plain, sandy surfaces prone to crusting limited estimates of sand and clay content via partial least-squares and regression with common band ratios. Estimates of iron oxide content were a function of mineralogy and best accomplished using specific band ratios, with regression explaining 36 to 65% of the variability at the Valley and Coastal Plain sites, respectively.

Effects of reduced inflation pressure and vehicle loading on off-road traction and soil stress and deformation state

Field experiments on off-road vehicle traction and wheel–soil interactions were carried out on sandy and loess soil surfaces. A 14 T, 6 × 6 military truck was used as a test vehicle, equipped with 14.00-20 10 PR tyres, nominally inflated to 390 kPa. Tests were performed at nominal and reduced (down to 200 kPa) inflation pressures and at three vehicle loading levels: empty weight, loaded with 3.6 and 6.0 T mass (8000, 11,600 and 14,000 kg, respectively). Traction was measured with a load cell, attached to the rear of the test vehicle as well as to another, braking vehicle. Soil stress state was determined with the use of an SST (stress state transducer), which consists of six pressure sensors. Soil surface deformation was measured in vertical and horizontal directions, with a videogrammetric system. Effects of reduced inflation pressure as well as wheel loading on traction and wheel–soil interactions were analyzed. It was noticed that reduced inflation pressure had positive effects on traction and increased stress under wheels. Increasing wheel load resulted in increasing drawbar pull. These effects and trends are different for the two soil surfaces investigated. The soil surface deformed in two directions: vertical and longitudinal. Vertical deformations were affected by loading, while longitudinal were affected by inflation pressure.

Mapping North African landforms using continental scale unmixing of MODIS imagery

We describe the production of a landform map of North Africa utilizing moderate resolution satellite imagery and a methodology that is applicable for sub-continental to global scale landform mapping. A mosaic of Moderate Resolution Imaging Spectroradiometer (MODIS) apparent surface reflectance imagery was compiled for Africa north of 10° N. Landform image endmembers were chosen to characterize ten different types of vegetated and unvegetated desert surfaces: alluvial complexes, dunes, dry and ephemeral lakes, open water, basaltic volcanoes and flows, mountains, regs, stripped, low-angle bedrock surfaces, sand sheets, and Sahelian vegetation. Multiple Endmember Spectral Mixture Analysis (MESMA) was applied to the MODIS mosaic to estimate landform and vegetation endmember fractions. The major landform in each MODIS pixel was identified based on the majority endmember fraction in two- or three-endmember models. Accuracy assessment was conducted using two data sources: the historic Landform Map of North Africa [Raisz, E. (1952). Landform Map of North Africa. Environmental Protection Branch, Office of the Quartermaster General.] and Landsat Thematic Mapper (TM) data. Comparison with the Raisz landform map gave an overall classification accuracy of 54% with significant confusion between alluvial surfaces and regs, and between sandy and clayey surfaces and dunes. A second validation using 20 Landsat images in a stratified sampling scheme gave a classification accuracy of 70%, with confusion between dunes and sand sheets. Both accuracy assessment schemes indicated difficulty in vegetation classification at the margin of the Sahel. A comparison with minimum distance and maximum likelihood supervised classifications found that the MESMA approach produced significantly higher classification accuracies. This digital landform map is of sufficiently high quality to form the basis for geomorphic studies, including parameterization of the surface in global and regional dust models.

The role of the mineral component in surface stabilization processes of a disturbed desert sandy surface

AbstractThe stabilization of sandy and loamy surfaces in semiarid and arid areas by topsoil crusts protecting the soil against wind or runoff erosion is well known. Destruction of such crusts, often by overgrazing, can enhance erosion and desertification. Crust recovery does not depend purely on biotic components of the crust and vegetation. Mineral components in the initial surface stabilization process are often overlooked. The present study focuses on the relative importance of the biotic and mineral components in the process of topsoil crust recovery in a sandy desert area located in the northwestern Negev Desert of Israel. Observations of the initial crust and of the disturbed surface, in the field and under the scanning electron microscope, showed that the mineral components of the crust recovered more quickly than its biotic elements. The implications for the rehabilitation of the disturbed ecosystem are discussed. Copyright © 2002 John Wiley &amp; Sons, Ltd.

