Response of soil aggregate disintegration to the different content of organic carbon and its fractions during splash erosion

Aggregate disintegration is a critical process in soil splash erosion. However, the effect of soil organic carbon (SOC) and its fractions on soil aggregates disintegration is still not clear. In this study, five soils with similar clay contents and different contents of SOC have been used. The effects of slaking and mechanical striking on splash erosion were distinguished by using deionized water and 95% ethanol as raindrops. The simulated rainfall experiments were carried out in four heights (0.5, 1.0, 1.5 and 2.0 m). The result indicated that the soil aggregate stability increased with the increases of SOC and light fraction organic carbon (LFOC). The relative slaking and the mechanical striking index increased with the decreases of SOC and LFOC. The reduction of macroaggregates in eroded soil gradually decreased with the increase of SOC and LFOC, especially in alcohol test. The amount of macroaggregates (>0.25 mm) in deionized water tests were significantly less than that in alcohol tests under the same rainfall heights. The contribution of slaking to splash erosion increased with the decrease of heavy fractions organic carbon. The contribution of mechanical striking was dominant when the rainfall kinetic energy increased to a range of threshold between 9 J m⁻² mm⁻¹ and 12 m⁻² mm⁻¹. This study could provide the scientific basis for deeply understanding the mechanism of soil aggregates disintegration and splash erosion.     

The transport of aggregates associated with soil organic carbon under the rain-induced overland flow on the Chinese Loess Plateau

Organic carbon (OC) is easily enriched in sediment particles of different sizes due to aggregate breakdown and selective transport for sheet erosion. However, the transport of aggregate-associated OC has not been thoroughly investigated. To address this issue, 27 simulated rainfall experiments were conducted in a 1 m × 0.35 m box on slope gradients of 15°, 10°, and 15°and under three rainfall intensities of 45 mm h⁻¹, 90 mm h⁻¹ and 120 mm h⁻¹. The results showed that OC was obviously enriched in sediment particles of different sizes under sheet erosion. The soil organic carbon (SOC) concentrations of each aggregate size class in sediments were different from those in the original soil, especially when the rainfall intensity or slope was sufficiently low, such as 45 mm h^–1 or 5°, respectively. Under a slope of 5°, the SOC enrichment ratios (ERocs) of small macroaggregates and microaggregates were high but decreased over time. As rainfall intensity increased, OC became enriched in increasingly fine sediment particles. Under a rainfall intensity of 45 mm h^–1, the ERocs of the different aggregate size classes were always high throughout the entire erosion process. Under a rainfall intensity of > 45 mm h^–1 and slope of > 5°, the ERocs of the different aggregate size classes were close to 1.0, especially those of clay and silt. Therefore, the high ERocs in sediments resulted from the first transport of effective clay. Among total SOC loss, the proportion of OC loss caused by the transport of microaggregates and silt plus clay-sized particles was greater than 50%. We also found that low stream power and low water depth were two requirements for the high ERocs in aggregates. Stream power was closely related to sediment particle distribution. Flow velocity was significantly and positively related to the percentage of OC-enriched macroaggregates in the sediments (P > 0.01). Our study will provide important information for understanding the fate of SOC and building physical-based SOC transport models. © 2019 John Wiley & Sons, Ltd.     

Comparing grain size distribution of sediment and original soil under raindrop detachment and raindrop-induced and flow transport mechanism

The grain size distribution (GSD) of sediment in comparison with the original soil GSD is discussed under different slopes (5, 15 and 25%) and rainfall intensities (30, 60 and 90 mm h^–1 with respective duration of 30, 15 and 10 min) but identical runoff (15 mm). The sediment quantification was carried out by raindrop-induced flow transport (RIFT) or/and transport by flow (FT) using a rainfall simulator and a 6 × 1 m² erosion plot and a silt loam. The results show a high degree of enrichment for size classes of 2–4 and 4–8 μm and a high degree of depletion for size classes of >63 μm under different slopes and rainfall intensities. In addition, the results show that the experimental enrichment ratio (ER) for particle size <16 μm under different slopes and rainfall intensities was greater than 1, while the ER for particle size >32 μm was less than 1.     

