『Abstract
The pedological mass balance (PMB) model is still among the best
quantitative geochemical approaches to estimate chemical weathering
and pedogenesis. This one-dimensional vertical approach permits
estimation of the enrichment factor for a given element in a soil
layer, based on changes in 1) residual enrichment, 2) strain,
and 3) mass transport. The first two components represent the
“closed-system” contributions to the enrichment factor since they
occur without movement of the element under consideration. The
last component represents the “open-system” contribution that
results from net element mass movement across soil layer boundaries.
Modelling the mass transport function represents a crucial step
in soil pedogenesis model definitions and in the estimation of
soil chemical weathering rates. We present here a method to empirically
model this mass transport function based on the change in soil
horizon composition within a soil profile, taking base cations
(Ca, Mg, K, and Na) and Ti composition in three northern forest
soil profiles as showcase. The empirically modelled compositional
trends explained between 81 and 94％ of the change in element composition
within the soil profiles. Among the studied elements, Ti was the
most recalcitrant one, except at one site where K tended to accumulate
(relative to Ti). The results suggest that changes in composition
within soil profiles are mostly linear. The calculated degree
of weathering (k) of a given soil horizon was linearly related
to the calculated gain/loss of base cations in the three soils
using the PMB model, and was correlated to observed soil organic
matter, carbon and N concentrations and its texture, pH, and bulk
density. Although the modelled trend can successfully predict
mass transport changes with depth as the composition of soil horizons
changes upon weathering, the question of time function for this
process to operate remains to be quantified.
Keywords: Soil chemical weathering; Compositional trend; Forest
soil; Pedological mass balance』
1. Introduction
2. Material and methods
2.1. The pedological mass balance model
2.2. Compositional data and their dimensional space
2.3. Linear compositional trend determination
2.4. Showcase soils
2.5. Soil sampling and analysis
2.6. Statistical analysis
3. Results and discussion
3.1. Bulk density changes
3.2. Strain factor
3.3. Mass transport factor
4. Conclusion
Acknowledgements
References