Surface Stone Research Articles

Hunter-Gatherers and the Archaeology of Discard Behavior: An Analysis of Surface Stone Artifacts from Sturt National Park, Western New South Wales, Australia

An analysis of surface scatters of stone artifacts from late Holocene contexts at Stud Creek, Sturt National Park in the northwest of New South Wales, Australia, is reported. A sedimentological and archaeological chronology for Stud Creek shows archaeological remains are no older than 2000 years and Stud Creek saw repeated occupation during the last two millennia. Methods are proposed whereby conflated stone artifact assemblages from different locations within the Stud Creek catchment can be analyzed to understand how use of the catchment differed from place to place. We propose "place use history," as a more useful concept than "settlement system" for understanding surface artifact assemblages.

Artifact Visibility at Open Sites in Western New South Wales, Australia

Surface visibility is a significant constraint in archaeological survey, and estimates of surface visibility are a common addition to cultural resource management reports. Despite this, relatively few studies have attempted to identify the factors affecting visibility and quantify their effects. We report the results of such a study based on analysis of surface stone artifacts deposited by prehistoric hunter-gatherers from the Stud Creek area in what is now Sturt National Park, western New South Wales, Australia. While we are able to demonstrate and quantify relationships between high artifact visibility and erosional surfaces, and low visibility and vegetated or depositional surfaces, our findings also indicate a high degree of local variability. This variability sometimes obscures the predicted relationships. The outcome of this research leads us to question the way some sampling designs for archaeological survey are constructed.

The 137Cs technique applied to steep Mediterranean slopes (Part I): the effects of lithology, slope morphology and land use

Concentrations in the soil of anthropogenic and natural radionuclides have been investigated in order to assess the applicability of the 137Cs technique in an area of typical Mediterranean steep slopes. This technique can be used to estimate net soil redistribution rates but its potential in areas with shallow and stony soils on hard rock lithology have not been evaluated so far. In this research, the validity of using this technique in stony shallow soils at very steep slopes is discussed together with the relations between radionuclide concentrations and other soil properties, lithology, slope morphology and land use in a Mediterranean environment. Both natural Potassium-40 ( 40K), Uranium-238 ( 238U), Thorium-232 ( 232Th) and anthropogenic Caesium-137 ( 137Cs) radionuclides have been determined in samples taken along slope transects on uncultivated serpentinite soils and cultivated gneiss soils. In addition to the radionuclide concentrations, parameters such as slope position, slope angle, aspect, soil depth, surface stone cover, moss, litter, vegetation cover, soil crust, stone content and bulk density have been quantified. All the natural radionuclides 40K, 238U, 232Th show significantly higher concentrations in the gneiss than in the serpentinite soils, opposed to the 137Cs concentration, which is found significantly higher in the serpentinite soils probably because of the difference in clay mineralogy. The exponential decreasing depth distribution of 137Cs and its homogeneous spatial distribution emphasise the applicability of the 137Cs technique in this ecosystem. Lithology determines the concentration of natural and anthropogenic radionuclides. Land use determines the relations between 137Cs concentration/inventory and some soil characteristics. Higher 137Cs concentration and inventory are associated with higher percentages of vegetation cover, higher percentage of stones in the soil and higher values of soil bulk density in cultivated gneiss soils. Slope morphology and land use influence the soil redistribution at slope scale. The gneiss slopes show a zonation of four to five areas of differential erosion/accumulation processes corresponding with more regular slopes and soil redistribution due to water erosion and to tillage translocation and erosion. The serpentinites, as an example of a more unstable slope type, show more erosion areas with less accumulation downslope and soil redistribution due to water erosion.

Microform bed clusters: are they preferred habitats for invertebrates in a flood‐prone stream?

