Gravel Cover Research Articles

Use of porphyry indicator zircons (PIZs) in the sedimentary record as an exploration tool for covered porphyry copper deposits in the Atacama Desert, Chile

This work explores the potential of geochemical and petrographic characteristics of detrital zircons coming from the sedimentary record of the Centinela District in Northern Chile to identify the presence of buried porphyry copper deposits under a transported gravel cover. The sampled sedimentary section was recovered from the pit of the exotic copper deposit of El Tesoro, located approximately 2 and 4 km west of the Esperanza and Mirador porphyries, respectively. The sedimentary cover comprises four units, Tesoro II, Tesoro III, Arrieros and Recent gravels, deposited since the late Cenozoic in an arid continental environment dominated by alluvial fans. Except for the Tesoro III gravels, all other units contain exotic-Cu mineralisation. In order to interpret the geochemical footprint of the investigated zircons, the Porphyry Indicator Zircon (PIZ) concept (Pizarro et al., 2020) is used. A PIZ need to comply with each of the following geochemical values: Hf >8750 (ppm), Ce/Nd >1, Eu/Eu* >0.4, 10,000 × (Eu/Eu*)/Y > 1, (Ce/Nd)/Y > 0.01, Dy/Yb <0.3 and 0.1 < Th/U < 1. These zircons also have Ti <9 ppm and Ce/Ce* <100 and usually show euhedral morphologies characterised by prismatic forms of type {110}. The geochemical and petrographic characteristics of the PIZs collected in the gravels are similar to zircons from the nearby Mirador and Esperanza porphyries. The highest PIZ concentration coincides with the gravel horizons with exotic-Cu mineralisation. Therefore, the PIZs found in the sedimentary record are a potential tracer of adjacent copper porphyries and represent a promising exploration tool for this type of hidden ore deposits in challenging sediment-covered areas.

Field observed GCL panel shrinkage for five GCLs in composite liners

Field observed shrinkage was quantified and compared for one geosynthetic clay liner (GCL) type left covered only by a black geomembrane, a white geomembrane, and 0.3 m of gravel cover. Shrinkage is reported for up to 28 months field exposure of an additional four GCLs beneath a black geomembrane. All GCLs were needle-punched geotextile encased: one containing fine granular bentonite, two with powdered bentonite, one with polymer amended granular bentonite, and one multicomponent GCL with a film coating installed film up. All the GCLs examined have the potential to shrink with the magnitude of the shrinkage primarily dependent on the thermal/moisture cycles to which it is subjected and the degree of adhesion between panel overlaps. It is shown that the panel overlap adhesion can be highly variable and this is primarily attributed to condensation of water vapour below geomembrane wrinkles during daily thermal cycles. With a an initial GCL overlap of 300 mm, the shrinkage observed over 28 months left ≥32% of the original overlap; however, if the overlap had been only 150 mm, then gaps or ineffective seams would have occurred for several GCLs. Guidance regarding mitigating GCL panel shrinkage is provided.

Perencanaan Geometrik Dan Perkerasan Lentur Jalan Wisata Lut Atas Waq Pondok Sayur Kabupaten Bener Meriah, Aceh

Jalan Wisata Lut Atas Bener Meriah Aceh is a road leading to the tourist attraction of the lake, located at 2,100 meters above sea level. The lake called Lut Atas located in Bener Meriah, Aceh, exactly in Waq Pondok Sayur Village, Bukit District. The current status of the Lut Atas Tourist Road is still in the form of a rock and gravel cover, making it difficult to access the tourist area. The purpose of this study is to calculate the throughput capacity and road age plan on the Lut Atas Tourism section, knowing the required soft pavement thickness on the Lut Atas Tourism section with the manual road design method. 2017, knows how to climb slopes and bends to ensure safety and comfort for road users. Based on the results of the 4-day LHR survey, the total number of vehicles is 125 vehicles. Calculation results of pavement thickness of Upper Lut tourist road Waq Pondok Sayur village from STA 0+000 - 3+000, with pavement thickness AC-WC 40 mm, AC-BC 60 mm, aggregate layer 400mm material (LFA) and optional 100mm backfill. The Lut Atas Tourist Trail has a geometric road plan to guide the route according to the plan of 3 bends, namely PI1 Spiral Curve (SCS), PI2 Turn Spiral Circle (SCS), Turn PI3 Spiral bend (SS). The section of Thuong Lut Tourist Road has an expected longitudinal profile of 4 vertical curves with the following details: PPV1 (vertical intersection centre) vertical convex type, PPV2 (vertical intersection centre) concave longitudinal type, PPV3 (vertical intersection centre) concave longitudinal type, PPV4 (vertical intersection centre) convex longitudinal type

