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Stormwater control measures (SCMs) such as retention basins, bioswales, and bioinfiltration systems are used to reduce peak flows and remove pollutants from stormwater in temperate urban landscapes. However, the application of de-icing salts to roadways can substantially increase the salinity of stormwater basin media (i.e., engineered soil), likely impacting the physical properties of these soils. Further, SCM soils can become moderately compacted, potentially altering the extent and effects of salinization on soil physical properties. Although many studies have documented the high salinity of roadside soils in winter, the effects of salinity on soil hydraulic properties is not well understood, especially in the context of urban stormwater basins. Here, we compared the water retention properties (spanning pressure potentials of -10 to -1,000,000 hPa) of salinity-affected stormwater media (1-100 dS m-1, using Na+ and Mg2+ salts) that was either uncompacted or compacted. The effects of salinity on both matric and osmotic potential included shifts in the plant-available range with the magnitude depending on a combination of salt type and concentration. We attribute these changes to salinity inducing shifts in both surface tension and pore size distributions. Further, compaction increased the severity of salinization under low salinity conditions but not high. Climate change may increase the number and intensity of snow events in many temperate urban regions, which may increase salt loads to stormwater control measures, exacerbating the aforementioned effects.

Lordsburg Playa, a dry lakebed in the Chihuahuan Desert of southwestern New Mexico (USA), is crossed by Interstate Highway 10 (I-10). Dust from the playa threatens highway safety and has caused dozens of fatal accidents. Two numerical models—the U.S. Department of Agriculture’s Single-Event Wind Erosion Evaluation Program (SWEEP) and the American Meteorological Society and U.S. Environmental Protection Agency Regulatory Model (AERMOD)—were used to simulate and predict the generation and dispersion of windblown soil, dust, and PM10 from playa hotspots and estimate PM10 concentrations downwind. SWEEP simulates soil loss and particulate matter emissions from the playa surface, and AERMOD predicts the concentration of transported dust. The modeling was informed by field and laboratory data on Lordsburg Playa’s properties, soil and land use/land cover databases, and weather data from meteorological stations. The integrated models predicted that dust plumes originating on the playa—including a large, highly emissive area away from the highway and a smaller, less emissive site directly upwind of the interstate—can lead to hourly average PM10 concentrations of tens, to hundreds of thousands, of micrograms per cubic meter. Modeling results were consistent with observations from webcam photos and visibility records from the meteorological sites. Lordsburg Playa sediment contains metals, as will its dust, but human exposures will be short-term and infrequent. This study was the first to successfully combine the SWEEP wind erosion model and the AERMOD air dispersion model to evaluate PM10 dispersion by wind erosion in a playa environment. With this information, land managers will be able to understand the potential levels of dust and PM10 exposure along the highway, and better manage human health and safety during conditions of blowing dust and sand at Lordsburg Playa.

Many grass-dominated ecosystems in dryland regions have experienced increasing woody plant density and abundance during the past century. An example is the Chihuahuan Desert in the southwestern US, which experienced different stages of shrub encroachment in the past 150 years. We synthesize recent developments in the roles and feedbacks of abiotic and biotic drivers of shrub encroachment in the Chihuahuan Desert using an ecosystem dynamics context through intercomparison of Long Term Ecological Research (LTER) sites. Experimental and modeling studies support a conceptual framework which underscores the roles of erosion and fire in woody plant encroachment. Collectively, research at the Jornada LTER provided complementary, quantitative support to the well-known fertile-islands framework. Studies at the Sevilleta LTER expanded the framework, adding fire as a major disturbance to woody plants. Conceptual models derived from the synthesis may guide management interventions aimed at reducing or mitigating undesirable ecosystem state change elsewhere in the world.

