scholarly journals Three dimensional soil organic matter distribution, accessibility and microbial respiration in macro-aggregates using osmium staining and synchrotron X-ray CT

2016 ◽  
Author(s):  
Barry G Rawlins ◽  
Joanna Wragg ◽  
Christina Rheinhard ◽  
Robert C Atwood ◽  
Alasdair Houston ◽  
...  
Keyword(s):  
Organic Matter ◽  
Transition Probabilities ◽  
Solid Phase ◽  
Pore Space ◽  
Three Dimensional ◽  
Soil Core ◽  
Length Scales ◽  
X Ray ◽  
Mineral Phases ◽  
Indicator Variograms

Abstract. The spatial distribution and accessibility of organic matter (OM) to soil microbes in aggregates – determined by the fine-scale, 3-D distribution of organic matter, pores and mineral phases – may be an important control on the magnitude of soil heterotrophic respiration (SHR). Attempts to model SHR at fine scales requires data on the transition probabilities between adjacent pore space and soil OM, a measure of microbial accessibility to the latter. We used a combination of osmium staining and synchrotron X-ray CT to determine the 3-D (voxel) distribution of these three phases (scale 6.6 μm) throughout nine aggregates taken from a single soil core (range of organic carbon (OC) concentrations 4.2–7.7 %). Prior to the synchrotron analyses we had measured the magnitude of SHR for each aggregate over 24 hours under controlled conditions (moisture content and temperature). We test the hypothesis that larger magnitudes of SHR will be observed in aggregates with shorter length scales of OM variation (i.e. more frequent, and possibly more finely disseminated, OM and a larger number of aerobic microsites). After scaling to their OC concentrations, there was a six-fold variation in the magnitude of SHR for the nine aggregates. The distribution of pore volumes, pore shape and volume normalised surface area were similar for each of the nine aggregates. The overall transition probabilities between OM and pore voxels were between 0.02 and 0.03, significantly smaller than those used in previous simulation studies. We computed the length scales over which OM, pore and mineral phases vary within each aggregate using indicator variograms. The median range of models fitted to variograms of OM varied between 178 and 487 μm. The linear correlation between these median length scales of OM variation and the magnitudes of SHR for each aggregate was −0.42, providing some evidence to support our hypothesis. We require a larger number of observations to make a statistical inference. There was no evidence to suggest a statistical relationship between OM:pore transition probabilities and the magnitudes of aggregate SHR. The solid-phase volume proportions (45–63 %) of OM we report for our aggregates were surprisingly large by comparison to those assumed in previous modelling approaches. We suggest this requires further assessment using accurate measurements of OM bulk density in a range of soil types.

scholarly journals Three-dimensional soil organic matter distribution, accessibility and microbial respiration in macroaggregates using osmium staining and synchrotron X-ray computed tomography

SOIL ◽  
2016 ◽  
Vol 2 (4) ◽  
pp. 659-671 ◽  
Author(s):  
Barry G. Rawlins ◽  
Joanna Wragg ◽  
Christina Reinhard ◽  
Robert C. Atwood ◽  
Alasdair Houston ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Organic Matter ◽  
Transition Probabilities ◽  
Pore Space ◽  
Pearson Correlation ◽  
Soil Core ◽  
Length Scales ◽  
X Ray ◽  
Mineral Phases ◽  
X Ray Computed

