A patch hierarchy approach to modeling surface and subsurface hydrology in complex flood‐plain environments

Geomorphology interacts with surface‐ and ground‐water hydrology across multiple spatial scales. Nonetheless, hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale. Using an existing hydrogeologic computer model, we implemented a simple hierarchical approach to modeling surface‐ and ground‐water hydrology in a complex geomorphic setting. We parameterized the model to simulate ground‐ and surface‐water ?ow patterns through a hierarchical, three‐dimensional, quantitative representation of an anabranched montane alluvial ?ood plain (the Nyack Flood Plain, Middle Fork Flathead River, Montana, USA). Comparison of model results to ?eld data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge, temporal patterns of ?ood‐water storage on the ?ood plain, and rates of ground‐water movement from the main river channel into a large lateral spring channel on the ?ood plain, and water table elevation in the alluvial aquifer. These results suggest that a hierarchical approach to modeling ground‐ and surface‐water hydrology can reproduce realistic patterns of surface‐ and ground‐water ?ux on alluvial ?ood plains, and therefore should provide an excellent ‘quantitative laboratory’ for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales. Copyright © 2004 John Wiley & Sons, Ltd.     

A simple low‐cost sand catcher for wind‐tunnel simulations

A simple low‐cost sand catcher has been developed for use in wind‐tunnel experiments. It is 500 mm high with a 300 mm by 20 mm inlet opening, and is designed to measure total mass transport directly. The length is 280 mm and its walls slowly expand at an angle of 5·6°. The top view is similar to that of the widely used BSNE sampler. Each sidewall is vented with three ventilation screens. Two sets of experiments were conducted on dune sand and at different wind velocities to investigate to what degree the catcher samples isokinetically, ef?ciently and non‐selectively. The results indicate that the catcher measures suf?ciently isokinetically (inlet wind velocity over outside wind velocity >0·9). Catch ef?ciency was around 0·75 and the degree of non‐selectivity was >0·80 for 95 per cent of the particle sizes of the test material. It was also observed that the in?uence of wind velocity on the tested sampler characteristics was of minor importance so that no speci?c corrections need to be made for different wind velocities. Copyright © 2003 John Wiley & Sons, Ltd.     

Dust emission from wet and dry playas in the Mojave Desert,USA

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.     

Dust provenance and its role as a potential fertilizing agent for the Okavango Delta,Botswana

Dust plays a globally important role in supplying biologically essential elements to landscapes underlain by nutrient-poor substrates. Here we show that dust may play a significant role in sustaining productivity in the vast wetlands of the Okavango Delta in southern Africa, one of the world's richest biodiversity hotspots. Dust accumulates preferentially on tree-covered islands in the seasonal swamps of the Delta, creating pockets of fine-grained, nutrient-rich material within the semi-arid landscape of the Kalahari Desert. Strontium and neodymium isotopes reveal that this dust likely originates predominantly from the Makgadikgadi salt pans, located 300 km away, and contributes 10–80% of the fine-grained material present in Okavango island soils. Surface material sourced from the Makgadikgadi Pans contains relatively high amounts of bioavailable phosphorus and iron, potentially influencing Okavango Delta biological productivity. We propose that long-term ecosystem productivity and nutrient availability in the Okavango may be strongly mediated by regional dust inputs. Understanding the influence of dust deposition on nutrient loads and biogeochemical cycling is thus critical for predicting the response of the Okavango Delta to future changes in climate. We suggest that dust inputs may play a significant role in the supply of nutrients to other large, global wetland systems located in dryland environments. © 2020 John Wiley & Sons, Ltd     

Environmental controls on blowing dust direction at lubbock,Texas, U.S.A.

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.     

Evidence for direct suspension of loessial soils on the Columbia Plateau

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.     

