Redox-driven changes in the distribution of Fe minerals between aggregate-size classes in illuvial and elluvial horizons of a hydromorphic soil

2021 ◽  
Author(s):  
Beatrice Giannetta ◽  
Danilo Oliveira De Souza ◽  
Giuliana Aquilanti ◽  
Daniel Said Pullicino
Keyword(s):  
Particle Size ◽  
Clay Fraction ◽  
Aggregate Size ◽  
Redox Cycling ◽  
Paddy Soils ◽  
Organic C ◽  
X Ray ◽  
Size Classes ◽  
Particle Size Classes

<div> <p><span>Paddy soils experience long-term redox alternations affecting the interactions between the biogeochemical cycling of iron (Fe) and carbon (C). Although the higher soil organic matter (SOM) accumulation rates in paddy topsoils with respect to non-paddy soils is generally assumed to be due to limited mineralization under anoxic soil conditions resulting from frequent field flooding, there is growing evidence questioning this assumption. Moreover, differences in particle aggregation and SOM turnover are likely to both affect and be affected by the trajectory of Fe mineral evolution/crystallinity with redox fluctuations. We hypothesized that redox cycling in paddy soils will affect the particle aggregation, the distribution and mineralogy Fe (hydr)oxides between aggregate size fractions, and consequently the mechanisms of SOM stabilization. In particular, we expect finer aggregate and particle size classes to have a higher proportion of short-range ordered (SRO) Fe oxides with respect to larger aggregates under paddy management, compared to non-paddy management, and that paddy management can result in lower amounts of Fe(hydr)oxides in the topsoil with respect to non-paddy soils. </span><span> </span></p> </div><div> <p><span>We tested these hypotheses by evaluating mineralogical changes, and the distribution of Fe species and organic C between different aggregate and particle-size fractions in topsoil (eluvial) and subsoil (illuvial) horizons of soils under long-term paddy (P) horizons (Arp1, Arp2, Arpd, Brd1, Brd2) and non-paddy (NP) horizons (Ap1, Ap2, Bgw) in NW Italy. Soil aggregates (microaggregates: <200 </span><span>μ</span><span>m, free silt: (53-2 </span><span>μ</span><span>m), free clay: <2 </span><span>μ</span><span>m, and, after sonication, fine sand, silt and clay within microaggregates) have been obtained from</span><span>bulk soils using an aggregate and particle size physical fractionation method. After fractionation, Fe phases were evaluated by selective extraction procedures, X-ray diffraction (XRD) and Fe K-edge extended X-ray fine structure (Fe EXAFS) spectroscopy (Elettra XAFS beamline). </span></p> </div><div> <p>Our results indicate: (1) a <span>depletion in the contents of ferrihydrite in the P topsoil horizons with respect to NP, though redox cycling favoured an increase in ferrihydrite in the P subsoil, possibly due to Fe(II) translocation from topsoil to subsoil, with consequent ferrihydrite precipitation and aggregates formation; </span>(2) more crystalline Fe mineral phases were associated with intra-aggregate clay fraction in the P topsoil<span>. In the clay fraction in the Brd2 subsoil horizon </span>magnetite was observed. <span>In the NP soil the illuvial horizons were not characterized by a significant increase in ferrihydrite. Our hypothesis that finer aggregate and particle size classes have a higher proportion of SRO Fe oxides with respect to larger aggregates under P management, with respect to NP management, </span>was confirmed; (3) more organic C was associated with the fine fraction in P with respect to NP suggesting that redox cycling enhances the chemical stabilization of mineral-associated SOM.</p> </div><div> <p>These findings focused on localized Fe dynamics and biogeochemical coupling with SOM, suggesting that <span>redox-driven changes in aggregate-size classes distribution were also linked to the differences in organic C and Fe stocks in these two agro-ecosystems.</span></p> </div>

Carbon flows by soil organic matter formation: A review based on 13C natural abundance

