Clay-size Fraction Research Articles

Geotechnical and geochemical appraisal of IFON clay, Southwestern Nigeria: Implications for industrial utilization

Clays are geological materials of economic potential in the manufacturing and environmental industries. Geotechnical properties and geochemical composition of Ifon clay deposits in Ondo State, Nigeria were investigated with the aim of determining their economic potentials. The geotechnical investigation includes consistency limits, strength, permeability and firing tests, while, X-ray fluorescence (XRF) method was used for determination of the bulk elemental composition of the clays using standard techniques. Geotechnical appraisal of the clay deposits revealed that high proportion of clay size fractions (52.3 – 66.1%) makes the clays suitable in their natural state for industrial raw materials. Activity of the clays was found to be low at approximately 0.3 – 0.7 and classified as inactive clays. Unconfined compressive strength varies between 3.4 N/mm2 and 4.7 N/mm2 and moderate shrinkage values (≤ 12%) indicate that the clays could be used as building construction materials. Coefficient of permeability of 7.75 × 10-8 to 1.72 × 10-5 cm/sec described the clays as low to impermeable soils suitable as barrier soils. SiO2 (64.41 – 68.74%) and Al2O3 (22.98 – 28.45%) contents dominate the clay geochemistry followed by iron oxide, Fe2O3 (3.57 – 8.31%) content among other oxides in traces, imply that they originated from underlying basement rocks subjected to varying degree of weathering. Low MgO, CaO, K2O and Na2O indicate no expandable clay minerals in the clays. The clays show low heavy metal concentrations which guarantee their suitability as raw materials in chemical industries. Thus, Ifon clay deposits are suitable for the production of ceramics, refractory bricks, paper, paints, rubber and fertilizer. Â

Maize root‐derived C in soil and the role of physical protection on its relative stability over shoot‐derived C

Evidence is accumulating that belowground crop residues contribute more efficiently to the build‐up and maintenance of native soil organic carbon (SOC) than aboveground plant parts. We corroborated previous testing of the hypothesis that root‐C would preferentially accumulate in soil microaggregates, where it is physically protected against microbially mediated decomposition. In three European field trials with C3 to C4 crop transitions, we compared the content of maize‐C (Zea mays L.) in soil from rotations with grain maize (MG) or silage maize (MS) (i.e. with incorporation of roots and shoots or roots only). After decades of maize cultivation, SOC content did not differ within three out of four MG–MS pairs, although obviously larger amounts of shoot biomass were added to soil in the case of MG. We found that relative contribution of roots was on average 3.5 times more than shoots to the build‐up of SOC per equivalent mass of residue C added to soils. Preferential occlusion of root‐C as silt‐sized intra‐microaggregate particulate organic matter (iPOM) was not observed. There were much larger effects from shoot incorporation on maize‐C in the >53‐μm fraction and free silt and clay. Storage of root‐C as sand‐sized iPOM was not quantified here, but first estimates suggested that physical entrapment at this level could only partly explain the longevity of root‐C in soil. We reconfirm the relative stability of root‐C in soil, but do not conclude that this stems from preferential physical entrapment over shoot‐C. Future work should investigate the cause of preferential root‐C association with the clay‐sized fraction and if this occurs before or after microbial processing.Highlights The hypothesized preferential physical stabilization of root‐C was assessed. Aboveground biomass had a minor effect on SOC storage in European long‐term trials. Contribution of maize root‐C to maintenance of SOC was three‐fold that of shoot‐C inputs. There was no preferential occlusion of root‐C in silt‐sized microaggregates.