Effect of the Release of Gravel Elements on Soil Nutrients and Jujube Fruit Yield under Wet-and-Dry Cycles

This study sought to evaluate the potential of mulched gravel to release nutrients in the field by conducting trials with three variations of wet-and-dry cycling of the soil beneath gravel mulch and bare soil. The results revealed that quartz, muscovite, clinochlore, and albite were the most abundant minerals in the gravels. Throughout the whole wet-and-dry cycle, the total content of 30 elements measured in the gravel-mulched soil was higher than in the bare soil treatment, and the content of the total element rose with increasing wet–dry cycle humidity. The enrichment ratio (Br) of each element in soil under gravel mulch relative to bare soil was in the sequence Mg &gt; Ca &gt; K &gt; Cr &gt; Na &gt; Mn &gt; V &gt; Zn &gt; Fe &gt; Ti &gt; Si &gt; C &gt; N &gt; B&gt; Co &gt; (Br = 0) &gt; Pb &gt; Cu &gt; Ga &gt; P &gt; Sn &gt; Sr &gt; Al &gt; Be &gt; Li &gt; Mo &gt; Ni &gt; Se &gt; As &gt; S. Under gravel mulch, the elements impacted by the wet–dry cycle are primarily rock-forming, whereas the elements affected under bare soil are primarily trace elements. The wet-and-dry cycles of gravel affected soil nutrients mainly by increasing soil K, Ca, Na, and Mg contents. The differences in soil K and Ca contents significantly affected the growth of jujube trees and the jujube fruit yield. A dry/wet cycle level of 5 L/d per tree under gravel cover conditions can effectively improve soil nutrients and increase the jujube fruit yield without causing environmental problems.

Soil wind erosion rate on rough surfaces: A dynamical model derived from an invariant pattern of the shear-stress probability density function of the soil surface

Landscape types with sparse vegetation, gravel cover and ridge-like tillage measures are widely distributed in dryland, and they are the main areas of soil loss and dust emissions caused by soil wind erosion. The widespread land degradation caused by soil wind erosion in these areas is the main reason for the low quality of life of the local people. Therefore, soil wind erosion control has become an urgent task for governments. As is well known, understanding the dynamic process of soil wind erosion is the premise on which effective measures of soil wind erosion control are developed. However, the spatial heterogeneity of shear-stress generated by wind on the soil of rough surfaces and its driving mechanism on soil wind erosion have not been fully understood. Based on a series of wind tunnel experiments, the distribution of wind-caused shear-stress on the exposed soil surface (τs) of rough surfaces with plants, gravels, and ridges was calculated, and the probability density function of τs on these rough surfaces followed the pattern of the logistic function. The location parameter and scale parameter in the logistic function were correlated with the lateral coverage, ridge index and friction wind velocity on rough surfaces. Subsequently, a soil wind erosion rate model with the characteristics of an upscaling point-scale process was established. Tested by multi-source experimental data, the model has a satisfactory prediction ability. These findings greatly improved the understanding of the spatial heterogeneity of τs and the driving mechanism of τs in soil wind erosion, which will help establish a dynamic-based wind erosion rate model in the future.

