Aggregation Of Soil Particles Research Articles

The physico-chemical properties and structural characteristics of artificial soil for cut slope restoration in Southwestern China.

Cut slopes are frequently generated by construction work in hilly areas, and artificial soil is often sprayed onto them to promote ecological rehabilitation. The artificial soil properties are very important for effective management of the slopes. This paper uses fractal and moment methods to characterize soil particle size distribution (PSD) and aggregates composition. The fractal dimension (D) showed linear relationships between clay, silt, and sand contents, with coefficients of determination from 0.843 to 0.875, suggesting that using of D to evaluate the PSD of artificial soils is reasonable. The bias (CS) and peak convex (CE) coefficients showed significant correlations with structure failure rate, moisture content, and total porosity, which validated the moment method to quantitatively describe soil structure. Railway slope (RS) soil has lower organic carbon and soil moisture, and higher pH than natural slope soil. Overall, RS exhibited poor soil structure and physicochemical properties, increasing the risk of soil erosion. Hence, more effective management measures should be adopted to promote the restoration of cut slopes.

Alkali and alkaline earth metallic (AAEM) species leaching and Cu(II) sorption by biochar

Alkali and alkaline earth metallic (AAEM) species water leaching and Cu(II) sorption by biochar prepared from two invasive plants, Spartina alterniflora (SA) and water hyacinth (WH), were explored in this work. Significant amounts of Na and K can be released (maximum leaching for Na 59.0mgg−1 and K 79.9mgg−1) from SA and WH biochar when they are exposed to contact with water. Cu(II) removal by biochar is highly related with pyrolysis temperature and environmental pH with 600–700°C and pH of 6 showing best performance (29.4 and 28.2mgg−1 for SA and WH biochar). Cu(II) sorption exerts negligible influence on Na/K/Mg leaching but clearly promotes the release of Ca. Biochars from these two plant species provide multiple benefits, including nutrient release (K), heavy metal immobilization as well as promoting the aggregation of soil particles (Ca) for soil amelioration. AAEM and Cu(II) equilibrium concentrations in sorption were analyzed by positive matrix factorization (PMF) to examine the factors underlying the leaching and sorption behavior of biochar. The identified factors can provide insightful understanding on experimental phenomena.

Agregação de um latossolo vermelho-amarelo submetido a métodos de controle de plantas invasoras na cultura do café

O controle de plantas daninhas em cultivos de cafeeiros tem expressivo efeito na qualidade física do solo, influenciando, entre outros atributos, na sua estabilidade estrutural. Neste trabalho, objetivou-se avaliar o estado de agregação das partículas primárias de um Latossolo Vermelho-Amarelo (LVA) cultivado com cafeeiros, quando submetido a diversos métodos de controle de plantas invasoras. Os métodos de controle de plantas invasoras avaliados foram: manutenção da entrelinha coberta com amendoim-forrageiro (Arachis pintoi L.) e capim-braquiária (Brachiaria decumbens); controle mecânico com grade, roçadora, trincha e capina manual; controle químico com herbicidas de pós e pré-emergência; e ausência de controle, mantendo a entrelinha sem capina. O delineamento experimental foi em blocos casualizados em um fatorial 9 × 2 em parcelas subdivididas, sendo nove métodos de controle e duas profundidades do solo (0-15 e 15-30 cm), com três repetições. Determinaram-se a estabilidade dos agregados em água, expressa pelo diâmetro médio geométrico, o potencial dispersivo da fração argila, estimado pelos teores de argila dispersa em água e do índice de floculação, além dos teores de matéria orgânica do solo. Os atributos avaliados foram influenciados pelos diferentes métodos de controle, contudo essa influência não foi dependente da camada de solo amostrada. A utilização contínua de grade e herbicida de pré-emergência no controle de invasoras na cultura do café diminuiu a agregação das partículas do solo, confirmado pelos menores valores de diâmetro médio geométrico. Os métodos biológicos de controle das invasoras mantiveram melhor estado de agregação das partículas do solo. O estado de agregação das partículas não mostrou-se associado à dispersibilidade da fração argila do solo.