2020 ◽  
Author(s):  
Anna Gunina ◽  
Yakov Kuzyakov
Keyword(s):  
Particle Size ◽  
Organic Matter ◽  
Aggregate Size ◽  
Climatic Conditions ◽  
Natural Abundance ◽  
Density Fractions ◽  
Size Classes ◽  
Microbial Utilization ◽  
Particle Size Classes ◽  
Organic Particles

<p>Aggregation of mineral and organic particles is a key process of soil development, which promotes carbon (C) stabilization by hindering decomposition of plant and microbial residues. All microbial utilization and C stabilization processes lead to <sup>13</sup>C fractionation and consequently to various δ<sup>13</sup>C values of organic matter in aggregate size classes, sand, silt, and clay-sized particles, as well as density fractions. Differences in δ<sup>13</sup>C within the aggregates and density fractions may have two reasons: 1) preferential stabilization of organic compounds with light or heavy δ<sup>13</sup>C and/or 2) stabilization of organic materials after passing one or more microbial utilization cycles, leading to respiring of <sup>13</sup>C depleted CO<sub>2</sub> and heavier δ<sup>13</sup>C in remaining C. Assuming these two reasons, the new approach based on the natural differences in stable C isotopic composition between SOM fractions was proposed and tested on soils developed solely under C3 vegetation (arable, coniferous and deciduous forests) in boreal climate (Gunina and Kuzyakov, 2014). This approach assumes that: 1) <sup>13</sup>C enrichment between the SOM fractions corresponds to successive steps of SOM formation; 2) <sup>13</sup>C fractionation (but not the δ<sup>13</sup>C signature) depends mainly on the transformation steps and not on the C precursors. Consequently, <sup>13</sup>C enrichment of SOM fractions allows reconstructing the SOM formation pathways. To prove these initial results we reviewed  δ<sup>13</sup>C values of soils globally and focused on the i) estimation of the validity of this approach for soils developed under various climatic conditions and parent materials, and depending on fertilization, and ii) C flows not only between aggregate size classes and density fractions but also between various particle size classes of the soils (i.e. sand, silt, and clay) and iii) on revealing the intensities of natural <sup>13</sup>C fractionation during the stabilization of litter C in aggregates, particle size classes, and density fractions. Results showed that density fractions were <sup>13</sup>C enriched in the order: free particulate organic matter (POM) < light occluded POM < heavy occluded POM < mineral fraction, with the strongest increase between the light occluded and heavy occluded POM. The maximum <sup>13</sup>C fractionation during stabilization of litter C in density fractions and aggregate size classes was < 2‰. Δ<sup>13</sup>C enrichment of the SOM fractions showed that the main direction of C flows within the aggregates and SOM fractions was from the macroaggregate-free POM to the mineral microaggregate fraction. Thus, despite some limitations, δ<sup>13</sup>C natural abundance approach based on <sup>13</sup>C fractionation within individual steps of SOM formation is very useful and probably the sole approach to estimate C flows under steady-state without labeling.</p>

Quality of soil from the nickel mining area of Southeast Sulawesi, Indonesia, engineered using earthworms (Pheretima sp.)

2021 ◽  
Vol 8 (4) ◽  
pp. 2995-3005
Author(s):  
Hasbullah Syaf ◽  
Muhammad Albar Pattah ◽  
Laode Muhammad Harjoni Kilowasid
Keyword(s):  
Tap Water ◽  
Soil Aggregates ◽  
Aggregate Size ◽  
Mining Area ◽  
Size Class ◽  
Soil Conditions ◽  
Total N ◽  
Organic C ◽  
Size Classes ◽  
Nickel Mining