SUMMARY 1. Microform bed clusters are bedform microunits in streams. They consist of an obstacle clast (a large surface stone) against which other stones are stacked in a specific manner. Stream ecologists have suggested that these clusters are better flood refugia and more valuable habitats for invertebrates than single surface stones because of their higher stability during high‐flow events and their greater diversity of microhabitats available for colonisation.2. To test these predictions in the Schmiedlaine, a flood‐prone prealpine stream, we sampled invertebrates on clustered and single stones on a total of seven occasions including before and after a moderate spate, two major floods and a minor spate. We also monitored surface particle stability during the second major flood and the minor spate.3. Before the second flood (return period 1–2 years), we determined the exact positions of 60 clusters (60 obstacle clasts with 136 associated smaller particles) and 50 single stones in a 250‐m reach. We sampled the fauna on stones in the clusters, on well‐embedded single stones, and on loose single stones. Only six obstacle clasts and one single stone remained after the flood, implying movement of almost the entire surface layer. Therefore, we sampled the invertebrates on stones in newly formed clusters, on well‐embedded and single loose stones 3 and 11 days after the flood. The minor spate, in contrast to the second flood, moved only one of 495 monitored surface particles.4. Three days after the flood, invertebrate density on clustered stones and both single stone categories were similar and equalled 34% of the mean pre‐flood density. Eight days later, density had almost doubled. The relatively high survival and rapid recovery suggest that invertebrates found refugia during the flood. However, the very low stability of clusters and single stones implied that surface particles were unimportant as refugia.5. Total invertebrate density and taxon richness were never higher on clustered than on single stones (regardless of the timing of sampling relative to the last previous high‐flow event). Densities of the seven most common taxa and invertebrate community structure were also generally similar between particle types. We conclude that microform bed clusters cannot be regarded as more valuable invertebrate habitats than single surface stones in the Schmiedlaine.

Organic litter: dominance over stones as a source of interrill flow roughness on low‐gradient desert slopes at Fowlers Gap, arid western NSW, Australia

AbstractThirty‐six runoff plot experiments provide data on flow depths, speeds, and Darcy–Weisbach friction coefficients (f) on bare soil surfaces, and surfaces to which were added sufficient extra plant litter or surface stones to provide projected cover of 5, 10 and 20 per cent. Precision flow depth data were derived with a computer‐controlled gantry and needle gauge for two different discharges for each plot treatment.Taking a fixed flow intensity (Reynolds number, Re = 150) for purposes of comparison shows means of f = 17·7 for bare soil surfaces, f = 11·4 for added stone treatments, and f = 23·8 for added litter treatments. Many individual values of f for stone treatments are lower than for the bare soil surface, but all litter treatments show increases in fcompared to bare soil.The lowering of f in stone treatments relates to the submerged volume that the stones occupied, and the associated concentration of flow onto a smaller part of the plot surface. This leads to locally higher flow intensities and lower frictional drag along threads of flow that the obstacles create.Litter causes higher frictional drag because the particles are smaller, and, for the same cover fraction, are 100 times more numerous and provide 20 times the edge or perimeter length. Along these edges, which in total exceed 2·5 m g−1 (equivalent to 500 m m−2 for a loading of 2 t ha−1), surface tension draws up water from between the litter particles. This reduces flow depth there, and as a consequence of the lower flow intensity, frictional drag rises. Furthermore, no clear passage remains for the establishment of flow threads.These findings apply to shallow interrill flows in which litter is largely immobile. The key new result from these experiments is that under these conditions, a 20 per cent cover of organic litter can generate interrill frictional retardation that exceeds by nearly 41 per cent that of a bare soil surface, and twice that contributed by the same cover fraction of surface stones. Even greater dominance by litter can be anticipated at the many dryland sites where litter covers exceed those tested here. Copyright © 2002 John Wiley & Sons, Ltd.

Analysis of stone artefact assemblages from a recent survey of the Howqua River, Victoria

Staff and students from the third year Honours course in archaeology at La Trobe University recently undertook a survey of a 10 km section of the Howqua River Valley in the Central Victoria Uplands. The survey identified twelve previously un-recorded surface stone artefact scatters. In addition, detailed artefact recording was conducted at a previously recorded location. Clear spatial patterning in the distribution of artefacts made on different types of raw material was noted. Greenstone artefacts were concentrated at two that spatial differences in artefact discard represent variability in the span of occupation in different areas of the valley.

