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1.
The importance of glacigenic dust in the Earth's system during glacial periods is widely acknowledged. Under contemporary conditions, the world's largest dust sources are in low‐lying, hot, arid regions and this is where most aeolian research is focused. However the processes of dust production and emissions are still operating in cold climate regions, particularly in proglacial areas. This paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle. It focuses on how elements in the glacial and aeolian geomorphic sub‐systems interact to determine the magnitude, frequency and timing of aeolian dust emissions, and on feedback mechanisms between the systems. Where they have been measured, dust emission intensity and deposition rates in glacierised catchments are very high, in some cases far exceeding those in lower latitudes, however, few studies span long time scales. The impact of future glacier retreat on the balance between sediment supply, availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered. This balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths, which promote dust emissions, and patterns and rates of soil development and vegetation succession on recently‐deglaciated terrain which protect sediments from deflation. Retreat of the Antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non‐glacigenic sources in the southern hemisphere. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
Blowing dust is a common phenomenon at Lubbock, Texas, on the Southern High Plains. The directional variability of blowing dust estimated with the ‘sand rose’ technique, using wind speed and direction data, suggest that dust transport occurs from all directions. An empirical method of determining directional variability using meteorological data on visibility reductions due to blowing dust, however, indicates that most dust comes from the west and south-west. In addition to wind speed and direction, other environmental factors must be considered in explaining the spatial pattern of dust transport. Soil erodibility is variable in the region, with the most extensive area of highly erodible soils to the west and south-west of Lubbock. Rangeland dominates land use to the east, while agriculture is extensive to the north, west and south. Local farming techniques leave bare soil during the winter and spring, when most airborne dust is produced and also when strong winds are common from the west and south-west. Soil moisture is lowest to the southwest of Lubbock, which leads to a decrease in soil structure and an increase in the potential for wind erosion in that direction. Relative humidities affect threshold wind speeds and are lowest during March and April, when winds are common from the west and south-west. The spatial and seasonal variability and interactions between many factors, both natural and human-controlled, must therefore considered in explaining the directional variability of aeolian sediment transport at Lubbock.  相似文献   

3.
Near‐surface airflow over a morphologically simple, vegetated, 8 m high foredune with a small wave‐cut scarp was measured for onshore to oblique‐onshore conditions during a low‐moderate (5–6 m s‐1 ) wind event and a high velocity (11–18 m s‐1) sand‐transporting gale event. Flow across the foredune was characterized by significant flow compression and acceleration up and across the foredune during both events. During the gale, a pronounced jet (speed bulge) developed at the foredune crest, which increased in magnitude with increasing wind speed. The vertical (W) velocity component of the 3D flow field was positive (upwards) across the stoss slope under low wind conditions but negative (downwards) during gale wind conditions, with upslope acceleration. During the low velocity event, there was speed‐down within the vegetation canopy, as would be expected for a porous roughness cover. During the strong wind event there was speed‐up in the lower portion of the vegetation canopy, and this was found up the entire stoss slope. Sediment transport during the gale force event was substantial across the beach and foredune despite the moderate vegetation cover and minimum fetch. Aeolian suspension was evident in the lee of the dune crest. The observations presented herein show that strong storm winds are an effective mechanism for translating sediment landwards across a high vegetated foredune, contributing sediment to the stoss slope, crest and leeward slopes of the foredune and backing dunes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

4.
Wind erosion modelling efforts, both ?eld and wind tunnel studies, have traditionally focused on saltation‐based processes for estimating dust emissions from high wind events. This approach gives generally good results when saltation‐sized particles, 90 µm to 2 mm mean diameter, are prevalent on the exposed soil surface. The Columbia Plateau, located in north‐central Oregon and south‐central Washington, is a region with extensive loess deposits where up to 90 per cent of sieved particles (by mass) are less than 100 µm mean diameter. During high‐wind events, large amounts of soil and ?ne particulate matter are suspended. However, ?eld surfaces typically show little evidence of surface scouring or saltation, e.g. soil drifts or covered furrows. Velocity pro?le analysis of two high‐wind events and additional data from a third event show evidence of direct suspension process where saltation is not a major mechanism for eroding soil or generating dust emissions. Surface roughness heights are less than saltation roughness height estimates during peak wind speeds. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

