Transport Of Soil Particles Research Articles

Numerical modelling of internal erosion during hydrate dissociation based on multiphase mixture theory

SummaryIt has been reported that sand production, which is a simultaneous production of soil particles along with gas and water into a production well, forced to terminate the operation during the world's first offshore methane production test from hydrate‐bearing sediments in the Eastern Nankai Tough. The sand production is induced by internal erosion, which is the detachment and migration of soil particles from soil skeleton due to seepage flow. The inflow of the eroded soil particles into the production well leads to damage of the production devices. In the present study, a numerical model to predict the chemo‐thermo‐mechanically coupled behavior including internal erosion during hydrate dissociation has been formulated based on the multiphase mixture theory. In the proposed model, the internal erosion is expressed as mass transition of soil particles from soil skeleton to the fluidized soil particles. Since the internal erosion is considered to depend on the soil particle size, mass of soil particles are divided into several groups that have different representative particle diameters, and the constitutive equations for the onset condition and the mass transition rate of the internal erosion are formulated for each group. Also, transportation of soil particles in the liquid phase is formulated for each particle size group in the proposed model. Finally, a simulation of the methane gas production from the hydrate‐bearing sediment by depressurization method is presented, and the internal erosion and the dissociation behavior are discussed.

Effects of land use on soil organic and inorganic C and N at 137Cs traced erosional and depositional sites in mountain agroecosystems

Patterns of erosion, transport and deposition of soil particles not only affect the distribution of mineral fraction of the soil but their organic components. The spatial variability of soil nutrients in Mediterranean mountain agroecosystems that combine complex land uses and abrupt topography is poorly documented despite emerging concerns on nutrients fate require understanding the potential impact of soil erosion on nutrients redistribution across landscapes. This study aims to assess at catchment scale the spatial patterns of soil organic and inorganic carbon (SOC, SIC), soil organic carbon fractions and total nitrogen (TN) in relation to land uses and soil redistribution. To this purpose we selected a well characterized endorheic catchment located in NE Spain where soil erosion and deposition rates derived from 137Cs measurements were previously documented and we mapped the distribution of cropland and rangeland areas. A grid of 100 × 100 m was established for collecting a total of 205 soil samples for nutrients and standard soil analyses.In both rangeland and cropland the patterns of SOC and TN stocks were clearly related to 137Cs inventories thus significantly lower nutrient stocks (SOC: 34.1 ± 18.6 Mg ha−1, TN: 2.9 ± 1.7 Mg ha−1) were found in erosional sites whereas higher stocks (SOC: 44.9 ± 24.2 Mg ha−1, TN: 3.9 ± 2.3 Mg ha−1) were recorded in depositional areas. In cropland the mean nutrients contents (SOC: 1.1 ± 0.8%, TN: 0.1 ± 0.1%) were significantly lower than in rangeland (SOC: 3.2 ± 2.1%, TN: 0.2 ± 0.1%). The highest C/N ratios (29) were found in rangeland, while in cropland they occurred in depositional areas with their values below 10 in the erosional sites. In turn, the SIC content (range 0.4 to 10.2%) was slightly lower at the depositional sites (4.9 ± 2.2%) but not significantly different from the erosional sites (5.1 ± 2.2%). Cultivated and steep slopes led to loss of soil and nutrients due to intense erosion processes also related to tillage and crop productivity. Our findings provide evidence that the combined effect of land use and soil redistribution exert an important control on the spatial distribution of nutrients, highlighting a significant decrease of SOC and TN stocks with increasing soil erosion in croplands. The information gained achieves a better understanding of soil nutrients dynamics and further knowledge for effective land management of mountain agroecosystems in the Mediterranean region.

Mathematical modeling of the development of the long profile of a deluvial slope

The process of formation of gentle deluvial (dominated by sheet erosion) slopes under the influence of anthropogenic load is investigated using a deterministic balance model in a 2D formulation. It is shown that the non-linear erosion model as a diffusion equation in partial derivatives with boundary conditions makes it possible to adequately reflect the dynamics of sheet erosion. The physical aspects of mass transfer in a laminar flow are considered, taking into account the mechanisms of separation and transport of soil particles in connection with the concept of critical velocity. The evolution of the profile of a deluvial slope is investigated. The results of the numerical experiment were used to analyze the mechanism of transfer of erosion products and the formation of profiles. The concept of diffusion-balance modeling is expanded by numerical, as well as computational experiments. Taking into account the detected high adequacy of the model, it can be used to describe the evolution of deluvial slopes.