THE INFLUENCE OF RAINFALL ON TRANSPORT OF BEACH SAND BY WIND

This paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments. Although sediment transport by splash is of secondary importance on coastal dunes, splash–saltation processes can move sediments in conditions where no motion is predicted by aeolian processes. The effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler. In general, an increase of particle movement by wind at the sensor heights was observed during rainfall. Rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface. The influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel. Moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles.     

A methodology to study rain splash and wash processes under natural rainfall

The complex interactions between rainfall‐driven erosion processes and rainfall characteristics, slope gradient, soil treatment and soil surface processes are not very well understood. A combination of experiments under natural rainfall and a consistent physical theory for their interpretation is needed to shed more light on the underlying processes. The present study demonstrates such a methodology. An experimental device employed earlier in laboratory studies was used to measure downslope rain splash and ‘splash‐creep’, lateral splash, upslope splash and rainfall‐driven runoff transport (wash) from a highly aggregated clay‐rich oxisol exposed to natural rainfall in West Java, Indonesia. Two series of measurements were made: the first with the soil surface at angles of 0°, 5°, 15° and 40°; and the second all at an angle of 5° but with different tillage and mulching treatments. A number of rainfall erosivity indices were calculated from rainfall intensity measurements and compared with measured transport components. Overall storm kinetic energy correlated reasonably well with sediment transport, but much better agreement was obtained when a threshold rainfall intensity (20 mm h^?1) was introduced. Rain splash transport measurements were interpreted using a recently developed theory relating detachment to sediment transport. Furthermore, a conceptually sound yet simple wash transport model is advanced that satisfactorily predicted observed washed sediment concentrations. The lack of replication precluded rigorous assessment of the effect of slope and soil treatment on erosion processes, but some general conclusions could still be drawn. The results stress the importance of experiments under conditions of natural rainfall. Copyright © 2002 John Wiley & Sons, Ltd.     

Water flux and sediment transport within a forested landscape: the role of connectivity,subsurface flow,and slope length scale on transport mechanism

The connectivity and upscaling of overland runoff and sediment transport are important issues in hillslope hydrology to identify water flux and sediment transport within landscape. These processes are highly variable in time and space with regard to their interactions with vegetation and soil surface conditions. The generation of overland runoff and its spatial connectivity were examined along a slope to determine the variations in the transport mechanism of runoff and soil particles by rain splash and overland runoff. Field experiments were conducted by erosion plots on a steep hillslope at lengths of 5, 10, and 15 m. The overland runoff connectivity and flow transport distance decreased with the slope length, while spatial variability of infiltration increased significantly with the slope length. Observation of subsurface flow revealed that surface soil and litter layer could have important role in water transport. However, the surface soil water content and water flux transport along the slope was highly variable for different storm events; the variability was related to the complexity of the system, mainly by way of the initial wetness conditions and infiltration characteristics. Only net rain‐splashed soil was measurable, but examination of the water flux, overland runoff and sediment transport connectivity, characteristics of sheetwash, and the variability in spatial infiltration indicated an increase in the contribution of the rain splash transport mechanism along the slope. Copyright © 2013 John Wiley & Sons, Ltd.     

Measuring sheet erosion using synthetic color‐contrast aggregates

The bulk of eroded soils measured at the outlets of plots, slopes and watersheds are suspended sediments, splash‐induced sheet erosion. It is depending on rainfall intensity and antecedent soil moisture contents and contributes to a significant proportion of soil loss that usually is ignored in soil erosion and sediment studies. A digital image processing method for tracing and measuring non‐suspended soil particles detached/transported by splash/runoff was therefore used in the present study. Accordingly, fine mineral pumice grains aggregated with white cement and coloured with yellow pigment powder, with the same size, shape and specific gravity as those of natural soil aggregates, called synthetic color‐contrast aggregates, were used as tracers for detecting soil particle movement. Subsequently, the amount of non‐suspended soil particles detached and moved downward the slope was inferred with the help of digital image processing techniques using MATLAB R2010B software (Mathworks, Natick, Massachusetts, USA). The present study was conducted under laboratory conditions with four simulated rainfall intensities between 30–90 mm h^‐1, five antecedent soil moisture contents between 12–44 % v v^‐1 and a slope of 30%, using sandy loam soils taken from a summer rangeland in the Alborz Mountains, Northern Iran. A range of total transported soil between 90.34 and 1360.93 g m^‐2 and net splash erosion between 36.82 and 295.78 g m^‐2were observed. The results also showed the sediment redeposition ratio ranging from 87.27% [sediment delivery ratio (SDR) = 12.73%] to 96.39% (SDR = 3.61%) in various antecedent soil moisture contents of rainfall intensity of 30 mm h^‐1 and from 80.55% (SDR = 19.45%) to 89.42% (SDR = 10.58%) in rainfall intensity of 90 mm h^‐1. Copyright © 2013 John Wiley & Sons, Ltd.     