Wind erosion on the north‐eastern Tibetan Plateau: constraints from OSL and U‐Th dating of playa salt crust in the Qaidam Basin

The arid Qaidam Basin is the largest (~3.88 × 10⁴ km²) basin on the north‐eastern Tibetan Plateau. Wind erosion in the area has been regarded as an important trigger for intra‐basin tectonic balance upheaval, geomorphologic development and as a major supplier of dust to the Chinese Loess Plateau downwind. An initial estimate of the rate of wind erosion (Kapp et al., 2011) based on geological cross‐sections has suggested up to 3.2 × 10⁴ km³ of sediments has been deflated over the past 2.8 Ma, lowering the landscape by an average of 0.29 mm/yr. In this paper we re‐evaluate this estimate by dating surface crusts present on three playas within the basin. Understanding the development of these playas is crucial to assessing the overall role of the wind in shaping the regional landscape because they are typically capped with a thick salt crust which effectively protects them from wind erosion. Optically stimulated luminescence (OSL) and U‐series dating from a pit section and from the top of a deep drill core, together with results from magnetostratigraphy and a climate proxy record correlated to the marine oxygen isotope record, are used here to determine the age of the playa plains and suggest that the salt crusts have an age of c. 0.1 Ma. This young age and the wide distribution of resistant thick salt crusts of the playa plains indicate a much lower degree of wind erosion than previously suggested. The crusts protect the surface from significant surface erosion (including sediment exhumation and unloading) and whilst some wind erosion does occur, it is unlikely to be sufficient to trigger tectonic uplift of the basin or to be a major dust source for the Loess Plateau as previously suggested. Copyright © 2013 John Wiley & Sons, Ltd.     

The dynamic effects of sediment availability on the relationship between wind speed and dust concentration

Where sediment supply is unlimited, previous research suggests that a strong, positive relationship between wind speed and dust concentration exists at the event scale. This relationship can break down if sediment availability is limited or changes during an event. This paper explores the dynamic effects of sediment availability on the relationship between wind speed and dust concentration using data from nine high‐latitude dust events recorded in Iceland. Of these events, six showed a strong positive relationship between wind speed and dust concentration. For the remainder, the relationship breaks down periodically during the event due to changing surface moisture conditions and atmospheric humidity. Results suggest a need to understand how spatial and temporal changes in humidity, surface soil moisture, soil texture and threshold velocity interact and control sediment availability for dust emissions in all environments, including at high latitudes. Copyright © 2018 John Wiley & Sons, Ltd.     

Near-surface flow structure over wind-generated water waves,part I: wave-induced flow characteristics

We report on an experimental study conducted to investigate the influence of small-scale wind waves on the airflow structure in the immediate vicinity of the air–water interface. PIV technique was used to measure the two-dimensional velocity fields at wind speeds of 3.7 and 4.4 m?s^?1 and at a fetch of 2.1 m. The flow structure was analyzed as a function of wave phase. In the near-surface region, significant variations were observed in the flow structure over the waveform. The phase-averaged profiles of velocity, vorticity, and Reynolds stress showed different behavior on the windward and leeward sides of the wave in the near-surface region. The influence of wave-induced velocity was restricted within a distance of three significant wave heights from the surface, which also showed opposite trends on the windward and leeward sides of the crest. The results also show that the turbulent Reynolds stress mainly supports downward momentum transfer whereas the wave-induced Reynolds stress is responsible for the upward momentum transfer from wave to wind. In the immediate vicinity of the air–water interface, the momentum is transferred from waves to wind along the windward side, whereas, the momentum transfer is from wind to waves along the leeward side.     

Relative quantification of wind erosion in argan woodlands in the Souss Basin,Morocco

