Aeolian Research最新文献

The grain size characteristics of aeolian sediments are the combined result of sand sources, regional airflow regimes, dune morphology, etc., and are essential for understanding the formation and evolution of barchan dunes. Based on field investigations and laboratory experimental data, in this paper, we explored differences in the grain size characteristics of the surface sediments of barchan dunes at the southeastern edge of the Taklimakan Desert (TKLM-SE), the western (QB-W) and southern parts of the Qaidam Basin Desert (QB-S), the sand belt connecting the Badain Jaran Desert and the Tengger Desert (BT-B), and their responses to sand sources, dune morphology, and wind regimes. The main results were as follows: (i) The mean grian size distribution patterns of the windward slope toe to the leeward slope toe through the dune crest/ridge varied with different transects of the barchan dunes and different deserts, showing four types including gradually fining (GF), gradually coarsening (GC), coarsening followed by fining (CF), and fining followed by coarsening (FC). The patterns were GF and CF in the TKLM-SE; GF, GC, and FC in the BT-B; GF, GC, and CF in the QB-W; and GF in the QB-S. (ii) The interdune sediments provided the source material for the formation and development of barchan dunes and their grain size varied in different deserts. The interdune sediments were composed of gravel and very fine sand in the TKLM-SE, while they were composed of medium and fine sand in the QB-W, QB-S, and BT-B. (iii) The windward side of the barchans varied with different wind directions, and dune height affected dune surface airflow velocity and direction, changing the pattern of grain size distribution on the dune surface. The wind regime over a ten-day or half-month scale could explain the variance in the grain size distribution patterns better than that on an annual scale. (iv) Grain size characteristics of dune surface sands changed with dune shape due to changes in the surface airflow velocity and direction and the sediment-carrying capacity of the airflow. With an increasing ratio of dune height to dune width, the grain size of the dune crest sands became coarser. These results help advance our understanding of the grain size characteristics of barchan dunes and regional variabilities in their patterns.

Dust particles are considered as a very important way of soil contamination by heavy metals. Therefore, this study was conducted to evaluate the concentration of heavy metals and their health risk in windborne sediments. For this purpose, sediment traps were installed in five dominant wind directions including north, northeast, northwest, west, and southwest, and center of Tabas city (Iran) to collect the suspended sediments in the air. Sediment sampling was conducted monthly from January to December 2021. The concentrations of heavy metals were measured using atomic adsorption method followed by extraction by aqua regia, and the carcinogenic and non-carcinogenic health risks of heavy metals for children and adults were evaluated during different months of the year. According to the results, the maximum and minimum amounts of windborne sediments found in northwest (85.66 gm⁻²) and west (29.3 gm⁻²), respectively. Monthly variations in windborne sediments discharge also revealed that the maximum amounts of windborne sediments occurred in September and November 2021 from northeast (125 and 117 mgkg⁻¹, respectively). The maximum concentrations of cadmium (0.82 mg/kg) were found in the west of Tabas, while those of lead (192.72 mg/kg), and nickel (227.34 mg/kg) were obtained in the city center. In addition, the highest carcinogenic and non-carcinogenic risks belonged to nickel and the lowest risks were obtained for lead. Also, the carcinogenic risk of cadmium was higher than lead but lower than nickel. In general, the carcinogenic and non-carcinogenic risks of the studied heavy metals were low (less than 1).

Dust events are caused by strong winds that lift dust particles into the air. Due to surrounding deserts and agriculture, West Texas experiences many dust events. This study examines dust events that occurred between 2000 and 2020 across four locations: Amarillo, Lubbock, Midland, and El Paso. A total of 1,834 dust events were identified across the four locations with an average of 22 dust events annually. 227 dust events were observed in Amarillo, 609 in Lubbock, 545 in Midland, and 453 dust events were observed in El Paso. A slight increasing trend of dust events over time was observed for Amarillo, Lubbock, and Midland while El Paso showed a decreasing trend. Most dust events occurred during the spring to early summer months and they lasted an hour or less. Many dust events occurred during times of drought and periods of La Niña. Separation of the dust events based on the meteorological disturbance that caused them (convective vs. synoptic) showed that synoptic disturbances contribute to >60 % of the dust events, while convective disturbances were responsible for most of the remaining. Synoptic disturbances were predominately in spring while convective disturbances were common in the early summer months. A comparison of meteorological parameters measured during each disturbance shows that synoptic dust events were associated with lower temperatures, dew point, and relative humidity, but with higher wind speeds and gusts.