Evaluating the impact of soil redistribution on the in situ mineralization of soil organic carbon

Soil erosion, transport and deposition by water drastically affect the distribution of soil organic carbon (SOC) within a landscape. Moreover, soil redistribution may have a large impact on the exchange of carbon (C) between the pedosphere and the atmosphere. One of the large information gaps within this research domain, concerns the fate of SOC after erosion by water. According to different (mainly laboratory) studies, soil redistribution leads to aggregate breakdown, thereby exposing the contained SOC to mineralization. Our study aims to quantify the extent to which such increased mineralization occurs in a real field situation. Carbon dioxide (CO₂)‐efflux was measured in the field after an important erosion event for a continuous period of 112 days. The specific situation on the field ensured that almost none of eroded SOC was exported from the field. Measurements of CO₂‐efflux were done in areas with sediment deposition, as well as in comparable areas without sedimentation. Comparison of these measurements allowed the net effect of soil deposition on CO₂‐efflux to be assessed. Field data were complemented by measurements on incubated, undisturbed soil core samples, in order to disentangle the contribution of environmental factors (moisture, temperature) from any erosional effect on CO₂‐efflux. Results of these measurements on the field showed that CO₂‐efflux was regulated by a complex interplay of different factors (mostly soil porosity, soil moisture and soil temperature). In combination with the incubation measurements, it could be concluded that the processes of erosion and transport indeed led to an increased mineralization of SOC, as a result of aggregate breakdown and exposure of previously encapsulated SOC. This effect was, however, much smaller than observed in previous laboratory studies. Moreover, it was only important in the first weeks, immediately after the erosion event. The calculated net erosional effect on CO₂‐efflux represented a mere 1·6% of total SOC, originally present in the soil. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of organic matter on splash detachment and the processes involved

The influence of organic matter on splash detachment was investigated using soils with grass and peat treatments. The relationship between organic matter and aggregate stability to water disruption was positive for soils with grass treatment while it was negative for those with peat treatment. Organic matter from both treatments, however, reduced splash detachment by rainfall. Soils with grass did this by increasing aggregate stability while peat acted as a mulch on the soil surface. This implies that though organic matter always reduces splash detachment, different processes may be involved, depending on the form of the organic material. Because of the different processes involved, both negative and positive relationships between splash detachment and aggregate stability as reported in literature were obtained for the soils with grass and peat respectively.     

A relook at NEH‐4 curve number data and antecedent moisture condition criteria

This paper investigates the variation of the popular curve number (CN) values given in the National Engineering Hand Book–Section 4 (NEH‐4) of the Soil Conservation Service (SCS) with antecedent moisture condition (AMC) and soil type. Using the volumetric concept, involving soil, water, and air, a significant condensation of the NEH‐4 tables is achieved. This leads to a procedure for determination of CN for gauged as well as ungauged watersheds. The rainfall‐runoff events derived from daily data of four Indian watersheds exhibited a power relation between the potential maximum retention or CN and the 5‐day antecedent rainfall amount. Including this power relation, the SCS‐CN method was modified. This modification also eliminates the problem of sudden jumps from one AMC level to the other. The runoff values predicted using the modified method and the existing method utilizing the NEH‐4 AMC criteria yielded similar results. Copyright © 2006 John Wiley & Sons, Ltd.     