The endemic argan woodlands cover large parts of South Morocco and create a characteristic landscape with areas of sparsely vegetated and bare soil surfaces between single trees. This unique ecosystem has been under extensive agrosilvopastoral management for centuries and is now at risk of degradation caused by overgrazing and increasing scarcity and variability of rainfall. To investigate susceptibility to wind erosion, we conducted an experimental–empirical study including wind tunnel tests and a drone-generated digital elevation model and quantified wind-erodible material on five different associated surface types by means of sediment catchers. The highest emission flux was measured on freshly ploughed surfaces (1875 g m^–2 h^–1), while older ploughed areas with a re-established crust produced a much lower emission flux (795 g m^–2 h^–1). Extensive tillage may have been a sustainable practice for generations, but increasing drought and uncertainty of rainfall now lead to an acute risk of severe soil erosion and dust production. The typical crusted surfaces characterized by residual rock fragment accumulation and wash processes produced the second highest emission flux (1,354 g m^–2 h^–1). Material collected from tree-shaded areas (933 g m^–2 h^–1) was revealed to be a considerable source of organic material, possibly affecting substrate conditions positively on a larger regional scale. The lowest flux was measured on rock fragment-covered surfaces (301 g m^–2 h^–1). The data show that open argan woodland may be a considerable source for wind erosion and dust production, depending on surface characteristics strongly related to management. An adapted management must include the conservation of argan trees to offer a promising approach to prevent severe wind erosion and dust production and mitigate possible impacts of land-use change and climate change related shifts in wind and rainfall patterns. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd     

Erodibility of some crust forming soils/sediments from the Southern Aral Sea Basin as determined in a wind tunnel

Severe dust storms in the Southern Aral Sea Basin have become common with the desiccation of the sea. The high incidence of dust in the area has had severe ecological consequences. Within the framework of efforts to reduce this phenomenon, deflatability as well as deflatability‐related characteristics of some prominent soils/sediment surfaces in the Southern Aral Sea Basin were examined. The materials included a salt crust from a developed Solonchak, a Takyr crust and a Takyr‐like soil, and salt crusts from undeveloped Solonchaks formed on the exposed bottom of the Aral Sea. Characteristics determined were particle size distribution, dry aggregate size distribution and salt, carbonate and organic carbon contents. Deflatability was examined using a suction type wind tunnel with a SENSIT‐type sensor to detect airborne unconsolidated material, on materials treated to different moisture levels and with a chemical stabilizer, and on restored crusts created from the unconsolidated materials. Fine sand dominates in the materials, and in the Takyr crust and Takyr‐like soils is accompanied by significant amounts of silt and clay. All materials contain moderate amounts of carbonate and are low in organic matter. All soils/sediments contain salts, but in the salt crusts of the Solonchaks the salt fraction dominates. They all have more than 50 per cent PM₈₅₀ (particles with diameter <850 µm), indicating a relatively high deflatability potential. The materials from the Takyr crusts and Takyr‐like soil with a high proportion of fine aggregates had the lowest threshold friction velocities, while the salt crusts of the Solonchaks with a high proportion of coarse aggregates had the highest. This suggests that Takyrs and Takyr‐like soils are the most deflatable and Solonchak soils the least deflatable. These differences are attributed to the presence of salts that create stable, large aggregates in the Solonchak crusts. Wetting of the materials to three moisture levels considerably increased threshold friction velocity. The increase was most prominent in the salt‐rich materials, and was attributed to the rapid formation of surface films by drying in the course of the wind tunnel determinations. Applications of chemical stabilizers at two levels also considerably increased threshold friction velocity. On the restored crusts, threshold friction velocity dramatically increased, occasionally to non‐recordable values. This increase was monitored with both the salt crusts characteristic for the Solonchak soils and the fine‐grained crusts characteristic for the Takyr soils. The stability was attributed to the tightly packed salt particles in the salt crusts, and to the cohesive properties of the fine‐grained materials in the Takyr crusts. Once the crusts were ruptured, however, strong deflation commenced. These results suggest that by maintaining moisture in the soils/sediments (for example, by maintaining a high water table in the Amu‐Darya river flood plain) deflation can be reduced. By the same means, deflation can be reduced by creating new crusts or by preserving existing crusts. Copyright © 2005 John Wiley & Sons, Ltd.     