The evolution of large star dunes, because of their remote location, size and surface complexity, is barely recorded and understood. This lack of understanding applies to surface and subsurface features alike. In order to detect the transformation, the detailed subsurface stratigraphy and the relative chronology of large star dunes, we used ground penetrating radar (GPR) on all major arms of a complex star dune of Erg Chebbi, south-eastern Morocco. We used a 350 MHz digital antenna from Geophysical Survey Systems, Inc (GSSI), reaching a depth of 12.5 m to identify main radar facies associated with former downwind dune flanks describing the depositional history. Our results enable the determination of former dune crest positions, their potential past movement and in consequence the construction of the paleo-dune topography. In accordance with simulated historical wind data, we found a potential sediment deficit on the south-eastern side of the dune. This also correlates with surface data describing an oblique form of the star dune and the spatial distribution frequency of its major arms. Our detailed recordings show, for the first time, the complex internal composition of all arms of one large star dune and surface sensitive form-flow interactions. Our results allow the discrimination of deposition phases and therefore, we have constructed a relative chronology as a basis for future sampling and the reconstruction of star dune evolution in general.

On many metropolitan and developed coasts foredunes are narrow, vegetated, highly stable and confined by hinterland development. Such foredunes are most likely to erode, rather than landward migration, in response to ongoing eustatic sea-level rise. Foredune notching may be undertaken on such coasts to facilitate sand transport through the foredune zone and accomplish degrees of foredune landward migration; however, the efficacy of this method has not been examined in relation to the backdune topography, which in many instances takes the form of a dyke or similar infrastructure.

Computational Fluid Dynamics (CFD) is used to investigate how the space behind a notch, and the slope of the seaward face of the backdune topography, modifies near-surface wind through foredune notches. Incident winds are simulated parallel to the notch long axis and the effects of changing backdune morphology on the secondary winds through the notch are examined. Swale widths between 3 and 53 m and hinterland gradients between 0° and 90° are examined.

Air flow through the notch is strongly influenced by the morphology of backdune infrastructure. Wind speed increases through the notch as the spacing behind the notch increases and the slope of the hinterland topography decreases. An increase in spacing reduces the landward extension of wind recirculation in the lee of the notch. To maximise notch efficiency and sediment accumulation in the lee of the foredune the minimum spacing should be 8 and 30 m when the slope of the backdune infrastructure is 20° and 90°, respectively.

Sand dunes are a landscape feature with a quick response time to climate change and human influences (e.g. grazing, greening projects, and fixation structures). Their migration rates and their development can help to gather information about changing environmental conditions over time. The Source Area of the Yellow River (SAYR), located upon the Tibetan Plateau, is highly complex with topographical, hydrological, and climatological influences on active dunes, making it a good study area for these interactions. Based on remote sensing datasets, spanning the last 54 years, 415 dunes were mapped for migration rate calculations. Further, climate data from ERA-5 reanalysis and a local climate station was used to assess their changes within a changing climate. Generally, dune migration rates are rather slow with an average of 3.62 m y^-1. In accordance, the averaged resultant drift potential (RDP) values are lower than 10 m3/s⁻³(−|-). Further, we assessed the density development of the main active barchan dune field in direct premise of the Yellow River. Throughout the past 54 years, we observed the emergence of more than 5 new barchans per square kilometer. This increase is likely attributed to higher sand flux from the Yellow River, which has resulted from increased discharge due to declining snowfall and rising precipitation levels.

The southern margins of the northern European loess belt on the foothills of Eastern Sudetes Mountains are less explored sedimentation zones. This study provides new data about the development of aeolian silty-sandy sediments overlying the glaciofluvial succession on the rugged topography near the village of Kolnovice. The Kolnovice sand quarry (360 × 200 m), which lies at the margin of the upland plateau, is the only active-mined outcrop on the foothills of the Eastern Sudetes and is large enough to study Pleistocene (peri-)glacial sediments. To examine the origin of these sediments, we applied lithofacies analysis (both macro-description of outcrop walls and micromorphological study of thin sections) and surface analysis of quartz grains. Periglacial structures have been identified within the sediments, allowing us to further interpret the post-sedimentary evolution of the sedimentary succession. The studied sediments resulted from colluvial redeposition of aeolian sediments, which was controlled particularly by the topography, glaciofluvial substrate, and climatic conditions. The underlying glaciofluvial sediments are the most crucial source of the studied sediments, although the fine-grained material could have been transported from more distant areas.