Effects of gravel and sand mulches on dew deposition in the semiarid region of China

Information regarding dew deposition on the stone-covered surface is scarce. The effects of gravel and sand mulches on dew condensation were studied during the late summer and fall of 1999 in the semiarid loess region of China. The results indicated that there were significant difference in daily dew amount between gravel mulch, sand mulch and dry loess soil (control). The average dew amount for gravel mulch was 0.071 mm d −1 with extreme 0.022 and 0.20 mm d −1. The average values for sand mulch and dry loess soil was 0.12 and 0.15 mm d −1, respectively. The minimum dew amount was 0.048 mm d −1 for sand mulch and 0.071 mm d −1 for dry loess soil, and the maximum dew amount was approximate 0.25 mm d −1 for both treatments. The results suggest that surface stone mulch can reduce dew deposition as compared to sand and dry loess soil.

Frictional retardation of laminar flow by plant litter and surface stones on dryland surfaces: A laboratory study

The relative contributions of plant litter and surface stones to the frictional retardation of laminar flows were investigated in a series of laboratory experiments on a glued sand board. A computer‐controlled measuring gantry was used for precise recording of flow depths, and retardation was quantified using the Darcy‐Weisbach friction factor ƒ. Surface stones had relatively little effect on flow retardation or flow speeds but increased flow depths in comparison with the same discharge across a stone‐free surface. In contrast, plant litter produced larger reductions in flow speed and increases in flow depth, associated with large increases in flow retardation. These effects were most marked at the highest loading tested, 80 g m−2. Results show that the retardation caused by a given surface cover fraction of litter significantly exceeds that caused by the same cover of surface stones, emphasising the need for measures other than surface cover to be employed in work on overland flow. Neither nonsubmerged obstacles such as surface stones nor plant litter contribute increased roughness with rising discharge in the laminar regime. Instead, values of ƒ decline as Reynolds number rises. These findings contrast notably with relationships established for turbulent flow and suggest that for correct modeling of overland flow in drylands, the temporal and spatial ranges of laminar flows must be distinguished from those where turbulent flows occur.

Estimating the mean speed of laminar overland flow using dye injection‐uncertainty on rough surfaces

AbstractA common method for estimating mean flow speeds in studies of surface runoff is to time the travel of a dye cloud across a measured flow path. Motion of the dye front reflects the surface flow speed, and a correction must be employed to derive a value for the profile mean speed, which is always lower. Whilst laminar flow conditions are widespread in the interrill zone, few data are available with which to establish the relationship linking surface and profile mean speeds, and there are virtually none for the flow range 100 < Re < 500 (Re = Reynolds number) which is studied here. In laboratory experiments on a glued sand board, mean flow speeds were estimated from both dye speeds and the volumetric flow relation v = Q/ wd with d measured using a computer‐controlled needle gauge at 64 points. In order to simulate conditions applicable to many dryland soils, the board was also roughened with plant litter and with ceramic tiles (to simulate surface stone cover). Results demonstrate that in the range 100 < Re < 500, there is no consistent relation between surface flow speeds and the profile mean. The mean relationship is v = 0·56 v surf, which departs significantly from the theoretical smooth‐surface relation v = 0·67 v surf, and exhibits a considerable scatter of values that show a dependence on flow depth. Given the inapplicability of any fixed conversion factor, and the dependence on flow depth, it is suggested that the use of dye timing as a method for estimating v be abandoned in favour of precision depth measurement and the use of the relation v = Q/ wd, at least within the laminar flow range tested. Copyright © 2001 John Wiley & Sons, Ltd.

Cholesteric liquid crystals as weathering indicators for marble surfaces

Cholesteric liquid crystals have been used to study the weathered surfaces of marble from the Sanctuary of Demeter in Eleusis, near Athens. Previous investigations have shown that when a cholesteric phase is spread across the surface of the stone, the pitch of the mesophase is sensitive to the topography of the surface. The wavelength of the maximum in the reflected spectrum varies therefore with the microtexture of the surface. Small samples of surface stone from the temple which had been weathered in distinctive ways, were investigated in the laboratory. There appears to be a significant correlation between the optical reflectance spectra and the surface microtopography investigated by SEM, as indicated by computer aided analysis (Digital Image Processing). The results point to the development of an effective in situ method of monitoring the weathering of marble surfaces using cholesteric liquid crystals.

