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Titel |
Fractal characterization of the intra-aggregate pore heterogeneity in macro-aggregates from contrasting land use and management treatments |
VerfasserIn |
Alexandra N. Kravchenko, Wei Wang, Andrew Worth, Alvin J. M. Smucker, Mark L. Rivers |
Konferenz |
EGU General Assembly 2011
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250058105
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Zusammenfassung |
Soil aggregates play a key role in a number of soil processes, and are considered to be of
particular importance for soil carbon sequestration. However, lack of measurement and
analysis tools has hindered progress in understanding the mechanisms by which complex
internal aggregate structures influence various soil processes. Recent advances in computed
tomography allow addressing internal heterogeneity of soil aggregates at micron resolutions.
Aggregate images can then be subjected to a variety of data analyses techniques that will
allow estimation and evaluation of the complexity and heterogeneity of the intra-aggregate
pore and solid structures. Fractal analysis is one such tool. However, the nature of some
fractal measures when they are applied to pore distributions, e.g., box-counting dimension, is
such that it can be substantially affected by the total porosity. This influence of porosity on
fractal dimension values limits its usefulness as a measure of heterogeneity of the pore
distributions. Standardization of the fractal dimension values so as to eliminate the influence
of the initial pore voxel numbers on the heterogeneity assessment can greatly increase
applicability of fractal analysis in soil image studies. The objectives of this study are (i) to
develop a technique to standardize the box-counting fractal dimension with respect to
the total number of pore voxels; (ii) to use the computed tomography scanning
and fractal analysis tools to examine the characteristics of the intra-aggregate pore
space in macro-aggregates (4-6 mm in size); and (iii) to compare heterogeneity of
intra-aggregate pore space in macro-aggregates from the same soil subjected to
long-term contrasting management practices, namely conventional tillage, no-till,
and native succession vegetation. Intact soil aggregates 4-6 mm in size have been
selected from long-term ecological experiments located in Michigan, USA (LTER).
Three-dimensional images of the aggregates have been obtained at the Advanced Photon
Source (APS), Argonne National Laboratory (ANL), IL, with resolution 14.6 μm.
The proposed method of standardizing box-counting fractal dimension allowed
obtaining information on heterogeneity of pore voxel distributions without bias
generated by the effects of the total pore numbers. The results indicated that in the
studied Alfisol, macro-aggregates under long-term conventionally tilled (chisel plow)
management had greater number of pore voxels (>15 μm) than the aggregates under  20
years of no-till and aggregates under  20 years of native succession vegetation.
Large pores (>120 μm ) prevailed in the aggregate interior, but their distributions
were more heterogeneous in the exterior parts; while 30-75 μm pores were equally
abundant, although more heterogeneous in the interior than in the exterior parts
of the aggregates. Overall, greatest heterogeneity in pore voxel distribution was
observed in aggregates from native succession, followed by those from no-till,
and the highest uniformity observed in conventionally tilled aggregates. Observed
differences in pore voxel numbers and fractal characteristics are consistent with
differences in magnitudes and variabilities of a number of processes occurring in soil
aggregates, including microbial activity, nutrient availability, and carbon sequestration. |
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