Sand Depth Research Articles

Foraging behaviour and habitat selection in pit-building antlion larvae in constant light or dark conditions

Pit-building antlion larvae are small sit-and-wait arthropod predators that dig conical pits in sandy soils. We investigated the effect of exposure to constant light versus constant dark conditions on antlion behaviour. Antlions tended to relocate less often, construct pits more frequently and construct larger pits in constant light. We interpret this as an indication of dichotomous behaviour under light versus dark conditions such that antlion larvae hunt during the day and modify their positions at night. Antlion larvae immediately responded to the complete switch in this illumination treatment and adapted their behaviour to fit the new conditions. Prey capture success did not differ between the constant light and constant dark conditions. When provided with a choice between light and dark conditions, the vast majority of larvae preferred the former. Those that preferred constant dark, however, were on average larger than those that preferred constant light. We thus suggest that since larger antlion larvae possess larger fat reserves, they can afford reductions in foraging activity (possibly to increase safety). An examination of the antlion trade-off between their preference for light and their preference for sand depth (which may affect their ability to evade predators) showed that their response to illumination was much more prominent, irrespective of the sand depth. Finally, combining light with other factors such as temperature and density may further elucidate microhabitat selection in pit-building antlion larvae.

Responses of biological soil crusts to sand burial in a revegetated area of the Tengger Desert, Northern China

Little information is available regarding the responses of biological soil crusts to sand burial in desert ecosystems. Therefore, in this study, we evaluated the effects of sand burial (sand depth of 0, 1, 2, 3 and 4 mm) followed by simulated precipitation (1, 3 and 5 mm distilled water, sprayed at 2-day intervals) on CO 2 exchange and growth by four types of crust collected from a revegetated area of the Tengger Desert (Northern China) in 2007. The results revealed that the respiration rate was significantly decreased and that moss shoot elongation was significantly increased ( P < 0.001) following burial. Both of these responses may have acted as compensatory mechanisms that favoured the recovery of crust after burial. The burial responses among the four crusts were also compared by measuring the cryptogam cover variations after burial and then computing the speed of emergence and a tolerance index (by standardizing the speed of emergence with a burial ratio of sand burial depth to the initial maximum height of the crust). Among the four crusts evaluated, Bryum argenteum crust showed the fastest speed of emergence (average 11.5% cover week −1) and highest tolerance index (average 0.182), followed by Didymodon vinealis crust (emergence, 11.3% week −1; tolerance, 0.129), Syntrichia caninervis crust (emergence, 7.7% week −1; tolerance, 0.097) and Collema tenax crust (emergence, 4.2% week −1; tolerance, 0.022). This sequence was in agreement with the successional order of these crusts that has been observed in the revegetated area evaluated in this study, which suggests that sand burial is one of the most important factors driving the succession of crusts in desert ecosystems. Furthermore, water played a role in the recovery process, as evidenced by pronounced decreases in dark respiration and increases in photosynthesis, speed of emergence and tolerance index for each crust type, as well as by shoot elongations by three mosses in response to the accretion of water. The restriction of tolerance against sand burial under limited precipitation conditions emphasizes the necessity for sand-binding measures to alleviate the negative effects of sand burial on crusts, which are crucial to preventing revegetated areas from undergoing desertification.

Effects of Sand Depth on Domestic Wastewater Renovation in Intermittently Aerated Leachfield Mesocosms

The depth of soil below the absorption trench of a septic system is considered an important factor in protection of groundwater. We examined the effects of depth on the ability of intermittently aerated sand-filled leachfield mesocosms to renovate domestic wastewater. Mesocosms (n=3) consisted of lysimeters with a headspace O2 concentration maintained at 0.21 mol∕mol and containing 7.5, 15, or 30 cm of sand that were dosed with septic tank effluent every 6 h for 328 days (12 cm∕d) . Sand depth had no effect on pH, dissolved O2 , PO4 , NH4 , or BOD5 levels in percolate water. Nitrate levels in percolate water were higher for 30 cm than for 7.5 and 15 cm during the first 70 d of the experiment, after which no differences were observed. Time-averaged removal rates of N, P, fecal coliform bacteria, and BOD5 were 22–28, 13–18, 81–92, and 81–99%, respectively, and were unaffected by depth. Wastewater renovation in intermittently aerated leachfield mesocosms appears to take place in a narrow zone (≤7.5 cm) below...