Effects of surface and sub-surface soil horizons on the seasonal performance of Larrea tridentata (creosotebush)

1. In warm arid and semiarid environments, the accumulation of clay minerals produces increasingly well developed soil horizons with the passage of time. Differences in the strength of development of two prominent soil horizons, silt- and clay-rich surface vesicular (Av), and clay-enriched subsurface argillic (Bt), may strongly influence the amount and seasonal continuity of plant-available water and the physiological activity of long-lived desert shrubs. Three sites were selected on an alluvial piedmont (bajada) in the Mojave Desert that varied in surface and subsurface horizon development. The first site, a deep deposit of stabilized dune sand, entirely lacked soil horizon development. The second site had a well developed surface stone pavement and underlying Av horizon, but lacked an argillic horizon in the sandy subsoil. The third had a well developed surface pavement and Av horizon, and a deeper, well developed clay-rich argillic horizon. Seasonal water potential and gas-exchange responses of the evergreen desert shrub Larrea tridentata[DC.] Cov., and volumetric soil water content (θ), were measured monthly in 1996 on these three soils in order to test the hypothesis that desert pavements, Av and subsurface Bt horizons differentially affect the effectiveness and utilization of seasonal precipitation. 2. Predawn and midday water potentials (ψpd and ψmid), net photosynthetic rates (Anet), and stomatal conductances (gs) in L. tridentata were highest in the deep, sandy dune soils lacking horizons that could restrict surface and subsurface infiltration. Plants growing in these soils also showed no physiological response to summer precipitation events. Following a single large precipitation event during the growing season (3·8 cm), the water potentials, Anet and gs in L. tridentata were similar in the first (sand dune) and second (pavement and Av horizon) sites. However, plant performance on these soil surfaces showed marked seasonal declines, and did not respond to a small pulse of summer rainfall. Plants growing at the third site (older soils with strongly developed pavement, Av and Bt horizons) had very low gas-exchange rates and water potentials. However, following convectional summer thunderstorms L. tridentata showed improved water relations and gas exchange in these soils. 3. Midday water potentials were frequently anomalously higher than predawn water potentials, up to +6 MPa late in the growing season, especially on soil surfaces with well developed soil horizons. This anomaly was due to seasonal decreases in ψpd accompanied by invariant midday ψ. In general, ψpd was correlated with θ across the depths measured. 4. Correlations between ψmid with θ at 35 cm increased dramatically with increasing Bt horizon development, suggesting that seasonal ψmid may have been due to the vertical translocation of water (‘hydraulic lift’). 5. Our results show that subsurface and surficial soil horizon development differentially affects the seasonal availability of water for desert plants. During wetter parts of the season, subsurface horizons limit the degree of water availability, while surface soil characteristics have the greatest influence on the effectiveness of summer precipitation. These findings suggest that the effectiveness of climatic precipitation and attendant plant utilization of water resources in warm desert systems may depend on the physical soil condition.

Effects of surface and sub-surface soil horizons on the seasonal performance of Larrea tridentata (creosotebush)