Key sites for seedling emergence in degraded areas of the monte ecoregion of the Rio Negro Province, Argentina

In disturbed shrublands of the Monte ecoregion in the Rio Negro province, herbaceous vegetation occurs in patches of high plant cover beneath shrubs, interspersed with patches of low cover between them, which leads to the existence of differential microsites in the environment. The protected understory in the shrub patches is occupied by other functional groups that conform this system: perennial grasses, annuals and biological crusts. The areas between the shrubs may be more or less degraded by grazing, and may exhibit physical impediments to the germination and establishment of seeds and to seedling emergence and survival, in the form of vesicular crusts that develop on the soil surface and contribute to desertification in those systems where they appear. The objective of our study was to relate the presence of seedlings in three microsites of the environment: a) beneath shrubs, and in the open spaces between them discriminated into b) flat and c) rough places, with different covers of the soil surface (biological crust, litter, perennial grasses and gravel), and with the presence and thickness of vesicular crusts, in a semi-arid shrubland of the south-eastern Monte ecoregion. We found that the presence of seedlings differed between the microsites and was related to the different soil cover in each microsite. In flat microsites, that presence was positively related with litter and biological crust covers and negatively related to vesicular crust thickness and gravel cover; in rough places we only found a positive influence of litter, and beneath shrubs, there were beneficial effects due to perennial grass cover and scarce negative effects due to vesicular crusts.

Scale-dependent patterns and drivers of vascular plant, bryophyte and lichen diversity in dry grasslands of the Swiss inneralpine valleys

The inner-alpine dry valleys of the Swiss Alps are characterized by subcontinental climate, leading to many peculiarities in dry grassland species composition. Despite their well-known uniqueness, comprehensive studies on biodiversity patterns of the dry grasslands in these valleys were still missing. To close this gap, we sampled 161 10-m2 vegetation plots in the Rhône, Rhine and Inn valleys, recording vascular plants, terricolous bryophyte and lichen species, as well as environmental data. Additionally, we tested the scale-dependence of environmental drivers using 34 nested-plot series with seven grain sizes (0.0001–100 m2). We analysed the effects of environmental drivers related to productivity/stress, disturbance and within-plot heterogeneity on species richness. Mean species richness ranged from 2.3 species in 0.0001 m2 to 58.8 species in 100 m2. For all taxa combined, the most relevant drivers at the grain size of 10 m2 were southing (negative), litter (negative), mean annual precipitation (unimodal), gravel cover (negative), inclination (unimodal) and mean annual precipitation (unimodal). For vascular plants the pattern was similar, while bryophyte and lichen richness differed by the opposite relationship to mean annual precipitation as well as negative influences of mean herb layer height, grazing and mowing. The explained variance of the multiple regression model increased with grain size, with very low values for the smallest two grain sizes. While southing and litter had high importance for the fiver larger grain sizes, pH and gravel cover were particularly important at the intermediate grain sizes, and inclination and mean annual precipitation for the two largest grain sizes. The findings emphasize the importance of taxonomic group and grain size for patterns and drivers of species richness in vegetation, consistent with ecological theory. Differences in the diversity–environment relationships among the three taxonomic groups can partly be explained by asymmetric competition that leads to low bryophyte and lichen diversity where vascular plants do well and vice versa. The relatively low alpha diversity of vascular plants in dry grasslands in Swiss inner-alpine valleys compared to similar communities in other parts of the Palaearctic remains puzzling, especially because Swiss stands are often large and well-preserved.