5.
Changes in wind speed and sediment transport are evaluated at a gap and adjacent crest of a 2 to 3 m high, 40 m wide foredune built by sand fences and vegetation plantings on a wide, nourished fine sand beach at Ocean City, New Jersey. Anemometer masts, cylindrical sand traps and erosion pins were placed on the beach and dune during two obliquely onshore wind events in February and March 2003. Results reveal that: (1) changes in the alongshore continuity of the beach and dune system can act as boundaries to aeolian transport when winds blow at an angle to the shoreline; (2) oblique winds blowing across poorly vegetated patches in the dune increase the potential for creating an irregular crest elevation; (3) transport rates and deflation rates can be greater within the foredune than on the beach, if the dune surface is poorly vegetated and the beach has not had time to dry following tidal inundation; (4) frozen ground does not prevent surface deflation; and (5) remnant sand fences and fresh storm wrack have great local but temporary effect on transport rates. Temporal and spatial differences due to sand fences and wrack, changes in sediment availability due to time‐dependent differences in surface moisture and frozen ground, combined with complex topography and patchy vegetation make it difficult to specify cause–effect relationships. Effects of individual roughness elements on the beach and dune on wind flow and sediment transport can be quantified at specific locations at the event scale, but extrapolation of each event to longer temporal and spatial scales remains qualitative. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

6.
This study simulates how spatial variations in particle‐size emissions from a playa affect bulk and size‐resolved dust concentration profiles during two contrasting wind erosion events (a small local and a large regional event) in the Channel Country, Lake Eyre Basin, Australia. The regional event had higher dust concentration as a result of stronger frontal winds and higher erodibility across the playa. For each event, two emission scenarios are simulated to determine if measured size‐resolved dust concentration profiles can be explained by spatial variability in source area emissions. The first scenario assumes that particle‐size emissions from source areas occur at a uniform rate, while the second scenario assumes that particle‐size emissions vary between and within source areas. The uniform emission scenario, reproduced measured bulk dust concentration profiles (R2 = 0·93 regional and R2 = 0·81 local), however simulated size‐resolved dust concentration profiles had poor statistical fits to measured size‐resolved profiles for each size class (the highest were R2 = 0·5 regional and R2 = 0·3 local). For the differential particle‐size emission scenario, the fit to the measured bulk dust concentration profiles is improved (R2 = 0·97 regional and R2 = 0·83 local). However, the fit to the size‐resolved profiles improved dramatically, with the lowest being R2 = 0·89 (regional) and R2 = 0·80 (local). Particle‐size emission models should therefore be tested against both bulk and size‐resolved dust concentration profiles, since if only bulk dust concentration profiles are used model performance may be over‐stated. As the source areas in the first 90 m upwind of the tower were similar for both events, the percentage contributions of each particle‐size class to total emissions can be compared. The contribution of each particle‐size class was similar even though the wind speed, turbulence and dust concentrations were significantly different; suggesting that the contribution of each particle‐size to the total emitted dusts is not related to wind speed and turbulence. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

7.
Comparison of eolian transport during five high-velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms?1. Mean wind direction was oblique to the shoreline (63° from shore-normal) during one event but was within 14° of shore-normal during the other events. Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm?1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events. Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.  相似文献   

8.
Dust emission from wet and dry playas in the Mojave Desert,USA   总被引：1，自引：0，他引：1  
The interactions between playa hydrology and playa‐surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion. The production of evaporite minerals during evaporative loss of near‐surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas. Observations that characterize the texture, mineralogic composition and hardness of playa – surfaces at Franklin Lake, Soda Lake and West Cronese Lake playas in the Mojave Desert (California), along with imaging of dust emission using automated digital photography, indicate that these kinds of surface sediment are highly susceptible to dust emission. The surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly, primarily in response to fluctuations in water‐table depth, rainfall and rates of evaporation. In contrast, dry playas are characterized by ground water at depth. Consequently, dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water. Although not the dominant type of global dust, salt‐rich dusts from wet playas may be important with respect to radiative properties of dust plumes, atmospheric chemistry, windborne nutrients and human health. Published in 2007 by John Wiley & Sons, Ltd.  相似文献   