1. In warm arid and semiarid environments, the accumulation of clay minerals produces increasingly well developed soil horizons with the passage of time. Differences in the strength of development of two prominent soil horizons, silt- and clay-rich surface vesicular (Av), and clay-enriched subsurface argillic (Bt), may strongly influence the amount and seasonal continuity of plant-available water and the physiological activity of long-lived desert shrubs. Three sites were selected on an alluvial piedmont (bajada) in the Mojave Desert that varied in surface and subsurface horizon development. The first site, a deep deposit of stabilized dune sand, entirely lacked soil horizon development. The second site had a well developed surface stone pavement and underlying Av horizon, but lacked an argillic horizon in the sandy subsoil. The third had a well developed surface pavement and Av horizon, and a deeper, well developed clay-rich argillic horizon. Seasonal water potential and gas-exchange responses of the evergreen desert shrub Larrea tridentata[DC.] Cov., and volumetric soil water content (θ), were measured monthly in 1996 on these three soils in order to test the hypothesis that desert pavements, Av and subsurface Bt horizons differentially affect the effectiveness and utilization of seasonal precipitation. 2. Predawn and midday water potentials (ψpd and ψmid), net photosynthetic rates (Anet), and stomatal conductances (gs) in L. tridentata were highest in the deep, sandy dune soils lacking horizons that could restrict surface and subsurface infiltration. Plants growing in these soils also showed no physiological response to summer precipitation events. Following a single large precipitation event during the growing season (3·8 cm), the water potentials, Anet and gs in L. tridentata were similar in the first (sand dune) and second (pavement and Av horizon) sites. However, plant performance on these soil surfaces showed marked seasonal declines, and did not respond to a small pulse of summer rainfall. Plants growing at the third site (older soils with strongly developed pavement, Av and Bt horizons) had very low gas-exchange rates and water potentials. However, following convectional summer thunderstorms L. tridentata showed improved water relations and gas exchange in these soils. 3. Midday water potentials were frequently anomalously higher than predawn water potentials, up to +6 MPa late in the growing season, especially on soil surfaces with well developed soil horizons. This anomaly was due to seasonal decreases in ψpd accompanied by invariant midday ψ. In general, ψpd was correlated with θ across the depths measured. 4. Correlations between ψmid with θ at 35 cm increased dramatically with increasing Bt horizon development, suggesting that seasonal ψmid may have been due to the vertical translocation of water (‘hydraulic lift’). 5. Our results show that subsurface and surficial soil horizon development differentially affects the seasonal availability of water for desert plants. During wetter parts of the season, subsurface horizons limit the degree of water availability, while surface soil characteristics have the greatest influence on the effectiveness of summer precipitation. These findings suggest that the effectiveness of climatic precipitation and attendant plant utilization of water resources in warm desert systems may depend on the physical soil condition.

Stable surface stones as refugia for invertebrates during disturbance in a New Zealand stream

We tested whether stable surface stones serve as invertebrate refugia in a New Zealand gravel-bed stream. Two-hundred stones were marked in situ in a systematic grid across 20 transects (40–60 cm between stones, 1 m between transects). Six days prior to a spate, we sampled invertebrates on 24 unmarked stones. Twelve were randomly chosen among well-embedded stones, the others among stones of similar size lying loosely on top of the bed. (Previous work had shown the former to be more stable than the latter during high-flow events.) As soon as possible after the spate, we sampled another set of stones. Ten were marked stones that had remained stable during the spate, whereas 12 were chosen at random among loose stones. Nineteen days after the spate, we sampled a final set of 8 stable and 12 unstable stones in the same way. Taxon richness, area-standardized total densities of invertebrates, and densities of Chironomidae, Deleatidium spp., Austrosimulium spp., Zelandoperla spp., and Oligochaeta were similar on both stone categories before the spate. Shortly after the spate, their densities (and taxon richness) were all significantly higher on stable than on unstable stones, and values on the former exceeded pre-disturbance levels in several cases. By day 19, most of these differences had disappeared, although densities of 3 of the 5 taxa on unstable stones had not yet recovered to pre-disturbance levels. We concluded that stable surface stones were important invertebrate refugia during the spate. The higher densities of several taxa relative to pre-disturbance levels implied that invertebrates may actively seek stable refugium stones, whereas many leave or are dislodged from unstable stones. It remains to be determined how invertebrates can identify stones that remain stable during high-flow events.

Distribution of Armillaria species in upland Ozark Mountain forests with respect to site, overstory species composition and oak decline

SummaryArmillaria root disease is a contributing factor to oak decline in the Ozark Mountains of central USA. We have identified Armillaria gallica, Armillaria mellea, and Armillaria tabescens in Quercus‐Carya‐Pinus forests of the region. Presence/absence patterns of each Armillaria species as well as all possible Armillaria species combinations were analysed by contingency tables and/or stepwise logistic multiple regressions with principal characteristics of the studied sites and forest stands, both quantitative and qualitative: geographic land‐type association, bedrock type, landform position, slope direction (aspect), soil type and soil surface stone cover, down woody debris, abundance and basal area of woody vegetation and decline mortality by species. Most decline mortality consisted of two red oak species (section Erythrobalanus, Quercus coccinea and Quercus velutina), which also were most sensitive to Armillaria infection. Site characteristics related to the distributions of Armillaria species and decline mortality were also related to the preponderance of Q. coccinea and Q. velutina, regional vegetation history (i.e. conversion of Pinus echinata stands to hardwoods), and the different strategies of territory acquisition and spread of the Armillaria species involved. The presence of A. gallica may reduce the activity of more virulent Armillaria species.