Geochemical investigations in bulk and clay size fractions from lower Krishna river sediments, southern India: implications of elemental fractionation during weathering, transportation and deposition

Major and trace elements, including rare earth elements (REEs) geochemistry of bed sediments from the lower reaches of Krishna river suggest their origin mainly from weathering of Deccan basalts and Precambrian rocks of the southern India. The elemental compositions indicate evidence of sedimentary sorting during weathering, transportation and deposition. Highly depleted Na2O and high values of Chemical Index of Alteration (CIA) are suggestive of moderate to strong chemical weathering environment in lower reaches of Krishna river. Major, trace and REE concentrations of bulk sediments suggest marginal variations in relative contribution from mafic and felsic minerals. The bed sediments contain significantly low concentrations of trace elements like Ba, Sr, La, Ce and Nd and moderately low concentrations of V, Zr, Rb, Zn, Ni and Cr relative to upper continental crust (UCC) composition. Most of the other trace elements and REEs are almost similar to UCC indicating their origin from weathering of mixed rock types in catchment areas of Krishna river. Strong relationships of ΣREEs with Ti and Zr in bed sediments suggest that REEs are mainly controlled by heavy minerals such as titanite and zircon. A marked increase in REEs in clay fractions of sediments indicates their adsorption and/or substitution on clay lattice.

Particle Size Specific Magnetic Properties Across the Norwegian‐Greenland Seas: Insights Into the Influence of Sediment Source and Texture on Bulk Magnetic Records

AbstractWe make fundamental observations of the particle size variability of magnetic properties from 71 core tops that span the southern Greenland and Norwegian Seas. These data provide the first detailed regional characterization of how bulk magnetic properties vary with sediment texture, sediment source, and sediment transport. Magnetic susceptibility (MS) and hysteresis parameters were measured on the bulk sediment and the five constituent sediment particle size fractions (clay, fine silt, medium silt, coarse silt, and sand). The median MS value of the medium silt size fraction is ~3–5 times higher than that of the sand and clay size fractions and results in a strong sensitivity of bulk MS to sediment texture. Hysteresis properties of the clay size fraction are relatively homogeneous and contrast that silt and sand size fractions which show regional differences across the study area. These coarser fractions are more transport limited and using medium silt hysteresis measurements and low temperature MS behavior we establish three endmembers that effectively explain the variability observed across the region. We model the response of bulk magnetic properties to changes in sediment texture and suggest that variations in sediment source are required to explain the bulk magnetic property variability observed in cores across the southern Greenland and Norwegian Seas. These findings imply that sediment source has a greater influence on driving bulk magnetic property variability across this region than has previously been assumed.

Distribution of methane production and methanogenic archaeal community structure across soil particle size fractions along a rice chronosequence

Methanogens, a phylogenetic group of archaea, are a key microbial community that mediate carbon (C) cycling and methane (CH4) production in submerged soils. In this study, we analyzed the potential of CH4 production and the archaeal community structure of different soil particle fractions in a chronosequence of rice (Oryza sativa L.) soil subjected to prolonged rice cultivation. The chronosequence of five age groups of a paddy soil formation was determined in a coastal area from East China, subjected to 50 to 700 years of rice cultivation. Undisturbed bulk soils were fractionated by low-energy ultra-sonication dispersion and centrifugation into four classes of particle size fractions (PSFs; coarse sand, fine sand, silt, and clay). The abundance and diversity of archaeal communities from each of the four fractions were analyzed by quantitative polymerase chain reaction and denaturing gradient gel electrophoresis, respectively. Among the size fractions, a high abundance of archaea and methanogens was found in both coarse sand- and clay-sized fractions. During prolonged rice cultivation, CH4 production potential (MPP) and methanogenic gene abundance increased in the soil cultivated for 100 years, and thereafter changed more or less in the soils cultivated for longer periods. Moreover, marked changes in gene abundance and community diversity were observed in coarse sand- and clay-sized fractions, but not in fine sand- and silt-sized fractions. Sequencing analysis of 61 selected archaeal 16S rRNA genes revealed that Methanocellales was an abundant group of methanogens in all sized fractions of soils across the chronosequence, whereas Methanosarcinaceae and Methanosaetaceae were less widespread in the clay fractions across the soils. This study indicated that methanogens and their activities can be heterogeneously distributed among soil PSFs, and their distribution and activities change in response to years of paddy cultivation that affect PSFs formation.