Jointed setae – their role in locomotion and gait transitions in polychaete worms

Many families of polychaete worms have jointed setae in which the joint is external to the body and is not directly controlled by muscles or nerves. We assessed the role of these specialized structures in the hesionid polychaete, Ophiodromus pugettensis, by examining speed, step length, stride distance, stride frequency and gait transitions in worms with and without setal joints. Individual worms were videotaped while they moved over sandy surfaces at a range of speeds. The worms were then anaesthetized and all their compound setae were trimmed either distally or proximally to the setal joints. After two days of recovery the worms were videotaped a second time while they again moved over sandy surfaces at a range of speeds. From the video tapes we analyzed their locomotory performance before and after setal ablation. Animals in which the setae were shortened but in which the joint was left intact showed no consistent change in speed, step length, stride distance, stride frequency or gait transitions. Animals in which the joint had been removed both changed gaits at slower speeds (walking to undulatory walking and undulatory walking to swimming) and showed a significant decrease in maximum swimming speeds and stride distance. A subset of data containing only cases where the worms were moving at the same speed in the same gait before and after setal ablation was analyzed. In these instances, after the removal of the joint, the worms had significantly smaller stride distances and compensated for this by increasing stride frequency. In O. pugettensis, the undulatory walking gait is analogous to the trot–gallop transition in quadrupedal mammals because the animal switches from moving the appendages on a relatively rigid body to using a combination of body flexion and appendage movement to achieve propulsion, however, unlike quadrupedal mammals this transition takes place over a wide range of speeds and at different sites on the body as speed increases. These experiments indicate that jointed setae may be important both in allowing a worm to better control setal contact and traction with the substrate as well as in altering the effectiveness of its swimming stroke.

The taxonomic diversity of quarry vegetation in northwest Siberia and Chukotka

Data on the floras of quarries from different sites in the Russian Far North are presented. Thirty‐two quarries with different substrate textures were studied (ranging from sandy‐loamy to stony) ‐17 in northwestern Siberia and 15 in Chukotka. The paper presents a complete list of vascular plants found in the quarries, and analyzes the taxonomic diversity of quarry vegetation and its relationship to disturbed‐area size, age since abandonment, and type of substrate texture. It appears that the highest level of taxonomic diversity is typical of quarries with rubbly substrates, and the lowest level with quarries with sandy surfaces.

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

In a greenhouse pot study, we examined the availability of N to grain sorghum from organic and inorganic N sources. The treatments were15N-labeled clover residues, wheat residues, and fertilizer placed on a sandy clay loam and loamy sand soil surface for an 8-week period. Soil aggregates formed under each soil texture were measured after 8 weeks for each treatment. Significantly greater 15N was taken up and recovered by grain sorghum in sandy clay loam pots compared with loamy sand pots. Greater 15N recovery was consistently observed with the inorganic source than the organic sources regardless of soil texture or time. Microbial biomass C and N were significantly greater for sandy clay loam soil compared with the loamy sand. Microbial biomass 15N was also significantly greater in the sandy clay loam treatment compared to the loamy sand. The fertilizer treatment initially had the greatest pool of microbial biomass 15N but decreased with time. The crop residue treatments generally had less microbial biomass 15N with time. The crop residues and soil texture had a significant effect on the water-stable aggregates formed after 8 weeks of treatments. Significantly greater water-stable aggregates were formed in the sandy clay loam than the loamy sand. Approximately 20% greater water-stable aggregates were formed under the crop residue treatments compared to the fertilizer only treatment. Soil texture seemed to be one of the most important factors affecting the availability of N from organic or inorganic N sources in these soils.

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

Nitrogen availability to grain sorghum from organic and inorganic sources on sandy and clayey soil surfaces in a greenhouse pot study

Analysis of Tire Performance on Sand

Abstract Recently, vehicles on sand have been operated at higher speeds with diversified usage, and requests for the development of radial tires, applicable to both pavements and sandy areas have emerged. Although a large number of studies and analyses of tire performance on paved surfaces have been reported, few reports are available for tire performance on sandy surfaces. This study deals with the behavior of radial tires on the sand. A simple theoretical equation was derived in which the sand traction performance could be expressed as the difference between the propulsive force and the driving resistance on sand. The theoretical equation was found to be highly related to the empirical equation derived from previous work. Sand samples from typical deserts were used for analyses of shearing stress and compressive breaking force of sand through unique measuring techniques, resulting in modification of the theoretical equation to give more precise prediction of the tire performance on sand for most areas in the world.

Numerical simulations of the nearsurface phenomena on Mars

We use a system of univelocity equations for a multi-phase fluid as a description of the Mars atmosphere to achieve a better understanding of the dependence of the structure and governing mechanisms of the mesoscale processes on the thermal andorographic inhomogeneities and on dust transport. The major advantage of using this particular type of equations is that it allows us to describe uniformily the atmospheric flow over mountains, craters and sandy surfaces. This lets us to analyse the structure of wind flows over complex terrain in the important case of non-stationary conditions of dust lifting and dust deposition.