The entrainment and movement of aeolian sediments is determined by the direction and intensity of erosive winds. Although erosive winds may blow from all directions, in most regions there is a predominant direction. Dust emission causes the removal preferentially of soil nutrients and contaminants which may be transported tens to even thousands of kilometers from the source and deposited into other ecosystems. It would be beneficial to understand spatially and temporally how the soil source may be degraded and depositional zones enriched. A stable chemical tracer not found in the soil but applied to the surface of all particles in the surface soil would facilitate this endeavor. This study examined whether solution-applied rare earth elements (REEs) could be used to trace aeolian sediment movement from a point source through space and time at the field scale. We applied erbium nitrate solution to a 5 m2 area in the center of a 100 m diameter field 7854 m2 on the Southern High Plains of Texas. The solution application resulted in a soil-borne concentration three orders of magnitude greater than natively found in the field soil. We installed BSNE sampler masts in circular configurations and collected the trapped sediment weekly. We found that REE-tagged sediment was blown into every sampler mast during the course of the study but that there was a predominant direction of transport during the spring. This preliminary investigation suggests that the REEs provide a viable and incisive technique to study spatial and temporal variation of aeolian sediment movement from specific sources to identifiable locations of deposition or locations through which the sediments were transported as horizontal mass flux and the relative contribution of the specific source to the total mass flux.

Models of aeolian processes rely on accurate measurements of the rates of sediment transport by wind, and careful evaluation of the environmental controls of these processes. Existing field approaches typically require intensive, event-based experiments involving dense arrays of instruments. These devices are often cumbersome and logistically difficult to set up and maintain, especially near steep or vegetated dune surfaces. Significant advances in instrumentation are needed to provide the datasets that are required to validate and improve mechanistic models of aeolian sediment transport. Recent advances in robotics show great promise for assisting and amplifying scientists’ efforts to increase the spatial and temporal resolution of many environmental measurements governing sediment transport. The emergence of cheap, agile, human-scale robotic platforms endowed with increasingly sophisticated sensor and motor suites opens up the prospect of deploying programmable, reactive sensor payloads across complex terrain in the service of aeolian science. This paper surveys the need and assesses the opportunities and challenges for amassing novel, highly resolved spatiotemporal datasets for aeolian research using partially-automated ground mobility. We review the limitations of existing measurement approaches for aeolian processes, and discuss how they may be transformed by ground-based robotic platforms, using examples from our initial field experiments. We then review how the need to traverse challenging aeolian terrains and simultaneously make high-resolution measurements of critical variables requires enhanced robotic capability. Finally, we conclude with a look to the future, in which robotic platforms may operate with increasing autonomy in harsh conditions. Besides expanding the completeness of terrestrial datasets, bringing ground-based robots to the aeolian research community may lead to unexpected discoveries that generate new hypotheses to expand the science itself.

Soil loss due to wind and water erosion degrades the soil on-site and results in environmental problems due to deposition in off-site areas downstream and downwind of the source field. Wind and water erosion may both occur to varying extents particularly in semi-arid environments. Soil conservation strategies require information about the processes of soil redistribution to mitigate its impact. However, very few studies have partitioned soil erosion between contributions of wind and water. We quantified wind and water erosion on six graded terraces under a uniform crop rotation since 1949 and two tillage management practices begun in 1981. Detailed runoff and sediment yield data have been recorded on all the terraces since 1984. We used a stratified random sampling design to collect soil which were then bulked to form six composites for each terrace. From an adjacent undisturbed native prairie, soil cores were collected and composited similarly to provide a reference. The cores were composited by 15 cm layers in the terraces and, in the reference area, the upper 15 cm layer was subdivided into 5 cm layers and all were measured for 137 Cs activity which was converted to 137 Cs inventory. We then employed an established computer model that equates loss of 137 Cs inventory with soil loss and direct measurement of water-borne sediment loss to estimate 30 year mean wind erosion losses on the terraces by tillage type. We found that no-till management reduced total soil loss by one-third compared with stubble mulch tillage, reduced water-borne sediment loss by about the same amount, and that for both tillage systems, wind erosion was responsible for about 75% of the total soil loss.