Research on variability characteristics of micropore of Zhanjiang clay under ambient temperature and pressure, normal atmospheric

Soils are generally used as building material and foundation, are normally under the atmospheric with ambient temperature and pressure, nevertheless, effect of oxidation of soil proceeding so slowly that it is no easy to perceive, long-term deterioration of soil properties, cannot be ignored. Zhanjiang Clay was taken as the object of study, studied the reformation effect on the micro-structures under the influence of the atmospheric and its impacting mechanism to soil properties, by scanning electron microscopy, mercury intrusion porosimetry and nitrogen absorption method. Research shows, after oxidized, the color of soil changes from grayish green and light grayish green to yellow and yellowish brown; while aggregation of soil particles increases, not only Swelling-shrinkage properties, but also plasticity of soil particles decreases, as for the sensitivity and structure yield strength reduced. Furthermore, atmospheric environment has an effect of shrinkage and closure on pores (<italic>d</italic><0.1 μm), and enlargement and dispersion on pores (<italic>d</italic>>1 μm), which results in a decrease of total pores volume of oxidized clay. As far as pores (<italic>d</italic>>1 μm) are concerned, pores volume increases remarking, with appearance of fracture porosity and reduction of ink-bottle type pores, as well as conversion from open pores to close ones. The transformation of soil properties by the influence of atmospheric is not caused by inherent changes of mineral, but the remodeling effect of micro-structures because of motion effects and chemical reactions of water-soil-electrolytes- atmosphere leading to coupling and transforming of soil particles. It is the variation of ultra-micro-structure that generates this phenomenon. Prolonged influence with comparatively large potential harmful impact on soil stability caused by damage effects on structural strength during oxidation, it turns out to be necessary to strengthen monitoring the effect on geotechnical engineering of physical and chemical factors in environment.

Soil aggregation in a semiarid soil amended with composted and non-composted sewage sludge—A field experiment

The addition of exogenous organic matter derived from organic wastes has been widely used to restore semiarid, degraded soils, favoring the development of plant cover. After organic amendment, soil particle aggregation can increase due to the increase of organic matter, plant roots and microbially derived compounds. However, the effect of organic amendment addition over time on aggregate formation is not clear. The aim of this work was to study soil particle aggregation of a semiarid, degraded soil 5years after the addition of a sole dose (120Mgha−1) of non-composted (SS) and composted sewage sludge (cSS). For this purpose, soils were separated into four aggregate-size fractions (8000–2000, 2000–250, 250–53 and <53μm) by wet sieving. Macroaggregates were further separated into coarse particulate organic matter (>250μm), microaggregrates within macroaggregates (250–53μm) and silt and clay (<53μm). In addition, phospholipid fatty acids (PLFAs) of the treated soils were measured. After 5years, the amended soils had a higher plant cover and greater amounts of large macroaggregates and microaggregates within macroaggregates than the control soil. Soil organic carbon (OC) was preferentially protected in the microaggregates within macroaggregates of the SS-treated soils, which tended to have higher fungal biomass than the rest of treatments. In contrast, the cSS-treated soils tended to have a lower microbial biomass than the SS-treated soils and showed the greatest relative enrichment of OC in the coarse particulate organic matter occluded in the macroaggregates. These results indicate that, depending on the pretreatment of the sewage sludge, the protection of OC over time occurs in different soil aggregate-size fractions, promoting a higher aggregate-associated OC in the composted amendments as coarse particulate organic matter.

Estimating the collapse of aggregated fine soil structure in a mountainous forested catchment

This paper describes the relationship of forest soil dryness and antecedent rainfall with suspended sediment (SS) yield due to extreme rainfall events and how this relationship affects the survival of forest plants. Several phenomena contribute to this relationship: increasing evaporation (amount of water vapour discharged from soil) due to increasing air temperature, decreasing moisture content in the soil, the collapse of aggregates of fine soil particles, and the resulting effects on forest plants. To clarify the relationships among climate variation, the collapse of soil particle aggregates, and rainfall–runoff processes, a numerical model was developed to reproduce such aggregate collapse in detail. The validity of the numerical model was confirmed by its application to the granitic mountainous catchment of the Nagara River basin in Japan and by comparison with observational data. The simulation suggests that important problems, such as the collapse of forest plants in response to decreases in soil moisture content and antecedent rainfall, will arise if air temperature continues to increase.