9.
Large-scale geomorphic drivers that operate at continental scale are often climate driven. Changes in land use can accelerate wind erosion. The range of land management practises within one land use can have dramatic effect on ground cover and wind erosion. This study uses meteorological observations, land use, land management and dust concentration measurements of 129 dust events recorded between 1990 and 2007 to describe a dust chronology of Mildura, in south-eastern Australia. Frontal and frontal trough weather systems account for 74% of dust events. Furthermore, 88% of dust events come from rangelands in the northwest and the cropping lands to the southwest. The cropping areas to the southwest are the most common source of dust, accounting for 66% of events There is no relationship between rainfall and dust activity in this study, suggesting that land-management practices, especially on cropping lands, over-ride the controlling effect of rainfall. When cropping lands received above average rainfall in spring and summer during the 1990s, cultivation for weed control lead to rapid decline in ground cover that predisposed the land to wind erosion in following summer and autumn. In drought years, dust blows into Mildura from all directions suggesting that dust is climate driven rather than controlled by land use. © 2019 John Wiley & Sons, Ltd.  相似文献   

10.
Ephemeral aeolian sand strips are commonplace on beaches. Their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns. However, due to their temporary nature, little is known of their formation, mobility or the specifics of their interaction with beach surface characteristics. Similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems, yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales. Whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well, their resolution over mainly dry sand, close to the aeolian transport threshold is not ideal, particularly where moisture gradients close to the surface are large. In this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development, surface roughness and surface moisture. Our results demonstrate that as the beach surface dries, sand transport increases, with sediment erosion occurring at the wet/dry surface boundary, and deposition further downwind. This dynamic structure, dependent upon changing surface moisture characteristics, results in the formation of a rippled sand strip and ultimately a protodune. Our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings. The terrestrial laser scanner provides a suitable apparatus with which to accomplish this. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

11.
Deposition of suspended dust near eroding source fields can have detrimental effects on vegetation, as well as on soil and water quality. This study was undertaken to quantify dust deposition within 200 m of a source field during wind erosion events. Erosion was measured with BSNE samplers on a small field of Amarillo fine sandy loam at field at Big Spring, TX. Suspension‐sized dust discharge averaged 33 ± 5 per cent of the total sediment discharge and ranged from 18·0 to 147·4 kg m?1 during eight selected storm events. Within 200 m of the source field boundary, dust collected in deposition samplers placed above a vegetated surface averaged 34 per cent of initial dust discharge. Predicted deposition, according to a line source model, was 43 per cent. Actual deposition was likely near that predicted, because of lateral diffusion of the dust and some under‐sampling by the disk samplers. Thus, the line source model seems useful in estimating both the pattern and quantity of deposition. About 30 per cent of the suspended dust was deposited within the initial 50 m of vegetated surface, but only about 12–15 per cent was deposited in the initial 10 m. Published in 2006 by John Wiley & Sons, Ltd.  相似文献   

12.
The event‐ and physics‐based KINEROS2 runoff/erosion model for predicting overland flow generation and sediment production was applied to unpaved mountain roads. Field rainfall simulations conducted in northern Thailand provided independent data for model calibration and validation. Validation shows that KINEROS2 can be parameterized to simulate total discharge, sediment transport and sediment concentration on small‐scale road plots, for a range of slopes, during simulated rainfall events. The KINEROS2 model, however, did not accurately predict time‐dependent changes in sediment output and concentration. In particular, early flush peaks and the temporal decay in sediment output were not predicted, owing to the inability of KINEROS2 to model removal of a surface sediment layer of finite depth. After 15–20 min, sediment transport declines as the supply of loose superficial material becomes depleted. Modelled erosion response was improved by allowing road erodibility to vary during an event. Changing the model values of erosion detachment parameters in response to changes in surface sediment availability improved model accuracy of predicted sediment transport by 30–40%. A predictive relationship between road erodibility ‘states’ and road surface sediment depth is presented. This relationship allows implementation of the dynamic erodibility (DE) method to events where pre‐storm sediment depth can be estimated (e.g., from traffic usage variables). Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