The National Wind Erosion Research Network was established in 2014 as a collaborative effort led by the United States Department of Agriculture’s Agricultural Research Service and Natural Resources Conservation Service, and the United States Department of the Interior’s Bureau of Land Management, to address the need for a long-term research program to meet critical challenges in wind erosion research and management in the United States. The Network has three aims: (1) provide data to support understanding of basic aeolian processes across land use types, land cover types, and management practices, (2) support development and application of models to assess wind erosion and dust emission and their impacts on human and environmental systems, and (3) encourage collaboration among the aeolian research community and resource managers for the transfer of wind erosion technologies. The Network currently consists of thirteen intensively instrumented sites providing measurements of aeolian sediment transport rates, meteorological conditions, and soil and vegetation properties that influence wind erosion. Network sites are located across rangelands, croplands, and deserts of the western US. In support of Network activities, http://winderosionnetwork.org was developed as a portal for information about the Network, providing site descriptions, measurement protocols, and data visualization tools to facilitate collaboration with scientists and managers interested in the Network and accessing Network products. The Network provides a mechanism for engaging national and international partners in a wind erosion research program that addresses the need for improved understanding and prediction of aeolian processes across complex and diverse land use types and management practices.

A cyclone type continuous-weigh sand trap (CCST) has been constructed. The performance of the CCST was investigated for farmland environment during two storms in the Kangbao County of the agro-pastoral ecotone of northern China. The results revealed that the CCST captures the real-time variations in aeolian sediment flux caused by fluctuations in wind speed measured at 1 min resolution. Significant power relationships between the horizontal sediment flux and wind speed was observed for the inlet heights of 5, 15 and 40 cm, respectively. The sediment flux collected by the Big Spring Number Eight (BSNE) closely linearly correlated with that by the CCST. From all testing performed to date, the CCST appears to be a useful device to examine the relationship between horizontal sediment flux and wind speed for field use. Further improvements on a wind-driven rotating and lower-cost CCST are needed.

Heavy metal contamination in the environment is detrimental to human and environmental health. Air emissions from industry, especially ore smelting and refining, are a source of heavy metal contamination that affects land and populations downwind. A smelter constructed in 1887 in El Paso, Texas, USA and later decommissioned in 1999 resulted in significant environmental contamination and subsequent remediation of nearby neighborhoods. We sampled dust accumulated in attics from two distinct neighborhoods different distances and topographic positions downwind from the smelter site to determine if we could detect metal-bearing particulates related to smelter emissions and to evaluate potential spatial and temporal patterns of deposition. Both neighborhoods showed evidence of accumulation of smelter-related particulates the depositional environment of vented attics. The proportion of smelter-associated elements in attic dust from the neighborhood nearer the smelter was greater than the neighborhood further away and across a ridge. A temporal pattern of deposition defined by the construction of a 252 m tall smokestack in 1967 and other engineering controls significantly reduced the deposition of smelter particulates in both neighborhoods. However, we found the reduction effect was more significant in the neighborhood nearer the smelter, once again demonstrating the spatial effect of distance from source.

Atwater University (AU) administration is struggling with an increased number of student alcohol-related problems. In particular, during the annual homecoming parade, students are extremely intoxicated and belligerent toward alumni. The new dean of students is appalled by the condoned student behavior. He also received two complaint letters from members of the AU community. The dean of students charges his subordinates with fixing the related problems.

On the Ground Wind erosion is a major resource concern for rangeland managers because it can impact soil health, ecosystem structure and function, hydrologic processes, agricultural production, and air quality. Despite its significance, little is known about which landscapes are eroding, by how much, and when. The National Wind Erosion Research Network was established in 2014 to develop tools for monitoring and assessing wind erosion and dust emissions across the United States. The Network, currently consisting of 13 sites, creates opportunities to enhance existing rangeland soil, vegetation, and air quality monitoring programs. Decision-support tools developed by the Network will improve the prediction and management of wind erosion across rangeland ecosystems.