Wave climate, sediment supply and the depth of the sand–mud transition: A global survey

The influences of wave climate and sediment supply on the depths of sand–mud transitions ( h SMT) are investigated. Depths of sand–mud transitions (SMT) are based on published granulometric data from surface samples gathered from 14 sites in different wave-dominated coastal environments with fluvial input, including high energy (Columbia, Eel, Russian, San Lorenzo, Copper, and Nepean rivers), moderate energy (Ebro, Nile, Santa Clara, Tseng-wen and Kao-ping rivers), and low energy (Po, Pescara and Tronto rivers) regimes. Geometric mean diameter (GMD) and mud percent are compiled from samples along shore-normal transects, and significant correlation is found between these two textural descriptors. Nominally, the SMT is defined as the transition from GMD > 63 µm to < 63 µm. The correlation between mud percent and GMD permits an alternative, complementary definition of the SMT as the transition from < 25% mud to > 25% mud. This dual definition is applied to the 14 systems, and h SMT is tabulated for each system. Correlation is found between h SMT and the depth at which wave-induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between h SMT and significant wave height. Lack of correlation between h SMT and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand–mud transition is small or is not adequately represented in this study. Shelf width and slope do not correlate with residuals from a formalized linear relationship between h SMT and significant wave height. The relationship between h SMT and wave climate is useful for calibration of numerical models of erosion and deposition in wave-dominated coastal environments, for prediction of seabed properties in remote or inaccessible areas, and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks.

Vertical uplift capacity of horizontal anchors using upper bound limit analysis and finite elements

The vertical uplift capacity of strip anchors embedded horizontally at shallow depths in sand is examined by using an upper bound limit analysis in conjunction with finite elements and linear programming. Velocity discontinuities were allowed along the interfaces of all the elements. The plastic strains within elements were incorporated by using an associated flow rule. The collapse load was expressed in terms of a nondimensional uplift factor Fγ, which was found to increase continuously with an increase in both embedment ratio (λ) and the friction angle (ϕ) of sand. Even though the analysis considers the development of plastic strain within all elements, however, at collapse, the soil mass just above the anchor was found to move as a single rigid block bounded by planar rupture surfaces making an angle ϕ with the vertical. The results were found to be almost the same as reported in the literature for those based upon a simple rigid wedge mechanism.

Potential of simple filters to improve microbial quality of irrigation water used in urban vegetable farming in Ghana

Irrigation water used for growing vegetables in urban areas in many low-income countries is contaminated with untreated wastewater. Many wastewater treatment methods are economically prohibitive and continued use of such irrigation water pose health risks for vegetable consumers and farmers. As part of a larger study on possible interventions for health risk reduction, the potential of simple interventions was explored. Column slow sand filters with three levels of sand depths (0.5 m, 0.75 m and 1 m) and fabric filters made of nylon, cotton and netting were assessed. More than 600 water samples were analyzed for helminth eggs and thermotolerant coliforms. Flow rates were also measured. From slow sand filters, 71–96% of helminths and 2 log units (from 7 to 5 log units) of thermotolerant coliforms were removed. Sand depths had no significant influence in the removal. Lower removal rates were achieved by fabric filters, with an average removal of 12–62% for helminth eggs and 1 log unit for thermotolerant coliforms. Nylon filters had higher removal rates especially for helminth eggs (58%). Average flow rates for sand filters were 3 m per day and fabric filters had steady flows of about 1.5 liters per second, but flow reduced with time in cotton filters. The simple filters tested improved the microbial quality of irrigation water and could easily be used in combination with other interventions to further reduce health risks. The unit cost of the filters tested also appear acceptable to farmers and some incentives like better prices will motivate many farmers to invest in such simple interventions.

