Bulk Fractions Research Articles

Scallop farming impacts on dissolved organic matter cycling in coastal waters: Regulation of the low molecular weight fraction

To elucidate the impacts of scallop farming on the biogeochemical characteristics of low molecular weight (LMW, <1 kDa) dissolved organic matter (DOM), samples collected from a bay scallop mariculture area (MA) and its surrounding areas were determined for absorption and fluorescence spectroscopy after microfiltration and centrifugal ultrafiltration. The values of absorption coefficient a350 showed a spatial variation trend of inshore area (IA) > MA > non-mariculture area (NMA) for both bulk (<0.7 μm) and LMW fractions. Four fluorescent components, namely two protein-like components (tryptophan-like C1 and tyrosine-like C2) and two humic-like components (microbial humic-like C3 and terrestrial humic-like C4), were identified. Scallop farming influenced DOM transformation by altering phytoplankton abundance and promoting microbial degradation. In July, the net contributions of phytoplankton to the spectroscopy parameters of LMW-DOM in the surface seawater were 11.0% for a350, 4.3% for C1, 0.8% for C2, 0.6% for C3 and 3.0% for C4, respectively; the corresponding values of bulk DOM in the surface seawater were 24.3% for a350, 20.1% for C1, 5.9% for C2, 2.0% for C3, 2.9% for C4, respectively. Compared with NMA, the contributions of microbial degradation to a350 in MA's surface seawater increased by 9.0% for LMW-DOM and 6.9% for bulk DOM in July; however, the effects on different fluorescent components varied. In August, compared with NMA, the contributions of microbial degradation to spectroscopy parameters in the bottom water of MA decreased by 35.7% for a350, 6.3% for C2, 1.3% for C3, and 4.4% for C4 for LMW-DOM fraction; for bulk DOM, the corresponding contribution decreased by 10.8% for C1. These variations indicate that protein-like substances from scallop aquaculture are easily degraded into LMW substances, while humic-like substances degradation diminishes over time.

Origin and distribution of clay minerals in semi-arid Sahelian soils: case of Kori Ouallam watershed, south-western Niger

Abstract This study examines the origin and distribution of clay minerals of the pedological horizons of Kori Ouallam watershed (south-western Niger). It is based on field sampling campaigns and a series of laboratory analyses. A total of 49 samples were analysed, 28 from surface horizons (0–10 cm depth) and 21 from pedological profiles (0–1 m depth). The samples were analysed by X-ray diffraction on bulk and clay (&lt;2 μm) fractions, X-ray fluorescence spectrometry, laser granulometry, organic matter and calcium carbonate content, macroscopic observations (binocular loupe) and scanning electron microscopy equipped with an energy-dispersive spectrometry system. The pedological horizons are characterized by low organic matter contents (&lt;1%) and no calcium carbonate. The particle-size distribution shows net textural differentiation, with a predominance of sandy loam to sandy clay loam textures in the upper horizons and clay loam to clay in the deep horizons. The main major oxides were SiO2 (46.3–89.0%), Al2O3 (5.0–24.2%) and Fe2O3 (1.0–27.9%). Kaolinite (64–98%) is the predominant clay mineral at all horizons, associated with low to moderate proportions of illite (1–34%) and traces of chlorite. Kaolinite is essentially inherited from the parent rock, whereas illite results from chemical alteration by bisialitization of the primary minerals initially rich in potassium feldspar contained in the parent rock. However, soil texture and organic matter vary independently with clay mineralogy. An extended study of all of the pedological facies that make up south-western Niger, combined with supplementary analyses, would further improve our understanding of clay mineralogy in the Sahelian zone.

Budesonide Attains Its Wide Clinical Profile by Alternative Kinetics.