Earthworms (Pheretima sp.) could survive under abiotic stress soil conditions. Furthermore, their activities as ecosystem engineers allow for the creation of soil biostructures with new characteristics. Therefore, this study aimed to investigate the effect of the abundance of Pheretima sp. on the aggregate size, physicochemistry, and biology of the topsoil from the nickel mining area of Southeast Sulawesi, Indonesia. It was carried out by first grouping their abundance into zero, two, four, six, and eight individuals per pot and then carrying out tests. The Pheretima sp. were then released onto the surface of the topsoil and mixed with biochar that was saturated with tap water in the pot overnight. The results showed that the abundance of the species had a significant effect on the size class distribution, and aggregate stability of the soil. Furthermore, the size of the soil aggregates formed was dominated by the size class 2.83 - 4.75 mm under both dry and wet conditions. Under dry conditions, three size classes were found, while under wet conditions, there were five size classes. The results also showed that the highest and lowest stability indexes occurred with zero and eight Pheretima sp., respectively. Furthermore, the abundance had a significant effect on pH, organic C, total N, CEC, and total nematodes. However, it had no significant effect on the total P, C/N ratio, total AMF spores, and flagellate. The highest soil pH occurred with zero Pheretima sp., while with six and two members of the species, the total nematode was at its highest and lowest populations, respectively. Therefore, it could be concluded that the species was able to create novel conditions in the topsoils at the nickel mining area that were suitable for various soil biota.

scholarly journals Effects of Ultrasound on Zinc Oxide/Vermiculite/Chlorhexidine Nanocomposite Preparation and Their Antibacterial Activity

Nanomaterials ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 1309 ◽  
Author(s):  
Karla Čech Barabaszová ◽  
Sylva Holešová ◽  
Kateřina Šulcová ◽  
Marianna Hundáková ◽  
Barbora Thomasová
Keyword(s):  
Antimicrobial Activity ◽  
Particle Size ◽  
Zinc Oxide ◽  
Antibacterial Activity ◽  
Ultrasonic Treatment ◽  
Nanocomposite Materials ◽  
Hybrid Nanocomposite ◽  
X Ray Diffraction ◽  
X Ray

Microbial infection and biofilm formation are both problems associated with medical implants and devices. In recent years, hybrid organic-inorganic nanocomposites based on clay minerals have attracted significant attention due to their application potential in the field of antimicrobial materials. Organic drug/metal oxide hybrids exhibit improved antimicrobial activity, and intercalating the above materials into the interlayer of clay endows a long-term and controlled-release behavior. Since antimicrobial activity is strongly related to the structure of the material, ultrasonic treatment appears to be a suitable method for the synthesis of these materials as it can well control particle size distribution and morphology. This study aims to prepare novel, structurally stable, and highly antimicrobial nanocomposites based on zinc oxide/vermiculite/chlorhexidine. The influence of ultrasonic treatment at different time intervals and under different intercalation conditions (ultrasonic action in a breaker or in a Roset’s vessel) on the structure, morphology, and particle size of prepared hybrid nanocomposite materials was evaluated by the following methods: scanning electron microscopy, X-ray diffraction, energy dispersive X-ray fluorescence spectroscopy, carbon phase analysis, Fourier transforms infrared spectroscopy, specific surface area measurement, particle size analysis, and Zeta potential analysis. Particle size analyses confirmed that the ultrasonic method contributes to the reduction of particle size, and to their homogenization/arrangement. Further, X-ray diffraction analysis confirmed that ultrasound intercalation in a beaker helps to more efficiently intercalate chlorhexidine dihydrochloride (CH) into the vermiculite interlayer space, while a Roset’s vessel contributed to the attachment of the CH molecules to the vermiculite surface. The antibacterial activity of hybrid nanocomposite materials was investigated on Gram negative (Escherichia coli, Pseudomonas aeruginosa) and Gram positive (Staphylococcus aureus, Enterococcus faecalis) bacterial strains by finding the minimum inhibitory concentration. All hybrid nanocomposite materials prepared by ultrasound methods showed high antimicrobial activity after 30 min, with a long-lasting effect and without being affected by the concentration of the antibacterial components zinc oxide (ZnO) and CH. The benefits of the samples prepared by ultrasonic methods are the rapid onset of an antimicrobial effect and its long-term duration.

