FRACTAL ANALYSIS OF SOIL AGGREGATE STRUCTURES AND ASSOCIATIONS WITH ORGANIC CARBON
Open Access
- Author:
- Gibson, Jody Russell
- Graduate Program:
- Soil Science
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 10, 2004
- Committee Members:
- Maryann Victoria Bruns, Committee Chair/Co-Chair
Hangsheng Lin, Committee Member
Carmen Enid Martinez, Committee Member
William Ewart Easterling Iii, Committee Member
Abraham Grader, Committee Member - Keywords:
- computed tomography
fractal geometry
pore-solid fractal
carbon sequestration
soil aggregates
aggregate hierarchy - Abstract:
- Between 1850 and 1998, the atmospheric carbon stock increased by about 174 Gt C, or 30%. Recent investigations suggest that soils could sequester as much as 30% of this excess carbon. One possible mechanism of soil carbon sequestration is the development of small soil aggregates (microaggregates) within larger aggregates, meaning that hierarchical soil structure may provide clues about the nature of soil organic matter (SOM) dynamics. In this context, fractal theory is useful. Specifically, a soil can be considered a fractal object whose pores obey a number-size power law (solid mass fractal) or whose particles and pores each obey number-size power laws (pore-solid fractal, or PSF). In the first part of this study, soil aggregates (~3 mm in size) from the Hunter Rotation Experiment (HRE) at Rock Springs, PA were analyzed with computed tomography (CT) to obtain images of the undisturbed aggregate structures. Objectives were to 1) compare the PSF and solid mass fractal models in representing aggregate structures, and 2) assess the sensitivity of derived fractal parameters to 2-D or 3-D image analysis. Results showed that the solid mass fractal parameters were most reliable, and that fractal dimensions obtained from 2-D images were comparable to their 3-D counterparts. This analytical approach was extended to aggregates of three different size classes, but no single fractal model could account for the trends observed in either of two soil types from the HRE. In an effort to expand on the potential applications of the PSF model, a modified PSF model was created, accounting for SOM explicitly over time. Out of many possible formulations, this model was developed because of its compatibility with our understanding of microaggregate formation. Subsequent tests of the modified PSF model were successful, although few constraints exist for the input parameters. If the model is accurate, it underscores the significance of the fractal parameter b, low values of which were associated with increased soil carbon storage. This agrees with other findings that low b values are associated with clayey, stable soils.