The introduction of inhaled corticosteroids (ICSs) changed over a few decades the treatment focus of mild-to-moderate asthma from bronchodilation to reduction in inflammation. This was achieved by inhaling a suitable corticosteroid (CS), giving a high, protracted airway concentration at a low total dose, thereby better combining efficacy and tolerance than oral therapy. Successful trials with the potent, lipophilic "skin" CS beclomethasone dipropionate (BDP) paved the way, suggesting that ICSs require a very low water solubility, prolonging their intraluminal dissolution within airways. The subsequent ICS development, with resulting clinical landmarks, is exemplified here with budesonide (BUD), showing that a similar efficacy/safety relationship is achievable by partly alternative mechanisms. BUD is much less lipophilic, giving it a 100-fold higher water solubility than BDP and later developed ICSs, leading to its more rapid intraluminal dissolution and faster airway and systemic uptake rates. In airway tissue, a BUD fraction is reversibly esterified to intracellular fatty acids, a lipophilic conjugate, which prolongs airway efficacy. Another mechanism is that the rapidly absorbed bulk fraction, via short plasma peaks, adds anti-inflammatory activity at the blood and bone marrow levels. Importantly, these plasma peaks are too short to provoke systemic adverse actions. Controlled clinical trials with BUD changed the use of ICS from a last resort to first-line treatment. Starting ICS treatment immediately after diagnosis ("early intervention") became a landmark for BUD. An established dose response made BUD suitable for the treatment of patients with all degrees of asthma severity. With the development of the budesonide/formoterol combination inhaler (BUD/FORM), BUD contributed to the widely used BUD/FORM maintenance and reliever therapy (MART). Recent studies demonstrated the value of BUD/FORM as a generally recommended as-needed therapy for asthma ("anti-inflammatory reliever", AIR). These abovementioned qualities have all influenced international asthma management and treatment guidelines.

Potential gains in soil carbon and nitrogen as a result of systems perenniality: Insights from on‐farm experiments and soil organic matter fractions

AbstractUnderstanding soil organic matter (SOM) dynamics along gradients of land intensification is critical to guide conservation goals towards improvements in soil carbon (C) and nitrogen (N) storage. In this study, we clarified (a) how the C and N concentrations within SOM fractions of distinct ecological relevance responded to soil management representing a cropland‐grassland gradient and (b) how these operationally defined fractions affected soil physicochemical and biological properties. We compared sites with annual row crop rotations with and without cover crops (i.e. cropland soils) with perennial grassland sites (i.e. reference soil) by sampling near‐surface soils from statewide on‐farm cover crop experiments replicated across four agro‐ecoregions in Midwest USA. Soil management had a significant main effect on C and N content in SOM fractions, but responses were site‐ and fraction‐specific. We found that C content of free particulate organic matter and water‐extractable organic matter (WEOM) of reference soils were 58%–76% and 31%–59% greater than those of the cropland soils in two of the four sites. Differences in N content of WEOM because of soil management were observed in two of the four sites. These reference soils had between 40% and 60% greater N than cropland soils. Additionally, the N content of aggregate occluded POM (o‐POM) of reference soils was three times greater than those of the cropland soils in one of the four sites. Broadly across bulk and SOM fractions, high declines in cropland C and N relative to reference soils were observed in non‐irrigated and strip‐till sites and coarse‐texture soils. Free and o‐POM C and N were strongly associated with aggregate stability, water infiltration and enzyme activity, whereas C and N contents of WEOM and MAOM were correlated with soil's ability to hold onto essential nutrients (e.g. calcium, magnesium, potassium and sodium). Although the potential of cover crops to drive changes on ecologically meaningful SOM fractions is less pronounced in the short (3 year) term, the findings demonstrate the potential of continuous living cover as an approach to agroecosystem design to improve soil functions closely related to SOM characteristics.

The local atomic and electronic structure of quasicrystal i-Al65Cu23Fe12 powder

This work presents an experimental and theoretical study of the atomic and electronic structures of the icosahedral Al65Cu23Fe12 quasicrystalline (QС) powder. The i-Al65Cu23Fe12 QС powder was investigated using X-ray diffraction, scanning electron microscopy, Mössbauer spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS) and X-ray photoelectron spectroscopy. It was found that the i-Al65Cu23Fe12 quasicrystal surface consisted of an oxidized shell of Al2O3 and Cu2O, whereas the bulk fraction consisted of icosahedral Al65Cu23Fe12 quasicrystal and cubic β-Al(Cu0.5Fe0.5) phases. The proposed theoretical model of the structure of i-Al65Cu23Fe12 QC, based on the transformation of the crystalline analogue of Al7Cu2Fe, has good agreement with the experimental structural data obtained from EXAFS and XANES analysis. The electronic structure of the top of the valence band and the bottom of the conduction band of the i-Al65Cu23Fe12 QC was investigated using X-ray photoelectron spectroscopy, analysis of XANES, and ab initio calculations.