Geomorphic and sedimentological signature of a two‐phase outburst flood from moraine‐dammed Queen Bess Lake,British Columbia,Canada

On 12 August 1997, the lower part of Diadem Glacier in the southern Coast Mountains of British Columbia fell into Queen Bess Lake and produced a train of large waves. The waves overtopped the broad end moraine at the east end of the lake and ?ooded the valley of the west fork of Nostetuko River. The displacement waves also incised the out?ow channel across the moraine. Stratigraphic and sedimentologic evidence supports the conclusion that the ?ood had two phases, one related to wave overtopping and a second to breach formation. Empirical equations were used to calculate the peak discharge of the ?ood at various points along the west fork of the Nostetuko valley and to describe the attenuation of the ?ood wave. The velocity of the ?ood was also calculated to determine the time it took for the ?ood to reach the main fork of Nostetuko River. The highest peak discharges were achieved in the upper reach of the valley during the displacement phase of the ?ood. Peak discharge declined rapidly just below the moraine dam, with little change thereafter for approximately 7 km. Empirical formulae and boulder measurements indicate a rise in peak discharge in the lower part of the west fork valley. We suggest that ?ow in the upper part of the valley records the passage of two separate ?ood peaks and that the rise in discharge in the lower part of the valley is due to amalgamation of the wave and breach peaks. Hydraulic ponding in con?ned reaches of the valley extended the duration of the ?ood. In addition, erosion of vegetation and sediment in the channel and valley sides may also have exerted an in?uence on the duration and nature of ?ooding. Sediments were deposited both upstream and downstream of channel constrictions and on a large fan extending out into the trunk Nostetuko River valley. This study extends our understanding of the variety and complexity of outburst ?oods from naturally dammed lakes. It also shows that simple empirical and other models for estimating peak discharges of outburst ?oods are likely to yield erroneous results. Copyright © 2005 John Wiley & Sons, Ltd.     

Wind effects on sediment transport by raindrop‐impacted shallow flow: a wind‐tunnel study

In wind‐driven rains, wind velocity and direction are expected to affect not only energy input of rains but also shallow ?ow hydraulics by changing roughness induced by raindrop impacts with an angle on ?ow and the unidirectional splashes in the wind direction. A wind‐tunnel study under wind‐driven rains was conducted to determine the effects of horizontal wind velocity and direction on sediment transport by the raindrop‐impacted shallow ?ow. Windless rains and the rains driven by horizontal wind velocities of 6 m s^?1, 10 m s^?1, and 14 m s^?1 were applied to three agricultural soils packed into a 20 by 55 cm soil pan placed on both windward and leeward slopes of 7 per cent, 15 per cent, and 20 per cent. During each rainfall application, sediment and runoff samples were collected at 5‐min intervals at the bottom edge of the soil pan with wide‐mouth bottles and were determined gravimetrically. Based on the interrill erosion mechanics, kinetic energy ?ux (E_rn) as a rainfall parameter and product of unit discharge and slope in the form of q^bS^c_o as a ?ow parameter were used to explain the interactions between impact and ?ow parameters and sediment transport (q_s). The differential sediment transport rates occurred depending on the variation in raindrop trajectory and rain intensity with the wind velocity and direction. Flux of rain energy computed by combining the effects of wind on the velocity, frequency, and angle of raindrop impact reasonably explained the characteristics of wind‐driven rains and acceptably accounted for the differences in sediment delivery rates to the shallow ?ow transport (R₂ ≥ 0·78). Further analysis of the Pearson correlation coef?cients between E_rn and qS_o and q_s also showed that wind velocity and direction signi?cantly affected the hydraulics of the shallow ?ow. E_rn had a smaller correlation coef?cient with the q_s in windward slopes where not only reverse splashes but also reverse lateral raindrop stress with respect to the shallow ?ow direction occurred. However, E_rn was as much effective as qS_o in the sediment transport in the leeward slopes where advance splashes and advance lateral raindrop stress on the ?ow occurred. Copyright © 2004 John Wiley & Sons, Ltd.     

Contemporary glacigenic inputs to the dust cycle

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.     