Effects of the ephemeral stream on plant species diversity and distribution in an alluvial fan of arid desert region: An application of a low altitude UAV.

Biodiversity conservation, plant growth and spatial distribution of plant species are the central issues in contemporary community ecology. Ephemeral stream may influence soil properties, which in turn may determine biodiversity and function of an ecosystem in alluvial fan of arid desert region. Ephemeral stream is one of the most common natural disturbances, yet the effects of the ephemeral stream on plant communities in terms of species diversity and plant species distribution remain poorly studied. In this study, the information of species distribution, ephemeral stream beds (‘washes’), and the characteristics of plant growth, i.e. height, crown area, were interpreted at different heights using the images of low altitude unmanned aerial vehicle (UAV). After that, soil properties such as soil texture (sand, silt and clay), soil water content, pH, soil organic matter, soil electric conductivity, soil bulk density and the percentage of gravel content, and their relationships with UAV data were assessed in order to explore the influences of ephemeral stream on species diversity, plant growth characteristics and species distribution in an alluvial fan of arid desert region. The results showed that deep-rooted plants were only distributed in washes whereas shallow-rooted plants were distributed in both washes and the outside of washes (‘non-washes’). Species richness was significantly higher in washes than that in non-washes whereas the opposite pattern was true for abundance. Soil properties, plant height and crown area were higher in washes than that in non-washes. Plant height, crown area and the total number of individual plants increased with increasing wash width and per unit length of stream flow. This study highlights that the coupling factors of ephemeral stream, such as soil erosion, particle transport and sedimentation, can dramatically cause changes in soil properties and total number of individual plants, and hence, can influence species diversity, plant growth characteristics and spatial distribution of plant species in an alluvial fan of arid desert regions.

Soil Particle Transport and Mixing Near a Hillslope Crest: 1. Particle Ages and Residence Times

We examine probabilistic elements of soil particle ages and residence times measured from their entry into the mechanically active soil column, focusing on steady conditions near a hillslope crest, where particles steadily move into and through a soil mantle with fixed thickness in the presence of erosion. Our objective is to clarify consequences of the geometry of the particle trajectories and disturbance‐driven mixing in relation to the arrangement of the surfaces through which the particles enter and leave the soil element. We introduce an Eulerian‐Lagrangian description of particle motions to characterize effects of a nonuniform (two‐dimensional) mean motion with superimposed depth‐dependent mixing. With weak mixing, the forms and moments of the probability distributions of particle residence times and ages are distinct and are largely controlled by the geometry of the mean particle motion within the soil element. The average particle age is systematically less than the average residence time. These distributions converge to exponential forms with equal means only in the idealized limit of a “well‐mixed” system. The analysis provides the foundation for considering particle weathering and chemical losses in relation to residence times and ages and for describing the spatiotemporal structure of tracers, for example, cosmogenic nuclide concentrations and optically stimulated luminescence particle ages, in relation to what these reveal about particle mixing.

Soil Particle Transport and Mixing Near a Hillslope Crest: 2. Cosmogenic Nuclide and Optically Stimulated Luminescence Tracers

We examine probabilistic elements of how cosmogenic nuclide (e.g., 10Be) concentrations and optically stimulated luminescence (OSL) particle ages are distributed within a soil mantle near a hillslope crest as a consequence of disturbance‐driven transport and particle mixing. We use an Eulerian‐Lagrangian algorithm in which fluctuating particle motions, representing depth‐dependent mixing, are superimposed on a two‐dimensional mean motion. The intensity of mixing is characterized by a Péclet number involving the vertical speed of particles entering the soil mantle at the soil‐bedrock interface, the mechanically active soil thickness, and a particle diffusivity at the soil surface. With weak mixing, the vertical profile of 10Be concentration reflects the strong influence of the mean motion in which particles spend much of their lives in the higher part of the soil column with higher 10Be production rates. With increasing mixing intensity, the profile becomes linear, then uniform, and the vertically averaged concentration is larger than that expected with one‐dimensional motion. With weak mixing, particles possessing a finite OSL age tend to remain near the soil surface; with increasing mixing they become more uniformly distributed with depth. Depth‐interval‐averaged OSL ages increase linearly with depth and then become uniform with strong mixing. With moderate to strong mixing, the probability distribution of OSL ages is approximately exponential with an average much less than the mean residence time of particles. The formulation is consistent with profiles of 10Be concentrations and interval‐averaged OSL particle ages compiled from published data, suggesting moderate to strong mixing in the cases examined.

