Aeolian Research最新文献

The Free State has been identified as the region with the most dust sources in South Africa. These dust sources can be linked with the large, heavily cultivated cropland areas in this province, which leaves fields vulnerable to wind erosion after the harvest in the winter. For this study, the focus was on the factors that influence the emission from bare, flat surfaces on agricultural lands in this region. The Portable In-Situ Wind Erosion Laboratory (PI-SWERL) was used to measure the emission flux from adjacent crusted and loose surfaces, which was combined with shear strength, moisture, and soil texture measurements. Boosted regression tree (BRT) analyses were used to identify the variable with the highest relevance on the emission flux.

On the whole dataset, that the shear strength is the most important variable that controls the emission. This is reflected in the significantly lower emission from the crusted surfaces (0.49 mg m⁻² s⁻¹) compared to that of loose surfaces (2.34 mg m⁻² s⁻¹). However, for crusted surfaces, the presence of abraders appeared to be the most significant factor in emission, showing a power relationship between the abrader count and the emission flux (R² = 0.76). In the case of the loose surfaces, the presence of clay and silt was a major influence in emissivity, with a linear relationship between the two variables (R² = 0.68). This difference in factors depending on the agricultural disturbance, asks for a more holistic approach when predicting emission from such arid cropland areas.

This paper discussed the loesses of the East European loess province and their geological context through the prism of a rich research heritage and new data on their primary litho-facial features, distribution, sedimentary architecture and specific landforms. This allows determining Loess Formation including facies of proper aeolian loess and loess-derivatives: loess-like slopewash and loess-like balka alluvium. The permanent factor of loess deposition is considered to be the fallout of globally transported dust. It lasted from the Early Pleistocene to the Holocene inclusive. It was slow and uniform, with some periods of high (Last Glacial) and slackened (interglacial epochs) rates. Wind scouring of bare loose deposits in river valley bottoms and coastal bluffs as well as glacial deposits provided neighbor loess deposition during short spans at the end of the Middle and Late Pleistocene continental glaciations. Loess-derivative slopewash and balka alluvium deposited during periods of heavy rainfall or intense snow melting as a result of sheet erosion. Both main processes resulted in: aggradation of the East European Plain; burial or smoothing of previous negative landforms and creation of new positive ones (loess “waves”, ridges, long gentle slopes, slopewash fans and aprons). The aggradation as well as physical and mechanical properties of loess favored sagging with origin of local depressions, intensified rill-gully and balka erosion and coastal abrasion. During the consideration of loess-paleosol stratigraphy, doubts are expressed about the correctness of long-range correlations of the loess derivatives sequences or loess belonging to riverside areas due to different depositional dynamics.

The study of the chronology of the red dune sands in tropical coastal areas of China, and the environmental significance thereof, is a weak link in studies of Quaternary geology. Therefore, in this study, optically stimulated luminescence (OSL) dating was carried out on two red dune sand profiles (YRS and PQR2) from Wenchang coast in the north-eastern area of Hainan Island. The results showed that the periods of red dune sands accumulation during Marine Isotope Stages MIS 5 and 3 with interglacial period and associated high sea-level stands, probably occurred by similar to, or more humid than, present conditions. The red dune sands in southern of China are controlled by global background factors such as insolation, the East Asian monsoon, and sea level changes on the million-year scale.

The Khuzestan Sand Sea extends from the Wasit and Maysan provinces in Iraq (22%) to the Ilam (10%) and Khuzestan (68%) provinces in Iran. In order to determine wind regimes and sand transport characteristics, hourly wind data records from 21 meteorological stations for the period 2000–2016 were analyzed using aeolian-sediment transport methods. The analysis of the wind energy based on drift potential (DP) revealed rather large spatial variations in the Khuzestan Sand Sea. The Iraqi part of the desert, as well as the southern regions of the Ilam province and the western edge of the Khuzestan province were characterized by particularly high wind energy (DP greater than 400), while towards the central area of the Khuzestan Sand Sea near Ahvaz city a sharp decrease to DP less than 200 was detected. In the southern and southeastern parts of the Khuzestan Province, the wind energy increased again and the DP reached more than 200 vector units. The temporal analysis of the DP showed no considerable temporal trends between 2000 and 2014 in this study area. The dune morphology analysis revealed a bimodal wind regime, which was also supported by the dominance of sand sheets and transverse dunes. Additionally, the local topography has an important influence on the formation of topographic dunes in the southeastern parts of the Sand Sea.