Abstract. The spatial distribution and accessibility of organic matter (OM) to soil microbes in aggregates – determined by the fine-scale, 3-D distribution of OM, pores and mineral phases – may be an important control on the magnitude of soil heterotrophic respiration (SHR). Attempts to model SHR on fine scales requires data on the transition probabilities between adjacent pore space and soil OM, a measure of microbial accessibility to the latter. We used a combination of osmium staining and synchrotron X-ray computed tomography (CT) to determine the 3-D (voxel) distribution of these three phases (scale 6.6 µm) throughout nine aggregates taken from a single soil core (range of organic carbon (OC) concentrations: 4.2–7.7 %). Prior to the synchrotron analyses we had measured the magnitude of SHR for each aggregate over 24 h under controlled conditions (moisture content and temperature). We test the hypothesis that larger magnitudes of SHR will be observed in aggregates with (i) shorter length scales of OM variation (more aerobic microsites) and (ii) larger transition probabilities between OM and pore voxels. After scaling to their OC concentrations, there was a 6-fold variation in the magnitude of SHR for the nine aggregates. The distribution of pore diameters and tortuosity index values for pore branches was similar for each of the nine aggregates. The Pearson correlation between aggregate surface area (normalized by aggregate volume) and normalized headspace C gas concentration was both positive and reasonably large (r  =  0.44), suggesting that the former may be a factor that influences SHR. The overall transition probabilities between OM and pore voxels were between 0.07 and 0.17, smaller than those used in previous simulation studies. We computed the length scales over which OM, pore and mineral phases vary within each aggregate using 3-D indicator variograms. The median range of models fitted to variograms of OM varied between 38 and 175 µm and was generally larger than the other two phases within each aggregate, but in general variogram models had ranges  <  250 µm. There was no evidence to support the hypotheses concerning scales of variation in OM and magnitude of SHR; the linear correlation was 0.01. There was weak evidence to suggest a statistical relationship between voxel-based OM–pore transition probabilities and the magnitudes of aggregate SHR (r  =  0.12). We discuss how our analyses could be extended and suggest improvements to the approach we used.

Obvious and less obvious processes of aggregate formation in soil

2021 ◽  
Author(s):  
Hans-Jörg Vogel ◽  
Mar­ia Balseiro-Romero ◽  
Philippe C. Baveye ◽  
Alexandra Kravchenko ◽  
Wilfred Otten ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Structure ◽  
Solid Phase ◽  
Pore Space ◽  
Imaging Techniques ◽  
Mineral Soil ◽  
Aggregate Formation ◽  
Conceptual Approach ◽  
Soil Matrix ◽  
Biophysical Processes

&lt;p&gt;Soil structure, lately referred to as the ''architecture'' is a key to explain and understand all soil functions. The development of sophisticated imaging techniques over the last decades has led to significant progress in the description of this architecture and in particular of the geometry of the hierarchically-branched pore space in which transport of water, gases, solutes and particles occurs and where myriads of organisms live. Moreover, there are sophisticated tools available today to also visualize the spatial structure of the solid phase including mineral grains and organic matter. Hence, we do have access to virtually all components of soil architecture.&lt;/p&gt;&lt;p&gt;Unfortunately, it has so far proven very challenging to study the dynamics of soil architecture over time, which is of critical importance for soil as habitat and the turnover of organic matter. Several largely conflicting theories have been proposed to account for this dynamics, especially the formation of aggregates. We review these theories, and we propose a conceptual approach to reconcile them based on a consistent interpretation of experimental observations and by integrating known physical and biogeochemical processes. A key conclusion is that rather than concentrating on aggregate formation in the sense of how particles and organic matter reorganize to form aggregates as distinct functional units we should focus on biophysical processes that produce a porous, heterogeneous organo-mineral soil matrix that breaks into fragments of different size and stability when exposed to mechanical stress.&amp;#160; The unified vision we propose for soil architecture and the mechanisms that determine its temporal evolution, should pave the way towards a better understanding of soil processes and functions.&lt;/p&gt;

scholarly journals Reconstruction and Analysis of Tight Sandstone Digital Rock Combined with X-Ray CT Scanning and Multiple-Point Geostatistics Algorithm

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Yun Lei
Keyword(s):  
Pore Space ◽  
Full Range ◽  
Three Dimensional ◽  
Ct Scanning ◽  
Multiple Point ◽  
Tight Sandstone ◽  
Sandstone Sample ◽  
X Ray ◽  
Digital Rock ◽  
Experimental Values

Unconventional rocks such as tight sandstone and shale usually develop multiscale complex pore structures, with dimensions ranging from nanometers to millimeters, and the full range can be difficult to characterize for natural samples. In this paper, we developed a new hybrid digital rock construction approach to mimic the pore space of tight sandstone by combining X-ray CT scanning and multiple-point geostatistics algorithm (MPGA). First, a three-dimensional macropore digital rock describing the macroscopic pore structure of tight sandstone was constructed by micro-CT scanning. Then, high-resolution scanning electron microscopy (SEM) was performed on the tight sandstone sample, and the three-dimensional micropore digital rock was reconstructed by MPGA. Finally, the macropore digital rock and the micropore digital rock were superimposed into the full-pore digital rock. In addition, the nuclear magnetic resonance (NMR) response of digital rocks is simulated using a random walk method, and seepage simulation was performed by the lattice Boltzmann method (LBM). The results show that the full-pore digital rock has the same anisotropy and good connectivity as the actual rock. The porosity, NMR response, and permeability are in good agreement with the experimental values.