Soil Organic Fractions in Cultivated and Uncultivated Soils of Costal Area in Bangladesh

Assessment of soil organic matter fractions can be instrumental in understanding the causes of limited nitrogen supply, and thus soil fertility restoration. A study was conducted in cultivated and uncultivated saline soil, in order to assay soil organic carbon (SOC), its particle-size fractions and their influence on cultivation and soil fertility at Sundarbans costal area in Bangladesh. Soil samples were taken from the 0 - 15 and 15 - 30 cm depths from four cultivated fields and from four nearby sites in a native mangrove forest as references. Soil samples were physically fractionated into sand (2000-50 μm), silt (50-2 μm) and clay ( silt > sand. The SOC pool and N in the clay-sized fraction were correlated to soil fertility indicators. More N was stored in the silt + clay size fractions, a generally more stable pool, than in the more labile sand-sized pool. The SOC pool in sand size fractions was far below in cultivated soils than in a reference uncultivated soil. Thus, the sand-sized pool emerged as the most likely cause of limited N supply in cultivated soils.

Paleoenvironmental considerations based on geochemistry and mineralogy of a Miocene lacustrine calcrete, southern Portugal

A lacustrine carbonate facies has been investigated in Middle Miocene successions of the western side of the Moura-Marmelar basin, Southern Portugal in order to evaluate paleoenvironments in which carbonates formed, by using geochemistry and mineralogy. The studied formation corresponds to a recent unearthed section of a calcrete with an homogeneous carbonate facies comprising fine, whitish, and powdery material, and the only detected difference is a slightly hardness decrease towards the top, as well as an increase of weathered rock fragments (schist). The calcrete is calcium rich, even some magnesium enrichment was observed at the middle level, which is differentiated by a general depletion of all chemical elements, particularly REE, in both the bulk and clay-size fraction. Regarding the mineralogy, calcite prevails, and dolomite is only present in the middle level of the calcrete, together with a smectite enrichment, suggesting changes to more alkaline and low drainage, lacustrine and arid to semi-arid conditions.

Paleoclimatic implications of hydrogen and oxygen isotopic compositions of Cretaceous–Tertiary kaolins in the Douala Sub-Basin, Cameroon

Increased interest in paleoenvironmental studies is a result of climatic changes occurring at present and predicted for the future. Such studies could be done using the stable isotope compositions (δ2H and δ18O) of kaolins, which provide knowledge on the paleoenvironmental conditions prevailing during the time of kaolinisation. In this study, the stable isotopic compositions of clay-size fraction of kaolins occurring in Cretaceous and Tertiary Formations of the Douala Sub-Basin in Cameroon are presented, with the aim of reconstructing the paleoenvironmental conditions of the Sub-Basin. To achieve this, the clay-size fraction (<2μm fraction) of 8 kaolinite-rich samples were analysed for their δ2H and δ18O compositions, and results were reported as part per mil (‰) relative to the SMOW standard. The δ18O values of kaolins found in the Cretaceous–Tertiary Formations of the Douala Sub-Basin varied between +18.2 and +21.0‰, whereas the δ2H values varied between –69 and –53‰. Nine of the eleven samples plotted on the right of the supergene–hypogene line. Five of these nine samples plotted very close to the kaolinite line, which represents the composition of kaolinite in equilibrium with meteoric water at 20°C; suggesting a supergene weathering origin of these kaolins. The determination of the temperature of kaolinisation yielded mean formation temperatures of 22±2°C and 27±6°C for Cretaceous and Tertiary kaolins, respectively. Excluding the two samples falling in the hypogene field, averages of kaolinisation temperatures were 20 and 25°C during the Cretaceous and Tertiary periods, respectively. These temperatures are slightly below the present mean annual temperature in Douala (27°C), thereby suggesting that the climate was becoming warmer from the Cretaceous to the Present. Therefore, Douala had a cooler and rainy climate during the Cretaceous, and the climate is gradually becoming hotter and more humid, favouring the refinement of existing kaolins and the kaolinisation of kaolin-forming minerals in the Sub-Basin.