An Experimental Study on Sediment Discharge in River Channel for the Reduction of Sediment Disaster

최근 기후변화의 영향으로 집중호우 및 토사재해 발생빈도가 증가하고 있다. 이러한 토사재해로 인한 하도 내 피해예방 및 종합적인 토사 관리를 위해서는 정량적이고 시계열적인 토사이동량 파악이 필수적이다. 그러나 우리나라의 재래식관측기를 이용한 직접적인 측정방법은 실제 측정이 용이하지 않고 많은 비용과 인력, 시간이 소요된다. 특히 연속적인 측정이 거의 불가능한 상태에 있어 토사 이송에 관한 수문학적 요인과 메커니즘 관계를 정량적으로 분석한 연구는 부족한 실정에 있다. 따라서 본 연구에서는 하도 내 토사이동량 측정의 어려움을 개선하기 위해 실내수로실험에 하이드로폰을 활용하였고 하이드로폰의 인지능력을 파악하기 위해 충돌음향 계측 및 분석을 수행하였다. 연구결과 하이드로폰이 인지할 수 있는 개별입자별 main충돌시의 최소 임계치 기준은 공급유량과 토사입자의 크기가 커질수록 증가하는 것으로 나타났다.Due to recent climate change, the frequency of heavy rainfalls and sediment disasters is increasing. In order to prevent damages caused by sediment disaster and implement a comprehensive sediment control, a time-series analysis of sediment discharge data is essential. However, in South Korea, it is difficult to measure them directly as they use conventional meters as measurement, which prevents research from presenting a quantitative relationship between hydrological factors and mechanisms with regard to sediment transport. In this regard, the study attempted to overcome difficulties related to the measurement of soil particle transport in river channel. It used acoustic signals to recognize the transport of sediment particles and established an indoor waterway experiment equipment with a hydrophone. As a result, it is found that the minimum threshold value for the main collision of individual particles perceived by hydrophone increased as the supply flow rate and the size of sediment particles increased.

Soil erosion and transport simulation and critical erosion area identification in a headwater catchment contaminated by the Fukushima nuclear accident

Radiocesium released by the accident at the Fukushima Dai-ichi Nuclear Power Plant in 2011 contaminated a large land surface area. Due to the strong and size-dependent adsorption capability of soil particles to radionuclides, a better understanding of erosion and transport of soil particles and identification of erosion prone areas within watersheds are significant for contaminant management. For this purpose, we simulated soil erosion and transport in a partially forested catchment for multiple particle size classes. Critical erosion areas were identified by the spatial distribution of net soil erosion. Comparisons between simulated and measured suspended solids concentration at multiple locations throughout the catchment demonstrated successful model performance. For the period Mar. 12, 2011 through Dec. 31, 2014, model results indicated that 5500 tonnes of clay, 52000 tonnes of silt, and 22000 tonnes of sand are transported from the catchment. The results showed that soil erosion in the middle part of the catchment is greater mainly because of steep slopes and large fraction of agricultural lands. These simulations suggest that soil decontamination of erosion-prone agricultural lands in the mid- catchment areas would be effective in reducing radiocesium migration with soil particles.

Abordagem morfopedológica na avaliação da suscetibilidade à erosão dos solos em Vale de São Domingos (MT)

