EGU2020-18948
https://doi.org/10.5194/egusphere-egu2020-18948
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil

Genoveva Burca1, Stephen Hillier2,3, Pawala Ariyathilaka4, Jumpei Fukumasu2, Anke Herrmann2, Mats Larsbo2, Oxana Magdysyuk5, and John Koestel2
Genoveva Burca et al.
  • 1ISIS Facility, Rutherford Appleton Laboratory, Harwell OX11 0QX, United Kingdom
  • 2Swedish University of Agricultural Sciences, Soil and Environment, Uppsala, Sweden
  • 3Environmental and Biochemical Sciences, James Hutton Institute, Aberdeen AB15 8QH, Scotland UK
  • 4Scitech Precision Limited, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK
  • 5Diamond Light Source, Rutherford Appleton Laboratory, Harwell OX11 0DE, UK

Soil organic carbon (SOC) is of key importance for soil functioning. It strongly impacts soil fertility, greenhouse gas emissions, nutrient retention, and contaminant degradation. The soil pore network determines how oxygen, water and nutrients are transported and exchanged in soil, and the architecture of the soil is therefore equally fundamental to soil functions. For a thorough understanding of the microbial habitat, the soil pore network architecture needs to be evaluated alongside with the spatial distribution of SOC, but the challenge ahead is the 3-D visualization of organic carbon at the micro-scale. At present, such visualizations are undertaken using staining agents, but their non-specific binding to other features in the soil aggravates evaluation of organic carbon at the micro-scale.

In the present study, we investigated the potential and limitations of using joint white-beam neutron and X-ray imaging for mapping the 3-dimensional organic carbon distribution in soil. This approach is viable because neutron and X-ray beams have complementary attenuation properties. Soil minerals consist to a large part of silicon and aluminium, elements which are relatively translucent to neutrons but attenuate X-rays. In contrast, attenuation of neutrons is strong for hydrogen, which is abundant in SOC, while hydrogen barely attenuates X-rays. When considering dried soil samples, the complementary attenuation for neutrons and X-rays may be used to quantify the fractions of air, SOC and minerals for any imaged voxel in a bi-modal 3-dimensional image, i.e. a combined neutron and X-ray image.

We collected neutron data at the IMAT beamline at the ISIS facility and X-ray data at the I12 beamline at the Diamond Light source, both located within the Rutherford Appleton Laboratory, Harwell, UK. The neutron image clearly showed variations in neutron attenuation within soil aggregates at approximately constant X-ray attenuations. This indicates a constant bulk density with varying organic matter and/or mineralogy. For samples with identical mineral composition, neutron attenuation data of sieved and repacked soil samples exhibited a large coefficient of determination (R2) in a regression between volumetric SOC content and neutron attenuation (0.9). Even larger R2 (0.93) were obtained when the volumetric clay content was also included into the regression. However, when comparing soil samples with different mineralogy, R2 dropped to 0.24 and 0.37, depending whether the clay content was considered or not. To improve the method, it is necessary to include specifics of the soil mineralogy. Here, analysing the time-of-flight neutron attenuation data collected at the IMAT beamline will provide further insights. In summary, our approach yielded promising results. We anticipate that quantitative 3-D imaging of organic carbon contents in soil will be possible in the near future.

How to cite: Burca, G., Hillier, S., Ariyathilaka, P., Fukumasu, J., Herrmann, A., Larsbo, M., Magdysyuk, O., and Koestel, J.: Potential of combined neutron and X-ray imaging to quantify local carbon contents in soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18948, https://doi.org/10.5194/egusphere-egu2020-18948, 2020

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Presentation version 1 – uploaded on 06 May 2020
  • CC1: Comment on EGU2020-18948, Andreas Pohlmeier, 07 May 2020

    Hello Genoveva,

    Your quantitative combination of NCT and XCT is a really nice work!

    Two questions:

    1) slide 17: To which materials belong the different color-coded spots in the correlation diagram?

    2) did you cross-check the organic material in the XCT images by staining methods?

    Cheers

    Andreas Pohlmeier

    • AC1: Reply to CC1, John Koestel, 07 May 2020

      Hej Andreas, 

      thanks for the encouraging feedback!

      a) I should have labelled the materials and will do so after the chat. The regions on the top left correspond to seeds and plastics. They have large H contents and strongly scatter the N-ray beam. The materials to the far right are minerals contaning heavy metals, but no or very little protium (or other strong neutron interacting isotopes). The materials in between include quartz, apatite and aluminium, among others.

      b) No, unfortunately we did not have the resources to carry out carbon staining approaches. It would be interesting to compare the results, but this was not within the scope of this particular study, anyway. 

      Thanks for asking and cheers, 

      /John