Ca2+ and Cu2+ Induced Aggregation of Variably Charged Soil Particles: A Comparative Study

The different surface reactions of metal ions with variably charged soil particles can considerably influence the particle interactions, which will further influence soil particle aggregation, sedimentation, dispersion, and transportation. This paper presents a study of the aggregation kinetics of variably charged soil colloidal particles at different Ca2+ and Cu2+ concentrations by using dynamic light scattering (DLS) and then investigating the formed aggregates structures by static light scattering (SLS). From the comparison of the experimental results, we found Cu2+ adsorption‐induced aggregation was much faster than Ca2+ adsorption‐induced aggregation. An aggregation process referred to as “attraction‐diffusion‐limited cluster aggregation” (ADLCA) was observed in the Cu2+ adsorption‐induced aggregation of the soil particles, resulting from electrostatic attraction forces between oppositely charged particles. The fractal dimensions of the Cu2+ specific adsorption‐induced aggregation were much higher than those of the Ca2+ electrostatic adsorption‐induced aggregation, irrespective of whether aggregation for the former was by the ADLCA, diffusion‐limited cluster aggregation (DLCA), or an ADLCA + DLCA process. Also, the ADLCA process led to the lowest fractal dimension, the DLCA process led to the highest fractal dimension, and the ADLCA + DLCA process led to an intermediate moderate fractal dimension, which shows the complexity of interactions between variably charged particles interactions when specific adsorption occurs at a particle surface. The above observations were well explained by analysis of the net interaction forces between particles in suspension.

宁南山区植被恢复对土壤团聚体水稳定及有机碳粒径分布的影响

土壤团聚作用和土壤有机碳固定之间密切相关.对宁南山区不同植被恢复措施和年限下土壤团聚体粒径分布及稳定性、土壤团聚体中有机碳及其组分分布进行了研究,探讨了有机碳及其组分对植被恢复的响应.结果表明,不同植被恢复措施下,土壤团聚体粒径分布表现为"V"字分布:> 5 mm和< 0.25 mm这两个粒径的团聚体含量最多,5-2 mm、1-0.25 mm团聚体的含量次之,2-1 mm粒径的团聚体含量最少.坡耕地的平均重量直径(MWD)最低,为1.4,其他植被恢复措施下土壤的平均重量直径MWD在1.9-3.1之间.不同的植被恢复措施下,0-20 cm土层和20-40 cm土层全土有机碳含量在7.4-17.7 g/kg之间、微生物碳含量分布在50.3-664.7 mg/kg之间、腐殖质碳含量在0.9-2.5 g/kg之间.胡敏酸碳含量分布在0.2-0.6 g/kg,富里酸碳含量在0.6-1.9 g/kg之间.全土有机碳、微生物碳、腐殖质碳、富里酸碳均为坡耕地最低,其他植被恢复措施的有机碳、微生物碳、腐殖质碳、富里酸碳含量分别是坡耕地的1.1-2.3倍、2.0-8.4倍、1.0-2.0倍、1.2-2.4倍.不同粒径团聚体有机碳相比较,大多呈现中间高两边低的变化趋势,最大值出现在中间粒径,即5-2 mm、2-1 mm、1-0.25 mm这3个粒径.逐步回归表明,5-2 mm团聚体和1-0.25 mm团聚体有机碳含量的提高有助于土壤水稳性团聚体的形成.研究结果表明,植被恢复提高了土壤团聚体有机碳含量,在碳形态上,富里酸碳和微生物生物量碳对不同植被恢复措施的敏感度较高,胡敏酸碳含量则相对稳定.;A close correlation exists between soil aggregation and soil organic carbon sequestration. Soil organic matter is the main material needed in the formation of soil aggregates and soil aggregates provide a place for soil organic matter to sequester carbon. The effects of different revegetation types on the aggregation of soil particles, the stability of soil aggregates, as well as carbon and fractions in soil aggregates were studied in a loess hilly-gully area; soil organic carbon and fraction's micro-response to different revegetation types are discussed. The results show the distribution of soil aggregates has a V distribution under a variety of revegetation and restoration measures. Small (< 0.25 mm) and large (> 5.0 mm) particle sizes form the most aggregates. The next largest aggregate size classes were 2-5 mm and 0.25-1.0 mm, while the 1-2 mm size class had the fewest aggregates. The mean weight diameter (MWD) of cropland is approximately 1.4. After land is revegetated the MWD increased to 1.9-3.1 in the soil indicating soil aggregate stability and porosity increased significantly. The aggregate stability of an area of natural grassland and also in a stand of 25-year-old <em>Caragana korshinskii </em>Kom. was higher than aggregate stability in a stand of 15-year-old <em>C. korshinskii </em>Kom. We measured various soil conditions under different revegetation types and found differences between the 0-20 cm and 20-40 cm soil layers. The soil organic carbon content was 7.4 and 17.7 g/kg; the microbial carbon content was 50.3 and 664.7 mg/kg; the carbon content of humus was 0.9 and 2.5 g/kg; the content of humic acid carbon was 0.2 and 0.6 g/kg; and the fulvic acid was 0.6 and 1.9 g/kg for the 0-20 cm and 20-40 cm soil layers, respectively. The organic carbon and the fraction in 0-20 cm soil layer were higher than measurements in 20-40 cm soil layer. The content of organic carbon, microbial carbon, humus carbon and fulvic acid carbon in the soil are the lowest in cropland; these contents under other revegetation types were 1.1-2.3 times, 2.0-8.4 times, 1.0-2.0 times and 1.2-2.4 times higher than those of cropland soils, respectively. Most of the soil organic carbon content was concentrated on intermediate sized aggregates (2-5 mm, 1-2 mm, 0.25-1.0 mm). The result of stepwise regression analysis show the higher the content of soil organic carbon was in the small and large particles (0.25-1.0 mm and 2-5 mm diameter aggregate, respectively) the more stable the water-stable aggregates were. The findings suggest vegetation restoration improved the soil organic carbon aggregate content, and in terms of forms of soil carbon, soil microbial biomass carbon and fulvic acid carbon, their content in the soil was sensitive to changes in aggregate size, while humic acid carbon was stable regardless of aggregate size.