Characterization of multiphase flow through Venturi nozzle using gamma-ray tomography

Venturi-based differential pressure flow meters have proven to be robust and well suited to measure the flowrate of multiphase flow in combination with other measurement techniques. However, important challenges remain in order to reduce the effect of flow regime dependent measurement uncertainties from non-homogeneous flow.Understanding the complexities of multiphase flow through a Venturi is critical, not only for the Venturi flow measurement but also for the potential implications it might have on adjacent measurements affected by the constriction-induced flow perturbations.In this study, we examine the evolution of multiphase flow through a vertically oriented Venturi situated downstream of a T-bend, with a particular emphasis on the effects this might have on associated measurements within a multiphase metering context. Using Gamma-ray tomography, we conducted measurements at the inlet, throat, outlet, and downstream of the Venturi across a wide range of flow rates and Gas Volume Fractions (GVFs). We evaluated gas fraction (GF), slip, and cross-sectional distribution, quantified using measures of asymmetry and annularity.Our findings suggest that deviations between GF and GVF, relative slip velocity, annularity, and asymmetry are generally less at the outlet and downstream of the Venturi compared to the inlet and throat. Notably, annularity exhibits a greater impact than asymmetry on the estimation of bulk fractions from cord measurements.Overall, the study suggests that there may be more favorable conditions for measurements that require a homogeneous mix and less difference between GF and GVF at the outlet or a short distance downstream of the Venturi. However, despite the inlet results showing larger deviations due to inhomogeneous flow compared to the outlet and downstream, these results demonstrate a more predictable pattern in line with predictive models, offering potential benefits for the application of corrective models.

Dissolved organic matter promoted hydroxyl radical formation and phenanthrene attenuation during oxygenation of iron-pillared montmorillonites

The oxygenation of Fe(II)-bearing minerals for hydroxyl radicals (HO•) formation and contaminant attenuation receives increasing attentions. However, information on dissolved organic matter (DOM) with different types, concentrations, and molecular weights (MWs) in manipulating HO• formation and contaminant attenuation during mineral oxygenation remain unclear. In this study, four iron-pillared montmorillonites (IPMs) and two DOM samples [e.g., humic acids (HA) and fulvic acids (FA)] were prepared to explore the HO• formation and phenanthrene attenuation during the oxygenation of IPMs in the presence or absence of DOMs. Results showed that iron-pillared and high-temperature calcination procedures extended the interlayer domain of IPMs, which provided favorable conditions for a high HO• production from 1293 to 14537 μmol kg−1. The surface-absorbed/low crystalline Fe(Ⅱ) was the predominant Fe(Ⅱ) fractionations for HO• production, and presence of DOMs significantly enhanced the HO• production and phenanthrene attenuation. Moreover, regardless of the types and concentrations, the low MW (LMW, <1 kDa) fraction within DOM pool contributed highest to HO• production and phenanthrene attenuation, followed by the bulk and high MW (HMW-, 1 kDa∼0.45 μm) fractions, and FA exhibited more efficient effects in promoting HO• production and phenanthrene attenuation than HA. The fluorescent spectral analysis further revealed that phenolic-like fluorophores in LMW-fraction were the main substances responsible for the enhanced HO• production and phenanthrene attenuation. The results deepen our understandings toward the behaviors and fate of aquatic HO• and contaminants, and also provide technical guidance for the remediation of contaminated environments.

The H content of aubrites: An evaluation of bulk versus in situ methods for quantifying water in meteorites

Aubrites and enstatite chondrites (ECs) are isotopically similar to the Earth and therefore may resemble the primary materials that accreted to form our planet. Recent bulk H elemental and isotopic analyses of ECs and the Norton County aubrite suggest that enstatite-rich materials are H-rich and may represent a significant source of terrestrial water, with measured values of 3000±2000 μg/g H2O and 5300±900 μg/g H2O in the bulk and enstatite fractions of Norton County (Piani et al., Science, 2020). Here, we present a detailed investigation of in situ H2O concentrations in enstatite, diopside, forsterite, and plagioclase from a suite of main group aubrites, including Norton County, and Shallowater. We find that enstatite (4±2 μg/g H2O), diopside (4.8±0.5 μg/g H2O), and forsterite (5±3 μg/g H2O) have similar H2O concentrations, and all are significantly lower than plagioclase (24±3 μg/g H2O). We combine our in situ analyses of H2O contents with equilibrium partition coefficients and bulk mineralogies to estimate the bulk H2O content of our samples. We compare these first order estimates with bulk volatile analyses conducted using sample pyrolysis and find that the previous bulk H2O analyses of aubrites predominantly reflect terrestrial contamination and alteration. If our conclusion that the reported bulk H2O analyses of Norton County primarily reflect terrestrial contamination and alteration extends to bulk analyses of ECs, then EC-like material may not be a significant source of terrestrial water. Our results support the hypothesis that thermal metamorphism, melting, and differentiation leads to efficient desiccation of planetesimals relative to chondrites, and that differentiated planetesimals contributed, at most, trace amounts to Earth's water budget.