Top-down degradation of alpine meadow in the Qinghai-Tibetan Plateau: Gravelization initiate hillside surface aridity and meadow community disappearance

Alpine gravelization by glacier melting may subsequently cause degradation of downstream vegetation. The thinning rates of glaciers outside ice sheet peripheries in some regions has doubled over the past 20 years.However, no study is available about the effects of alpine gravelization on alpine meadow ecosystem. Here, by investigating and measuring the community characteristics, soil moisture, and soil temperature of alpine meadows under three different gravel coverage levels (No gravel covered meadow, half gravel covered meadow, and fully gravel covered meadow),we examine the response of surface microhabitats and community to gravel cover on a typical hillside alpine meadow. Results showed that gravel cover significantly decreased soil/gravel ratio and topsoil moisture. Topsoil water content of the half-covered and the fully-covered gravel meadow was outstandingly low and reached<8% and 5%, respectively. Meanwhile, the larger decrease rates for coverage (−72.53%), above- and below-ground biomass (−76.61% and −94.09%), community density (−81.76%), species richness (−77.75%) and diversity (−55.98%) were found after gravel cover. Gravel cover induced the changes of the dominant species composition from Kobresia pygmaea to Setaria viridis, and ultimately to Trigonotis peduncularis and Ranunculus pedatifidus. Cyperaceae functional group species almost disappeared with increasing gravel coverage. In general, the increase in gravel coverage caused a decrease in soil water content, coverage, above-ground and under-ground biomass, community density, species richness, and the disappearance of Cyperaceae functional group species.Our results provide a new insight into the effect of alpine gravelization on soil water environment and alpine meadow degradation.

Effects of gravel cover on the near-surface airflow field and soil wind erosion

Gravel cover is a traditional farming practice to improve soil properties and advance soil productivity. In arid areas, gravel cover can directly affect the near-surface airflow field to inhibit the soil wind erosion rate (q). The effectiveness of gravel cover in wind erosion control has been recognized in practice, but there are few reports about experimental data. This study aimed to identify the mechanism under which gravel changes the near-surface airflow field and q. The wind profiles at different positions around gravel roughness elements and q were measured under five inlet friction wind velocities (u*∞), five gravel sizes (D) and five gravel coverages (GC) in a large wind tunnel, and an equation of q was established. The results showed significant differences among the wind profiles due to the effects of u*∞, D and GC. Although the wind profile at any position did not represent the average state of the rough surface, the average wind profile of the different positions did. When the density of gravel roughness elements increased, the near-surface airflow changed from isolated-roughness flow to wake interference flow and skimming flow, which directly affected the spatial pattern and the rate of wind erosion. The equation of q established in this study not only integrated the effects of variables on the q, including D, GC, the average friction wind velocity (u*¯) and threshold friction wind velocity (u*t), but also represented the behavior of wind erosion being aggravated by gravel cover when GC ≤ 10 % and D ≥ 3.15 cm. This study can contribute to an understanding of the structural change to the near-surface airflow field and to the prediction of q on gravel-covered surfaces, which provides guidance information for rational utilization of gravel-covered fields in arid areas.

Experiments on restoring alluvial cover using gravel augmentation in a variable width channel with irregular meanders

In partially-alluvial channels, an understanding of cover formation over a non-alluvial substrate is necessary for effective river management or restoration. Urban rivers, for example, are often sediment starved such that the underlying substrate may be exposed. Few experiments have investigated cover development in meandering channels, particularly where width and meander geometry are irregular as is often the case for partially alluvial channels. The purpose of this work is to support the development of sediment augmentation strategies to mitigate channel degradation and restore alluvial cover. The experiments also provide new insight into the impact of sediment supply rates on alluvial cover dynamics in variable-width channels. Under constant flow discharge and a continuous supply of sediment, sediment disperses downstream of the feed location and cover develops in a fragmented fashion. Cover initiation occurs downstream of bend apexes and develops as a series of discrete fixed bars whose morphology differs as a function of bend geometry and channel width. Cover expands and bars merge with time under steady sediment supply and discharge, eventually thickening to an equilibrium state in which sediment supply and output are approximately balanced. Higher sediment supply rates result in more extensive and thicker cover at equilibrium, including cover expanding into the cross-overs between the main bars. Coarse and fine fractions of the sediment supply are preferentially retained in the cover sediment because of fine particle deposition on bar tops and burial of initial coarse deposits. Models of areal cover with feed rate and cover thickness are proposed and compared with other studies. More experimentation is needed, but augmentation of alluvial gravel cover is a feasible approach to maintaining a sediment balance in partially-alluvial channels and for developing mobile alluvial cover in engineered channels.