Effects of environment on electric field detection by small spotted catshark Scyliorhinus canicula (L.)

This study evaluated the influence of environment (substratum type and depth) on the electroreception capabilities of small spotted catsharks Scyliorhinus canicula in response to prey‐simulating electric fields. In experiments where electric fields (applied current 15 μA) were presented beneath different substrata (sand, pebbles, rocks and control) it was found that search effort was not different between substrata or S. canicula sexes, however, both rates of turning and biting towards active electrodes were decreased over pebbles and rocks compared with sand and the control (no substratum). There was no significant effect of sex on turn and bite rates over any substrata. Electric fields were then presented beneath different depths of sand to examine the depth‐limits of fish electroreception. Turn and bite rates were significantly lower at depths below 10 mm, with no bites towards electrodes made when they were &gt;30 mm depth. Search effort was not found to be different between different burial depth treatments or between sexes. These results indicate substratum type and depth influences the ability of S. canicula to detect prey‐simulating electric fields. This variation in electroreceptive performance may influence space use of sharks.

The interplay between foraging mode, habitat structure, and predator presence in antlions

Antlion larvae are sand-dwelling insect predators, which ambush small arthropod prey while buried in the sand. In some species, the larvae construct conical pits and are considered as sit-and-wait predators which seldom relocate while in other species, they ambush prey without a pit but change their ambush site much more frequently (i.e., sit-and-pursue predators). The ability of antlion larvae to evade some of their predators which hunt them on the sand surface is strongly constrained by the degree of sand stabilization or by sand depth. We studied the effect of predator presence, predator type (active predatory beetle vs. sit-and-pursue wolf spider), and sand depth (shallow vs. deep sand) on the behavioral response of the pit building Myrmeleon hyalinus larvae and the sit-and-pursue Lopezus fedtschenkoi larvae. Predator presence had a negative effect on both antlion species activity. The sit-and-wait M. hyalinus larvae showed reduced pit-building activity, whereas the sit-and-pursue L. fedtschenkoi larvae decreased relocation activity. The proportion of relocating M. hyalinus was negatively affected by sand depth, whereas L. fedtschenkoi was negatively affected also by the predator type. Specifically, the proportion of individual L. fedtschenkoi that relocated in deeper sand was lower when facing the active predator rather than the sit-and-pursue predator. The proportion of M. hyalinus which constructed pits decreased in the presence of a predator, but this pattern was stronger when exposed to the active predator. We suggest that these differences between the two antlion species are strongly linked to their distinct foraging modes and to the foraging mode of their predators.

Blue foxes’ motivation to gain access to solid floors and the effect of the floor material on their behaviour

Farmed blue foxes are willing to work to gain access to a sand floor from a wire mesh floor. It is not clear whether the foxes work for the sand floor because of its solidity or because it enables them to perform certain behaviours, e.g. exploration and digging. Here, we measured blue foxes’ motivation to gain access from a wire mesh floor to a floor with 15–30 cm deep sand, a floor with 3–4 cm deep sand, a solid concrete floor, and another wire mesh floor. In addition, we analysed the foxes’ behaviour on these floor materials. Seven male blue foxes were trained and tested in self-constructed operant apparatuses. In an apparatus, the fox could move a bottomless test cage from a wire mesh floor to a neighbouring, alternative floor material for a 4-min visit by pressing a lever in the test cage for a fixed number of times (Fixed Ratio, FR). The foxes worked for each floor material for 12 days. In each daily test session, the foxes were exposed to work on one of the four workloads (FR 6, 12, 24, 48), for 3 h. The behaviour of the foxes was analysed during the 4-min visits on each floor material. The results showed that there was no difference between the floor materials, either in the demand elasticity of the fragment of the demand curve (ranging from −0.46 to −0.33), or in the intensity of the demand. However, the foxes’ behaviour varied between the floor materials. More digging, play, rooting (exploration with the muzzle), and vole jumping were observed on the floor materials with sand, than on the concrete floor and the wire mesh floor. Both the presence and the depth of the sand layer stimulated these behaviours. It is concluded that juvenile blue foxes do not value solid floor materials more than a wire mesh floor. However, the sand floor stimulates more digging, play, vole jumping, and exploration than the concrete floor or wire mesh floor. Furthermore, the depth of sand may be an important factor in eliciting these behaviours. Access to a floor material with sand may improve the welfare of farmed blue foxes by providing the possibility to perform species-specific behaviours.

