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| Titel |
Multifractal analysis of soil porosity based on mercury porosimetry and nitrogen adsorption |
| VerfasserIn |
J. Paz-Ferreiro, E. Vidal Vázquez, J. G. V. Miranda |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250030579
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| Zusammenfassung |
| The soil pore space is composed of a continuum of pores extremely variable in size which
include structures smaller than nanometres and as large as macropores > 20 mm in diameter,
i.e. with an upper size limit of the order of centimetres. Thus, a ratio of at least 106 is
displayed in soil pore sizes. Soil pore size distribution directly influences many soil physical,
chemical and biological properties. Characterization of soil structure may be achieved by
pore size distribution analysis. There is not a unique method for determining soil pore size
distributions all over the size scale. Mercury injection porosimetry and N2 adsorption
isotherms are techniques commonly used for assessing equivalent pore size diameters in
selected ranges. The Hg injection technique provides pore size distributions in the range from
about 50 nm to 100 μm, whereas N2 adsorption isotherms may be used for finer pores
ranging in size from about 2 to 500 nm. In this work, multifractal formalism has been used to
describe Hg injection porosimetry and N2 adsorption isotherms measured in a Mollisol
and in a Vertisol with four different soil use intensities, ranging from native, never
cultivated, land to continuous cropping. Three samples per treatment were analyzed
resulting in a total of twelve samples per soil. All the Hg injection curves and N2
adsorption isotherms exhibited multifractal behaviour as shown by singularity spectra
and Rényi dimension spectra. The capacity dimension, D0, for both Hg injection
and N2 adsorption data sets was not significantly different from 1.00. However,
significantly different values of entropy dimension, D1, and correlation dimension, D2,
were obtained for mercury injection and nitrogen adsorption experimental data.
For instance, entropy dimension, D1, values extracted from multifractal spectra of
Hg intrusion porosimetry were on average 0.913 and varied from 0.889 to 0.939.
However, the corresponding figures for N2 adsorption isotherms were on average
0.507 with a range from 0.401 to 0.666. The entropy dimension D1 is a measure of
diversity and in our study case gauges the concentration degree of the pore size
distribution on a specific pore size range. Values of D1 for Hg injection curves
were close to 1.00 and consequently they indicate more or less homogeneous pore
size distribution pattern distributed over the range of pore sizes measured with this
method. In opposite D1 values for N2 adsorption isotherms were much lower, which
reflects clustering and indicates that most of the measure concentrates in a small
size domain for finer pore scales. The use of multifractal indixes as indicators for
characterizing soil structure and as well as for deriving soil physical properties is
discussed.
Acknowledgements. This work was financed by by MEC (Spain) under project
CGL2005-08219-C02-01. |
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