Patchy surface stone movement during disturbance in a New Zealand stream and its potential significance for the fauna

A patchy movement of surface stones during disturbance in streams has been proposed from field observations, but few attempts have been made to quantify this phenomenon. If spates produce a mosaic of stable and disturbed areas, the former could serve as refugia for benthic invertebrates. We monitored the stability of surface stones at three geomorphically contrasting sites in a river with an unstable bed during three spates and one large flood. Stones were marked in situ by drilling holes in them or by scraping them with a chisel. For each stone, we determined visible surface area, embeddedness in the substratum, water depth, size of surrounding stones, and presence or absence of large stones upstream. During the first monitoring period, which covered one spate and the large flood, we marked 400 stones at each 20‐m‐long site in a systematic grid with 40 to 60 cm between stones. Stones were relocated after each disturbance, but each stone set was used to monitor both subsequent events. After the large flood, few marked stones were left. Therefore, additional sets of 200 stones were marked for a second monitoring period covering the remaining two spates; these stones were located at the same sites, but the distance between transects was doubled. Patchy bed movement occurred during all four disturbances, especially during the three smaller ones, which moved only 33 to 72% of marked stones. Stability of individual stones was mainly influenced by their size and embeddedness and sometimes by the water depth above the stone. Larger‐scale parameters (e.g., the position of the stone across the transect) were less important. Whole‐site stability differed little among sites. During the three smaller events, many stable surface stones were available as potential invertebrate refugia. In contrast, invertebrate refugia may have been restricted to the hyporheic zone and inundated flood‐plain gravels during the large flood. Because patchy stone movement was observed in a river with an unstable bed, it is likely to be a feature of most rivers. Therefore, small‐scale experiments may be able to simulate the effects of disturbance on the benthic community more effectively than previously thought.

Clast exposure on boulder‐covered desert slopes

Variation in the degree of clast exposure on stony desert slopes is examined in an area of northeast Jordan. Geological influences on the characteristics of stone mantles are modified by relative slope position. Observations that the nature of the surface stone cover changes downslope because of the transport and accumulation of the underlying substrate are confirmed by quantitative analysis. An elliptic function is described as a means of estimating relative clast exposure from simple field measurements of clast dimensions. There are no significant differences in mean clast exposure between the four main basalt lithologies of the study area, but a distinctive pattern of clast exposure catenas can be identified. Convex slopes maintain relatively high levels of clast exposure from crest to toe. About two-thirds of the variation in clast exposure is accounted for by lithology and four slope variables: relative relief, slope length, gradient and curvature. Copyright © 1999 John Wiley & Sons, Ltd.

Influence of slope and stone cover on tillage operations in the Ethiopian highlands

Human population pressure has forced smallholder farmers in some areas of the central plateau region of the Ethiopian highlands to cultivate plots located on slopes or hillsides having varying amounts of stone cover. The objectives of this pilot study were to determine if slope and(or) stone cover influenced tillage operations on smallholder farms in the Debre Birhan area of the Ethiopian highlands, and to examine the relationship between different soil/tillage-related factors and draft of the indigenous single-tined ard ( maresha). This paper also briefly describes the traditional systems of cropping and soil management, and provides data on selected physical and chemical properties of soils found in the study area. A land classification (LC) system was developed to categorize plots according to the slope and stone cover. Surface stone cover of plots was calculated and a method of estimating subsurface stones was tested. Tillage measurements included plowing frequency or number (PN) per area per annum, soil moisture tension, plowing depth, furrow “wedge” of soil moved, area plowed, contour angle, and the speed of travel and pulling force exerted by oxen. Plots were located on slopes ranging from 0% to 23%. Degree of slope was a key factor in determining the acuteness of angle of the contour at which plowing is done prior to seed covering, but had no significant effect on maresha draft. Stone cover of plots ranged up to 27%, with individual stones moved by the ard weighing up to 2.5 kg. Plowing depth ranged from 10.1–15.3 cm for all PN across LC. Oxen travelled at speeds of 0.35–0.58 m s −1. Mean values for draft of the maresha across LC ranged from 0.83–1.04 kN. Farmers plowed from 0.10–0.15 ha during a 5–6 h work period, irrespective of LC or PN. Soil moisture tension (range 16–33 kPa) was found not to have a significant effect on draft, due to tillage being carried out prior to the major and minor rains. Percent stone cover explained very little of the variation in implement draft ( R 2=0.10). Adding stone weight to the model increased R 2 slightly (0.22), but significance was low ( P<0.16). Furrow wedge of soil displaced by the ard head accounted for most of the variation in draft of the maresha across all LC and PN ( R 2=0.75, P<0.008). The design and construction of the maresha allows it to be used equally well for tillage operations on plots having minimal or high stone cover which may be located on flat or gentle sloping land, or on steep hillsides.

