『Abstract
Chemical or mineralogical profiles in regolith display reaction
fronts that document depletion of leachable elements or minerals.
A generalized equation employing lumped parameters was derived
to model such ubiquitously observed patterns:
C = C0/{[(C0-Cx=0)/Cx=0]exp(Γini・k（頭に＾）・x) + 1}
Here, C, Cx=0, and C0
are the concentrations of an element at a given depth x, at the
top of the reaction front, or in parent respectively. Γini
is the roughness of the dissolving mineral in the parent and k（頭に＾） is a lumped kinetic parameter. This kinetic
parameter is an inverse function of the porefluid advective velocity
and a direct function of the dissolution rate constant times mineral
surface area per unit volume regolith. This model equation fits
profiles of concentration versus depth for albite in seven weathering
systems and is consistent with the interpretation that the surface
area (m2 mineral m-3 bulk regolith) varies
linearly with the concentration of the dissolving mineral across
the front. Dissolution rate constants can be calculated from the
lumped fit parameters for these profiles using observed values
of weathering advance rate, the proton driving force, the geometric
surface area per unit volume regolith and parent concentration
of albite. These calculated values of the dissolution rate constant
compare favorably to literature values. The model equation, useful
for reaction fronts in both steady-state erosional and quasi-stationary
non-erosional systems, incorporates the variation of reaction
affinity using pH as a master variable. Use of this model equation
to fit depletion fronts for soils highlights the importance of
buffering of pH in the soil system. Furthermore, the equation
should allow better understanding of the effects of important
environmental variables on weathering rates.
Keywords: Weathering; Dissolution; Surface area; Soils; Regolith;
Saprolite; Erosion; Kinetics』
1. Introduction
1.1. Types of soil profiles
1.2. Erosion
1.3. Reaction fronts
1.4. The model
1.5. Treating affinity across the front
1.6. Treating surface area across the front
1.7. Deriving the analytical expression for C versus depth
1.8. Fitting to soil profile data
1.9. Surface area across the reaction front
1.10. Interpretation of lumped parameters
2. Conclusions
Acknowledgements
Appendix A
References