Field studies on the influence of rainfall intensity,vegetation cover and slope length on soil moisture infiltration on typical watersheds of the Loess Plateau,China

Soil moisture is a key process in the hydrological cycle. During ecological restoration of the Loess Plateau, soil moisture status has undergone important changes, and infiltration of soil moisture during precipitation events is a key link affecting water distribution. Our study aims to quantify the effects of vegetation cover, rainfall intensity and slope length on total infiltration and the spatial variation of water flow. Infiltration data from the upper, middle and lower slopes of a bare slope, a natural grassland and an artificial shrub grassland were obtained using a simulated rainfall experiment. The angle of the study slope was 15° and rainfall intensity was set at 60, 90, 120, 150, and 180 mm/hr. The effect these factors have on soil moisture infiltration was quantified using main effect analysis. Our results indicate that the average infiltration depth (ID) of a bare slope, a grassland slope and an artificial shrub grassland slope was 46.7–73.3, 60–80, and 60–93.3 cm, respectively, and average soil moisture storage increment was 3.5–5.7, 5.0–9.4, and 5.7–10.2 mm under different rainfall intensities, respectively. Heavy rainfall intensity and vegetation cover reduced the difference of soil infiltration in the 0–40 cm soil layer, and rainfall intensity increased surface infiltration differences on the bare slope, the grassland slope and the artificial shrub grassland slope. Infiltration was dominated by rainfall intensity, accounting for 63.03–88.92%. As rainfall continued, the contribution of rainfall intensity to infiltration gradually decreased, and the contribution of vegetation cover and slope length to infiltration increased. The interactive contribution was: rainfall intensity * vegetation cover > vegetation cover * slope length > rainfall * slope length. In the grass and shrub grass slopes, lateral flow was found at a depth of 23–37 cm when the slope length was 5–10 m, this being related to the difference in soil infiltration capacity between different soil layers formed by the spatial cross-connection of roots.     

Modifying Transition Matrix to Evaluate Soil Quality: A Case Study in Karst Region in the West‐Southern China

The soil aggregate stability is a key property of soil quality and reflects soil quality and anti‐erosion ability. The transition matrix between initial and final aggregates condition was established by modifying Niewczas and Witkowska‐Walczak's method by not considering the artificial weights and each size of aggregates fraction on the basis of three reasonable assumptions, and soil aggregate stability index (ASI) was formed through preserving each size of aggregates probability. This ASI is identical to the result by reference, and the transition matrix can be showed to evaluate the soil aggregates stability. Using the transition matrix was furthermore to analyze anti‐breaking ability of different size aggregate by reference material. We found there were different effects for each size aggregate by four methods, simulation rainfall, one cycle of wetting–drying, ten cycles of wetting–drying, and Yoder wetting–sieving. The Yoder wetting–sieving is a severe method that destructed soil aggregates. The ASI by modifying transition matrix method was used to evaluate the aggregates stability under different land utilization in Karst region in Chongqing, China. The ASI of agricultural utilization was lower than abounded cultivated land, shrub‐grass land, secondary forest land, and primeval forest land. For some selected soil properties, when SOM content was <60 g/kg, ASI increased along with the SOM increase. Once the SOM content was >60 g/kg, the ASI was almost unchanged. The sorption moisture content of air‐drying acutely affected ASI too, and the ASI increased along the sorption moisture increasing. SOM content and sorption markedly affected the preserving probability of larger aggregates such as 10–5, 5–3, 3–2, 2–1, and 1–0.5 mm size class. Although CaCO₃ and clay content did not influence preserving probability of each size class of aggregates fiercely, but the influence on small aggregates was higher than that of larger aggregates. The modified transition matrix method could not only calculate soil aggregates stability index, but also analyze more parameters of aggregate experiment, and bring out the each size aggregates characteristics. Thus, the modified transition matrix method could be a better tool to understand soil quality.     

The influence of soil properties on the erodibility of Belgian loamy soils: A study based on rainfall simulation experiments

Twenty soils from the Leuven region were tested in the laboratory with a rainfall simulator. Their texture varied from loam to loamy sand. On the basis of the results obtained, they were classified as a function of the runoff and splash erodibility. For every soil, several properties were determined and tentatively used to explain the classifications based on the runoff and splash erodibility. Significant negative correlations were found between silt content, aggregate stability, C_5–10 index, water content at saturation, and cohesion on the one side and erodibility on the other; a positive correlation was found between sand content and erodibility.     