Effect of inorganic fertilisers and organic amendments on soil aggregation and biochemical characteristics in a weathered tropical soil

Highly weathered laterite soils are a characteristic feature of humid tropics with undulating topography and high rainfall. The crop of cashew (Anacardium occidentale L.) has been cultivated in such landscapes, mainly to prevent further degradation due to the drought hardiness of cashew and requirement of very limited soil disturbances for its cultivation. Providing proper nutrient management is important for balancing the nutrient removal by tree crops especially in poor fertile soils. A study was initiated, after 5 years of application of inorganic fertilisers and organic amendments to cashew in a weathered tropical soil, to evaluate the effects of organic and inorganic sources of nutrients on soil aggregation and biochemical characteristics. The experiment consisted of 11 treatments as Farm Yard Manure (FYM) alone; FYM + biofertiliser consortia; FYM, rock phosphate and wood ash; poultry manure; In situ composting using recyclable cashew biomass and weeds; In situ composting using recyclable cashew biomass and weeds + green manuring; vermicomposting of recyclable cashew biomass; FYM + organic cakes + recyclable cashew biomass + biofertiliser consortia; recommended dose of nitrogen, phosphorus and potassium fertiliser (NPK fertiliser); recommended NPK fertiliser + FYM; and control without nutrient application. Soil samples were collected from surface 0–30 cm layer. The soil samples were fractionated into three aggregate sizes, i.e., >2 mm (large macroaggregates), 0.25–2 mm (small macroaggregates), 0.053 to 0.25 mm (microaggregates) and <0.053 mm (silt + clay size fraction) using wet sieving. The results indicated that the organic sources of nutrient application increased the proportion of large and small macroaggregates. The treatments receiving only inorganic nutrients and no nutrients contained significantly higher silt + clay fractions (47.7 and 45.5% respectively). A higher percentage of water stable aggregates (47.4–70.7%) and increased aggregate stability (mean weight diameter) (0.78–1.26 mm) was recorded with the application of organic sources of nutrients. Aggregates in the silt + clay size faction and microaggregates recorded significantly higher carbon compared to small and large macroaggregates. Compared to control, the application of different organic amendments increased the soil organic matter (SOM) by 2.2–12.7% in silt + clay size fraction; 14.6–37.0% in microaggregates; 18.4–51.7% in small macroaggregates and 17.7–50.9% in large macroaggregates. Our findings reinforce that the annual application of manures and amendments to weathered tropical soil is important to improve biological properties of soil in terms of soil enzyme activities, microbial carbon and nitrogen, and to prevent further degradation of soil under such fragile environment.

Comparison of site-specific and empirical correlations for drained residual shear strength

Analyses of landslides, slopes and embankments often require reliable drained residual shear strength estimates for cohesive deposits involving pre-existing shear surfaces. Laboratory tests to measure residual shear strength can be costly and time consuming. Therefore, empirical correlations based on more readily available index properties such as liquid limit and clay-size fraction appear as an attractive alternative in practice. This paper presents residual strength and index properties for 25 natural samples, predominantly claystone and siltstone, collected from a single geologic setting over an approximately 0·25 km2 site. The data show substantial variability in residual strength against any single index parameter considered in a site-specific correlation. Comparisons of these data, along with three additional data sets, generally indicated notable variability among data sets and relatively poor fit to published empirical correlations. Empirical correlations for residual strength may be useful in approximating the expected range of residual strength. However, given the significant variability in the data, both within and between data sets, empirical correlations should not entirely replace carefully performed site-specific laboratory tests measuring residual strength, when reliable values are required.

Identifying the controlling mechanism of geogenic origin chromium release in soils

A laboratory study was conducted to assess the mobility and mechanisms of chromium release from soils obtained from an area of wide spread geogenic contamination. The agricultural soil sample used in this study was taken from the Schimatari area in Asopos River basin in Greece. In order to refine the isolation of minerals contained in the soil, two types of separation analysis were conducted. First, a size fractionation with hydrocyclone and second, a weight fractionation with heavy liquids. The separated fractions were characterized using chemical, mineralogical and surface analysis. The results provided consistent evidence that the heavy fraction of the soil is related directly to the mobile fraction of chromium. At acidic pHs, the clay-sized fraction also plays an additional important role in the mobility of Cr, due to the fact that this fraction has high surface area and chromium reactivity index. In addition, pH-edge leaching studies showed a high correlation between Cr-Ni, Cr-Mn and Cr-Y released from the soil which also suggests that the mobility of chromium is controlled by chromite weathering which is the case observed in Asopos river basin.