Enhanced heavy metal immobilization in soil by grinding with addition of nanometallic Ca/CaO dispersion mixture

This study investigated the use of a nanometallic Ca and CaO dispersion mixture for the immobilization of heavy metals (As, Cd, Cr and Pb) in contaminated soil. Simple grinding achieved 85–90% heavy metal immobilization, but it can be enhanced further to 98–100% by addition of a nanometallic Ca/CaO dispersion mixture produced by grinding. Observations using SEM-EDS elemental maps and semi-quantitative analysis showed that the amounts of As, Cd, Cr, and Pb measurable on the soil particle surface decrease after nanometallic Ca/CaO treatment. The leachable heavy metal concentrations were reduced after nanometallic Ca/CaO treatment to concentrations lower than the Japan soil elution standard regulatory threshold: <0.01mgL−1 for As, Cd, and Pb; and 0.05mgL−1 for Cr. Effects of soil moisture and pH on heavy metal immobilization were not strongly influenced. The most probable mechanisms for the enhancement of heavy metal immobilization capacity with nanometallic Ca/CaO treatment might be due to adsorption and entrapment of heavy metals into newly formed aggregates, thereby prompting aggregation of soil particles and enclosure/binding with Ca/CaO-associated immobile salts. Results suggest that the nanometallic Ca/CaO mixture is suitable for use in immobilization of heavy-metal-contaminated soil under normal moisture conditions.

Methodological aspects of determining soil particle‐size distribution using the laser diffraction method

AbstractThis paper presents the influence of selected methodological aspects on the results of particle‐size distribution (PSD) as measured by the laser diffraction method (LDM). The investigations were carried out using the Mastersizer 2000 with Hydro MU attachment (Malvern Ltd., UK). It was found that for the investigated soils: (1) optimal speed of pump and stirrer was 2500 rpm, (2) optimal measurement time was ≈ 1 min, (3) there are two, practically equivalent methods for soil‐sample dispersion: chemical (with the use of a solution of sodium hexametaphosphate) or physical (by means of ultrasound application for 4 min at a maximum power of 35W), (4) one must not use the chemical and physical dispersing methods simultaneously, because this can lead to aggregation (not dispersion) of soil particles, (5) the Fraunhofer theory (physical models) can be used to convert scattered‐light data to PSD. In the case of the Mie theory, the best results were obtained for a refractive index (RI) in the range of 1.5–1.6 and an absorption index (AI) of 1.0. It was also found that most of the discussed parameters depend on design of the measuring device and on the type and volume of the investigated suspensions. It is necessary, therefore, to explain how the data was obtained every time and to specify the details in the methodological part of the paper.