Shadow dunes develop at the lee side of obstacles and are scale-dependent on the obstacle size. However, our recent field investigations showed that the lengths of shadow dunes are not always proportional to the size of obstacles. In this work, field investigations and computational fluid dynamics (CFD) simulations were conducted to study the effects of the scale and vortex of nebkhas on shadow dune development. Results show that although the shadow dune lengths are proportionate to the width (W) and height (H) of nebkhas, the increment rate decreased massively when the W and H of nebkhas are larger than 6 and 2 m, respectively. The CFD simulations suggest that the vortex core regions of the paired symmetrical reversing flow gradually move to the upwind region as the aspect ratio (H/W) of the nebkhas decreases. The size of the paired symmetrical reversing flows is reduced, and the merging of the reversing flows is prevented, potentially entraining the sediments far from the wake region. The sediments could rotate and deposit on both sides of the leeward face of the nebkhas and therefore contribute to the occurrence of short, tongue-like shadow dunes, which are particularly notable when H/W < 1. The vortex core region always occurs at the foot of the lee side of nebkhas with the same H/W regardless of the scale of the nebkhas or the incident wind speed.

Soil erosion by water and wind is a critical challenge for sustainable management of catchments in drylands and accurate spatial information can help in mitigation of its destructive consequences. Here, seven machine learning (ML) models were applied to map simultaneously the water and wind erosions in the Bakhtegan catchment, south Iran, with three dried lakes in its southern part and three dams established in upstream parts of the lakes. The analysis identified 10 and 11 effective variables controlling water and wind erosions, among 20 and 17 potential variables, respectively, via the MARS feature selection algorithm. According to the most accurate ML models (artificial neural network for water erosion, and Cubist for wind erosion), an integrated model was developed to map soil erosion by water and wind simultaneously. Permutation feature importance (PFI) and Shapley additive exPlanation (SHAP) interpretation techniques were employed to explain the model outputs, revealing that 19.7 % of the total area belonged to high and very high susceptibility classes to soil erosion by water and wind. The PFI plot revealed that the slope and wind speed were the most influencing factors for water and wind erosion, respectively. According to SHAP decision plot, slope had the highest contribution on the predictive water erosion model’s output, whereas vegetation cover exhibited the highest contribution on the predictive wind erosion model’s output. Due to climate change and intensified drought during the recent years, as well as due to construction of dams upstream of the lakes, the southern part of the study area was converted to a source of sand and dust storms. The hotspots with severe water erosion are distributed all over the study area, rendering it quite vulnerable to adverse climate change projections.

The floodplain of the Yellow River (FPYR) is threatened by severe soil erosion. Soils are often susceptible to wind erosion owing to their coarse-textures and weak aggregation, yet studies are yet to describe the ability of soils to resist wind erosion in this region. Accordingly, this study aimed to quantify how soil wind erosion potential is affected by soil aggregate properties, such as dry aggregate geometric mean diameter (GMD), aggregate geometric standard deviation (GSD), aggregate stability, and soil bulk density, and to assess the effects of soil type, crop rotation, irrigation, fertilization, and tillage treatments on these aggregate properties in the main wind erosion area across the FPYR. Significant differences in GMD and aggregate stability were found between crop rotation treatments, whereas crop rotation marginally affected the soil bulk density. Further, the impact of management practices on aggregate properties differed for each soil type. The soil aggregate erodible fraction (EF) in the FPYR ranged from 1.14 to 82.73% across sites, with a mean of 26.14% across soil types and management practices, which was lower than that previously reported in other wind erosion regions. We incorporated these measured EFs into the Revised Wind Erosion Equation (RWEQ) to evaluate the wind erosion risk of the FPYR. The results indicated that the central FPYR was more susceptible to wind erosion than the other regions, although the total wind erosion potential in the FPYR was small. Adoption of soil conservation practices could help minimize wind erosion and improve atmospheric quality in the region.