Environmental and spatial factors affecting surface water quality in a Himalayan watershed, Central Nepal

Various spatial interrelationships among sampling stations are not well explored in the spatial modeling of water quality literature. This research explores the relationship between water quality and various social, demographic, and topographic factors in an urbanizing watershed of Nepal with a comparison of different connectivity matrices to conceptualize spatial interrelationships. We collected electrical conductivity and dissolved oxygen data from surface water bodies using a handheld probe and used the data to establish relationships with land use, topography, and population density-based explanatory variables at both watershed and 100-m buffer scales. The linear regression model was compared with different eigenvector-based spatial filtering models. These spatial filtering models were constructed using five different spatial conceptualizations based on different graph types generated from the geographic coordinates of the sampling sites. Population density, elevation, and percentage of sand in the watershed and riparian regions are most important in explaining dissolved oxygen concentration and electric conductivity. A human signature as population density and increased sand and gravel cover can be detected in this watershed impacting water quality. Among different graph types compared, the relative graph type provided the highest model strength signifying a stronger upstream-downstream relationship of dissolved oxygen, while k-nearest graph types with four neighbors provided the strongest model performance, indicating the impact of local factors on electrical conductivity. The relationships between socio-environmental factors and water quality and their spatial interrelationships identified in this work shed light on the source, mobilization, and transport of dissolved oxygen and electrical conductivity and can assist the water quality management endeavor.

Portable wind tunnel experiments to study soil erosion by wind and its link to soil properties in the Fars province, Iran

Soil erosion controlled by the wind effect on the surface, has been largely studied by field in-situ measurements as well as laboratory or numerical simulations. Nevertheless, more in-situ measurements and observations are needed to document this phenomenon for various desert areas. In the present study, we focus on the documentation of different properties of a wide range of semi-arid and arid soils of the Fars province, and how they control the soil erosion by wind. By improving our knowledge on soil properties which lead to the limitation of soil erosion by wind, it will be possible to better prevent wind erosion in the Fars province. Extensive wind tunnel experiments were conducted in 20 different arid and semi-arid regions. For each region, three wind tunnel experiments were done to encounter local soil variability. We determined threshold wind speeds for which soil erosion was observed. Other experiments were conducted at the same high wind speed, and duration conditions, allowing discussing soil erosion rates by wind regarding soil properties. As already documented in the literature, our results pointed out a significant negative power relationship between wind erosion rate and different soil physical properties, including soil surface gravel cover, the mean weight diameter (MWD) of soil particles, and soil clay and moisture contents. Moreover, a nonlinear relationship as a power function was found between the increase of soil organic carbon and the decrease of soil losses by wind in the studied semi-arid and arid soils. We determined critical values of these soil properties for which wind erosion in Fars province is limited under high wind speed conditions. Additionally, the effects of the electrical conductivity (EC), sodium adsorption ratio (SAR), and calcium carbonate equivalent (CCE) on wind erodibility were discussed at low and high concentrations and for different soil textures.