Seed Size Effects on Seedling Emergence of Desert Psammophytes in China

To investigate the effects of seed size on the behavior of seeds and seedlings in sand, seedling emergence from sand was examined in Caragana korshinskii (Fabaceae; mean seed weight 65 mg) and Atraphaxis bracteata (Polygonaceae; mean seed weight 5.7 mg), two shrubs with nonphotoblastic seeds that grow on desert sand dunes in China. Seeds were sown at depths of 0 to 50 mm in sand-filled pots, and the pots were irrigated under different regimes. The results suggest that for both species, a high proportion of the seeds buried fairly deep germinate during the summer rainy season with or without producing emergent seedlings, whereas at shallow depths, where moisture is more likely to be lost by evaporation, some proportion of the seeds remain ungerminated and viable. Comparison of results in this study with those on several smaller-seeded species used in our previous studies shows that larger seeds did not always give rise to seedlings capable of emerging from deeper depths in sand. We suggested that for nonphotoblastic seeds, seed size is not a crucial determinant of the proportion of seeds that produce emergent seedlings in field conditions.

Velocity effect of vehicle rolling resistance in sand

Vehicle rolling resistance is important to vehicle and aircraft ground movement in loose soil and sand conditions, especially in military operations. Off-road rolling resistance measurements have been taken at relatively low velocities, 2.1–4.6 m/s (meters per second) (7–15 ft/s) (4–9 knots), which has precluded studying any potential velocity effect on rolling resistance. With the emergence of aircraft designed to be used on unimproved soil runways and the military’s proposed new vehicles, especially the lighter-weight, 23–500-kg (50–1100-lbs) robotics, capable of high-velocity off-road movement, it is important that the rolling resistance be measured at velocities closer to the expected operating conditions. This paper presents data from rubber tire rolling resistance measurements in three depths of uniform-density dry sand at velocities from 2.1 up to 18 m/s (7–58 ft/s) (4–34 knots) and three load ranges from 4534 to 10,266 N (1020–2308 lbs). In dry sand the rolling resistance increases with velocity until the tire starts to “plane,” where it levels off or decreases and it is modified by load. Limited past work in this area is presented along with some existing analytical descriptions of rolling resistance versus velocity. Limited agreement between the published equations and the test data, along with contradictory published results, indicate that additional work on this topic is needed.

Adaptation of Nitraria sphaerocarpa to wind-blown sand environments at the edge of a desert oasis

This study addresses the adaptation of Nitraria sphaerocarpa to blown sand at the edge of a desert oasis with regard to the aspects of soil seed banks seedlings and population. Horizontally the total number of seeds per unit area decreased from the shrub canopy center to intershrub areas and most seeds were found under shrub canopies. Vertically the highest proportion of seeds was found at depths of 5–10 cm. The emergence percentage seedling mass and seedling height which were significantly affected by both burial depth and seed size were highest at the optimal burial depth of 2 cm and decreased with increasing burial depth in each seed size-class. Although seedling mass was usually greatest for large seeds and least for small seeds at each burial depth little difference was observed in seedling height at shallow burial depths of 0–3 cm. The population shows a patchy and discontinuous distribution pattern. Population height increases with increasing sand depth. Also the density increases with increasing depth of sand in the desert; however there is a steady decrease when the depth of sand is more than 100 cm. This result indicates that the depth of sand that is most suitable for the growth of Nitraria sphaerocarpa is 100 cm. The size of the population is significantly correlated with the sand depth which increases with increasing depth in the desert.