Direct observation of active material interactions in flowable electrodes using X-ray tomography

2017 ◽  
Vol 199 ◽  
pp. 511-524 ◽  
Author(s):  
Kelsey B. Hatzell ◽  
Jens Eller ◽  
Samantha L. Morelly ◽  
Maureen H. Tang ◽  
Nicolas J. Alvarez ◽  
...  
Keyword(s):  
Structural Properties ◽  
Structural Changes ◽  
Solid Phase ◽  
Active Material ◽  
Carbon Particle ◽  
Three Dimensional ◽  
Static Structure ◽  
Flow Process ◽  
X Ray ◽  
Biphasic Systems

Understanding electrical percolation and charging mechanisms in electrochemically active biphasic flowable electrodes is critical for enabling scalable deionization (desalination) and energy storage. Flowable electrodes are dynamic material systems which store charge (remove ions) and have the ability to flow. This flow process can induce structural changes in the underlying material arrangement and result in transient and non-uniform material properties. Carbon-based suspensions are opaque, multi-phase, and three dimensional, and thus prior characterization of the structural properties has been limited to indirect methods (electrochemical and rheology). Herein, a range of mixed electronic and ionically conducting suspensions are evaluated to determine their static structure, function, and properties, utilizing synchrotron radiation X-ray tomographic microscopy (SRXTM). The high brilliance of the synchrotron light enables deconvolution of the liquid and solid phases. Reconstruction of the solid phase reveals agglomeration cluster volumes between 10 μm3 and 103 μm3 (1 pL) for low loaded samples (5 wt% carbon). The largest agglomeration cluster in the low loaded sample (5 wt%) occupied only 3% of the reconstructed volume whereas samples loaded with 10 wt% activated carbon demonstrated electrically connected clusters that occupied 22% of the imaged region. The highly loaded samples (20 wt%) demonstrated clusters of the order of a microliter, which accounted for 63–85% of the imaged region. These results demonstrate a capability for discerning the structural properties of biphasic systems utilizing SRXTM techniques, and show that discontinuity in the carbon particle networks induces decreased material utilization in low-loaded flowable electrodes.

scholarly journals Quantitative determination of mineral matter in lignite by X-RAY spectrometry, using the Compton effect.

2016 ◽  
Vol 47 (4) ◽  
pp. 1645
Author(s):  
V. Perdikatsis
Keyword(s):  
Organic Matter ◽  
Absorption Coefficient ◽  
Quantitative Determination ◽  
Calorific Value ◽  
Matter Content ◽  
Compton Effect ◽  
Mineral Matter ◽  
X Ray ◽  
Mineral Phases

For the evaluation of lignite quality, apart from the calorific value, it is necessary to determine the mineral phases, which are deposited simultaneously with the organic matter during the formation of peat or formed epigenetically during the coalification stages. The mineral matter content is usually expressed as ash, after the combustion of lignite, and its determination is a quite time consuming process. In this paper an attempt is made for a fast and easy quantitative determination of mineral matter in lignite samples with unknown concentrations, with the use of an X-ray spectrometer and in particular the Compton effect of the X-ray tube. The intensity of the Compton peak is a function of the mass absorption coefficient of the lignite sample, which in turn depends on the type and amount of the mineral matter contained. Using this property of the Compton Effect, the percentage of mineral matter of lignite was determined. The method was verified by analyzing lignites with known concentrations of inorganic mater. The results of this study showed, that the mineral matter content can be determined, by the proposed method, fast and accurately without lignite combustion.

scholarly journals Petrophysical characterization of coquinas from Morro do Chaves Formation (Sergipe-Alagoas Basin) by x-ray computed tomography

