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| Titel |
Modelling and interpreting biologically crusted dryland soil sub-surface structure using automated micropenetrometry |
| VerfasserIn |
Stephen R. Hoon, Vincent J. M. N. L. Felde, Sylvie L. Drahorad, Peter Felix-Henningsen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111986
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| Publikation (Nr.) |
 EGU/EGU2015-12140.pdf |
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| Zusammenfassung |
| Soil penetrometers are used routinely to determine the shear strength of
soils and deformable sediments both at the surface and throughout a depth
profile in disciplines as diverse as soil science, agriculture,
geoengineering and alpine avalanche-safety (e.g. Grunwald et al. 2001, Van
Herwijnen et al. 2009). Generically, penetrometers comprise two principal
components: An advancing probe, and a transducer; the latter to measure the
pressure or force required to cause the probe to penetrate or advance
through the soil or sediment. The force transducer employed to determine the
pressure can range, for example, from a simple mechanical spring gauge to an
automatically data-logged electronic transducer. Automated computer control
of the penetrometer step size and probe advance rate enables precise
measurements to be made down to a resolution of 10's of microns, (e.g. the
automated electronic micropenetrometer (EMP) described by Drahorad 2012).
Here we discuss the determination, modelling and interpretation of
biologically crusted dryland soil sub-surface structures using automated
micropenetrometry. We outline a model enabling the interpretation of depth
dependent penetration resistance (PR) profiles and their spatial
differentials using the model equations,
\textit{$\sigma $}${\rm}(z) ={\rm}$\textit{$\sigma $}$_{c0{\rm}{\rm }}+$\Sigma _{{\rm 1}}^{n}$[\textit{$\sigma $}$_{n}{\rm}(z){\rm}+{\rm a}_{n}z$ +
$b_{n}z^{2}$]
and
\textit{d$\sigma $} /\textit{dz} = $\Sigma _{{\rm 1}}^{n}$[d\textit{$\sigma $}$_{n}(z) $\textit{/dz}${\rm}$
${\rm}+{\rm}$F_{rn}(z)$]
where \textit{$\sigma $}$_{c{\rm 0}}$ and \textit{$\sigma $}$_{n}$ are the plastic deformation stresses for the surface and $n^{th}$ soil
structure (e.g. soil crust, layer, horizon or void) respectively, and
$F_{rn}(z)$\textit{dz} is the frictional work done per unit volume by sliding the penetrometer rod
an incremental distance, \textit{dz,} through the $n^{th}$ layer. Both \textit{$\sigma $}$_{n}(z)$ and $F_{rn}(z)$ are related to soil structure. They determine the form of
\textit{$\sigma $}${\rm}(z){\rm}$ measured by the EMP transducer. The model enables pores (regions of zero deformation stress) to be distinguished from changes in layer structure or probe friction.
We have applied this method to both artificial calibration soils in the
laboratory, and \textit{in-situ} field studies. In particular, we discuss the nature and detection of surface and buried (fossil) subsurface Biological Soil Crusts (BSCs), voids, macroscopic particles and compositional layers. The strength of surface BSCs and the occurrence of buried BSCs and layers has been
detected at sub millimetre scales to depths of 40mm. Our measurements and
field observations of PR show the importance of morphological layering to
overall BSC functions (Felde et al. 2015).
We also discuss the effect of penetrometer shaft and probe-tip profiles upon
the theoretical and experimental curves, EMP resolution and reproducibility,
demonstrating how the model enables voids, buried biological soil crusts,
exotic particles, soil horizons and layers to be distinguished one from
another. This represents a potentially important contribution to advancing
understanding of the relationship between BSCs and dryland soil structure.
\textbf{References:}
Drahorad SL, Felix-Henningsen P. (2012) An electronic micropenetrometer
(EMP) for field measurements of biological soil crust stability, \textit{J. Plant Nutr. Soil Sci.}, 175,
519-520
Felde V.J.M.N.L., Drahorad S.L., Felix-Henningsen P., Hoon S.R. (2015)
Ongoing oversanding induces biological soil crust layering -- a new approach
for BSC structure elucidation determined from high resolution penetration
resistance data (submitted)
Grunwald, S., Rooney D.J., McSweeney K., Lowery B. (2001) Development of
pedotransfer functions for a profile cone penetrometer, \textit{Geoderma}, 100, 25-47
Van Herwijnen A., Bellaire S., Schweizer J. (2009) Comparison of
micro-structural snowpack parameters derived from penetration resistance
measurements with fracture character observations from compression tests,
\textit{Cold Regions Sci. {\&} Technol.}, 59, 193-201 |
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