Modelling the influence of total suspended solids on E. coli removal in river water

2015 ◽  
Vol 73 (6) ◽  
pp. 1320-1332 ◽  
Author(s):  
Jueying Qian ◽  
Evelyn Walters ◽  
Peter Rutschmann ◽  
Michael Wagner ◽  
Harald Horn
Keyword(s):  
Particle Size ◽  
Large Scale ◽  
Suspended Solids ◽  
Total Suspended Solids ◽  
Sensitivity Coefficient ◽  
Fecal Indicator ◽  
E Coli ◽  
Size Classes ◽  
Sedimentation Process ◽  
Particle Size Classes

Following sewer overflows, fecal indicator bacteria enter surface waters and may experience different lysis or growth processes. A 1D mathematical model was developed to predict total suspended solids (TSS) and Escherichia coli concentrations based on field measurements in a large-scale flume system simulating a combined sewer overflow. The removal mechanisms of natural inactivation, UV inactivation, and sedimentation were modelled. For the sedimentation process, one, two or three particle size classes were incorporated separately into the model. Moreover, the UV sensitivity coefficient α and natural inactivation coefficient kd were both formulated as functions of TSS concentration. It was observed that the E. coli removal was predicted more accurately by incorporating two particle size classes. However, addition of a third particle size class only improved the model slightly. When α and kd were allowed to vary with the TSS concentration, the model was able to predict E. coli fate and transport at different TSS concentrations accurately and flexibly. A sensitivity analysis revealed that the mechanisms of UV and natural inactivation were more influential at low TSS concentrations, whereas the sedimentation process became more important at elevated TSS concentrations.

Semiquantitative Analysis by X-Ray Powder Diffraction (SQXRD) of the < 2 mm to 0.002 mm and < 0.002 mm Fractions of Soil

1988 ◽  
Vol 3 (3) ◽  
pp. 144-152 ◽  
Author(s):  
G. A. Raab
Keyword(s):  
Particle Size ◽  
Clay Fraction ◽  
Internal Standard ◽  
Xrd Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heat Treated ◽  
Freeze Dried ◽  
Strict Protocol ◽  
Attention To Detail

AbstractThe method described in this paper is a strict protocol for X-ray diffraction (XRD) analysis of mineral phases found in soils. Its application is not restricted to soils and is an attempt to standardize XRD sample preparation and analysis. The protocol requires the particle size of the < 2 mm - 0.002 mm fraction be reduced to 0.002 mm before analysis. In die qualitative section, the clay fraction ( < 0.002 mm particle size) is prepared as oriented slides. The suspended clay fraction is saturated with ethylene glycol, K +, and Mg+2; pipeted; air-dried; heat-treated at 110°C, 350°C, and 550°C; and X-rayed at each step in order to properly identify the clay minerals. In the quantitative section, the method employs a matrix-flushing agent, corundum (Al2O3). The corundum acts also as an internal standard, a calibration standard, and a reference standard. The suspended clay fraction is freeze-dried and corundum is added to each sample. Randomly oriented powder mounts are prepared from the < 2 mm - 0.002 mm fraction, and the < 0.002 mm fraction, and X-rayed. A series of reference standards are prepared based on the existing mineralogy, corundum is added, and each mixture is X-rayed. The software integrates the area under specific peaks (chosen for intensity and no overlap) in each sample, calculates the reference intensity ratios (RIRs) and calculates the percentage of each mineral based on the equation of Chung (1974). The attention to detail allows documentation and verification of the results yielding data of known quality.

scholarly journals Effects of reclamation years on composition and diversity of soil bacterial communities in Northwest China

2018 ◽  
Vol 64 (1) ◽  
pp. 28-40 ◽  
Author(s):  
Zhibo Cheng ◽  
Fenghua Zhang ◽  
William Jeffrey Gale ◽  
Weichao Wang ◽  
Wen Sang ◽  
...  
Keyword(s):  
Bacterial Communities ◽  
Phylogenetic Diversity ◽  
Aggregate Size ◽  
Soil Aggregate ◽  
Soil Electrical Conductivity ◽  
Soil Organic C ◽  
Organic C ◽  
Size Classes ◽  
Soil Bacterial Communities ◽  
Soil Bacterial