Polyacrylamide Effects on Aggregate and Structure Stability of Soils with Different Clay Mineralogy

Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high‐molecular‐weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to −5.0 J kg−1 for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic &gt; illitic &gt; smectitic soils. The SR of PAM‐treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic &lt; illitic &lt; smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). The effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability.

Comparison of transport and attachment behaviors of Cryptosporidium parvum oocysts and oocyst-sized microspheres being advected through three minerologically different granular porous media

In order to gain more information about the fate of Cryptosporidium parvum oocysts in tropical volcanic soils, the transport and attachment behaviors of oocysts and oocyst-sized polystyrene microspheres were studied in the presence of two soils. These soils were chosen because of their differing chemical and physical properties, i.e., an organic-rich (43–46% by mass) volcanic ash-derived soil from the island of Hawaii, and a red, iron (22–29% by mass), aluminum (29–45% by mass), and clay-rich (68–76% by mass) volcanic soil from the island of Oahu. A third agricultural soil, an organic- (13% by mass) and quartz-rich (40% by mass) soil from Illinois, was included for reference. In 10-cm long flow-through columns, oocysts and microspheres advecting through the red volcanic soil were almost completely (98% and 99%) immobilized. The modest breakthrough resulted from preferential flow-path structure inadvertently created by soil-particle aggregation during the re-wetting process. Although a high (99%) removal of oocysts and microsphere within the volcanic ash soil occurred initially, further examination revealed that transport was merely retarded because of highly reversible interactions with grain surfaces. Judging from the slope of the substantive and protracted tail of the breakthrough curve for the 1.8-μm microspheres, almost all (>99%) predictably would be recovered within ∼4000 pore volumes. This suggests that once contaminated, the volcanic ash soil could serve as a reservoir for subsequent contamination of groundwater, at least for pathogens of similar size or smaller. Because of the highly reversible nature of organic colloid immobilization in this soil type, C. parvum could contaminate surface water should overland flow during heavy precipitation events pick up near-surface grains to which they are attached. Surprisingly, oocyst and microsphere attachment to the reference soil from Illinois appeared to be at least as sensitive to changes in pH as was observed for the red, metal-oxide rich soil from Oahu. In contrast, colloidal attachment in the organic-rich, volcanic ash soil was relatively insensitive to changes in pH in spite of the high iron content. Given the fundamental differences in transport behavior of oocyst-sized colloids within the two volcanic soils of similar origin, agricultural practices modified to lessen C. parvum contamination of ground or surface water would necessitate taking the individual soil properties into account.

Physical properties of soddy-podzolic soils in a long-term field experiment

The main physical properties of soddy-podzolic soils in a long-term field experiment have been studied. It is shown that their changes under the impact of a century-long application of lime, fertilizers, and manure have been relatively small. Reliable differences in the parameters of approximation of the dependence of penetration resistance on the soil water content in the variant with regular application of organic fertilizers have been revealed. This attests to stronger interparticle bonds (within the studied moisture range) in this variant. Interparticle bonds in the control variant and in the variant with lime application tend to increase with a decrease in the soil water content more significantly than those in other experimental variants. This may be due to the coarser texture of the soil in the control variant and to the aggregation of soil particles under the impact of lime in the variant with lime application.