Distributions of trace elements within MSWI bottom and combined ash components: Implications for reuse practices

Concentrations of 25 inorganic elements were measured in both bulk ash and individual ash components from residuals at three municipal solid waste incineration (MSWI) facilities in the US (two combined ash (CA) and one bottom ash (BA)). Concentrations were assessed based on particle size and component to understand the contribution from each fraction. The results found that among facilities, the finer size fractions contained elevated concentrations of trace elements of concern (As, Pb, Sb) when compared to the coarse fraction, but concentrations varied among facilities depending on the type of ash and differences in advanced metals recovery processes. This study focused on several constituents of potential concern, As, Ba, Cu, Pb, and Sb, and found that the main components of MSWI ash (glass, ceramic, concrete, and slag) are sources of these elements in the ash streams. For many elements, concentrations were significantly higher in CA bulk and component fractions opposed to BA streams. An acid treatment procedure and scanning electron microscopy/energy-dispersive x-ray spectroscopy analysis revealed that some elements, such as As in concrete, are result of the inherent properties of the component, but other elements, such as Sb, form on the surface during or after incineration and can be removed. Some Pb and Cu concentrations were attributed to inclusions in the glass or slag introduced into the material during the incineration process. Understanding the contributions of each ash component provides critical information for developing strategies to reduce trace element concentrations in ash streams to promote reuse opportunities.

Coupling fluorescent probes to characterize S-containing compounds in a sulfate reducing bacteria involved in Hg methylation

The microbial methylation of inorganic mercury Hg(II) is governed by S-containing compounds such as thiols (RSH) and sulfides (S2−). Various S-containing molecules in an environmental or culture medium can be difficult to assess because of the complexity of the medium, poor stability, and low concentration ranges of sulfide and thiol compounds. Here, we applied two fluorescence spectroscopy-based methods using α, β-unsaturated ethanoylcoumarin fluorophore (DHC) for the quantification of sulfides, and monobromo (trimethylammonio) bimane (qBBr) to quantify total thiol concentrations (in extracellular and bacterial cell fractions). The potential interferences of both organic and inorganic compounds from the matrix were evaluated. In the presence of Hg species, both methods allowed the quantification of free sulfides or thiols (not forming complexes with Hg). The two methods were highly sensitive, with detection limits of 100 nM and 20 nM for thiols and sulfides, respectively. They also exhibited high selectivity for the detection of thiols or sulfides against other tested matrix compounds. Finally, both methods were applied to characterize S-containing compounds in a culture of Pseudodesulfovibrio hydrargyri strain BerOc1, a methylating sulfate-reducing bacterium (SRB) exposed to 0.1 mM of cysteine. During bacterial growth, we used (i) DHC probe to quantify sulfide concentration in the bulk fraction, (ii) qBBr for total extracellular thiols and total thiols adsorbed on the cells, and (iii) liquid chromatography-tandem mass spectrometry to track cysteine degradation and characterize other thiols. The time series until the end of BerOc1 growth showed biodegradation of cysteine, and biosynthesis of sulfides and other thiol compounds.