Wind tunnel experiments on dust emissions from different landform types

The measurement and assessment of dust emissions from different landforms are important to understand the atmospheric loading of PM10 (particulate matter ≤10 μm aerodynamic diameter) and to assess natural sources of dust; however, the methodology and technique for determining the dust still present significant research challenges. In the past, specialized field observation and field wind tunnel studies have been used to understand the dust emission. A series of wind tunnel tests were carried out to identify natural sources of dust and measure the magnitudes of dust emissions from different landforms. The method used in this study allowed the measurement of the PM10 emission rate using a laboratory based environmental boundary layer wind tunnel. Results indicated that PM10 emissions demonstrated strong temporal variation and were primarily driven by aerodynamic entrainment. Sand dunes, playa, and alluvial fans had the largest dust emission rates (0.8–5.4 mg/(m2•s)) while sandy gravel, Gobi desert and abandoned lands had the lowest emission rates (0.003–0.126 mg/(m2•s)). Dust emissions were heavily dependent on the surface conditions, especially the availability of loose surface dust. High dust emissions were a result of the availability of dustparticle materials for entrainment while low dust emissions were a result of surface crusts and gravel cover. Soil surface property (surface crusts and gravel cover) plays an important role in controlling the availability of dust-sized particles for entrainment. The dust emission rate depended not only on the surface conditions but also on the friction velocity. The emission rate of PM10 varies as a power function of the friction velocity. Although dynamic abrasion processes have a strong influence on the amount of dust entrainment, aerodynamic entrainment may provide an important mechanism for dust emissions. Large volumes of dust entrained by aerodynamic entrainment cannot only occur at low shear velocity without saltation, but may dominate the entrainment process in many arid and semi-arid environments. So it may also be responsible for large magnitude dust storms. Playa and alluvial fan landforms, prior to developing a surface crust, may be the main sources of dust storms in Qinghai Province.

Hydrological and erosive response of soil surfaces to rainfall intensity as affected by gravel fragment coverage

Gravel fragment cover is an important factor in determining soil erosion rate, particularly in arid and semiarid lands where vegetation coverage is very low. For example, in North China, soil is a shallow gravelly loam with 30% coarse fraction, and gravels affect local agriculture and forestry dramatically. This study was conducted to quantify the effects of gravel fragment coverage on slope erosion. Three rainfall intensities (30, 60, and 90 mm h−1) were conducted on five gravel fragment coverages (0%, 10%, 20%, 30%, and 40%) by simulated rainfall. The results showed that both runoff and sediment yield rates decreased significantly with the increase of gravel fragment coverage, and they were negatively correlated with rainfall intensity. Gravel fragment cover reduced cinnamon soil (Haplustalfs) loss from slopes. Equations were established to quantify the effects of rainfall intensity and gravel fragment coverage on runoff and sediment yield. Mean runoff velocity, Reynolds number, and Froude number of gravel fragment-covered slopes varied from 0.88 to 3.17 cm s−1, 8.35 to 46.21, and 0.21 to 0.59, respectively. They generally increased with increasing rainfall intensity and decreased with increasing gravel fragment coverage. Sediment yield rate was in a logarithmic function with resistance coefficient. Mean shear stress (τ), runoff power (ω) and unit runoff power (P) of gravel fragment-covered slopes ranged from 0.836 to 1.548 Pa, 0.013 to 0.072 N m−1 s−1, and 0.003 to 0.009 m s−1, respectively. Relationships between runoff shear stress and sediment yield rate, and runoff power and sediment yield rate were both linear. The critical shear stress of the bare slope was 0.48 Pa, which was increased by 0.30 to 0.82 Pa in fragment-covered slopes. The critical runoff power of the bare slope was 0.0003 N m−1 s−1, and gravel fragment cover increased runoff power by 0.0112 to 0.0187 N m−1 s−1. The results of Pearson analysis indicated that Reynolds number was the most sensitive parameter to estimate runoff hydraulic characteristics. In conclusion, gravel cover resulted an effective conservation measure to prevent erosion and conserve rainwater.

Relationship between socioeconomic vulnerability and ecological sustainability: The case of Aran-V-Bidgol’s rangelands, Iran

This study combines the Me-Bar and Valdez’s vulnerability assessment techniques with geographic information systems (GIS) to assess socioeconomic vulnerability and its relation to ecological sustainability in winter rangelands of Aran-V-Bidgol County, Isfahan province, Iran. Socioeconomic data were collected using a researcher-made questionnaire and ecological sustainability parameters (including plant, litter, soil, sand and gravel cover and forage yield) data were collected through field measurements. Results showed that “local problems”, “number of rangeland users”, “rangeland user’s access to rangeland experts”, “utilization pattern”, “livestock type”, “economic status of rangeland users”, “livestock number” and “increasing prices” were the most important socioeconomic indicators influencing socioeconomic vulnerability in the rangelands. In addition, a significant relationship was found between the socioeconomic vulnerability index and ecological sustainability parameters, including forage yield of annual forbs and total forage yield. Findings further indicated that a combination of the social and economic indicators with a focus on the local scale dimensions of vulnerability could create a useful tool for decision-makers, practitioners and rangeland users whose main recent concern is vulnerable rangeland ecosystems.

