Geochemical mass balances and weathering rates in forested watersheds of the southern Blue Ridge.

Abstract

Mass-balance equations expressing mineral weathering reactions have been derived on the basis of empirical determinations of mineral compositions and combination of compositional data with petrographic (micromorphological) data. Calculations of the rates of weathering for each of the three major rock-forming silicate minerals - as well as the rate of mineral nutrient uptake - in deeply weathered profiles of several small watersheds in the Nantahala Mountains, North Carolina, are presented. Published data on the elemental composition of forest biomass, elemental fluxes via rain and streams, and stoichiometries of mineralogical transformations serve as parameters for construction and constraint of the geochemical mass-balance calculations of the individual watersheds. They are quantitatively consistent with laboratory studies of mineral weathering and geomorphological studies of regional denudation rates. Possible sources of discrepancies are noted, and may be resolved by refinement of laboratory kinetic data and field surface area determinations. -M.S.