Insight into the Gluten-Free Dough and Bread Properties Obtained from Extruded Rice Flour: Physicochemical, Mechanical, and Molecular Studies

The present study aimed to evaluate the effect of the extrusion process and particle size on the properties of rice flour (microstructure, pasting properties), gluten-free dough (rheological properties), and bread (texture, specific volume, water absorption capacity, low-field nuclear magnetic resonance (LF NMR) relaxometry). Rice flours were extruded at 80 and 120 °C with feed moisture (15 and 30%) and with the same particle size (&lt;132 and &gt;132–200 µm). Significant differences were observed between the pasting profiles of the flours before and after extrusion. The pasting profile of extruded flours confirmed that hydrothermal treatment partially gelatinized the starch, decreasing the viscosity during heating. The water binding properties increased with the extrusion temperature and moisture content and also with the particle size of the flour. The most important parameter influencing the mechanical properties of the dough was the moisture content of the flour and significant differences were observed between fine (&lt;132 μm) and coarse flours (&gt;132–200 μm). The molecular dynamics of particles containing protons in the bound and bulk fractions in each sample do not depend on the extruder parameters or granulation of the obtained fraction. LF NMR results confirmed that extrusion of rice flour led to a significant decrease in the T21 value compared to the control sample and an increase in the T22 value in breads made with flours with particle size &lt;132 μm. A linear relationship was found between the spin-spin relaxation times (T1) changes and the equilibrium water activity (ar). The results showed that bread with extruded rice flour at the same die temperature resulted in a significantly higher bread volume (31%) and lower hardness (27%) compared to the control. The highest hardness was observed in the case of samples prepared with extruded flour with the addition of 15% moisture, regardless of temperature and particle size.

Distribution, chemical speciation and human health risk assessment of metals in soil particle size fractions from an industrial area

The problem associated with metal contamination in the soil is intensified in the vicinity of industrial areas as they are more susceptible to discharges from medium to small scale industries. However, limited studies are available that consider soil size fractions along with their speciation due to multi metal contamination. This information is essential to apprehend their individual and competitive mobility, bioavailability and possible de-contamination strategies. In the present study, soil samples (n = 10) were collected from Ranipet industrial area, India and analysed for total metal concentrations (Al, Cd, Cr, Cu, Fe, Mn, Pb, and Zn). The ecological risk assessment indicated substantial anthropogenic enrichment of chromium along with moderate enrichment of copper, manganese and zinc. Further, the samples were fractionized into 300–150, 150–50, 50–22 and < 22 µm; the finer fraction concentrations were used to assess human health risks. The Hazard Index (HI) values reached 2.37 for children and 0.30 in adults from non-carcinogenic risk; indicated children are at higher risk. The soil exposure risk assessment study in three different scenarios were considered; results indicated possible non-carcinogenic risk to the non-residents working in study area. The Cancer risk (CR) values followed the order CR (ingestion) > CR (dermal contact) > CR (inhalation). The speciation study performed in bulk and size fractions indicated the bioavailable forms dominated residual fractions irrespective of sizes but varied with metals. This study can be considered as a framework for risk identification and assessment from multi metal contamination in industrial area having small and shallow waterbodies.

Effect in soil and rhizosphere microbiota of Brachiaria inoculated with Azospirillum brasilense: a pilot trial in two Oxisol types

Context The Brachiaria genus includes several species of pastures distributed in tropical and subtropical regions. Plant growth-promoting bacteria (PGPB), such as Azospirillum brasilense, have been used as inoculants to increase crop production. Aims This study explored the effect of A. brasilense on Brachiaria seedlings, rhizosphere, and soil. Methods We inoculated A. brasilense on Brachiaria seeds sown in two types of soil mainly varying in texture (medium texture-Mt and clayey-C soils). We then collected the rhizosphere to evaluate the microbiota adhered to the plants by high-throughput 16S sequencing using bioinformatic tools. Shoot and root biomass were also evaluated. Key results Inoculation increased the aerial biomass of Brachiaria plants. However, it did not increase root biomass. Soil texture is a critical element in shaping rhizosphere communities. A. brasilense decreased the abundance of Firmicutes, mainly in C Oxisols. Network analysis showed that Proteobacteria, Acidobacteria, Actinobacteria, Firmicutes, and Bacteroidetes were the main phyla in the vicinity of Brachiaria roots. Furthermore, the abundance of specific phyla, such as Armatimonadetes, Tenericutes, and Fusobacteria (Mt) and Latescibacteria, Rokubacteria, and WS2 (C) increased in the bulk fraction. In the rhizosphere, Chlamydiae was exclusively related to Mt Oxisols. By contrast, Verrumicrobia and Fusobacteria were only found in the C soils. Conclusions Relative abundance of Acidobacteria and Actinobacteria increased after inoculation in the rhizosphere of both types of Oxisols. Implications These results indicate that inoculation can affect Brachiaria plants and their rhizospheric bacterial communities. The effect of taxonomic groups altered through inoculation and the relationship between the functional capacities of each group within the microbiota are yet to be elucidated.

