Use of a chemical equilibrium model to understand soil chemical processes that influence soil solution and surface water alkalinity

Generation of soil solution acid-neutralizing capacity by addition of dissolved inorganic carbon

“…The soil used in this work had low base cations and base saturation (Table II). Values for log KM and log Ks were calculated by using an Al activity relationship based on 2.66pH -pAl, rather than the 3pH -pAl originally used in the Reuss and Johnson (1) model and by David et al (6). Adjustment of the pH exponent was done in order to improve the fit of the data to the equilibrium model.…”

“…This work again supported the importance of pC02 and other factors in determining ANC and its influence on surface water chemistry after solution equilibrium with atmospheric C02. Negative ANC levels were produced in all E horizons (-69 to -37 ¿tequiv L"1) at each pC02 level used (0.3-2%), whereas ANC in B horizons was found to be dependent on pC02 levels (6).…”

“…Aluminum potential (2.66pH -pAl, designated log KM) was estimated by measuring the total Al concentration and the pH of a 0.002 M CaCl2 soil extract (by using a mechanical vacuum extractor) after passage through a GF/F glass fiber filter (8) . A Gaines-Thomas selectivity coefficient for Ca2+/Al3+ (log Kt) exchange was calculated from Ca2+ in the 0.002 M CaCl2 extract, neutral salt CEC, and the NH4C1 extractable bases (6). Total Al in the 0.002 M CaCl2 extract and in leachates was determined by using a pyrocatechol violet (PCV) procedure modified from Dougan and Wilson (9) .…”

“…Thus, the chemical equilibrium model determines changes that would occur under different soil pC02 conditions. David et al (6) present an application of the model to soil chemistry data from Maine and New York.…”