Shoreline development,longshore transport and surface wave dynamics,Pleistocene Lake Bonneville,Utah

Point of the Mountain spit and Fingerpoint spit are two of the largest geomorphic features of Pleistocene Lake Bonneville of the western Great Basin, USA. The spits and their associated shorelines show distinctly different geomorphic expression and genesis; this is a function of their positions within the lake and the dynamics of the waves and storms that formed them. Mapping of geomorphic features, geometry of erosional features, and detailed lithologic analysis of shoreline deposits are used to determine dominant modes of sediment erosion and deposition. The Point of the Mountain spit, located in the eastern portion of the basin, was formed as a result of highly fractured bedrock in a salient of the Wasatch Front being exposed to wave trains that approached from the north‐northwest causing north‐to‐south longshore sediment transport. Shoreline development and sediment transport on the southern portion of the spit were minimal. The Fingerpoint spit, located on an island in the northwest portion of the basin, was formed by bidirectional longshore sediment transport as the result of waves that approached from both the north‐northeast and the south‐southwest. Spit development is a function of surface wave energy and direction which in turn is the integrated result of wind direction, wind intensity, and fetch. Wave transport direction determined from ?eld measurements at Point of the Mountain spit corresponds very well to the direction of maximum fetch (c. 200 km). For the Fingerpoint spit, the hypothesized wave transport direction from the south corresponds with the direction of maximum fetch (c. 350 km). However, wave energy transport from the north had limited fetch (c. 100 km), implying that wind intensity from the north was relatively large. The geometry of the two large Bonneville spits suggests the predominant wind direction from storms during the Pleistocene was from the north and points the way for future studies that can aid in further understanding the nature of Pleistocene wind ?elds in the Great Basin. Copyright © 2004 John Wiley & Sons, Ltd.     

Reef to island sediment connections on a Maldivian carbonate platform: using benthic ecology and biosedimentary depositional facies to examine island‐building potential

Reef islands are low‐lying accumulations of unconsolidated sediment formed from the skeletal remains of carbonate‐producing reef organisms and are therefore perceived as highly vulnerable to environmental change. However, basic elements of island composition are not well described and given their high inter‐ and intra‐basinal variability a better understanding of reef and island sedimentary environments (and the connections between them) are needed to predict future morphological response. Here, we use detailed ecological and sedimentological datasets to delineate key sediment production zones and biosedimentary depositional facies across the surface of Vabbinfaru platform, Maldives. Field measurements of platform hydrodynamics are applied to sedimentary deposits to determine the potential mobility of grains and identify transport pathways. Carbonate production was dominated by coral framework (mean: 52%) within a narrow zone on the outer reef rim (22% of platform area) resulting in coral‐rich detrital sediments (reef: 51%, island: 64%) that closely resemble living assemblages. The net transfer of sediment occurred lagoonward by wave‐driven processes leading to a decrease in grain size towards the island (R² = 0.502) which acts as a major control on depositional facies development within the lagoon. Island sediments were distinct from reefal deposits, comprising a restricted suite of durable sands (mean: 1.34?) throughout long‐term development. Our findings suggest that the production, breakdown and redistribution of coral‐derived sediment by platform currents is fundamental to future island stability at Vabbinfaru, and although alterations away from current ecological states may reduce sediment supply, the timescales over which island morphological response will occur depends upon phase lags between initial coral mortality and the conversion of this material into island‐grade sand. Copyright © 2016 John Wiley & Sons, Ltd.     

Dynamic controls on wind erosion and dust generation on west‐central Free State agricultural land,South Africa

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.     

