Calculating field weathering rates using a mechanistic geochemical model PROFILE

Amsterdam

Elsevier

1993

S. 273-283

4 Abb., 11 Tab., zahlr. Lit.

Bandaufführung

128642

Applied Geochemistry : Journal of the International Association of Geochemistry and Cosmochemistry ; Vol. 8, S. 273-283

A new model for base cation release due to chemical weathering of soil minerals has been developed based on transition state theory, and included in the integrated soil chemistry model PROFILE. The data required for model application can be operationally determined on soil samples, making the model generally applicable and independent of any type of calibration. The model considers the contribution to the weathering rate from 12 groups of the most common primary and secondary minerals of soils, reacting in separate reactions with H+-ion, H2O, CO2 and organic acids expressed as dissolved organic carbon (DOC). The weathering rate sub-model couples the effects of dissolved Al and base cations on the reaction mechanisms. The model takes into account changes in soil temperature, different chemical conditions, the effect of vegetation interactions with the soil and N transformations. The kinetic coefficients and reaction orders are based on a complete re-evaluation of weathering data available in the literature, and additional kinetic data determined by the authors. Data from 23 different independent determination of the field weathering rate from 15 sites in Scandinavia, Central Euope and North America were compiled and used to verify the model. The model is capable of estimating the release rate of base cations due to chemical weathering from information on soil mineralogy, texture and geochemical properties of the order of +/- 20 % of the rate determined by independent methods. The results indicate that small amounts of dark minerals like epidote and hornblende, and the plagioclase content, largely determine the field weathering rate.