Direct and indirect effects of rainfall and vegetation coverage on runoff,soil loss,and nutrient loss in a semi-humid climate

Soil and nutrient loss play a vital role in eutrophication of water bodies. Several simulated rainfall experiments have been conducted to investigate the effects of a single controlling factor on soil and nutrient loss. However, the role of precipitation and vegetation coverage in quantifying soil and nutrient loss is still unclear. We monitored runoff, soil loss, and soil nutrient loss under natural rainfall conditions from 2004 to 2015 for 50–100 m² runoff plots around Beijing. Results showed that soil erosion was significantly reduced when vegetation coverage reached 20% and 60%. At levels below 30%, nutrient loss did not differ among different vegetation cover levels. Minimum soil N and P losses were observed at cover levels above 60%. Irrespective of the management measure, soil nutrient losses were higher at high-intensity rainfall (Imax30>15 mm/h) events compared to low-intensity events (p < 0.05). We applied structural equation modelling (SEM) to systematically analyze the relative effects of rainfall characteristics and environmental factors on runoff, soil loss, and soil nutrient loss. At high-intensity rainfall events, neither vegetation cover nor antecedent soil moisture content (ASMC) affected runoff and soil loss. After log-transformation, soil nutrient loss was significantly linearly correlated with runoff and soil loss (p < 0.01). In addition, we identified the direct and indirect relationships among the influencing factors of soil nutrient loss on runoff plots and constructed a structural diagram of these relationships. The factors positively impacting soil nutrient loss were runoff (44%–48%), maximum rainfall intensity over a 30-min period (18%–29%), rainfall depth (20%–27%), and soil loss (10%–14%). Studying the effects of rainfall and vegetation coverage factors on runoff, soil loss, and nutrient loss can improve our understanding of the underlying mechanism of slope non-point source pollution.     

Sediment and solute transport on soil slope under simultaneous influence of rainfall impact and scouring flow

Soil erosion and nutrient losses with surface runoff in the loess plateau in China cause severe soil quality degradation and water pollution. It is driven by both rainfall impact and runoff flow that usually take place simultaneously during a rainfall event. However, the interactive effect of these two processes on soil erosion has received limited attention. The objectives of this study were to better understand the mechanism of soil erosion, solute transport in runoff, and hydraulic characteristics of flow under the simultaneous influence of rainfall and shallow clear‐water flow scouring. Laboratory flume experiments with three rainfall intensities (0, 60, and 120 mm h⁻¹) and four scouring inflow rates (10, 20, 30, and 40 l min⁻¹) were conducted to evaluate their interactive effect on runoff. Results indicate that both rainfall intensity and scouring inflow rate play important roles on runoff formation, soil erosion, and solute transport in the surface runoff. A rainfall splash and water scouring interactive effect on the transport of sediment and solute in runoff were observed at the rainfall intensity of 60 mm h⁻¹ and scouring inflow rates of 20 l min⁻¹. Cumulative sediment mass loss (Ms) was found to be a linear function of cumulative runoff volume (Wr) for each treatment. Solute transport was also affected by both rainfall intensity and scouring inflow rate, and the decrease in bromide concentration in the runoff with time fitted to a power function well. Reynolds number (Re) was a key hydraulic parameter to determine erodability on loess slopes. The Darcy–Weisbach friction coefficients (f) decreased with the Reynolds numbers (Re), and the average soil and water loss rate (M_l) increased with the Reynolds numbers (Re) on loess slope for both scenarios with or without rainfall impact. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of antecedent moisture conditions on sediment and phosphorus loss during overland flow: Mahantango Creek catchment,Pennsylvania, USA

