『Abstract
Solute-based geochemical mass balance methods are commonly used
in small-watershed studies to estimate rates of a variety of geochemical
processes at the Earth's surface, including primary-mineral weathering
and soil formation, and the quantitative contribution of these
elemental transfer processes to cation budgets, nutrient cycling,
and landscape susceptibility to acid deposition. Weathering rates
of individual minerals in watwershed mass-balance studies are
determined by soving a system of simultaneous linear geochemical
mass-balance equations with constant (stoichiometric) coefficienta.
These equations relate the measured net fluxes to the )known)
stoichiometries and (unknown) rates of weathering reactions for
multiple minerals in the weathering profiles. Solving the system
of equations requires petrologic, mineralogic, hydrologic, notanical,
and aqueous geochemical data. The number of mineral-weathering
rates that can be determined is limited by the number of elements
for which solute mass-balance equations can be written. In addition
to calculating mineral weathering rates, elemental transfer into
or out of the biomass may also be calculated. Elemental uptake
by aggrading forest vegetation can act as an intrawatershed sink
for at least some mineral-derived cations, producing mineral weathering
rates higher than would be estimated from solute fluxes alone;
similarly, element releases from decaying forest biomass can result
in higher solute fluxes than are produced by weathering alone.
The mathematics of, significant contributions from, role of biomass
in, and recent advances in, watershed geochemical mass-balance
methods are discussed using examples from the Appalachian headwaters
watersheds of the Coweeta Hydrologic Laboratory in the southern
Blue Ridge Physiographic Province of North Carolina, USA.』
1. Introduction
2. Study area
3. Methods and background
3.1. Mathematics of watershed geochemical mass balance
3.2. Histric background and significant contributions to watershed
geochemical mass-balance techniques
3.3. Overcoming more unknowns tha equations
3.3.1. Assumptions to reduce the number of unknowns
3.3.2. Increasing the number of equations
3.4. Calcium problem
4. Discussion
4.1. Use of assumed rather than actual mineral stoichiometries
4.2. Weathering products determined using thermodynamics
4.3. Exclusion of a biomass term
4.4. Future directions in watershed mass-balance calculations
5. Summary and conclusions
Acknowledgements
References