『Abstract
Immobile element-based weathering estimation methods assume that
Zr (or Ti) is an immobile element, and that weathering rates of
other elements can be estimated according to the enrichment of
Zr in weathered horizons relative to an unweathered parent material.
This approach was used to estimate base cation weathering rates
for 33 soil profiles on acid-sensitive terrain in north-eastern
Alberta. Zirconium generally showed enrichment within the rooting
zone, but the deepest (subsoil) samples were not always associated
with the lowest Zr concentrations. Weathering rates estimated
with the Zr depletion and Pedological Mass Balance (PMB) methods
were generally low (ranges: 0-51 and 0-58 mmolc
m-2 y-1, respectively); however, low base
cation oxide concentrations and heterogeneity within soil profiles
complicated weathering rate calculations and net base cation gains
were calculated for several (six) sites. Evaluation of the Zr
depletion and PMB weathering estimates against those calculated
with the process-oriented PROFILE model at a subset (n = 9) of
the sites indicated the estimates were poorly related, with PROFILE
rates typically being higher. The effects-based emissions management
strategy for acid precursors in this region requires spatial coverage
of soil properties (including weathering rates) across a large
area, but the apparent limitations associated with the immobile
element based methods in this region: identifying representative
parent soils and deriving weathering rate estimates comparable
to more robust methods are arguments against their candidacy for
future use.
Keywords: Acidic deposition; Base cations; Mineral soil weathering;
Pedological Mass Balance; PROFILE; Zirconium depletion
1. Introduction
2. Methods
2.1. Study area and sample collection
2.2. Laboratory analysis
2.3. Zirconium depletion method
2.4. Pedologic Mass Balance
2.5. PROFILE model
3. Results and discussion
3.1. Zirconium profiles
3.2. Weathering rates
4. Conclusions
Acknowledgments
References