| Autor: |
Ludwig, Bernard, Khanna, Partap, Prenzel, Jürgen |
| Zdroj: |
Journal of Environmental Quality; July 1999, Vol. 28 Issue: 4 p1327-1335, 9p |
| Abstrakt: |
A decrease in sulfate (SO4) deposition in recent years has been predicted to affect the long‐term changes in soil SO4dynamics differently, depending upon the equilibrium approaches (sorption isotherms or AlOHSO4solubility) used. This study reassesses the usefulness of equilibrium approaches using data from batch experiments where the solution concentrations were changed in small steps. Experiments were carried out using five highly acid German subsoils. The approaches included solubilities of SO4minerals, the classical one‐ and two‐site Langmuir isotherms, an empirical Freundlich isotherm with a pH‐dependent coefficient and modified Langmuir isotherm approaches considering the activity of protons (H+‐dependent Langmuir) or the square of the proton activity ((H+)2‐dependent Langmuir) in the equations. The ion activity product of AlOHSO4was not constant for most experiments but was a function of the SO4sorption for all five soils. Dynamics of the retention and release of SO4in these soils indicated the limitation in the use of one‐ and two‐site Langmuir isotherms considering the theoretical basis behind these isotherms. The (H+)2‐dependent Langmuir isotherm approach described SO4sorption better than one‐ and two‐site Langmuir isotherms, but not as well as the pH‐dependent Freundlich and the H+‐dependent Langmuir isotherms. For describing SO4sorption in highly acid soils it is important to include its relationship with protons. It would mean using any of the following approaches: (i) the empirical pH‐dependent Freundlich isotherm, (ii) the H+‐dependent Langmuir isotherm approach, or (iii) an ion activity product of AlOHSO4as a function of SO4sorption. |
| Databáze: |
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