Effects of Permaculture Practices on Soil Physicochemical Properties and Organic Matter Distribution in Aggregates: A Case Study of the Bec-Hellouin Farm (France)

The limitations of conventional agriculture have accelerated the need for a transition to an environmentally and economically sustainable agricultural model. In this regard, the role played by soil organic matter (SOM) is key. Here, we aimed to study the impact of permaculture and biointensive micro-gardening practices, characterized by intensive cultivation, the use of large and localized organic inputs and the non-use of mineral fertilizers and pesticides, on soil physico-chemical properties and SOM distribution in aggregate-size fractions. The physico-chemical properties of soils in permaculture farming implemented for seven years were compared with a soil under pasture. A soil experiencing conventional agriculture practices in similar geopedoclimatic conditions was simultaneously studied. Soils were separated into four aggregate-size fractions, into which organic carbon (OC) concentrations have been measured. The major soil physico-chemical properties were measured on the bulk soils. The concentrations of total OC and nitrogen (N) in bulk soils were higher under permaculture practices, due to significant inputs of manure and compost, resulting in higher concentrations of the bioavailable nutrients Ca, Mg, K and P. The permaculture practices sustained a level of macroaggregation similar to that of the pasture, and well above that of conventional practices. OC concentrations increased in the 250-2000 µm, 50-250 µm and occluded 50-250 µm fractions, but not in the <50 µm fraction compared to pasture. This can be explained by the too short duration of permaculture practices for allowing the decomposition of coarse particulate organic matter (POM) into fine sized SOM that is more associated with mineral particles in free clay and silt size fraction. The higher OC stocks in permaculture are therefore mainly governed by the coarse POM fraction. Our results show that permaculture/biointensive micro-gardening practices enhance SOM storage and modify the distribution of SOM in aggregate size fractions, while substantially improving nutrient bioavailability and suggests that permaculture practices strongly affect soil properties. The effects of permaculture practices on soil properties would certainly vary depending on geopedoclimatic context, justifying the need to implement the approach for other soil types. Finally, we recommend to compare biogeochemical budget and nutrients use efficiency of permaculture gardening with conventional horticulture gardening.

Chemical weathering in subtropical basalt-derived laterites: A mass balance interpretation (Misiones, NE Argentina)

Subtropical laterites are partially found in the Argentinian province of Misiones, covering the Jurassic-Cretaceous Serra Geral flood basalts (known as Posadas Formation in Argentina). Two hypotheses have been proposed to explain the origin of these laterites. The autochthonous theory attributes the origin of these deposits to the chemical weathering of the underlying tholeiitic basalts. However, during the last decade, an allochthonous “tropical loess” model was proposed. Several mineralogical/geochemical characteristics of a lateritic profile (~2 m thick, 26°9′58″S–54°35′3″W) are analyzed in this paper in order to constrain the nature of weathering processes in this region and the provenance of the lateritic layer. The basaltic bedrock at the sampling site exhibits intergranular texture and is mainly composed of clinopyroxene, plagioclase and opaque minerals (likely titanomagnetite and ilmenite). Altered glass and apatite were also identified in lower proportions. The X-ray diffraction of the clay-size fraction shows prevailing kaolinite and hematite in the most altered samples, complemented by amorphous Fe-Al (hydr)oxides. Serra Geral basalts-normalized spidergrams and mass balance calculations confirmed almost complete losses of all major oxides (i.e., ~50 g of material was removed by weathering from each 100 g of the original basalt) and depletions of some trace elements (e.g., Sc, V, Sr, Cr, Ni, Rb and U) in the uppermost and intermediate layers of the lateritic profile, reflecting the weathering of feldspars, clinopyroxenes, volcanic glass and apatite. In contrast, some elements are enriched in the topmost and intermediate layers, due to intrinsic immobility during weathering (e.g., Zr, Hf, Ta, Th) or adsorption onto clays (e.g., Cs). Rare earth elements (REEs) are depleted in the top layers and enriched in the middle section of the profile. The preferential leaching of REEs from the uppermost levels during weathering and its accumulation in the middle section can be caused by a pH increase in this level, the decomposition of organic matter and the consequent precipitation of REEs which exhibit an affinity to form aqueous organic complexes, or the presence of Fe and Mn (hydr)oxides in the intermediate level. Weathering intensity was appraised by means of different alteration indices, which showed the extreme leaching endured by the basaltic bedrock. The index of lateritization (IOL), which ranges between 35 and 55, and the accompanying SAF ternary plot (SiO2-Al2O3-Fe2O3), indicate an increasing weathering trend towards the profiles' top, reflecting the modest loss of SiO2 (relative to Al2O3 and Fe2O3) during kaolinitization. The geochemical approach used to constrain the origin of the lateritic mantle that partially covers Misiones province, clearly relates the analyzed laterites to the underlying tholeiitic basalts, supporting the autochthonous origin theory.