13.
《国际泥沙研究》2016,(4):330-340
The resuspension and transportation of sediments affect the nutrient or contaminants cycles in water column. Therefore, hurricane-induced sediment resuspension in coastal waters may cause environment impacts on coastal ecosystems. In this study, field observed data during a hurricane event from the Rookery Bay National Estuarine Research Reserve (Rookery Bay NERR), Florida, were studied. Based on the relationship between sediment and turbidity, variations of turbidity in the Rookery Bay NERR were discussed in this paper under the impact of the Hurricane Isaac in 2012. Time series analysis indicates that Hurricane Isaac causes the substantial increase of turbidity. Traditional direct regression analysis with raw data was found to result in poor correlation (R2 o 0.41) between wind speed and turbidity due to the impacts of multi-factors in coastal waters of study region during hurricane. Then Hanning Filter was used to remove tidal effect, which shows some improvement of correlations (R2 4 0.6) between wind speed and turbidity. Further improvement was made by introducing a phase factor to account for the lag time between the peak turbidity and peak wind speed, which lead to further improvement of the regression equation between wind speed and turbidity. By using Hanning Filter and phase factor, the regression equation between turbidity and wind speed fits well with observations (R2 4 0.96). Different lag time between wind speed and turbidity at different locations illustrated that wind had different effects on turbidity due to the locations and water depth. Based on the approximate empirical rela-tionship between turbidity and sediment concentration, a regression equation between wind speed and sediment concentration was derived approximately. The equation could be applied to approximately estimate the sediment concentration using wind speed during hurricane, especially with the strong wind speed above 4 m/s. It can be used to provide technical supports for sediment assessment and coastal zone research under extreme clime in the study region.  相似文献   

14.
通过分析苏干湖地区10个地表表层沉积物、9个大气降尘(含2个尘暴降尘)、16个湖泊表层沉积物等样品的8种常量-微量元素和11种稀土元素的含量,以及同类沉积不同元素含量和不同沉积同一元素含量的相关性,结果表明,在湖泊沉积体系中Al、Fe、Sc含量的变化与强风-尘暴过程有关,指示了湖泊沉积碎屑颗粒风成输入的可能性．元素Fe、Sc含量在3种不同的沉积物中差异不大,与尘暴事件的强度和频次有关．稀土元素结果显示3类沉积具有同源性．苏干湖沉积可以用来重建研究区尘暴演化历史．  相似文献   

15.
Dust storms are a major contributor to soil erosion in inland Australia, and the Simpson Desert–Channel Country region is one of the most active wind erosion regions. While information is available on wind erosion rates at the land‐type level, little is known about the influence that spatial variations in the erodibility within a land type have on the resulting dust concentration profile. A Gaussian plume model, DSIS, is presented along with tower‐based dust data, to describe the influence of different spatial combinations of dust source areas, during three dust events on the Diamantina River floodplain in Western Queensland, Australia. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

16.
High-latitude dust (HLD) depositions on four glaciers of James Ross Island (the Ulu Peninsula) were analysed. The deposition rate on the selected glaciers varies from 11.8 to 64.0 g m−2, which is one order of magnitude higher compared to the glaciers in Antarctica or elsewhere in the world. A strong negative relationship between the sediment amount and altitude of a sampling site was found. This is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer. General southerly and south-westerly wind directions over the Ulu Peninsula – with exceptions based on local terrain configuration – help to explain the significantly lower level of sediment deposition on San Jose Glacier and the high level on Triangular Glacier. X-ray fluorescence (XRF) spectrophotometry was used to estimate the relative proportions of the main and trace (lithophile) elements in the sediment samples. Both the sediment amount and the XRF results are analysed in a depth profile at each locality and compared among the glaciers, suggesting long-range transport of fine mineral material from outside James Ross Island. The distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the Ulu Peninsula. © 2020 John Wiley & Sons, Ltd.  相似文献   