Impulse loading resulting from shallow buried explosives in water-saturated sand

A transient non-linear dynamics analysis of the detonation of a landmine buried to different depths in water-saturated sand is carried out in order to determine the resulting impulse loading. The results obtained are compared with their experimental counterparts obtained using the vertical impulse measurement fixture (VIMF), a structural mechanical device that enables direct experimental determination of the blast-loading impulse. The mechanical response of the structural steel used in the construction of the VIMF and the hydrodynamic response of the TNT high-energy high-pressure detonation products generated during detonation of a mine and of the air surrounding the VIMF are represented using the standard materials models available in the literature. The mechanical response of the sand surrounding the mine, on the other hand, is represented using the present authors' recent modified compaction model [1], which incorporates the effects of degree of saturation and the rate of deformation, two important effects, that are generally neglected in standard constitutive models for sand. The results obtained indicate that the use of the modified compaction model yields a substantially better agreement with the experimentally determined impulse loads over the use the original compaction model. Furthermore, the results suggest that, in the case of fully saturated sand, the blast loading is of a bubble type rather than of a shock type, i.e. it resembles under-water explosion.

Sponge diversity and community composition in Irish bathyal coral reefs

Sponge diversity and community composition in bathyal cold water coral reefs (CWRs) were examined at 500-900 m depth on the southeastern slopes of Rockall Bank and the northwestern slope of Porcupine Bank, to the west of Ireland in 2004 and 2005 with boxcores. A total of 104 boxcore samples, supplemented with 10 trawl/dredge attempts, were analyzed for the presence and abundance of sponges, using microscopical examination of (sub)samples of collected coral branches, and semi-quantitative macroscopic examination. Approximate minimum size of identified and counted sponge individuals was 1 mm. Literature data were added to the Porcupine Bank results to compensate for a less intensive sampling program in that location. Species richness and abundance were determined at local (sample diversity, pooled-sample diversity, local reef diversity), between-reef (diversity of two reef areas at 15 km distance), and regional scales (diversity of three reef areas over a distance of 200 km). Abiotic and biotic parameters including depth, the presence and cover of live coral, dead coral and sand, local reef, and orientation towards the nearest reef mound summit, were included in a constrained ordination technique (RDA); a Monte Carlo forward selection procedure was used to obtain significant predictors of variation in composition. The results of this analysis were compared with unconstrained ordination (PCA) and cluster analysis. The presence of live coral, depth and the local reefs C1 and C3 proved to be significant predictors of variation in sponge composition. The PCA and cluster analysis confirmed these results. Sample species richness was consistently heterogeneous from zero species and individuals up to 57 species and 90 individuals per (boxcore) sample. Species richness of local reefs determined from pooled samples showed the three localities studied to have similar species richness, namely 105-122 species in each location. Species richness was highest in samples with relatively low live coral cover. As in the RDA, live coral presence and depth appeared to be responsible for most of the variation observed in the cluster results. Cluster analysis of Bray-Curtis dissimilarity values of the pooled samples of all three reef localities using presence/absence data of all available samples indicated that distance appeared to structure the composition of the sponge assemblages of the three reef mound areas, but much less so within and among local reefs. Bathyal reefs of the regions to the west of Ireland were found to have a combined sponge species richness of 191 species, exceeding the richness of individual reef mound areas by c. 38-45%. Sponge presence in CWRs is clearly structured and controlled by biotic and abiotic factors. In particular, live coral presence appears a significant predictor of CWR sponge composition and diversity.