The loss of P in overland flow from most cultivated soils is controlled by erosion, and in‐turn soil moisture. We evaluated the effect of soil moisture on erosion and P transport in overland flow by applying rainfall (7 cm h^?1) to packed soil boxes (1 m long and 0·15 m wide) and field plots (1 and 10 m long by 1 m wide) of silt loams in a central Pennsylvania (USA) catchment. Flow from packed soil boxes took longer to initiate as antecedent soil moisture decreased from field capacity (2 min) to air dried (8 to 9 min). Even in the more complex field plots (i.e. soil heterogeneity and topography), the wetter site (1 by 10 m plot; 70% field capacity) produced flow more quickly (3 min) and in greater volume (439 L) than the drier site (1 by 10 m plot; 40% field capacity, 15 min, and 214 L, respectively). However, less suspended sediment was transported from wetter soil boxes (1·6 to 2·5 g L^?1) and field plots (0·9 g L^?1) than drier boxes (2·9 to 4·2 g L^?1) and plots (1·2 g L^?1). Differences are attributed to their potential for soil aggregate breakdown, slaking and dispersion, which contribute to surface soil sealing and crusting, as dry soils are subject to rapid wetting (by rainfall). During flow, selective erosion and antecedent moisture conditions affected P transport. At field capacity, DRP and PP transport varied little during overland flow. Whereas P transport from previously dry soil decreased rapidly after the initiation of flow (6 to 1·5 mg TP L^?1), owing to the greater slaking and dispersion of P‐rich particles into flow at the beginning than end of the flow event. These results indicate that soil moisture fluctuations greatly effect erosion and P transport potential and that management to decrease the potential for loss should consider practices such as conservation tillage and cover crops, particularly on areas where high soil P and erosion coincide. Copyright © 2002 John Wiley & Sons, Ltd.     

Variability of interrill erosion at low slopes

Numerous models and risk assessments have been developed in order to estimate soil erosion from agricultural land, with some including estimates of nutrient and contaminant transfer. Many of these models have a slope term as a control over particle transfer, with increased transfer associated with increased slopes. This is based on data collected over a wide range of slopes and using relatively small soil flumes and physical principals, i.e. the role of gravity in splash transport and flow. This study uses laboratory rainfall simulation on a large soil flume to investigate interrill soil erosion of a silt loam under a rainfall intensity of 47 mm h^?1 on 3%, 6% and 9% slopes, which are representative of agricultural land in much of northwest Europe. The results show: (1) wide variation in runoff and sediment concentration data from replicate experiments, which indicates the complexities in interrill soil erosion processes; and (2) that at low slopes processes related to surface area connectivity, soil saturation, flow patterns and water depth may dominant over those related to gravity. Consequently, this questions the use of risk assessments and soil erosion models with a dominant slope term when assessing soil erosion from agricultural land at low slopes. Copyright © 2010 John Wiley & Sons, Ltd.     

Adsorption and affinity of Escherichia coli to different aggregate sizes of a silty clay soil

The sediments produced by water erosion are the main source of pollution of agricultural origin of surface water bodies. These sediments may be associated to bacteria, compromising the quality of nearby water bodies. Therefore, to understand this biological contamination, it is necessary to find out the adsorption capacity and bacterial affmity to aggregate sizes that may result in a differential sedimentation. To this end, in the present work, the distribution, adsorption capacity and affinity to different aggregate sizes of two strains of Escherichia coli in two liquid media of contrasting ionic strength were evaluated in a silty clay soil. The 〈2 μm fraction showed a higher proportion of bacteria than the other aggregate sizes （48%）, whereas among the fractions 〉2 μm, the 20-50μm fraction was the one that showed the highest bacterial adsorption in both liquid media （37.9%）. On the other hand, the highest values of bacterial affinity were found in the 20 to 50 lain fraction （coarse silt） in the low ionic strength media and 20--50 and 〉50 μm in the high ionic strength media. However, the bacterial strains used revealed only some trends in the modification of these variables. This work contributes to the development and implementation of strategies to mitigate pollution, such as control of sediment generation and its subsequent capture in filter strips.     

The relationship between the soil erodibility factor K (Universal soil loss equation), aggregate stability and micromorphological properties of soils in the Hornos area,S. Spain

Wischmeier's soil erodibility factor K calculated for 10 surface soils in the Hornos area, S. Spain, is compared with 3 aspects of aggregate stability. A significant correlation is found with the percentage of particles < 100 μm after aggregate breakdown, which is used as a measure of the vulnerability of the soil to erosion by overland flow. No significant correlation exists with the number of water drops required to cause breakdown of the aggregates nor with the mean size of the shattered aggregates, both being aspects of the resistance of aggregates to splash erosion. Of the micromorphological and analytical soil properties explaining aggregate stability, only the clay and silt content and the number of closed voids are significantly correlated with the factor K. The aggregate stability of the investigated soils is mainly determined by soil properties inherited from the parent material; the stabilizing effect of pedological features is small.     

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.