A geochemical investigation of the free and carbonate-bound organic matter in the clay-sized fraction of argillaceous source rocks and its significance for biogenic interpretation

The molecular composition and biomarker distribution of various occurrences of organic matter in argillaceous source rocks developed in fresh and saline lacustrine environments were revealed by successive treatments of solvent extraction followed by acid hydrolysis using gas chromatography–mass spectrometry. The free fraction obtained by solvent extraction provided abundant geochemical information concerning the sedimentary environment, thermal maturity and biogenic origin, and obvious differences existed between fresh and saline lacustrine source rock samples. Our research results indicate that the carbonate-mineral-bound (CM-bound) fraction released by successive acid hydrolysis could also serve as a significant biogenic indicator, as the bicyclic sesquiterpenoids, indicative of Botryococcus braunii origin, were specifically detected in quite high abundance in the acid-soluble fraction. In addition, the light end hydrocarbons were much better preserved in the acid-soluble fraction, and elemental sulfur was only detected in the CM-bound fraction, suggesting a relatively confined environment for the CM-bound fraction, which thus could preserve additional geochemical information compared to that of the free fraction. The CM-bound fraction also exhibited discernable differences between fresh and saline lacustrine samples. Therefore, it can be concluded that comprehensive analysis of free and CM-bound fractions in the argillaceous source rocks can provide a more authentic and objective interpretation of geologic conditions.

Structural Control on Clay Mineral Authigenesis in Faulted Arkosic Sandstone of the Rio do Peixe Basin, Brazil

Clay minerals in structurally complex settings influence fault zone behavior and characteristics such as permeability and frictional properties. This work aims to understand the role of fault zones on clay authigenesis in arkosic, high-porosity sandstones of the Cretaceous Rio do Peixe basin, northeast Brazil. We integrated field, petrographic and scanning electron microscopy (SEM) observations with X-ray diffraction data (bulk and clay-size fractions). Fault zones in the field are characterized by low-porosity deformation bands, typical secondary structures developed in high-porosity sandstones. Laboratory results indicate that in the host rock far from faults, smectite, illite and subordinately kaolinite, are present within the pores of the Rio do Peixe sandstones. Such clay minerals formed after sediment deposition, most likely during shallow diagenetic processes (feldspar dissolution) associated with meteoric water circulation. Surprisingly, within fault zones the same clay minerals are absent or are present in amounts which are significantly lower than those in the undeformed sandstone. This occurs because fault activity obliterates porosity and reduces permeability by cataclasis, thus: (1) destroying the space in which clay minerals can form; and (2) providing a generally impermeable tight fabric in which external meteoric fluid flow is inhibited. We conclude that the development of fault zones in high-porosity arkosic sandstones, contrary to other low-porosity lithologies, inhibits clay mineral authigenesis.