Plant-growth promotion by biochar-organic amendments mixtures explained by selective chemicals adsorption of inhibitory compounds

Biochar is known to promote plant growth and is marketed worldwide as a soil amendment. However, benefits of pure biochar on crop yields are, in some cases, limited, while its mixture with non-pyrogenic organic amendments (NPOAs) has a more consistent stimulatory effect. Here, we studied the biochar effect together with three NPOAs (fishmeal, Medicago, and maize straw) used alone and in all possible combinations on the growth of lettuce (Lactuca sativa), soybean (Glycine max), maize (Zea mays), and rice (Oryza sativa). The bulk fraction of organic materials was characterized by 13 C-CPMAS NMR spectroscopy and the liquid fraction by liquid chromatography-mass spectrometry (LC-MS). Biochar and NPOAs showed different effects, ranging from inhibition to strong stimulation of crops. For NPOAs, the major inhibitory effects were found in undecomposed materials, especially fishmeal with a low C/N ratio and a high nitrogen. The effect of the mixture depended on the chemical quality of the NPOAs and the target species, with fishmeal having a common synergistic effect on soybean and lentils. 13C-CPMAS NMR showed major changes in the bulk fraction of biochar-NPOA mixtures enriched in carbonyl C, alkyl C, and O-alkyl C types. Moreover, LC-MS showed a large effect of biochar in the liquid fraction by selective adsorption of many putative chemical compounds, especially when mixed with fishmeal and Medicago straw. This approach clarifies for the first time that biochar extensively adsorbs a number of organic compounds from the NPOA feedstock, which not only causes significant detoxification but also triggers remarkable biostimulation of plant growth.

A study of peatland-derived dissolved organic matter from headstream to sea using multiple analytical tools.

The River Thurso, North Scotland, receives substantial terrestrial deliveries of dissolved organic matter (DOM) leached from Europe's most extensive blanket bogs. The relatively short distance between peatlands and coastal ocean offers potential for research to investigate source-to-sea processing of terrigenous dissolved organic carbon (DOC). Here, we determined DOC concentrations in the bulk (< 0.4μm), truly dissolved (< 5kDa), and colloidal fraction (5kDa - 0.4μm) as well as DOM absorbance and fluorescence spectra during two river catchment surveys and two corresponding coastal plume surveys, in early spring (1st sampling period) and late spring (2nd sampling period). DOC concentrations ranged from 79 to 3799μM in early spring and from 115 to 5126μM in late spring. DOM exhibited conservative mixing across the plume in both surveys, but the plume extended further offshore in the second survey due to a pulse of freshwater caused by recent rainfall. Fluorescence excitation-emission matrices (EEMs) and fluorescence indices revealed that the flushed DOM was humic-like, recently synthesized DOM. Coupled with C/N ratio analyses and molecular weight fractionation, the fluorescence indices also provided evidence for the gradual altering of DOM characteristics along the bog - headstream - loch - river continuum. The same analytical tools revealed that seasonal variations occurred within the DOM pool of marine origin, i.e., greater abundance of low-molecular weight bacterial or algal DOM in the late spring survey. The time scale of such variations relative to the flushing time of water through the aquatic continuum should be taken into account when interpreting the DOM property-salinity distributions of major river plumes.

A coupled model for phase mixing, grain damage and shear localization in the lithosphere: comparison to lab experiments