Os processos erosivos são responsáveis pelo carreamento das partículas do solo, provocando o assoreamento de rios e nascentes. Objetivou-se avaliar a suscetibilidade à erosão dos solos e os conflitos de uso no município de Vale de São Domingos/MT, considerando que este vem apresentando nas últimas décadas crescimento populacional, o que implica em novas formas de utilização do espaço geográfico. Os procedimentos metodológicos adotados foram: compartimentação morfopedológica, realizada por meio da associação dos mapas municipais de pedologia e geomorfologia; geração do mapa de susceptibilidade à erosão, por meio da sobreposição dos mapas de grau de erodibilidade e declividade; susceptibilidade à erosão; geração dos mapas de cobertura vegetal e uso da terra; potencial à erosão, capacidade de uso das terras e conflito de uso do solo. No município de Vale de São Domingos foi identificada a predominância de Neossolos Quartzarênicos em 59,11% da área do município, em relevo suave ondulado. Houve a predominância da classe extremamente suscetível à erosão e foram identificadas no município a presença de áreas com alto potencial à erosão hídrica. Conforme a avaliação da capacidade de uso das terras foi possível definir que classe a VII de capacidade de uso das terras é mais adequada em 59,34% da área da municipalidade. A classe de alto conflito de uso dos solos foi a predominante, demonstrando que as atividades antrópicas estão afetando a qualidade do solo, bem como afetando os recursos naturais da área de estudo. Constatou-se a, demanda de práticas conservacionistas dos usos desses solos, devido a predominância de solos frágeis na área de estudo.

Phosphate fertilizer enhancing soil erosion: effects and mechanisms in a variably charged soil

The extensive application of phosphate fertilizers could produce a series of environmental problems by adsorbing on the surface of soil particle and migrating into water during soil erosion. Therefore, this study is to explore the effects of phosphate on soil aggregate stability and soil erosion and to analyze the mechanisms of phosphate enhancing soil erosion from the scope of soil charge density, electric field, and particle interaction. A variable charged soil (0–20 cm) was pre-treated firstly by KCl, K2HPO4, and KH2PO4, respectively. Under the conditions of KCl, K2HPO4, and KH2PO4 solutions with concentrations of 0.0001, 0.001, 0.01, 0.1, and 1 mol L−1, (1) the amounts of soil particle transport and erosion intensities were measured using rainfall simulation with electrolyte solutions instead of rainwater; (2) the aggregate stabilities were measured by weighing the particles and micro-aggregates of <2, 5, and 10 μm after soil aggregate breakdown in electrolyte solutions; and (3) the zeta potentials of soil particles were measured in electrolyte solutions. The application of K2HPO4 and KH2PO4 in soil strongly enhanced soil aggregate breakdown and soil erosion, while in KCl application, soil aggregates were stable and erosion did not occur. Moreover, the intensities of soil aggregate breakdown and soil erosion for K2HPO4 application were much stronger than that for KH2PO4 application. Phosphate, especially K2HPO4, strongly increased surface negative charge density of soil particles and thus increased the electrostatic repulsive pressure between adjacent soil particles in aggregates, and as a result, the soil erosion intensity increased. However, the surface charge density was not increased by the increased pH, specific adsorption, and dispersion force adsorption but possibly attributed to a non-classic induction force adsorption arising from the anionic non-classic polarization in the strong electric field around soil particle surface. The application of phosphate decreased aggregate stability and stimulated soil erosion through increasing charge density of particle surface by a new non-classic induction adsorption of phosphate.

Монгол орны хөрс салхиар элэгдэх үйл явцыг үнэлсэн судалгааны үр дүнгээс

Phenomenae commonly occuring in arid regions are dust storms. Adaptation mechanism associated with this phenomenon appears in various forms within ecological environments of the world largest desert and semi-deserts. However, due to adverse anthropogenic impacts as well as natural external and internal forces, transportation and accumulation of soil particles by wind intensifies, which accelerates the soil erosion processes in arid territories.An equation for wind erosion computation used for this assessment was based on the Universal Wind Erosion Equation developed in 1961 by the US Department of Agriculture. When the WEQ equation used for Mongolia, the factors of unsheltered distance or distance for undisturbed wind flowing were not taken into consideration assuming that there is no barrier to hinder the wind force in the given for study area. Meanwhile soil surface was considered as an influencing factor to wind flow and soil surface roughness and obstacles were calculated from the digital elevation data.The results demonstrate that there is a high degree of wind erosion along the desert zone, Great Lakes Depression, Lakes Valley. Especially soil around the Baruun Khuurain Khotgor, Altai Ovor govi, Ulaan Nuur Lake, Mandal-Ovoo territories have highest degree of wind erosion. Mongolia’s steppe, desert steppe zones, especially steppes of Dornod and areas of Zamyn Uud and Sainshand belong to lands with moderate degree of soil erodibility. Wind erosion changes can clearly be observed in southern part of Govi-Altai, Bayankhongor, Umnugovi aimags, particularly, in valleys and depressions of gobi areas like Sharga, Nomin, Ingen hoovor, Galba, Borzon.

