title: Predicting sulphate adsorption/desorption in forest soils: evaluation of an extended Freundlich equation.
abstract: Sulphate adsorption and desorption can delay the response in soil acidity against changes in acid input. Here we evaluate the use of an extended Freundlich equation for predictions of pH-dependent SO4 adsorption and desorption in low-ionic strength soil systems. Five B horizons from Spodosols were subjected to batch equilibrations at low ionic strength at different pHs and dissolved SO4 concentrations. The proton coadsorption stoichiometry (η), i.e. the number of H(+) ions co-adsorbed for every adsorbed SO4(2)(-) ion, was close to 2 in four of five soils. This enabled the use of a Freundlich equation that involved only two adjustable parameters (the Freundlich coefficient KF and the non-ideality parameter m). With this model a satisfactory fit was obtained when only two data points were used for calibration. The root-mean square errors of log adsorbed SO4 ranged from 0.006 to 0.052. The model improves the possibility to consider SO4 adsorption/desorption processes correctly in dynamic soil chemistry models.
authors: Department of Soil and Environment, Swedish University of Agricultural Sciences, Box 7014, 750 07 Uppsala, Sweden; Division of Land and Water Resources Engineering, KTH Royal Institute of Technology, Brinellvägen 28, 100 44 Stockholm, Sweden. Electronic address: jon-petter.gustafsson@slu.se.
authors: Jon Petter
authors: JP
authors: Gustafsson
authors: Division of Land and Water Resources Engineering, KTH Royal Institute of Technology, Brinellvägen 28, 100 44 Stockholm, Sweden.
authors: Muhammad
authors: M
authors: Akram
authors: Department of Soil and Environment, Swedish University of Agricultural Sciences, Box 7014, 750 07 Uppsala, Sweden.
authors: Charlotta
authors: C
authors: Tiberg
mesh_terms: D000327:Adsorption; D065928:Forests; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D012987:Soil / Q000737:chemistry*; D013431:Sulfates / Q000737:chemistry*; D013548:Sweden
chemical_list: D012987:Soil; D013431:Sulfates
keywords: Acidification; Freundlich; Spodosols; Sulphate adsorption; pH