 |
| Titel |
Characterizing Nitrogen adsorption and desorption isotherms in soils using multifractal analysis |
| VerfasserIn |
Jorge Paz Ferreiro, José G. V. Miranda, Eva Vidal Vazquez |
| Konferenz |
EGU General Assembly 2010
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033788
|
|
|
|
|
|
| Zusammenfassung |
| The specific surface area is an attribute known to characterize the soil ability to retain and
transport nutrients and water. A number of studies have shown that specific surface area
correlates cation exchange capacity, organic matter content, water retention, aggregate
stability and clay swelling. In the past fractal theory has been widely used to study different
gas adsorption isotherms like water vapour and nitrogen adsorption isotherms. More recently
we have shown that nitrogen adsorption isotherms showed multifractal nature. In this work,
both N2 adsorption and desorption isotherms measured in a Mollisol were examined as a
probability measure using the multifractal formalism in order to determinate its
possible multifractal behaviour. Soil samples were collected in two different series of
an Argiudoll located in the north of Buenos Aires and in the south of Santa Fe
provinces, Argentina. Two treatments of each soil series were sampled at three depths,
without replication, resulting in six samples per soil series and a total of twelve
samples analyzed. Multifractal analysis was performed using the box counting
method. Both, the N2 adsorption and desorption isotherms exhibited a well defined
scaling behaviour indicating a fully developed multifractal structure of each isotherm
branch. The singularity spectra and Rényi dimension spectra obtained for adsorption
and also for desorption isotherms had shapes similar to the spectra of multifractal
measures and several parameters were extracted from these spectra. The capacity
dimension, D0, for both N2 adsorption and desorption data sets were not significantly
different from 1.00. However, nitrogen adsorption and desorption data showed
significantly different values of entropy dimension, D1, and correlation dimension, D2. For
instance, entropy dimension values extracted from multifractal spectra of adsorption
isotherms were on average 0.578 and varied from 0.501 to 0.666. In contrast, the
corresponding figures for desorption isotherms were on average 0.761 with a range from
0.682 to 0.722. The entropy dimension D1 is a measure of diversity in a multifractal
system and it is also an index of the dispersion of the measure. The values of D1 for
adsorption isotherms were much lower than those for desorption isotherms. This
indicates that for adsorption isotherms most of the measure concentrates in a small
size domain of the study scale, whereas for desorption isotherms it was somewhat
more evenly distributed. On the other hand, the Hölder exponent of order zero, α0,
was significantly greater for adsorption isotherms (1.396) when compared with
desorption curves (1.246). Therefore, adsorption isotherms exhibit on average a
lower degree of mass concentration (i.e. the lowest local density) than desorption
isotherms. Moreover, the width of the singularity spectra was larger for adsorption
than for desorption isotherms, which means a higher heterogeneity in the local
scaling indices of the former variable. The potential usefulness in soil science of the
multifractal characteristics extracted from the adsorption and desorption isotherms is
discussed.
Paz-Ferreiro, J., Wilson, M., and Vidal Vázquez, E. (2009). Multifractal description on
Nitrogen adsorption isotherms. Vadose Zone Journal 8: 209-219.
Acknowledgement: This work was supported by Spanish Ministry of Education (Project
CGL2006-13068-C02) and Xunta de Galicia (Project INCITE08PXIB162169PR). |
|
|
|
|
|
|