SUMMARYThe occurrence of plate tectonics on Earth is rooted in the physics of lithospheric ductile weakening and shear-localization. The pervasiveness of mylonites at lithospheric shear zones is a key piece of evidence that localization correlates with reduction in mineral grain size. Most lithospheric mylonites are polymineralic and the interaction between mineral phases, such as olivine and pyroxene, especially through Zener pinning, impedes normal grain growth while possibly enhancing grain damage, both of which facilitate grain size reduction and weakening, as evident in lab experiments and field observations. The efficacy of pinning, however, relies on the mineral phases being mixed and dispersed at the grain scale, where well-mixed states lead to greater mylonitization. To model grain mixing between different phases at the continuum scale, we previously developed a theory treating grain-scale processes as diffusion between phases, but driven by imposed compressive stresses acting on the boundary between phases. Here we present a new model for shearing rock that combines our theory for diffusive grain mixing, 2-D non-Newtonian flow and two-phase grain damage. The model geometry is designed specifically for comparison to torsional shear-deformation experiments. Deformation is either forced by constant velocity or constant stress boundary conditions. As the layer is deformed, mixing zones between different mineralogical units undergo enhanced grain size reduction and weakening, especially at high strains. For constant velocity boundary experiments, stress drops towards an initial piezometric plateau by a strain of around 4; this is also typical of monophase experiments for which this initial plateau is the final steady state stress. However, polyphase experiments can undergo a second large stress drop at strains of 10–20, and which is associated with enhanced phase mixing and resultant grain size reduction and weakening. Model calculations for polyphase media with grain mixing and damage capture the experimental behaviour when damage to the interface between phases is moderately slower or less efficient than damage to the grain boundaries. Other factors such as distribution and bulk fraction of the secondary phase, as well as grain-mixing diffusivity also influence the timing of the second stress drop. For constant stress boundary conditions, the strain rate increases during weakening and localization. For a monophase medium, there is theoretically one increase in strain rate to a piezometric steady state. But for the polyphase model, the strain rate undergoes a second abrupt increase, the timing for which is again controlled by interface damage and grain mixing. The evolution of heterogeneity through mixing and deformation, and that of grain size distributions also compare well to experimental observations. In total, the comparison of theory to deformation experiments provides a framework for guiding future experiments, scaling microstructural physics to geodynamic applications and demonstrates the importance of grain mixing and damage for the formation of plate tectonic boundaries.

Trace Metal Enrichment in the Colloidal Fraction in Soils Developing on Abandoned Mine Spoils

The release of colloid-bound trace metals from abandoned coal mine spoils can potentially be a significant source of contamination during weathering. We examined the size-dependent enrichment of trace metals in mine spoil samples using centrifugation and acid extraction to compare metal loading in the bulk and colloid fractions. A combination of X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), and focused ion beam (FIB) sectioning of selected colloids for transmission electron microscopy (TEM) analyses was used to determine the morphology and elemental and mineral composition at the micro- and nanoscales. In contrast to bulk soils, primary Fe-sulfides (up to 11%) and secondary Fe(III)-bearing phases (up to 5%) were a significant portion of the colloid mineralogy. Secondary Fe-(hydro)oxides and (hydroxy)sulfates were enriched with Mn, Ni, Cu, and Zn, and these metals showed stronger correlations with Fe in the colloid fraction (R2 of 0.58, 0.77, 0.94, and 0.81, respectively) than in the bulk fraction (R2 of 0.40, 0.09, 0.84, and 0.62, respectively), indicating that Fe-bearing colloids are likely major trace-metal-bearing phases. The results from this study will help to design better remediation projects for abandoned mine spoils to better account for a potentially underappreciated mode of contaminant transport.

Quantification of the aeolian sand source in the Ulan Buh Desert using the sediment source fingerprinting (SSF) method within MixSIAR modelling framework

Identifying and quantifying source contributions of aeolian sands in desert where extensive dunes and paleo-lakes coexist is crucial to elucidate the formation mechanism of aeolian and lacustrine landforms in the earth system. In this study, we identified the aeolian sediment sources in the Ulan Buh Desert (UBD) using geomorphological and sedimentological methods, and further quantified the source contributions via the sediment source fingerprinting (SSF) method within MixSIAR modelling framework. Our results revealed that the mean contribution from each source to the UBD sediments were assessed to be 32.2 % for detrital deposits weathered and eroded from the Helan Mountains (HLM), Bayan Urals Mountains (BUM), and Langshan Mountains (LM), 26.2 % for aeolian and Gobi deposits from the adjacent Yamalik Desert (YMD) and Bayin Wendur Desert (BWD), 26.1 % for aeolian and Gobi sediments from the upwind Badain Jaran Desert (BJD), and 15.5 % for the paleo-lacustrine sediments in the UBD. The bulk fraction sands in the UBD are mainly contributed by detrital deposits from its surrounding mountains, whereas the fine sands are supplied by the upwind deserts of the UBD. As shown by the dunes migration rate (averaged 9.1 m/yr) and direction (averaged 118.3°) in the YMD, sands from upwind desert can be easily transported to the adjacent downwind desert, i.e., the UBD. Therefore, much attention should be paid to their role in sediment source contribution rather than ignore them for their limited area. Similarly, although the sediment source contribution from paleo-lacustrine deposits within the desert is relatively small, they served as a direct source for the UBD. The GOF evaluation demonstrated that the MixSIAR Bayesian model is an effective approach to aid aeolian sediment fingerprinting. In addition, we found that the aeolian sediments in the UBD is the combined results of wind and fluvial systems.