Energy balance and evaporation loss of an irrigation reservoir equipped with a suspended cover in a semiarid climate (south‐eastern Spain)

The main objective of this study was to assess the impact of a suspended cover on the evaporation loss of an agricultural water reservoir (AWR). To this aim, a detailed data collection was carried out in a typical AWR located in south‐eastern Spain during 2 consecutive years. During the first year, the reservoir remained uncovered, while during the second year it was covered with a double black polyethylene (PE) shade cloth. On an annual scale, it was observed that the cover can provide a reduction of evaporation loss of 85%. Two approaches, energy balance and mass transfer, were used to analyse the effect of the cover on the evaporation process. Important modifications were observed on the magnitude, sign, annual trend and relative weight of the components of the energy balance. The changes were ascribed to the strong reduction of net radiation and to the substantial weight of the heat storage and sensible heat flux in the energy balance. A relevant finding was the contrast between the patterns of the annual evaporation curve for open‐water and covered conditions. The mass transfer approach allowed discriminating between the wind‐ and radiation‐shelter effects on the evaporation term. The reduction in water‐to‐air vapour deficit was the main factor explaining the high efficiency of the cover, whereas the reduction of the mass transfer coefficient was a modulating factor that accounted for the wind‐shelter effect. Overall, both approaches provided a sound basis to describe and explain the physical mechanisms underlying the high performance of the tested cover. Copyright © 2010 John Wiley & Sons, Ltd.     

Wind erosion and dust emissions in central Asia: Spatiotemporal simulations in a typical dust year

The prediction of wind erosion and dust emissions is important for controlling erosion and identifying dust sources in arid and semiarid regions of the world. This study predicts quantitatively wind erosion and dust emissions in Xinjiang Province, central Asia. The wind erosion prediction system (WEPS) was used to simulate annual soil and PM10 (particulate matter ≤10 μm in aerodynamic diameter) loss at 64 meteorological stations across the province. Soil and PM10 loss were simulated from bare surfaces at all 64 stations and from cotton and wheat fields at 11 stations. Simulated annual bare soil and PM10 loss were lowest in the Junggar (soil and PM10 loss were, respectively, 121.7 and 7.6 kg m^-2) and Tarim basins (soil loss was 78.2 kg ha^-1 and PM10 loss was 6.5 kg m^-2) and highest in the Tu-ha Basin (soil and PM10 loss were, respectively, 638.2 and 37.7 kg m^-2). Stations with the highest annual soil loss in the Tarim and Tu-ha basins also had the highest number of days with wind speeds >8 m s^-1. This indicated wind influenced erosion, but other factors such as soil type also affect wind erosion. The maximum monthly bare soil and PM10 loss occurred in May in the three basins, substantiating that dust storms occur most frequently during spring in the region. Simulated soil and PM10 loss were lower for cotton and wheat than bare soil, thus suggesting that maintaining vegetative cover during a portion of the year provided some protection to the soil surface from wind erosion. © 2018 John Wiley & Sons, Ltd.     

Soil organic carbon enrichment of dust emissions: magnitude,mechanisms and its implications for the carbon cycle

Soil erosion is an important component of the global carbon cycle. However, little attention has been given to the role of aeolian processes in influencing soil organic carbon (SOC) flux and the release of greenhouse gasses, such as carbon dioxide (CO₂), to the atmosphere. Understanding the magnitude and mechanisms of SOC enrichment in dust emissions is necessary to evaluate the impact of wind erosion on the carbon cycle. This research examines the SOC content and enrichment of dust emissions measured using Big Spring Number Eight (BSNE) wind‐vane samplers across five land types in the rangelands of western Queensland, Australia. Our results show that sandy soils and finer particulate quartz‐rich soils are more efficient at SOC emission and have larger SOC dust enrichment than clay‐rich aggregated soils. The SOC enrichment ratios of dusts originating from sites with sand‐rich soil ranged from 2·1–41·9, while the mean enrichment ratio for dusts originating from the clay soil was 2·1. We hypothesize that stronger inter‐particle bonds and the low grain density of the aggregated clay soil explain its reduced capacity to release SOC during saltation, relative to the particulate sandy soils. We also show that size‐selective sorting of SOC during transport may lead to further enrichment of SOC dust emissions. Two dust samples from regional transport events were found to contain 15–20% SOC. These preliminary results provide impetus for additional research into dust SOC enrichment processes to elucidate the impact of wind erosion on SOC flux and reduce uncertainty about the role of soil erosion in the global carbon cycle. Copyright © 2013 John Wiley & Sons, Ltd.