Flume tests on fluvial erosion mechanisms in till‐bed channels

AbstractSemi‐alluvial stream channels eroded into till and other glacial sediments are common in areas of extensive glacial deposition such as the Great Lakes region and northern interior plains of North America. The mechanics of erosion and erosional weakness of till results in the dominance of fluvial scour and mass erosion due to spontaneous fracture at planes of weakness under shearing flow. There have been few controlled tests looking at erosional mechanisms and resistance of till in river channels. We subjected small blocks of till to unidirectional flows in a laboratory flume to measure the threshold shear stress for erosion and observed the erosion mechanics. Critical shear stress for erosion varied from 7 to 8 Pa for samples with initial saturated moisture content in which a combination of fluvial scour and mass cracking/block erosion dominated. When dried, micro‐fissures occurred in the sample and erosional resistance of the till was extremely low at &lt;1 Pa with erosion appearing to be by fluvial scour. When mobile gravel was added to the test conditions, the gravel reduced the erosion threshold slightly because of the enhanced scour around and below the gravel particles and the tendency for the gravel to aid in crack enlargement. Thus a partial or thin gravel cover over the till may provide no protection from erosion. The erosion processes and effects reflect the complex and contingent mechanics and properties of till, and suggest that the erosion characteristics of till bed semi‐alluvial channels differ from abrasion or plucking dominated processes in more resistant bedrock. Copyright © 2017 John Wiley &amp; Sons, Ltd.

GEOPHYSICAL, GEOTECHNICAL, AND SPELEOLOGIC ASSESSMENT FOR KARST-SINKHOLE COLLAPSE GENESIS IN CHERIA PLATEAU (NE ALGERIA)

Several sinkhole collapses were occurred in the many sites in urban areas and/or their rural periphery; in NE Algeria, in the last few years. The abrupt collapse causes damages to properties, infra-structures, and even lives. The most spectacular oneoccurred in February 2009 inside the Cheria city, Northwest of Tebessa department, with a diameter of more than a hundred meters. This abrupt collapse is due to a sudden rupture of the roof of a large underground karst cavity. It caused panic-stricken among the population living near the crater. In order to investigate the origin of this phenomenon, we combine several geophysical and geotechnical methods, such as Ground Penetrating Radar, Electrical Resistivity Tomography, Standard Penetration Test, Mechanical Drill Core, Cave Survey Photogrammetry, etc. It appears that each method may provide specific information. Their comparison allows to precise the results itself, the limits and the application field of each. Consequently a number of open karst voids and disturbed areas were detected in the study area. The results show that sinkholes originate from two different processes: a brutal collapse of karst voids located at shallow depth, by agravitational effect especially building surcharge on top of limestone. And progressive piping and erosion of the thick gravel cover, especially after storms making large depressions. The drawdown of the aquifer following intense pumping could have accelerated these processes. The extension plans of the study area could be established with this methodical acquaintance of the underground conditions of the karst cavities such as: occurrence, depth, geometry and dimensions.