Flow-driven soil erosion processes and the size selectivity of eroded sediment on steep slopes using colluvial deposits in a permanent gully

Colluvial deposits with loose, coarse material are easily erodible in permanent gullies, but the mechanisms of erosion and sedimentation during overland flow remain obscure. Hence, the processes and mechanisms of the transportation of soil particles by overland flow were investigated in this study. Experiments were carried out in a 5.0m long by 1.0m wide flume using colluvial deposits. The slope gradient varied from 36 to 84%, and the flow rate ranged from 0.72Lm−2min−1 to 2.88Lm−2min−1. The runoff rate and sediment yield rapidly increased with increasing overland duration. Runoff and sediment were highly variable when the flume was treated with a high flow rate compared with a low flow rate, with the fluctuation of sediment concentration under the high flow rate usually reaching 500gL−1. The slope gradient and overland flow rate have strong impacts on sediment transport capacity. The mean flow velocity and the unit stream power can be an optimal composite force predictor for estimating sediment transport capacity. Experimental results also revealed that the percentage of gravel-sized particles increased with increasing flow rate and slope gradient, but silt and clay fractions observed opposite trend. The average enrichment ratio (ER) of gravel was usually <1. However, the ER of silt and clay fractions decreased following the increase of the flow rate and slope gradient, and the values stabilized in the range of 1.1 to 1.4. The predicted values of runoff, sediment yield, and sediment concentrations were simulated by an empirical equation with measured values, and the regression coefficients were 0.983, 0.996 and 0.877, respectively. When the flow rate was >2.16Lm−2min−1, the bed load transport became an important mechanism; however, the simulation model overestimated these values.

River Water Quality and its Relation with Air Quality: A Long-Term Case Study in a Remote and Pristine NW Italian Headwater Catchment

This paper analyses the water quality characteristics of a remote and pristine basin, the Gallina small catchment, located in the Piemonte Region (NW Italy). In particular, the ion content of river water and precipitation are assessed for two distinct periods (October-December of years 1992 and 2011). These time frames are characterized by a change of air quality management rules for the study area which came into force after year 2000. Furthermore, late Autumn months, which are considered in this study, are characterized by a peak of recorded precipitations in the area under study. Moreover, this is a period of the year where atmospheric emission intensity and distribution are greater with respect to Spring and Summer. The chemical nature of the monitored water body was assessed through the use of Piper diagram. Research found evidence of erosional processes, which chemically altered the water compared to the quality of precipitation. The signature of air chemistry was also evident, through a shift to less sulphate, after the change of air quality regulations introduced in year 2000. The presence of marine ions, in case of major weather perturbations, typical of the late Autumn in the monitored area, was recorded. This fact was particularly evident for the month of November 2011, in association to a major flooding event occurred in the Piemonte Region. The presence of a minor ionic component, associated to rainfall waters, depending upon soil particle resuspension and transport was also detected. Finally, the prevailing origin of the measured ions was defined. The results show the importance of improved management actions, which should be taken in order to further reduce the trans-boundary atmospheric pollution, which constitutes a threat to water quality and a further element of indirect water pollution transfer across different areas.

The role of soil surface properties on the particle size and carbon selectivity of interrill erosion in agricultural landscapes

The selective nature of interrill erosion – the preferential mobilization and transport of soil particles – can lead to the enrichment of fine-grained soil particles (<63μm) and organic carbon (OC) within the mobilized soil. This study investigated the effects of slope gradient, vegetative cover, soil moisture content, texture and organic matter content, as well as their interactions on soil loss, particle size distribution and organic carbon content of soil mobilized under simulated rainfall within two contrasting agricultural regions in Canada. Overall, it was found that the eroded material was enriched in both fine-grained and carbon-rich particles relative to the source soil. It was demonstrated that dispersing and sieving both the source soil and the mobilized soil to <63μm (i.e., removal of sand and large particulate organic matter) reduced the relative enrichment of both fine-grained soil particles and OC, which would allow for a more direct comparison of physical and biogeochemical properties between the source and mobilized soil. Furthermore, it was demonstrated that while the soil loss and the degree of enrichment were negatively correlated, there were differences in which soil surface properties had a significant effect in determining soil loss and the selectivity of both fine-grained and organic-rich soil particles and how these surface properties interacted. This suggests that while soil loss may be a good predictor of the degree of enrichment, the factors that control these two processes are different, which is important in understanding the process of selectivity. It was also shown that the OC content of both the source and mobilized soil was positively correlated to the degree of soil aggregation in addition to the silt and clay content.