Effects of Hurricanes Emily and Wilma on coral reefs in Cozumel, Mexico

. The island was subsequently hit byWilma, the strongest hurricane ever registered in the Caribbean,between 21 and 24 October.After the passage of both hurricanes, there was extensive damagein the barrier reefs, with a large quantity of broken branches andplates from the coral dominant genera Agaricia and Porites (Fig. 1).Some coral heads were overturned (mainly Montastraea spp.), andthere were large numbers of sponges detached from the substrata.After Emily, sponges could be seen in aptly named ‘‘sponge-cemeteries’’ adjacent to the reefs (Fig. 2). On the shelf-edge reefs,there was less damage, but there had been extensive movement ofaccumulated sediment from between reef structures, and in someplaces more than 2 m depth of sand were removed (Fig. 3).Throughout the area surveyed, the damage was patchy with muchlive coral still remaining, particularly on the better developed reefs inthe south of the island. Most of the species suffering the greatestdamage were those with the highest growth rates (Fenner 1991;Bythell et al. 1993).Acknowledgments We thank G. Nava and M. Millet for their invaluablesupport. The Parque Nacional Arrecifes de Cozumel provided logisticalsupport and several volunteers helped in the reef surveys.

Vertical seismoelectric profiling in a borehole penetrating glaciofluvial sediments

Seismoelectric signals have been measured as a function of depth in a borehole penetrating glaciofluvial sands, silts, and glacial till using a broadband surface seismic source, and a downhole electrode array. Transient electric field pulses, with amplitudes of 1 to 4 μV/m accompanied the arrival of seismic P‐waves at the electrodes but no simultaneous interfacial signals were observed above the noise floor of approximately 0.2 μV/m. The co‐seismic effect was strongest in a sand and gravel layer where its amplitude is consistent with the predictions of a simplified theoretical model. Normalization of the amplitude logs by measurements of seismic particle velocity and electrical conductivity enhanced their sensitivity to changes in lithology and porosity. The results of this experiment suggest that co‐seismic seismoelectric effects show potential as a porosity/permeability logging tool in the borehole environment.

Sand intermittent filtration technology for safer domestic sewage treatment

The present investigation was undertaken to find out pollution reduction potential of Sand intermittent filtration bed in term of physico-chemical and microbiological characteristics of domestic sewage. The domestic sewage was filtered through Sand intermittent filtration beds of mixture of sand and soil at different ratio i.e. 1:1; 1:3; 3:1 and one set of 100% of each sand and soil were also taken. Results revealed that there was a significant pollution reduction in various physico-chemical and microbiological parameters of domestic sewage in sand soil mixture. In general sand and soil beds have shown better performance than only sand or soil bed for sewage treatment. Albeit Sand soil bed of 2 feet depth has been found better in term of pollution reduction ability than other depths used in the present study, but variation of pollution reduction potential has been recorded for different parameters in sand and soil bed of the same ratio. Mixture of Sand soil bed at ratio 3:1 has yielded better results in general than all other used ratio but for certain parameters stands equal with 1:1 ratio. Maximum percentage of reduction in pH i.e. 16.7% and in Temperature 27.9% was found at 2 feet depth in mixed sand and soil bed of 1:1 ratio. Maximum pollution reduction potential of intermittent filtration bed was recorded at 2 feet depth of sand and soil mixture at ratio of 3:1. Percentage of pollution reducing potential was found in CO2 83.4%, BOD 72.5%, COD 69.9%, Total alkalinity 37.9%, Total solids 88.5%, Total dissolved solids 86.1%, Total suspended solids 91.2%, MPN 82.4% and SPC 78.4%. Minimum reduction ability was found in 100% sand and soil bed without mixture. Journal of Applied Sciences and Environmental Management Vol. 10(1) 2006: 73-77

Variable vegetation cover and episodic sand movement on longitudinal desert sand dunes