Soil organic matter (SOM) is essential for soil water holding capacity, aggregation, and biodiversity. Little information is available regarding the carbon (C) functional groups carried away in wind eroded sediments away from the source soil. Mid-infrared (MidIR) spectroscopy was used on wind tunnel-blown sediments eroded from a loam soil during the fallow period of different cropping systems and tillage managements in Akron, Colorado. The soil was managed as fallow-winter wheat ( Triticum aestivum L.) under conventional tillage (F–Wct) or no tillage (F–Wnt) and fallow–wheat–corn under no tillage (F–W–Cnt). Two wind eroded sediments were evaluated: fine dust ( −1 ), and clays (3690–3620 cm −1 ). The saltation-sized material showed higher absorbance for quartz from 2000–1800 cm −1 and reduced absorbance from 1250–1050 cm −1 . Both wind eroded sediments showed higher absorbance for –OH/NH groups and aliphatic CH from no-till soil. Finer dust sediments, which travel greater distances from the source soil than saltation size material, can carry away higher levels of aliphatic-carbon compounds and clays with potential negative impacts on SOM quantity and quality, and consequently the sustainability of these agroecosystems.

Soil degradation is one of the most serious ecological problems in the world. In arid and semi-arid northern China, soil degradation predominantly arises from wind erosion. Trends in soil degradation caused by wind erosion in northern China frequently change with human activities and climatic change. To decrease soil loss by wind erosion and enhance local ecosystems, the Chinese government has been encouraging residents to reduce wind-induced soil degradation through a series of national policies and several ecological projects, such as the Natural Forest Protection Program, the National Action Program to Combat Desertification, the “Three Norths” Shelter Forest System, the Beijing-Tianjin Sand Source Control Engineering Project, and the Grain for Green Project. All these were implemented a number of decades ago, and have thus created many land management practices and control techniques across different landscapes. These measures include conservation tillage, windbreak networks, checkerboard barriers, the Non-Watering and Tube-Protecting Planting Technique, afforestation, grassland enclosures, etc. As a result, the aeolian degradation of land has been controlled in many regions of arid and semiarid northern China. However, the challenge of mitigating and further reversing soil degradation caused by wind erosion still remains.

Wind erosion is increasingly scrutinized as a causative factor in soil degradation and fugitive dust emissions. Although models have been developed to predict wind erosion and dust emissions, they are not accurate in all locations. The temporal and spatial variability of aeolian processes makes local estimates of long-term average erosion costly and time consuming. Atmospheric testing of nuclear weapons during the 1950s and 1960s resulted in anthropogenic radioisotopes that had not previously existed being injected into stratospheric global circulation and subsequently deposited on the Earth’s surface. Many of these radioisotopes are strongly adsorbed to soil particles and their movement on the landscape is a powerful method for investigating soil redistribution by wind, water, and tillage. 137Cs is the most commonly used anthropogenic radioisotope used to assess soil redistribution rates. Models have been developed to equate differences of radioisotope inventories with rates of soil redistribution and these models have been employed globally to assess soil redistribution on agricultural and natural landscapes. The radioisotope method for assessing soil redistribution rates has many advantages, but also a few limitations. One of the major limitations occurs when local sources of radioisotope contamination, particularly 137Cs, mask the pulse from global fallout, making temporal estimates of redistribution difficult or impossible. In this paper, I explore the importance, history, and applications of the radioisotopic technique using 137Cs, particularly as it applies to soil redistribution by wind.

In the previous paper, the use of soilborne 137 Cs from atmospheric fallout to estimate rates of soil redistribution, particularly by wind, was reviewed. This method relies on the assumption that the source of 137 Cs in the soil profile is from atmospheric fallout following the period of atmospheric weapons testing so that the temporal and, to a certain extent, the spatial patterns of 137 Cs deposition are known. One of the major limitations occurs when local or regional sources of 137 Cs contamination mask the pulse from global fallout, making temporal estimates of redistribution difficult or impossible. Like 137 Cs, Pu exhibits strong affinity for binding to soil particle surfaces, and therefore, re-distribution of Pu inventory indicates inferred soil re-distribution. Compared to 137 Cs, 239 Pu and 240 Pu offer several important advantages: (a) the two major Pu isotopes have much longer half-lives than 137 Cs and (b) the ratio 240 Pu/ 239 Pu is used to examine whether the Pu is from stratospheric fallout. In this paper, we review the literature concerning Pu in soil and of current attempts to use this tracer to estimate rates of soil redistribution. We also present preliminary, unpublished data from a pilot study designed to test whether or not 239+240 Pu can be used to estimate rates of soil redistribution by wind. Based on similarities of profile distribution and relative inventories between 137 Cs measurements and 239+240 Pu measurements of split samples from a series of fields with documented wind erosion histories, we conclude that 239+240 Pu may well be the anthropogenic radioisotope of choice for future soil redistribution investigations.