Impact of soil clay minerals on growth, biofilm formation, and virulence gene expression of Escherichia coli O157:H7

Soil, composed mainly of minerals, plays a central role in the circulation of microbial pathogens in the environment. Herein, the growth, biofilm formation, and virulence gene expression of the pathogenic bacteria Escherichia coli O157:H7 were monitored following exposure to montmorillonite, kaolinite, and goethite, three common soil minerals in the clay size fraction. E. coli O157:H7 growth was notably promoted (P < 0.05), while biofilm formation was inhibited in the presence of montmorillonite (P < 0.05), which is attributed to the suppression of colanic acid (CA) production and an increase in bacterial motility. Kaolinite not only promoted bacterial growth (P < 0.05), but also contributed to biofilm formation upon stimulating CA production. Upon exposure to goethite, notably slower bacterial growth and higher biomass of biofilm were observed as compared to the control (P < 0.05). Goethite stimulated the synthesis of CA to encase cells in a protective biofilm in response to the tight association between bacteria and goethite, which could cause bacterial death. Additionally, the transcription of virulence factors (stxA-1 and stxA-2) was significantly decreased in goethite or kaolinite system (P < 0.05). These findings indicate that minerals play important roles in the physiological state of bacteria and ultimately govern the fate of this pathogen in soils.

Curve-fitting techniques improve the mid-infrared analysis of soil organic carbon: a case study for Brookston clay loam particle-size fractions

Few studies have evaluated structural features of soil organic carbon (SOC) in different soil particle fractions, especially SOC changes induced by tillage, using Fourier transformed mid-infrared (MIR) spectroscopy. To make a contribution in this context, soil samples of a Brookston clay loam (mesic Typic Argiaquoll) with averaged pH and organic matter concentration at 7.28 and 43.9 g kg−1, respectively, were collected from short-term no-tillage (NT97) and mouldboard plow (CT97) treatments initiated in 1997 and long-term no-tillage (NT83) and mouldboard plow (CT83) treatments initiated in 1983 under a corn-soybean rotation, and were separated into sand, silt, and clay fractions using sonication. Structural features of SOC in these soil fractions were investigated using curve-fitting analysis of mid-infrared (MIR) spectra. Aromatic C content was found to be greater in clay- than in sand-sized fractions, while aliphatic C content was higher in sand- than in silt- and clay-sized particles. With decrease in tillage intensity, the aliphatic C gradually increased in sand- and clay-sized fractions but not in the silt-sized fraction. The aliphatic C content in sand fraction was significantly greater in NT83 than CT83 (P < 0.05). The aromatic C in silt- and clay-sized fractions was greater in NT83 than in both CT soils, whereas aromatic C contents were higher in both CT soils than in NT83 soil. Significantly higher aromatic/aliphatic C ratio in CT83 than NT83 was found in sand-sized fractions, while the opposite trend was found in the silt-sized fraction. These findings were not apparent until the curve-fitting technique was employed, which has the capacity to quantify many overlapped bands in the spectra. This study demonstrates that the curve-fitting of MIR spectra advances the analysis of organic matter in soil samples.

Appraisal of Heavy Metals in Soil/Sediments with Relation to their Physico-chemical Properties from Ankaleshwar Industrial Area, South Gujarat

Extensive industrialization in the southern part of Gujarat is characterized by regional pollution of soil and water resources. In view of this, the present study has been undertaken in Ankaleshwar, one of the biggest industrial townships of India. About, 25 surface sediment /soil samples were collected from top 10 cm representing entire study area and were analyzed for heavy metals by using X-ray fluorescence spectrometer (XRF). The heavy metals concentrations were compared with the standard shale to find out pollution index (PI), results shows the significant enrichment for arsenic, moderate enrichment for Pb and minimal enrichment for metals in descending order as Fe&gt;Mn&gt;Cr&gt;Ni&gt;Co&gt;Zn&gt;Cu&gt;Mo. Physico-chemical properties such as texture, cation exchange capacity, total carbonate and organic matter, as well as the percentages of the sand, silt, and clay fractions have been examined. It is observed that heavy metals like Ni, Cu, Zn, and Mo show a positive correlation with the silt size fraction. Similarly, Mn, Cr, As, and Pb show positive correlation with clay size fraction. Chemical properties like EC, CEC and organic matter have control over majority of heavy metals. High correlation with these properties suggests that higher ionic conductivity soils have high heavy metal content. The effect of these properties can be arranged in descending order as follows: EC &gt;OM &gt; Clay % &gt;Silt % &gt; CEC.