Habitat suitability and requirements for a threatened New Zealand amphibian

Habitat modification is one of the largest threats to global terrestrial biodiversity, yet management tools such as translocations often fail because of insufficient knowledge about species' habitat suitability and requirements in release areas. Resource selection is a useful technique that can address this issue. In 2014, we investigated resource selection of Hochstetter's frogs (Leiopelma hochstetteri) in mature (>30 year) exotic pine (Pinus radiata) plantations and regenerating native broadleaf forests in Torere Forest (Bay of Plenty, North Island), New Zealand, where harvesting of pines threatens this population. We then determined whether key habitats were present at the proposed target translocation site, Orokonui Ecosanctuary (Dunedin, South Island), New Zealand. In Torere Forest, we conducted daytime searches for frogs along streams and recorded microhabitats (e.g., cobbles) in used and random available plots. In Orokonui, we recorded microhabitats in randomly distributed plots because Hochstetters's frogs are presently absent. We used averaged mixed (binomial) models to identify important resources in pine plantations and native forests and to compare resource use between habitats. Finally, we predicted habitat use in Orokonui and Torere Forest to gain an indication of habitat suitability. Frogs predominantly selected cobble microhabitats in pine plantations and native forests but also partially decayed logs ≥15 cm in diameter within pine plantations. In contrast, high gravel cover and sand-silt were avoided by frogs. In response to limited cobble cover in pine plantations, frogs were more generalized in selecting resources (primarily logs) than in native forests. Habitat suitability was slightly lower in pine plantations compared to native forests, but mature pine plantations do provide suitable habitat for Hochstetter's frogs, at least in the short term prior to pine harvesting. Our study suggests that Orokonui provides suitable habitat for the proposed translocation of Hochstetter's frogs. © 2016 The Wildlife Society.

Implications of surface properties for dust emission from gravel deserts (gobis) in the Hexi Corridor

Gravel deserts (gobis) may be primary dust sources in China, where they occupy almost the same area as sandy deserts. The obvious difference between gravel and sandy deserts is the dominant grain size in the surface sediments: fine in sandy deserts versus coarse in gravel deserts. Potential sand transport, gravel cover, and the mean grain size of the surface sediments of gravel deserts are the main factors that affect dust release. However, little data is available on these properties. In the present study, we estimated gravel cover in surface photographs using ImageJ software, determined the proportion of the total weight accounted for by gravel (diameter>2mm), and described the grain size distribution for study areas in the Hexi Corridor of northern China. We found statistically significant differences between the proportions of total weight as gravel among five sub-regions. This proportion ranged from 22 to 91% of the total (66±17%; mean±SD), and the proportions in most of the samples (73%) ranged from 40 to 80%. The gravel cover ranged from 15 to 87% (52±17%), which was within the range in previous research that produced maximum aerodynamic roughness. The sandy material in the surface sediments was mainly medium sand, which accounted for 52.5% of the total sample. Potential sand transport was >200vector units in most gravel deserts, and 75% of the study sites had a physical soil crust. The high gravel cover and frequency of surface crusts is likely to decrease dust emission from the gravel deserts of the Hexi Corridor.

Rill length and plot‐scale effects on the hydrogeomorphologic response of gravelly roadbeds

AbstractAlthough unpaved roads are well‐recognized as important sources of Hortonian overland flow and sediment in forested areas, their role in agriculturally‐active rural settings still lacks adequate documentation. In this study, we assessed the effect of micro‐catchment size, slope, and ground cover on runoff and sediment generation from graveled roadbeds servicing a rural area in southern Brazil. Fifteen replications based on 30‐min‐long simulated rainfall experiments were performed at constant rainfall intensities of 22–58 mm h−1 on roadbeds with varying characteristics including ~3–7 m2 micro‐catchment areas, 2–11° slopes, 2–9.7‐m‐long shallow rill features, and 30–100% gravel cover. The contributions of micro‐catchment size and rill length were the most important physical characteristics affecting runoff response and sediment production; both the size of the micro‐catchment and the length of the rills were inversely related to sediment loss and this contradicts most of the rill erosion literature. The effect of micro‐catchment size on runoff and sediment response suggests a potentially problematic spatial‐scale subjectivity of experimental plot results. The inverse relationship between rill length and sediment generation is interpreted here as related to the predominance of coarse fragments within rills, the inability of the shallow flows generated during the simulations to erode this sediment, and their role as zones of net sediment storage. Copyright © 2015 John Wiley &amp; Sons, Ltd.