Irrigation Water Quality Effects on Soil Carbon Fractionation and Organic Carbon Dissolution and Leaching in a Semiarid Calcareous Soil

Irrigation water quality and soil organic matter content influence crop yields and soil properties such as salinity and soil particle aggregation. We used laboratory column and batch studies and soil carbon fractionation to study potential organic carbon (OC) losses from a Typic Torrifluvent with 0.79% total OC and 4.7% inorganic carbon ([IC] as carbonates). About 4% of the total OC fraction was determined to be water-soluble OC (SOC). Under saturated flow, a significant amount of SOC (20%-35%) was lost from this soil (Pima clay loam) with just two pore volumes of irrigation water. Sodium- and sulfate-rich waters and rainwater were up to twice as effective at releasing SOC as waters dominated by calcium and chloride ions. Not all OC losses can be attributed to well-known soil particle dispersive effects of sodium and rainwater. Soluble OC losses were also highly correlated to the progressive dissolution of the soil IC fraction. Water quality has a measurable impact on OC and IC losses from OC-poor carbonate-rich soils. Changes in irrigation water quality may increase OC leaching from the plow layer and favor increased denitrification and potentially carbon sequestration in and below the root zone of irrigated semiarid soils.

Impact of Experimental Factors in Soil Phosphorus Tests: Shaking Vessel, Filtration, and Centrifugation

In the analysis of Mehlich III, deionized water (DI), Bray, and Olsen soil phosphorus (P) extractions, variations in shaking vessel, centrifugation, and filter paper result in different soil test P (STP) values. Of these factors, centrifugation and type of filtration were found to have the greatest impact on the results of water‐extractable P (WEP), that is, extraction with DI. Further spectrophotometric experiments demonstrated that centrifugation removed fine soil particles from the extract. Without the commonly used 0.45‐µm filters or centrifugation, these particles scatter the radiation of the spectrometer. During colorimetric analysis, this scattering of radiation will be perceived as absorption. This misperception results in a falsely high STP. In WEP analysis with only qualitative filtration, the scattering is very significant and appears to be due to limited aggregation of soil particles in the low ionic strength extract.

Alteração de atributos físicos em latossolo com aplicação superficial de escória de aciaria, lama cal, lodos de esgoto e calcário

Os resíduos industriais e urbanos podem atuar como condicionadores do solo, pois possuem a capacidade de alterar suas propriedades físicas. Contudo, não há referência para os atributos físicos do solo quando esses resíduos são aplicados sobre a superfície do solo no sistema plantio direto. O objetivo deste trabalho foi avaliar o efeito da aplicação superficial de escória de aciaria, lama cal, lodos de esgoto e calcário nos atributos físicos de um Latossolo Vermelho distrófico sob sistema plantio direto. Os tratamentos foram constituídos por quatro resíduos: lodos de esgoto centrifugado - LC e de biodigestor - LB, escória de aciaria - E, e lama cal - Lcal, interagindo com quatro doses (0, 2, 4 e 8 t ha-1, aplicadas na forma seca) mais uma testemunha (controle), constituída da aplicação de 2 t ha-1 de calcário. O delineamento experimental foi em blocos casualizados no esquema fatorial 4 x 4 + 1, com quatro repetições. A presença de Ca na composição de lama cal, lodo de esgoto centrifugado, escória de aciaria e calcário permite o aumento da agregação das partículas, diâmetro médio ponderado, índice de estabilidade de agregados, porosidade e retenção de água, sendo essas alterações distintas para cada fonte, dose e profundidade de reação no solo. A aplicação superficial da lama cal na dose de 8 t ha-1, após 27 meses de reação, proporcionou a maior agregação das partículas no solo, desde a superfície até 40 cm de profundidade.

Water Infiltration and Redistribution in Soil Aggregate Packings

Aggregation of soil particles is crucial for water flow in the vadose zone. Recent studies demonstrated that the unsaturated water flow through an aggregate pair is controlled by the contacts between aggregates. In these studies, the hydraulic conductivity of an aggregate pair was calculated as the harmonic mean of the conductivities of one aggregate and one contact, and it was fitted increasing the tortuosity from 0.5 to 5. In the present study, we investigated whether the contacts between aggregates control the water flow also in large aggregate packings. Our hypothesis was that unsaturated water flow in aggregate packings is primarily a flow in series through aggregates and contacts, and therefore the hydraulic conductivity of the system is properly approximated with that of an aggregate pair. To verify this hypothesis, we used neutron radiography to image water infiltration and redistribution in a cylindrical packing of aggregates. Then we numerically simulated the experiment using the hydraulic properties obtained from the model of an aggregate pair—i.e., tortuosity equal to 5. The observed water flow showed that the water redistribution following infiltration was particularly slow and the wetting front was very sharp. These features are explained by the bottleneck effect of the contacts, which were rapidly drained and limited the flow. This flow behavior was well reproduced in the simulations with tortuosity equal to 5, while simulations with tortuosity equal to 0.5, which is the tortuosity obtained for the aggregates, could not reproduce the observations. This study shows that the contacts control the unsaturated water flow also in larger aggregate packings and the process can be in a first approximation modeled as a flow in series through aggregates and contacts.