T he 2012 drought, one of the worst during the last 80 years or more, reminds us of the dust bowl of the 1930s (figure 1) and indicates that climate change is a reality rather than a distant threat. The drought has had a severe impact on yields, reducing the predicted grain production for corn per acre at a farm level to levels of production that have not been seen since 1995 and severely impacting other crops such as soybeans. Analysis has predicted that these lower yields will contribute to spikes in wholesale prices for consumers in the United States and internationally since the United States is the world's leading exporter of these grains. It is projected that prices for meat, eggs, and milk will also increase as a result of the drought impacts on grain yields, animals, and forages among other factors. Many view the 2012 drought as an extension of the exceptional drought of 2011 in Texas and surrounding regions, during which 7.5 million ac (3 million ha) succumbed to wildfire in Texas, New Mexico, and Arizona. Additionally, many expect that these droughts will be the new norm during this century. These droughts are following recent droughts like the…

Dry playa lake beds can be significant sources of fine dust emission. This study used a portable field wind tunnel to quantify the PM10 emissions from a bare, fine-textured playa surface located in the far northern Chihuahua Desert. The natural, undisturbed crust and its subjection to two levels of animal disturbance (one and ten cow passes) were tested. The wind tunnel generated dust emissions under controlled conditions for firstly an initial blow-off of the surface, followed by two longer runs with sand added to the flow as an abrader material. Dust was measured using a GRIMM particle monitor. For the study playa, no significant differences in PM10 concentration and emission flux were found between the untrampled surface and following a single animal pass. This was the case for both the initial blow-offs and tests on plots under a steady abrader rate. Significantly higher dust loading was only associated with the effect of 10 animal passes. In the blow-offs, the higher PM10 yield after 10 passes reflected the greater availability of easily entrainable fine particles. Under abrasion, the effect of the heaviest trampling increased the emission flux by a third and abrasion efficiency by around 50% more than values on the untrampled surface. This enhanced abrasion efficiency persisted for a 30 min period under abrasion before the positive effect of the disturbance was no longer evident. The findings highlight the role of a threshold of disturbance that determines if supply-limited surfaces will exhibit enhanced wind erosion or not after undergoing perturbation.

T he weathering of mountain rocks and downhill movement of the resulting sediments form the building blocks of soil formation. Through eons of weathering and soil redistribution, complex landscapes are formed and reformed again in response to dynamic forces of geology, climate, and vegetation. Humans can also influence the formation of soils and landscapes through economic activities such as farming and pasturing livestock that disturb the stabilizing influence of native vegetation. As the global population increases, more and more of the earth's surface is impacted, and erosion of soil resources and sedimentation of the waterways is expected to increase. Assessing the rates of soil redistribution is a difficult endeavor. The spatial and temporal variabilities, at multiple scales, of the factors controlling erosion make simple measurements difficult, if not impossible (Chepil and Woodruff 1963; Stroosnijder 2005). Rainfall varies on timescales of minutes to decades, and wind speeds vary on timescales of seconds to months. Rainfall and other climatic factors also control the stabilizing influence of vegetation as long-term drought may result in bare unprotected landscapes. In the last few decades, fallout radionuclides, both natural and anthropogenic, have been used to assess rates of soil redistribution on time scales from a few weeks…

Current wind erosion and dust emission models neglect the heterogeneous nature of surface roughness and its geometric anisotropic effect on aerodynamic resistance, and over-estimate the erodible area by assuming it is not covered by roughness elements. We address these shortfalls with a new model which estimates aerodynamic roughness length (z0) using angular reflectance of a rough surface. The new model is proportional to the frontal area index, directional, and represents the geometric anisotropy of z0. The model explained most of the variation in two sets of wind tunnel measurements of aerodynamic roughness lengths (z0). Field estimates of z0 for varying wind directions were similar to predictions made by the new model. The model was used to estimate the erodible area exposed to abrasion by saltating particles. Vertically integrated horizontal flux (Fh) was calculated using the area not covered by non-erodible hemispheres; the approach embodied in dust emission models. Under the same model conditions, Fh estimated using the new model was up to 85% smaller than that using the conventional area not covered. These Fh simulations imply that wind erosion and dust emission models without geometric anisotropic sheltering of the surface, may considerably over-estimate Fh and hence the amount of dust emission. The new model provides a straightforward method to estimate aerodynamic resistance with the potential to improve the accuracy of wind erosion and dust emission models, a measure that can be retrieved using bi-directional reflectance models from angular satellite sensors, and an alternative to notoriously unreliable field estimates of z0 and their extrapolations across landform scales.