The present study is aimed at assessing the capability of plant species to adsorb particulate matter (PM) in an industrial city which hosts frequently occurring dust storms. To this end, samples were collected from different leaves (morphological properties) of different dominant species at 10 locations in Ahvaz, Iran which had different land uses (industrial, recreational, high-traffic and residential) in various time periods, including the first period (May 6-October 6), the second period (October 7-November 6), the third period (November 7-December 6), and the fourth period (December 7-March 6). Variations in mineral constituents of particulate matter and particle size distribution were analyzed using XRD and laser diffraction respectively. Results disclosed that the particle deposition of some plant species such as Phoenix dactylifera and Washingtonia filifera in various regions was significantly different from that of other species. The particles were generally composed of minerals such as calcite, silicate (quartz) and phyllosilicate which are derived from dust storms. Steel industries in Ahvaz are also one of the main sources of particles, but due to the fact that these particles are primarily made of iron, their adsorption is more likely to occur at distances close to this source. The findings of this study show that characteristics of different plant species have a significant effect on the adsorption of particles and the potential purification of urban air pollution. Therefore, the extension of green space using plant species with greater adsorption is recommended to pave the way for reducing urban air pollution.

Based on the 3D fluid–solid coupling numerical calculation method, a systematic study was conducted on the bearing characteristics of a perforated sheet-type sand fence at a given penetration rate, opening size, and wind velocity. According to the results of this study, both the displacement and stress of the sand fence experienced an impact stage, a coupling stage, and a stabilization stage under different wind velocities and times. At the initial moment of the impact stage, both the displacement and stress of the sand fence reached their maximum, i.e., the maximum position of the sand fence displacement was at the top of the panel central line, whereas the maximum position of the stress was at the site of the column 4.5 cm away from the column bottom. The duration of the impact stage was 1.5 s and did not change with the opening size or wind velocity. In the coupling stage, the displacement and stress of the sand fence underwent intense fluctuations, and the amplitude of fluctuations decreased with time. The duration of the coupling stage did not change with opening size, but increased with the increase in wind velocity. In the stabilization stage, both the displacement and stress of the sand fence reached a stable state and did not significantly change with time. In each stage, both the displacement and stress of the sand fence are inversely proportional to the opening size and directly proportional to the wind velocity, i.e., the lower the opening size, the higher the wind velocity, and the greater the displacement and stress of the sand fence. However, when the hole diameter drops below 1.03 cm, it is no longer a main influencing factor of sand fence displacement or stress change. For the sand fence in each stage, the panel displacement was higher than the column displacement, whereas the column stress was higher than the panel stress. This paper provides a basis for the design and optimization of sand fence structures, lays the foundation for establishing a mechanics-physics model for the stress distribution of sand fence structures, and presents relatively high research values.

Cattle feedlot surfaces can be an important aerosol source, but they have barely been studied. The action of the hooves on the loose, dry layer of soil and manure creates ideal conditions for particulate matter (PM) emissions. The objectives of this work were: a) to quantify the soil loss (Q) and the consequent emission of PM₁₀ (FvPM₁₀) from different surfaces within the feedlot: unpaved roads (UR), cropland (C) and cattle pen (CP); and b) to evaluate the cattle trampling effect in UR, C and CP on Q and FvPM₁₀. The study was carried out in three feedlots with different soil textures: Trenel (F_T), Santa Rosa (F_SR) and General Acha (F_GA). In a wind tunnel, erosion events were simulated at 10.5 m s⁻¹ (µ_*: 0.26 m s⁻¹) during 5 min. The results showed that Q and FvPM₁₀ were UR > C > CP and that the cattle trampling effect was generally directly proportional to Q and FvPM₁₀ (p < 0.05). In general the emission efficiency (calculated as FvPM₁₀/Q) was higher in the feedlot with the finest soil texture (F_T) than in the other two feedlots with coarser soil (F_SR and F_GA). Regarding the type of surface, emission efficiency from UR was lower than from C and CP surfaces. CP presented the lowest values of Q and FvPM₁₀, but it showed high RE so it could be considered a continuous source of wind derived emission of PM₁₀ due to the effect of permanent trampling.