17.
Winter wheat–summer fallow is the conventional cropping system employed on >1·5 million ha within the Columbia Plateau of eastern Washington and northern Oregon. Wind erosion contributes to poor air quality in the region, yet little is known concerning the magnitude of soil and PM10 (particulate matter of ≤10 µm in aerodynamic diameter) loss from agricultural lands. Therefore, loss of soil and PM10 was assessed from a silt loam in eastern Washington during 2003 and 2004. Field sites were maintained in fallow using conventional tillage practices in 2003 (9 ha field) and 2004 (16 ha field) and instrumented to assess horizontal soil flux and PM10 concentrations at the windward and leeward positions in the field during high‐wind events. Soil flux was measured using creep and airborne sediment collectors while PM10 concentrations were measured using high‐volume PM10 samplers. Aggregate size distribution of parent soil and eroded sediment was characterized by rotary and sonic sieving. Six high‐wind events occurred over the two year period, with soil loss ranging from 43 kg ha?1 for the 12–22 September 2003 event to 2320 kg ha?1 for the 27–29 October 2003 event. Suspension‐sized particulates (<100 µm in diameter) comprised ≥90 per cent of the eroded sediment, indicating that direct suspension may be an important process by which the silt loam eroded. The corresponding loss of PM10 for these two events ranged from 5 to 210 kg ha?1. Loss of PM10 comprised 9–12 per cent of the total soil loss for the six events. This study suggests that the relatively small loss of PM10 from eroding agricultural fields maintained in summer fallow can affect air quality in the Columbia Plateau. Therefore, alternative tillage practices or cropping systems are needed for minimizing PM10 emissions and improving air quality in the region. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

18.
The west‐central part of South Africa's Free State Province falls within the transition zone between South Africa's sub‐humid, temperate grasslands to the east, and the semi‐arid Karoo and arid Kalahari to the south and west, respectively. The area is characterized by low rainfall (typically 500 mm or less) with high variability, but environmental conditions allow widespread dryland commercial agriculture (maize, sunflowers and stock farming). However, human activity promotes wind erosion and the area is susceptible to dust emissions. This study is the first to quantify the degree of wind erosion on the agricultural soils in the region under prevailing winter to spring climatic conditions and land management practices. Using arrays of cup anemometers, dust deposition traps and saltation impact sensors (Safires), measurements were made of the key erosivity and erodibility drivers that control the degree of wind erosion. Results demonstrate that significant quantities of dust are mobilized, particularly during the months of September and October. Thresholds of wind erosion are shown to respond particularly closely to changes in surface and aerodynamic roughness (z0) with the amount of collected dust correlating well with measures of wind erosivity that weight the impact of higher wind speeds. Given the importance of surface roughness in controlling erosion thresholds, results show that the opportunity exists for well designed farming practices to control wind erosion. However, it is likely that climatically driven environmental change will impact on some of the identified controls on erosion (wind power, moisture availability) with the result that the wind erosion hazard is likely to increase within this marginal environment. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
This paper presents an erosion model, ARMOUR, which simulates time‐varying runoff, erosion, deposition and surface armour evolution down a hillslope either as a result of a single erosion event or as the cumulative impact of many events over periods up to decades. ARMOUR simulates sediment transport for both cohesive and non‐cohesive soil and dynamically differentiates between ‘transport‐limited’ and ‘source‐limited’ processes. A variety of feasible processes for entrainment of different size classes can be modelled and evaluated against data. The generalized likelihood of uncertainty estimation (GLUE) technique was used to calibrate and validate ARMOUR using data collected during rainfall simulator experiments at two contrasting sites: (1) non‐cohesive stony sediments at Ranger Uranium Mine, Northern Territory, Australia; and (2) cohesive silty sediments at Northparkes Gold Mine, NSW, Australia. The spatial and temporal variations of model predictions within the individual runoff events showed that some entrainment processes could not model the spikes in concentration and subsequent depletion, while the hiding model of Andrews and Parker best simulated the concentration trends for both calibrated and independent runoff events. ARMOUR also successfully captured the coarsening of the surface material, though small, over the duration of the rainfall simulator trials. This was driven by the depletion of the finest size class of the soil. For a constant discharge, ARMOUR simulated higher sediment flux at the start of the storm with the sediment flux and concentration diminishing with time. For natural rainfall a power law relationship between sediment flux and discharge was observed. The calibration exercise showed that sediment concentration and discharge alone are insufficient to calibrate all aspects of the physics, in particular the armour depth. This appears to be because the armouring during the short duration events is driven by depletion of the finest classes of the sediments (diameters less then 62·5 mm), which are not normally measured. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

20.
Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the influence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension) are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w′ (depending on the soil texture), these capillary forces are considered as not strong enough to significantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w′ is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coefficients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w′ and soil clay content has been established. The erosion threshold ratios simulated for different soil textures were found to be in good agreement with the experimental data.  相似文献   

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