The Separate and Combined Effects of Temperature, Soil Pco2, and Organic Acidity on Silicate Weathering in the Soil Environment - Formulation of a Model and Results

A model is used to evaluate the relative importance of temperature, soil pCO2, and organic acidity on silicate weathering rates in an average soil of warm temperate climate. The model has a structure, similar to the Model of Acidification of Groundwater in Catchments, (Cosby et al., 1985a, b) used to predict catchment responses to acid deposition, but it is modified to account for the effects of temperature, the partial pressure of carbon dioxide in the soil, and organic acidity on dissolution of silicate minerals. The model is run with a mean soil temperature of 15-degrees-C, and when equilibrium is achieved it is raised to 19-degrees-C. Soil pCO2 and organic acids adjust accordingly. It is found that temperature is the main control of the weathering rate; the other two factors have a very minor forcing effect. The transient after the step function disturbance occurs on a century to millennial timescale. Consequently, it is not possible to study weathering rates through either purposeful soil manipulations lasting several years or by examining the effect on soils of land use changes because steady state may have not been achieved yet.