Digital close range photogrammetry for the study of rill development at flume scale

Soil erosion is a continuous process of detachment, transportation, and deposition of soil particles. Obtaining accurate descriptions of soil surface topography is crucial for quantifying changes to the soil surface during erosion processes. The objective of this study was to develop an improved close-range photogrammetric technique to assess soil erosion under rainfall conditions. Based on high overlapping image acquisition, digital point cloud matching, digital elevation model (DEM) generation and soil erosion calculation, a digital close-range photogrammetric observation system was explored and established. The results showed that the established digital photogrammetric observation system could accurately calculate the digital point cloud from the underlying surface with a 2min time interval and a 1.5mm spatial resolution. In addition, based on the DEM generated from digital point clouds, the amount of soil erosion in different topographic positions within various time periods was calculated. The digital photogrammetric observation methods explored in our study provide a reliable way to monitor soil erosion processes, especially under rainfall conditions. This approach can accurately resolve the evolution of the underlying surface soil erosion, which is of great importance in understanding soil erosion mechanisms.

The role of surface microreliefs in influencing splash erosion: A laboratory study

Wu J., Zhao L., Wu F., Li Z. (2016): The role of surface microreliefs in influencing splash erosion: A laboratory study. Soil & Water Res., 11: 83–89. The detachment and transport of soil particles from soil mass are important effects of falling raindrops on soil erosion during rainfall. The objective of this study was to determine whether soil microrelief affects the detachability and transportability of soil particles by raindrop splash. Experimental microreliefs were manually simulated by two tillage practices: shallow hoeing, contour chisel plowing, and a smooth slope served as control treatment. The experiment included three simulated rainfall intensities (1.0, 1.5, and 2.0 mm/min). A splash board was used to collect sediment splashed upslope as well as that splashed downslope. Results show that microrelief has a positive effect on detachment rate (DRt) and has a negative effect on net downslope movement rate (SPnet). With the exception of DRt of which hoe treatment was less than smooth at the rainfall of 1.0 mm/min intensity, DRt of hoe and chisel treatments were twice as high as that of smooth to other treatments. For all treatments, SPnet of hoe and chisel treatments were less than half of smooth. Regression analysis showed that DRt change with increasing rainfall intensity could be described by a power function for all treatments. The change of SPnet could be described by a logarithmic function for hoe and chisel treatments, while the change of SPnet of the smooth treatment could not be described by a logarithmic function. Statistical results suggest that DRt was significantly influenced by rainfall intensity, while SPnet was not. Conversely, SPnet was significantly influenced by soil microrelief, while DRt was not.

Selective organic carbon losses from soils by sheet erosion and main controls

AbstractAlthough the impact of sheet erosion on the selective transportation of mineral soil particles has been widely investigated, little is yet known about the specific mechanisms of organic carbon (OC) erosion, which constitutes an important link in the global carbon cycle. The present study was conducted to quantify the impact of sheet erosion on OC losses from soils. Erosion plots with the lengths of 1‐ and 5‐m were installed at different topographic positions along a hillslope in a mountainous South African region. A total of 32 rainfall events from a three years period (November 2010 up to February 2013), were studied and evaluated for runoff (R), particulate and dissolved organic carbon (POCL and DOCL). In comparison to the 0–0·05 m bulk soil, the sediments from the 1‐m plots were enriched in OC by a factor 2·6 and those from the 5‐m long plots by a factor of 2·2, respectively. These findings suggest a preferential erosion of OC. In addition, total organic carbon losses (TOCL) were incurred mainly in particulate form (~94%) and the increase in TOCL from 14·09 ± 0·68 g C m−1 yr−1 on 1‐m plots to 50·03 ± 2·89 g C m−1 yr−1 on 5‐m plots illustrated an increase in sheet erosion efficiency with increasing slope length. Both TOCL and sediment enrichment in OC correspondingly increased with a decrease in soil basal grass cover. The characteristics of rainstorms had no significant impact on the selectivity of OC erosion. The results accrued in this study investigating the links between sheet erosion and OC losses, are expected to be of future value in the generation of carbon specific erosion models, which can further help to inform and improve climate change mitigation measures. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Effects of toposequence and land use-land cover on the spatial distribution of soil properties