Saltation Impact Sensors (SIS) of acoustic and piezo-electric design are increasingly used to study wind erosion in the laboratory and in the field. In spite of their wide-spread use, little is known about how to compare data collected with the different types of SIS or what physical limitations may exist. We tested four each of the Saltiphone, an acoustic sensor, and four each of the Sensit and Safire, two piezo-electric sensors, for sampling efficiency in a laboratory wind tunnel. We tested each SIS with seven diameter ranges of glass beads from 53 to 420 μm diameter inclusive at wind speeds of 7.5, 10, and 15 m s −1 both with a multiplexer in the circuit and without a multiplexer in the circuit. In another wind tunnel, we tested the sensors at the three wind speeds using Kootwijkerzand drift sand with a median diameter of 299 μm and also with a simulated 100 mm h −1 rainfall. All SIS appeared to be unable to detect impacts from beads of less than 100 μm diameter with the exception of the Sensit at the 15 m s −1 wind speed. The Sensit had the lowest threshold diameter of bead to which it would respond followed closely by the Saltiphone. The Safire was insensitive to beads of less than 200 μm diameter at any wind speed. The threshold diameter tended to decrease and all instruments became more efficient at detecting impacts as the wind speed and resulting particle momentum increased. The response of the SIS efficiencies to the presence of a multiplexer in the circuit varied among the SIS types. The Sensit was least sensitive to raindrop noise and the Saltiphone was most sensitive. Within each SIS type, inter-instrument variability of sampling efficiencies raised concerns about the use of SIS to quantify saltation in the field or laboratory. Further, radial bias in the piezo-electrically based sensors would contribute additive errors as wind direction varied during an event or between events. We believe that the use of SIS in wind erosion studies should be limited to the study of temporal or spatial patterns of saltation and should not be used to quantify saltation unless the sensors have been calibrated for the specific soil and wind conditions of the event.

A portable, open transparent chamber system for measuring canopy gas exchanges was developed and tested. Differentials between incoming and outgoing atmospheric H 2 O and CO 2 concentrations were used to calculate canopy transpiration (E) and net assimilation (A) at 10-s intervals using solenoid valve actuated sample lines connected to an infrared gas analyzer. A programmable data logger controlled fan speed and air flow rate to control daytime chamber air temperature to within 0.5°C of ambient air temperature. To validate the mass balance equations used to calculate E, the chamber was positioned over sealed soil potted cotton (Gossypium hirsutum L.) plants which were placed on a weighing scale. A second scale was used to measure E of cotton plants outside the chamber to quantify potential chamber effects. A wide range of crop canopy leaf areas and soil water contents were created with greenhouse-grown plants for these comparisons. Data analysis indicated agreement between chamber E measurements and the internal weighing scale (R 2 = 0.93), as well as comparison between the internal and external scales (R 2 = 0.88) across wide ranges of soil water contents and canopy leaf area. Transpiration ranged from near zero at night to 900 g (H 2 O) h -1 during the day. Bias estimates of E for chambervs.internalscale and the internal vs. externalscale were -6.0 and 4.6 g (H 2 O)h -1 . With minor chamber effect, the chamber accurately estimates E for many field applications such as comparison of canopy gas exchanges and water use efficiencies among irrigation treatments.