The objective of this study was to evaluate bacterial community structure and diversity in soil aggregate fractions when salinized farmland was reclaimed after >27 years of abandonment and then farmed again for 1, 5, 10, and 15 years. Illumina MiSeq high-throughput sequencing was performed to characterize the soil bacterial communities in 5 aggregate size classes in each treatment. The results indicated that reclamation significantly increased macro-aggregation (>0.25 mm), as well as soil organic C, available N, and available P. The 10-year field had the largest proportion (93.9%) of soil in the macro-aggregate size classes (i.e., >0.25 mm) and the highest soil electrical conductivity. The 5 most dominant phyla in the soil samples were Proteobacteria, Actinobacteria, Gemmatimonadetes, Acidobacteria, and Bacteroidetes. The phylogenetic diversity, Chao1, and Shannon indices increased after the abandoned land was reclaimed for farming, reaching maximums in the 15-year field. Among aggregate size classes, the 1–0.25 mm aggregates generally had the highest phylogenetic diversity, Chao1, and Shannon indices. Soil organic C and soil electrical conductivity were the main environmental factors affecting the soil bacterial communities. The composition and structure of the bacterial communities also varied significantly depending on soil aggregate size and time since reclamation.

Cultivation effects on dispersible clay of soil aggregates

1995 ◽  
Vol 75 (1) ◽  
pp. 101-107 ◽  
Author(s):  
L. G. Fuller ◽  
Tee Boon Goh ◽  
D. W. Oscarson
Keyword(s):  
Soil Aggregates ◽  
Aggregate Size ◽  
Exchange Capacity ◽  
Exchangeable Cations ◽  
Organic C ◽  
Size Fractions ◽  
Clay Dispersion ◽  
Native Prairie ◽  
Exchangeable Ca

The objective of this study was to examine the effect of long-term cultivation on clay dispersibility of four aggregate size fractions (2.0–9.5 mm, 0.85–2.0 mm, 0.25–0.85 mm, and < 0.25 mm) obtained from a Chernozemic soil by comparing two cultivated sites with an adjacent native prairie site. Aggregate size fractions (ASF) were subjected to increasing levels of ultrasonic energy and the amount of clay dispersed at each energy level was determined. Organic carbon, hexose carbon, soluble hexose C, total clay, cation exchange capacity (CEC), and exchangeable cations were measured for each ASF. Clay contained within prairie aggregates was held much more strongly within the aggregate and therefore showed greater stability towards dispersion by ultrasonic vibration. More energy was required to disperse one-half of the ASF clay under prairie than under cultivated soils (228–425, and 95–229 kJ L−1 for prairie and cultivated macroaggregates, respectively; 370–433, and 249–334 kJ L−1 for prairie and cultivated microaggregates, respectively). Clay dispersibility was significantly correlated with organic C, hexose C, soluble hexose C, non-hexose C, CEC, and exchangeable Ca and Mg but was not correlated with total ASF clay. Long-term cultivation of this soil resulted in a decrease in the energy required to disperse an equivalent proportion of clay from aggregates relative to that of the grassland soil. Thus, cultivation of these soils has resulted in aggregates which are more susceptible to clay dispersion and therefore prone to water erosion and surface crusting. Key words: Clay dispersion, aggregation, carbohydrate

scholarly journals Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

2017 ◽  
Vol 102 (2) ◽  
pp. 429-439 ◽  
Author(s):  
J. Hummel ◽  
F. Scheurich ◽  
S. Ortmann ◽  
L. A. Crompton ◽  
M. Gerken ◽  
...  
Keyword(s):  
Particle Size ◽  
Gastrointestinal Tract ◽  
Size Classes ◽  
Selective Retention ◽  
Particle Size Classes
Sign in / Sign up

Export Citation Format

Share Document