2018 ◽  
Vol 18 (3) ◽  
pp. 3-13
Author(s):  
Aline Maria Poças Belila ◽  
Michelle Chaves Kuroda ◽  
João Paulo Da Ponte Souza ◽  
Alexandre Campane Vidal ◽  
Osvair Vidal Trevisan
Keyword(s):  
Computed Tomography ◽  
Pore Space ◽  
Three Dimensional ◽  
Petroleum Reservoirs ◽  
Self Organizing Maps ◽  
X Ray ◽  
The Neural Network ◽  
Rock Structure ◽  
X Ray Computed

Carbonate rocks constitute a large number of petroleum reservoirs worldwide. Notwithstanding, the characterization of these rocks is still a challenge due to their high complexity and pore space variability, indicating the importance of further studies to reduce uncertainty in reservoir interpretation and characterization. This work was performed for coquina samples from Morro do Chaves Formation (Sergipe-Alagoas Basin), analogous to important Brazilian reservoirs. Computed tomography (CT) was used for three-dimensional characterization of rock structure. The neural network named Self-Organizing Maps (SOM) was used for CT images segmentation. According to our tests, CT demonstrated to be a consistent tool for quantitative and qualitative analysis of heterogeneous pore space, by the evaluation of porosity, connectivity and the representative elementary volume.

Looking for soil structure

2021 ◽  
Author(s):  
Ulrich Weller
Keyword(s):  
Soil Structure ◽  
Solid Phase ◽  
Pore Space ◽  
Imaging Techniques ◽  
Structural Development ◽  
X Ray ◽  
Long Time ◽  
Space Dynamics ◽  
The Stability ◽  
Soil Forming Processes

&lt;p&gt;Ever since mankind has started to dig up the earth for planting, we are concerned with soil structure. For a long time digging the soil and breaking it into pieces was the only way to get insight into its architecture. Many valuable things were learned by this way: how the stability of the structure depends on the constituents, which soils are accessible for roots. To study the soil constituents in detail and in their natural ensemble has only begun about 90 years ago with the establishment of micromorphology. Thus, describing the soil by looking at its pieces has a 100 times longer history.&lt;/p&gt;&lt;p&gt;The new endeavor started with looking at the solid constituents of soil. The arrangement gave a new insight on processes, and enabled to describe the development of minerals, the activity of soil fauna and the diffusion of substances. It was in a rather descriptive manner that the light of microscope was shed on the soil structure.&lt;/p&gt;&lt;p&gt;With the introduction of X ray CT a new chapter was opened. Now it became possible to generate sufficient data for a quantitative analysis of the soil space. And with that the study of a new aspect of soil structure became feasible: the description of the pore space. Most of the functions of soil architecture are directly related to the pore space, thus a quantitative tool to describe this feature was required to understand the influence of pore space architecture on soil functions. The possibility to quantify pore space has meanwhile gotten a new tool: a standardized quantitative evaluation routine together with a comprehensive and growing library of evaluated soil structure images.&lt;/p&gt;&lt;p&gt;Here we are. We have to go on. To study dynamics of structural development is still tedious and can only be achieved by getting small glimpses at points in time.&lt;/p&gt;&lt;p&gt;New techniques occur. As is X ray CT for pore space, imaging techniques for the composition and arrangement of the solid phase evolve. They will give rise for new quantitative descriptions of soil forming processes.&lt;/p&gt;&lt;p&gt;Yet all this insight has to be digested and put into meaningful concepts. To profit from the wealth of information on pore space dynamics we have to implement models that can deal with a dynamic pore space. For soil hydraulics such a model is in development. It shows a clear dependency of the soil&amp;#8217;s properties on the structure. With this, the importance of soil structure forming and preserving in agricultural management can be stressed.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

scholarly journals Grain-Scale Analysis of Solid-Phase Organic Matter and Arsenic Mobility in Mining-Impacted 1 Sediment from Sub‐Arctic Lakes, Northwest Territories, Canada