Accelerated erosion caused by deforestation and soil degradation has become the primary factor limiting sustainable utilization of soil resources on the Loess Plateau of Northwestern China. We studied the physical, chemical, and microbiological processes of soil degradation along a chronosequence of deforestation in the Ziwuling area of northwestern Shaanxi province. The results indicated that soil wet aggregate stability, mean aggregate diameter decreased with years following deforestation. Accelerated erosion resulted in soil nutrient loss, and a decrease in soil enzyme activities including notable losses of total soil N, organic C, alkaline phosphatase activity, and invertase activity. During the early time period, the rates of total soil N, organic C, alkaline phosphatase activity, and invertase activity decreasing were rapid and gradually decreased with deforestation years. Increased use of nitrogen fertilizers made determination of soil quality based on measured NO(3)-N and NH(4)-N inconclusive. The differences in measured parameters between the topsoil and subsoil horizons decreased with time since deforestation, and we concluded that soil erosion was the primary process responsible for the degradation of measured soil physical, chemical, and microbiological properties. (C) 2008 Elsevier B.V. All rights reserved.

In deserts, dunes are common aeolian landforms, and parallel ridges are common in cultivated land. A computational fluid dynamics (CFD) model is used to simulate a stable wind blowing over slope beds of varying height and coupled with the slope-compensating fluid threshold friction velocity formula. The model accurately reproduced patterns of flow deceleration at the slope toe and stoss flow acceleration. Based on the CFD-based model, quantitative analyses of slope gradient and particle position on the initiation of particle movement are performed. Results indicate that the slope has a great influence on particle saltation in the windward slope, and the initiation of particle movement is particularly sensitive to particle position with respect to the slope. Copyright © 2008 John Wiley & Sons, Ltd.

Wind erosion has degraded over one-half billion hectares of land worldwide. 137 Cesium ( 137 Cs) has been used as a tracer to study long-term rates of soil redistribution by water and, to a lesser extent, by wind. Early studies assumed that the decline in 137 Cs activity for a potentially eroded soil relative to that for an uneroded soil was linearly proportional to soil loss. More recently, models have emerged that consider the effects of soil cultivation and the particle surface area-dependent partitioning of 137 Cs on soils. We investigated the partitioning of 137 Cs in wind-eroded sediments and with soil surface samples sieved into contiguous ranges of particle sizes. We also compared the 137 Cs activities and stratification of several adjacent soils with known wind erosion and deposition histories. Finally, we tested 137 Cs-based soil loss models with measured data from sites with documented histories. 137 Cs activities and mean particle diameters of aeolian samples agreed well with the 137 Cs activities and respective mean diameters of the sieved surface soil samples. Good agreement between model estimations and measured data indicated that 137 Cs models developed to estimate soil redistribution by water were also applicable to soil redistribution by wind provided that the models contained an appropriate particle size correction parameter.

Soil C and N have long been recognized as important indicators of soil productivity. The current low levels of soil C and N of cropland soils have led to interest in sequestering C with reduced tillage cropping systems and the Conservation Reserve Program (CRP). Our objective was to assess agroecosystem effects on soil C and N pools in the Southern High Plains. The agroecosystems included three cotton (Gossypium hirsutum L.) cropping systems, CRP land, and native rangeland (NR). We sampled 0- to 5-, 5- to 10-, 10- to 15-, and 15-to 30-cm soil depths at 12 farm sites in five counties in West Texas. Total soil C and N, particulate organic matter (POM) C and N, natural abundance of carbon-13 isotope (δ 13 C) of POM and of whole soil, potentially mineralizable C and N, water-extractable carbon (WEC), and extractable ammonium (NH + 4 ) and nitrate (NO - 3 ) were determined. Total C and N in the 0- to 30-cm soil profile were 34 Mg C ha -1 and 2.5 Mg N ha -1 for NR, and 23 Mg C ha -1 and 1.9 Mg N ha -1 for cropland systems, respectively. Total soil C and N in CRP land were greater in cropland soils only in the 0- to 5-cm layer, and were 24 Mg C ha -1 and 2.1 Mg N ha -1 in 0 to 30 cm. Labile C and N pools were positively correlated with each other and with total soil C and N. Low soil test P may have limited C and N sequestration in CRP land and NR. Improved management practices are needed to sequester C and N in CRP and conservation-tillage cotton systems in the Southern High Plains.