Longitudinal (linear) sand dunes of the Simpson and Strzelecki dunefields in eastern central Australia present a paradox. Low levels of activity today stand in contrast to luminescence dating which has repeatedly shown deep deposits of sand on dune crests dating to within the late Holocene. In order to investigate the nature of dune activity in the Simpson–Strzelecki dunefield, vegetation and sand mobility were investigated by detailed vegetation survey and measurement of rippled area and loose sand depth of dunes at three sites along a climatic gradient. The response of both vegetation and sand movement to inter-annual climate variability was examined by repeat surveys of two sites in drought and non-drought conditions. Projected plant cover and plant + crust cover were found to have inverse linear relationships with rippled area and the area of deep loose sand. No relationship was found between these measures of sand movement and the plant frontal area index. A negative exponential relationship between equivalent mobile sand depth on dune surfaces and both vascular plant cover and vascular + crust cover was also found. There is no simple threshold of vegetation cover below which sand transport begins. Dunes with low perennial plant cover may form small dunes with slip faces leading to a positive feedback inhibiting ephemeral plant growth in wet years and accelerating sand transport rates. The linear dunefields are largely within the zone in which plant cover is sufficient to enforce low sand transport rates, and in which there is a strong response of vegetation and sand transport to inter-annual variation in rainfall. Both ephemeral plants (mostly forbs) and crust were found to respond rapidly to large (> 20 mm/month) rainfall events. On millennial time-scales, the level of dune activity is controlled by vegetation cover and probably not by fluctuations of wind strength. Land use or extreme, decadal time-scale, drought may destabilise dunes by removing perennial plant cover, accelerating wind erosion.

A Computational Analysis of Detonation of Buried Mines

A nonlinear‐dynamics transient computational analysis of the explosion phenomena associated with detonation of 100g of C4 high‐energy explosive buried at different depths in sand is carried out using the AUTODYN computer program. The results obtained are compared with the corresponding experimental results obtained in Ref. [1]. To validate the computational procedure and the materials constitutive models used in the present work, a number of detonation‐related phenomena such as the temporal evolutions of the shape and size of the over‐burden sand bubbles and of the detonation‐products gas clouds, the temporal evolutions of the side‐on pressures in the sand and in air, etc. are determined and compared with their experimental counterparts. The results obtained suggest that the agreement between the computational and the experimental results is reasonable at short postdetonation times. At longer post‐detonation times, on the other hand, the agreement is less satisfactory primarily with respect to the size and shape of the sand crater, i.e. with respect to the volume of the sand ejected during explosion. It is argued that the observed discrepancy is, at least partly, the result of an inadequacy of the generic materials constitutive model for the sand which does not explicitly include the important effects of the sand particle size and the particle size distribution, as well as the effects of moisture‐level controlled inter‐particle friction and cohesion. It is further shown that by a relatively small adjustment of the present materials model for sand to include the potential effect of moisture on inter‐particle friction can yield a significantly improved agreement between the computed and the experimentally determined sand crater shapes and sizes.

Seed germination and seedling emergence of three Artemisia species (Asteraceae) inhabiting desert sand dunes in China

Artemisia ordosica,A. arenariaandA. sphaerocephalaare semi-shrubs inhabiting desert sand dunes in China and often used to rehabilitate desertified areas. Improvement of dune rehabilitation success by sowing requires better understanding of the processes involved in the control of seed germination and seedling emergence in these species. Thus, (1) effects of temperature, light and osmotica (polyethylene glycol-6000) on seed germination, and (2) effects of seed burial depth in sand and irrigation regime on seedling emergence, were studied under controlled conditions. Seeds of the three species required light for germination, and the light fluence needed for germination was dependent on temperature. Seedling emergence of the three species was maximal (70–94%) for seeds sown at a depth of 2.5 mm, and decreased with increasing seed burial depth when the pots were initially and subsequently treated with 16 mm and 3 mm irrigation at 1-d intervals. However, when the pots were initially and subsequently treated with 8 mm and 3 mm irrigation at 2-d intervals, seedling emergence was almost completely suppressed due to water deficiency in sand. It is suggested that the probability of seed germination and seedling emergence of the three species in the field is very limited, because the light requirement restricts seed germination to shallow sand layers where water is lost rapidly due to evaporation. Temperature appeared to have secondary effects on seed germination, by modifying the light sensitivity of seeds.