Experimental estimation of the energy parameters of molecular interactions in soils

The feasibility of determining the parameters of solid-phase particle-adsorbed moisture interlayer molecular interactions in soil from the isotherms of water vapor sorption and the data on the compressive strength of soil particle aggregates are discussed. The calculations are based on the fundamental physicochemical laws, that is, the Gibbs equation for substance adsorption and the Griffith equation for brittle deformations. The obtained characteristics of molecular interactions (the Hamaker complex constants) vary over a narrow range (0.9–2.3) × 10−19 J for soils with different dispersities.

A new approach for mapping of Biological Soil Crusts in semidesert areas with hyperspectral imagery

Biological Soil Crusts (BSCs), consisting of cyanobacteria, algae, microfungi, lichens and bryophytes in varying proportions, live within or immediately on top of the uppermost millimeters of soil, where they form a more or less firm aggregation of soil particles and organisms. They mainly occur in soils of arid and semi-arid regions, which cover more than 35% of the earth's land surface and are assumed to play a major role as primary producers, C- and N-sinks and soil stabilizers.In order to establish a methodology for mapping of BSCs, their spectral characteristics with respect to different crust types were analyzed. The resulting reflectance spectra of different crust types had a shallow absorption feature centered around 680 nm in common, in which they differed from the spectra of bare soil.In October 2004, hyperspectral CASI data with a spatial resolution of 1 m were recorded in conjunction with field spectroscopic measurements in the Succulent Karoo, South Africa. Available spectral indices for Biological Soil Crusts were tested on the image but did not produce satisfying classifications. Therefore, an alternative approach was established based on spectral field data, field observations and the hyperspectral dataset. The newly developed Continuum Removal Crust Identification Algorithm (CRCIA) is based on small and narrow spectral characteristics, that were extracted by continuum removal and subsequently expressed as a set of logical conditions. Using this method, 16.2% of the area which covers 12 km2 of gently sloping hills with some granite outcrops were classified as BSCs. Validation of the classification resulted in a Kappa index of 0.831.In a next step, the methodology will be tested with regard to scale-dependent effects and applied to images covering areas with additional types of BSCs and soil to develop a robust and generally applicable method.

Enhanced photodegradation of phenolic compounds by adding TiO 2 to soil in a rotary reactor

Photodegradation of pentachlorophenol (PCP) and p-nitrophenol (PNP) in soil was carried out in a designed rotary reactor, which can provide the soil particles with continually uniform irradiation, and on a series of thin soil layers. TiO 2, as a kind of environmental friendly photocatalyst, was introduced to the soil to enhance the processes. Compared with that on the soil layers, photodegradation of PCP at initial concentration of 60 mg/kg was improved dramatically in the rotary reactor no matter whether TiO 2 was added, with an increase of 3.0 times in the apparent first-order rate constants. The addition of 1 wt% TiO 2 furthered the improvement by 1.4 times. Without addition of TiO 2, PNP (initial concentration of 60 mg/kg) photodegradation rate in the rotary reactor was similar to that on the soil layers. When 1 wt% additional TiO 2 was added, PNP photodegradation was enhanced obviously, and the enhancement in the rotary reactor was 2 times of that on the soil layers, which may be attributed to the higher frequency of the contact between PNP on soil particles and the photocatalyst. The effect of soil pH and initial concentrations of the target compounds on the photodegradation in the rotary reactor was investigated. The order of the degradation rate at different soil pH was relative to the aggregation of soil particles during mixing in the rotary reactor. Photodegradation of PCP and PNP at different initial concentrations showed that addition of TiO 2 to enhance the photodegradation was more suitable for contaminated soil with higher concentration of PCP, while was effective for contaminated soil at each PNP concentration tested in our study.