Evaluation of arid land systems using airborne video

This paper reports trials utilizing an airborne video system at different wavelengths and spatial resolutions in a range of arid land systems. We aimed to evaluate the range of arid landscape features discernible with airborne video and to assess whether the video may have a role as an adjunct to ground measurements for interpretation of satellite imagery. Low level colour visible airborne video images provided good discrimination of trees and perennial shrubs, while higher level visible and infra‐red images allowed clear mapping of landscape elements such as ground cover mosaics, erosional features and drainage lines. Significant correlations were developed between ground and image estimates of tree, perennial shrub and ground cover, and bare ground, although the interpretation of the video images considerably over‐estimated the plant components. Smaller ground cover components such as grasses, ephemeral plants and surface stone could not be discriminated at the resolution of the video imagery, unless present as significant aggregations, with the result that image estimates of their abundance were poor predictors of ground measured proportions. However, both the moving video and captured images provided a good record of fine scale ground cover patterns often not visible to the ground observer, which could help to interpret the broader land systems apparent in satellite imagery.

Evidence of high efficiency water-harvesting by ancient farmers in the Negev Desert, Israel

Ancient stone mounds and water conduits are found on hillslopes over large areas of the Negev desert. This paper presents results from field and laboratory studies, suggesting that ancient farmers were very efficient in harvesting water. A comparison of the volume of stones in the mounds to the volume of surface stones from the surrounding areas indicates that the ancient farmers removed only stones that had rested on the soil surface and left the embedded stones untouched. According to results of simulated rainfall experiments, this selective removal increased the volume of runoff generated over one square meter by almost 250% for small rainfall events compared to natural untreated soil surfaces.

The Role of Clays in the Decay of Ancient Egyptian Limestone Sculptures

One type of Egyptian limestone from Naga el-Deir (Abydos/Thebes region) exhibits an ongoing problem of deterioration typified in the form of continued delamination of the surface in a stela from Naga el-Deir acquired from archaeological investigations carried out in the early 20th century. Previous testing of this limestone type indicated the presence of sodium chloride and sodium nitrate. The sculptures have been treated and desalinated either by immersion in water or by aqueous poulticing, but the decay process was not halted, and major loss of surface stone was still noticeable after storage for a period of years.Mineralogical and petrographic data (x-ray diffraction [XRD], scanning-electron microscopy [SEM], and optical microscopy) indicate that this stone has a high proportion of clays (up to 10% by weight). Laboratory tests suggest that the clays, concentrated along bedding planes, are largely responsible for the type of deterioration noted. The role of clay minerals in the decay of this type of limestone was demonstrated by performing a series of experiments, including wetting/drying cycles and relative humidity changes, thermomechanical analysis, and accelerated decay tests using water and ethylene glycol. One conclusion of this study is that in some instances, desalination procedures can induce more deterioration than can rigid environmental control. Another conclusion is that attribution of deterioration to the presence of salts may be insufficient, and further petrographic analysis should be initiated prior to desalination of clay-rich limestones. Unconventional methods for possible stabilization of the clay structure (by means of ion exchange and/or surfactant treatment) are also discussed.