Topographic properties can influence pedogenic processes, soil profile depth and spatial variations of soil properties. The objectives of this study were to determine the spatial variation of soil properties at different slope positions and land use-land cover and also the relationships among soil properties, slope and land use-land cover. The study area was divided into five topographic positions by an elevation transect from 935 to 1370 m. These positions were shoulder, flat plateau-1, flat plateau-2, lower back slope, and toe slope which were sampled at 10 × 20 m grid size. A total of 500 soil samples were collected from 0 to 20 cm depth. Soil properties showed significant variation among slope positions and land use-land cover type when analysed with ANOVA and post hoc multiple comparison tests. Slope was responsible for large discrimination effects compared to land use-land cover. It was also the main factor contributing to the transportation and accumulation of fine soil particles when soil organic matter content and water stable aggregates amount were low. Moreover, different land use-land cover type affected soil organic matter content and water stable aggregate amount and caused significant variance in them. Overall, the spatial variability of soil physico-chemical properties was strongly affected by pedogenic factors, slope and land use.

Major and trace elements in soils and ashes of eucalypt and pine forest plantations in Portugal following a wildfire

Wildfires can play an important role in the environmental distribution of major and trace elements, including through their mobilization by fire-induced runoff and associated transport of soil and ash particles. In particular, fire-induced inputs of these elements into the environment are relevant due to their toxicity and environmental persistence. This study aimed to evaluate the role of wildfire and time-since-fire on the redistribution of major and trace elements, which is a topic poorly documented. To this end, levels of V, Mn, Co, Ni, Cu, Cd and Pb were assessed in soil and ash samples collected immediately following a wildfire in north-central Portugal as well as 4 (after the first post-fire rainfall events), 8 and 15months later. The role of forest type was determined by sampling burnt eucalypt and pine plantations. The main findings of this study were the following: (1) levels of V, Mn, Ni, Cd and Pb were consistently higher in the burnt than unburnt soils, while levels of Co and Cu revealed no differences; (2) time-since-fire affected major and trace elements in three different ways: concentrations of Mn and Cd declined abruptly after the first rainfall events while levels of V, Co and Ni increased during the first 8months and levels of Cu and Pb hardly changed during the study period; (3) all studied elements revealed peak concentrations in the ashes immediately after the fire, which then declined sharply four months later; (4) levels of Co and Ni soils and ashes were higher at the pine plantations than at the eucalypt plantations. This study highlighted the role of wildfire in enhancing levels of major and trace elements in ashes and topsoil of forest plantations and their mobilization within the first year after fire, pointing towards recently burnt forest areas as a potential source of environmental contamination.

Effects of strong ionic polarization in the soil electric field on soil particle transport during rainfall

SummarySpecific ion effects are now thought to be important in nature. We studied the specific ion effects on soil particle transport during rainfall simulation (150 mm hour−1, 110 minutes) in sodium nitrate (NaNO3), potassium nitrate (KNO3) and caesium nitrate (CsNO3) solutions. The results showed marked differences in the intensity of soil particle transport in Na+, K+ and Cs+ systems. The differences increased sharply with the decrease in electrolyte concentration, which indicated strong specific ion effects on soil transport and suggested that the differences could not be explained by ionic size, hydration effect or dispersion force. The cationic non‐classical polarization in a strong electric field increases the Coulomb attractive force between the cation and clay surface, and further adversely decreases the strength of the electric field. With the absolute effective charge coefficients, γ, of Na+ (1.110), K+ (1.699) and Cs+ (2.506), we recalculated the true surface potentials of soil particles in NaNO3, KNO3 and CsNO3 solutions. The true surface potentials decrease sharply with the increase in ionic non‐classical polarization, and then the electrostatic repulsive pressure between particles in the soil should decrease sharply. Comparison of fitting the equation for transport intensity in NaNO3 solution with that in KNO3 and CsNO3 solutions showed clearly that the soil electric field controlled the aggregate breakdown and particle transport. The results suggested that the stronger the non‐classical polarization for cations in the soil, the weaker is the electrostatic field that forms and the soil erosion at the same solution concentrations.