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ALUMINUM SOLUBILITY, CALCIUM-ALUMINUM EXCHANGE, AND PH IN ACID FOREST SOILS
Citation:
Reuss, J., P. Walthall, E. Roswall, AND R. Hopper. ALUMINUM SOLUBILITY, CALCIUM-ALUMINUM EXCHANGE, AND PH IN ACID FOREST SOILS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-94/562, 1990.
Description:
Important components in several models designed to describe the effects of acid deposition on soils and surface waters are the pH-A1 and Ca-A1 exchange relationships. f A1 solubility is controlled by A1 trihydroxide minerals, the theoretical pH-A1 relationship can be described by log (A13+) - logKo - 3pH. owever, in practice it is often better described by log(A13+) = logKo - apH, where Ko and a are empirical constants. hen this relationship is combined with equations for Ca-A1 exchange, a curvilinear relationship is predicted for pH as a function of Ca saturation in solutions with constant total ionic concentration. hese relationships were tested using selected forest soils. he pH-A13+ relationship in mineral horizons was reasonably well described by values near 2.35 for Ko and 1.65 for a. When the Ca saturation is based on an effective cation exchange capacity determined at or near soil pH, the predicted curvilinear relationships between pH (measured in 0.002 M CaC12) and Ca saturation was observed, supporting the interpretation of this relationship in terms of A1 solubility and Ca-A1 exchange. ecause A1 solubility in Spodosol E. horizons was much lower than that found in underlying horizons or in Ultisols, the E horizons did not fit the general pattern for the relationship between either pH and A1 saturation or pH and Ca saturation.