Impacts of small woody debris on slurrying, persistence, and propagation in a low-gradient channel of the Dongyuege debris flow in Nu River, Southwest China

Debris flows occurring in well-vegetated alpine areas usually contain a range of sizes of woody debris. Large woody debris (LWD), which has a retaining effect on further transportation of debris downstream, is mainly distributed in upstream reaches, and the amount of small woody debris (SWD) deriving from LWD increases dramatically midstream and downstream. The Dongyuege (DYG) bouldery debris flow with a sandy-matrix took place in a wildwood area, causing 96 deaths and its clay-sized fraction does not contain typical clay minerals. However, its total travel distance and runout distance in a low-gradient reach (between 2° and 5°) upstream of the depositional fan apex reached 11 km and 3.3 km, respectively. The abundant SWD in the DYG debris flow might have played a crucial role in slurrying, persistence, and the long runout over the low gradient. To understand why this debris flow extended so far, slurrying experiments, pore water escape experiments, and excess pore pressure experiments were performed. Crude debris (CD) collected from the DYG debris flow deposit was used throughout the experiments, the tested materials of which are separated into CD-containing SWD with a maximum grain size (MGS = 2 mm), purified debris (PD) without SWD with a MGS of 2 mm, and SWD < 2 mm in diameter. In the five slurrying experiments with PD-SWD-water mixtures, as the SWD content was elevated from 0.0 to 2.0 wt%, the current velocity of escaping pore water decreased uniformly from 17.2 to 0.9 mm/s. When the SWD content was 1.0 wt% or greater, the mixtures can be considered as one-phase flows of viscous fluids. The six pairs of pore water escape experiments based on the slurries remolded with CD and PD, respectively showed that the time needed for pore water to escape from the CD slurries was much greater than those from their PD counterparts. Also, measured was the dissipation rate of the relative excess pore pressure of CD and PD slurries of various densities and volumes, which showed that most of the rates of the PD-slurries were always greater than CD-slurries. Overall, the results show that SWD has a strong influence on the slurrying of the DYG debris without typical clay minerals found in other debris flows, and SWD helps to sustain the high excess pore pressure in the interior of the debris flow mass which resulted in the extended travel distance over such a low gradient. SWD favors the formation and stability of one-phase water-debris mixtures because of its large specific surface area and low density, which makes it able to absorb fine particles and able to be suspended in slurry flows over long timescales. In well-vegetated mountainous areas, SWD should be taken into account in the assessment of debris-flow hazards.

Mobility of trace elements between the river water, the sediments, and the pore water of Las Catonas Stream, Buenos Aires Province, Argentina

The composition of river water, sediments, and pore waters (down to 30 cm below the bed) of Las Catonas Stream was studied to analyze the distribution of trace elements in a peri-urban site. The Las Catonas Stream is one of the main tributaries of Reconquista River, a highly polluted water course in the Buenos Aires Province, Argentina. The semi-consolidated Quaternary sediments of the Lujan Formation are the main source of sediments for Las Catonas Stream. The coarse-grained fraction in the sediments is mainly composed of tosca (calcretes), intraclasts, bone fragments, glass shards, quartz, and aggregates of fine-grained sediments together with considerably amounts of vegetal remains. The clay minerals are illite, illite–smectite, smectite, and kaolinite. For the clay-sized fraction, the external surface area values are mostly between 70 and 110 m2g−1, although the fraction at 15 cm below the bottom of the river shows a lower surface area of 12 m2g−1. The N2 adsorption–desorption isotherms at 77 K for this sample display a behavior indicative of non-porous or macroporous material, whereas the samples above and below present a typical behavior of mesoporous materials with pores between parallel plates (slit-shaped). As, Cr, Cu, and Cd concentrations increase down to 15 cm depth in the sediments, where the highest trace element and total organic carbon (TOC) concentrations were found, and then decrease toward the bottom of the core. Except for As, the levels of the other heavy metals show higher concentration in surficial waters than in pore waters. Distribution coefficients between the sediments, pore water, and surficial water phases indicate that As is released from the sediments to the pore and surficial waters. Cu content strongly correlates with TOC (mainly from vegetal remains), suggesting that this element is mainly bound to the organic phase.