Biochar and Compost Application either Alone or in Combination Affects Vegetable Yield in a Volcanic Mediterranean Soil

The aim of this work was to compare the application of biochar, compost, and their mixtures on soil fertility and crop yields using a volcanic Mediterranean soil. For this reason, three types of organic amendments (OAs) were selected: compost1, made from olive mill waste and orchard pruning residues; compost2, made from olive mill waste, animal manure and wool residues; and biochar made from beech wood pyrolyzed at 550 °C. When selected, the OAs were characterized chemically for organic carbon (OC), total N, pH, electric conductivity (EC) and the bulk fraction of organic matter using 13C CPMAS NMR spectroscopy. In addition, soil chemistry was analysed at the end of each year for the following parameters: pH, OC, total N, CaCO3, P2O5, NH4, FDA and EC. Results showed that biochar had the highest OC and the lowest N and EC compared to both composts. Moreover, 13C CPMAS NMR showed that biochar had the lowest content of O-alkyl, methoxyl- and alkyl-C and the highest content of aromatic-C. On the other hand, compost2 and compost2+biochar mixture reduced Aubergine yield by −60% and −40%, respectively, and tomato yield by −50% and −100%, respectively. Nevertheless, a significant increase in onion and rape yields were observed when compost1, compost1+biochar and compost2 were applied, while biochar and compost2+biochar significantly decreased the yield of these crops. Overall, our results highlight that the effect of OAs on crops yield is largely variable and influenced by the interaction with soil chemistry.

The dynamic formation process of the CB chondrite Gujba

The many unique characteristics of CB chondrites have resulted in the impact hypothesis becoming the favoured model for their formation. Here, we further investigate the formation mechanisms of CB chondrites by analysing the elemental and K isotope compositions of chondrules and bulk fractions from the CBa chondrite Gujba. Similar to previous work, the refractory element ratios in the Gujba chondrules show evidence of a differentiated precursor, with the Nb/Ta, Zr/Hf, Sc/Th and Zr/Th ratios showing fractionation relative to other chondrites. In addition, the bulk fractions, and to a lesser extent the chondrules with attached matrix and metals, display significantly more refractory element fractionation and a large enrichment in light REEs. Based on EDS elemental mapping and comparisons with previous studies, the most likely source of this highly fractionated material appears to be the small amount of heterogeneously distributed interstitial fine-grained material within Gujba. These large refractory element fractionations (i.e., Nb/Ta, Zr/Hf, Sc/Th Zr/Th, and LREE/HREE) are best explained by a significant partial melting process such as crustal formation. Nevertheless, the mechanism of patrial melting cannot be conclusively determined with the data available here. The K isotopic compositions of the Gujba chondrules analyzed here range from −2.24‰ to −0.41‰ in δ41K, whereas the bulk analyses show δ41K values of −0.81‰ to −0.72‰. This range of chondrule K isotope compositions is significantly larger, and extends to much lighter compositions, compared to all other chondrites measured so far by bulk ICP-MS. In addition, the Gujba chondrules display a clear negative correlation of K isotopic composition with K concentration, with the chondrules showing the lightest K isotope compositions having the highest K concentrations. This distinctive correlation indicates that evaporation was likely the dominant process affecting the K isotopic variation observed in the Gujba chondrules. Nevertheless, the extremely light δ41K values seen in the most K-rich chondrules (which are lighter than any other early solar system material so far measured) indicate that incomplete condensation likely took place before evaporation. As such, we propose a two-stage model to explain the formation of chondrules in Gujba, with Stage 1 characterized by incomplete condensation of vaporized material with an average isotopic fractionation factor (α) of 0.9984 (when using the most K enriched chondrule to constrain the model), and Stage 2 representing partial evaporation in a vapor plume with an average α range of 0.9976 to 0.9990. Using these α values we calculate an approximate vapor saturation index value of 0.935 for condensation and between 0.903 and 0.960 for evaporation. This formation process requiring both condensation and evaporation for CB chondrules is consistent with an impact generated vapor plume and further expands our understanding of CB chondrite formation.