Loess deposits are spread widely over the eastern Tibetan Plateau (ETP), and constitute key terrestrial archives for reconstructing the paleoenvironments of the late Quaternary, which are still poorly understood. This study creates a detailed chronology of the Wenchuan loess sequence in the ETP through the quartz optically stimulated luminescence dating and radiocarbon dating. The results show that loess has accumulated in the area since at least ∼57.7 ka. We show that the variation in the history of the mass accumulation rate (MAR) spanned 4.8–108.0 g cm⁻² ka⁻¹, with a mean value of 43.9 g cm⁻² ka⁻¹ since the last glacial. The MAR of MIS 3 was the highest over the last glacial, with two peaks at 48–44 ka and 35–32 ka; whereas the MAR of MIS 2 was slightly lower and its peak appears at 21–18 ka. The MAR during the Holocene was generally low. Moreover, four enhanced dust events were superimposed on changes in the long-term MAR and correlated with the corresponding Heinrich events. The variation in the MAR of Wenchuan loess since the last glacial period has been similar to that in the eastern Chinese Loess Plateau (CLP) but differing from those of the western CLP. Our results reveal the spatial difference of MAR since last glacial, and can contribute to a better understanding of the link between the evolution of dust deposition and environmental changes in the ETP.

The charge-per-mass of sand grains in natural windblown sand fluxes is important for understanding its contribution to atmospheric electric field and its effect on dust transport in atmosphere and the evolution of windblown sand fluxes. In many existing studies, the charge-per-mass of sand grains were usually averaged values, namely, the total charges divided by total mass of sand sample collected in a sand grain trap. In this paper, by conducting a field site experiment in Tengger Desert in western China, the charge-per-mass of individual grains of natural near-surface windblown sand fluxes are measured for the first time. A method is established for this purpose, which includes a well-designed silicone oil box used to trap sand grains and the grain trajectory imaging system for the retrieval of sand grains’ charges and sizes. The charge-per-mass of more than 900 grains are measured individually with good accuracy, from which the probability distributions of both charge-per-mass and grain size are obtained. The probability distribution of charge-per-mass of individual sand grains may provide more accurate estimations of charge distribution in natural windblown sand fluxes. On the other hand, these results of charge-per-mass are helpful for the validation of existing theories of charging mechanism of windblown sand fluxes.

Wind tunnel measurements of the mean saltation length L and of different proxies of the mean saltation height H in saturated aeolian sand transport indicate that L and H are relatively insensitive to both the wind speed and grain diameter d. The latter result is currently unexplained and contradicts the theoretical prediction $L\propto H\propto d$. This prediction is based on the assumption that the characteristic velocity $\sqrt{\tilde{g}d}$ of bed grains ejected by the splash of an impacting grain controls the average saltation kinematics. Here, we show that a recent analytical saltation model that considers only rebounds of saltating grains, but neglects splash ejection, is consistent with the measurements. The model suggests that the buffer layer of the inner turbulent boundary layer, which connects the viscous sublayer with the log-layer, is partially responsible for the insensitivity of L and H to d. In combination, the measurements and model therefore indicate that splash ejection, though important to sustain saltation, does not significantly affect the average saltation kinematics. This finding represents a strong argument against the Ungar and Haff (1987)-scaling and in favor of the Durán et al. (2011)-scaling of the saturated saltation mass flux, with implications for ripple formation on Mars. Furthermore, it supports the recent controversial claim that this flux is insensitive to soil cohesion.