2021 ◽  
Author(s):  
Clare B Miller ◽  
Michael B Parsons ◽  
Heather E Jamieson ◽  
Omid H Ardakani ◽  
R Timothy Patterson ◽  
...  
Keyword(s):  
Organic Matter ◽  
Northwest Territories ◽  
Solid Phase ◽  
Arctic Lakes ◽  
Edge Structure ◽  
Near Surface ◽  
X Ray ◽  
Fine Grained ◽  
Arsenic Mobility ◽  
Co Precipitation

Abstract Arsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulphides. The results of this study demonstrate that the accumulation of solid-phase organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially-derived OM (cutinite; funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulphide minerals ( e.g., goethite, orpiment, lepidocrocite, mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62 % As (V), 18 % As (III); n = 20) and sediment (median = 80 % As (-I) and (III), 19 % As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred . Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface-enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.

scholarly journals Pore formation during dehydration of a polycrystalline gypsum sample observed and quantified in a time-series synchrotron X-ray micro-tomography experiment

Solid Earth ◽  
2012 ◽  
Vol 3 (1) ◽  
pp. 71-86 ◽  
Author(s):  
F. Fusseis ◽  
C. Schrank ◽  
J. Liu ◽  
A. Karrech ◽  
S. Llana-Fúnez ◽  
...  
Keyword(s):  
Time Series ◽  
Pore Space ◽  
Three Dimensional ◽  
Internal Stresses ◽  
Micro Computed Tomography ◽  
X Ray ◽  
Computer Codes ◽  
Micro Tomography ◽  
Effective Drainage

Abstract. We conducted an in-situ X-ray micro-computed tomography heating experiment at the Advanced Photon Source (USA) to dehydrate an unconfined 2.3 mm diameter cylinder of Volterra Gypsum. We used a purpose-built X-ray transparent furnace to heat the sample to 388 K for a total of 310 min to acquire a three-dimensional time-series tomography dataset comprising nine time steps. The voxel size of 2.2 μm3 proved sufficient to pinpoint reaction initiation and the organization of drainage architecture in space and time. We observed that dehydration commences across a narrow front, which propagates from the margins to the centre of the sample in more than four hours. The advance of this front can be fitted with a square-root function, implying that the initiation of the reaction in the sample can be described as a diffusion process. Novel parallelized computer codes allow quantifying the geometry of the porosity and the drainage architecture from the very large tomographic datasets (20483 voxels) in unprecedented detail. We determined position, volume, shape and orientation of each resolvable pore and tracked these properties over the duration of the experiment. We found that the pore-size distribution follows a power law. Pores tend to be anisotropic but rarely crack-shaped and have a preferred orientation, likely controlled by a pre-existing fabric in the sample. With on-going dehydration, pores coalesce into a single interconnected pore cluster that is connected to the surface of the sample cylinder and provides an effective drainage pathway. Our observations can be summarized in a model in which gypsum is stabilized by thermal expansion stresses and locally increased pore fluid pressures until the dehydration front approaches to within about 100 μm. Then, the internal stresses are released and dehydration happens efficiently, resulting in new pore space. Pressure release, the production of pores and the advance of the front are coupled in a feedback loop.

scholarly journals Assessment of geometrical and transport properties of a fibrous C/C composite preform as digitized by x-ray computerized microtomography: Part II. Heat and gas transport properties

2007 ◽  
Vol 22 (6) ◽  
pp. 1537-1550 ◽  
Author(s):  
Gerard L. Vignoles ◽  
Olivia Coindreau ◽  
Azita Ahmadi ◽  
Dominique Bernard
Keyword(s):  
Transport Properties ◽  
Pore Space ◽  
Three Dimensional ◽  
Carbon Composite ◽  
X Ray ◽  
Gas Transport Properties ◽  
Change Of Scale ◽  
Local Determination ◽  
Good Agreement

Raw and partially infiltrated carbon–carbon composite preforms have been scanned by high-resolution synchrotron radiation x-ray computerized microtomography. Three-dimensional high-quality images of the pore space have been produced at two distinct resolutions and have been used for the computation of transport properties: heat conductivity, binary gas diffusivities, Knudsen diffusivities, and viscous flow permeabilities. The computation procedures are based on a double change-of-scale strategy suited to the bimodal nature of pore space and on the local determination of transport anisotropy. Good agreement has been found between all calculated quantities and experimental data.

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