Interference by organic complexation of Fe and A1 on the SO 2‐ 4 adsorption in Spodic B horizons in Sweden

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SUMMARY The relations between pH, different fractions of Fe and A1 and Na 4 P 2 O 7 ‐soluble C and the amount of adsorbed SO 2‐ 4 were assessed by analysing 63 soil samples from 14 podsolized soils in Sweden. The amount of adsorbed SO 2‐ 4 was significantly better correlated with the calculated amount of the inorganic fraction of Fe and A1 oxides obtained by subtracting Na 4 P 2 O 7 ‐soluble Fe and A1 from oxalate‐soluble Fe and Al than with the oxalate extraction alone. There was a close correlation between C and organically‐bound S in the Na 4 P 2 O 7 extract which shows that the C:S ratio of the extracted fulvic acids is about constant in the soils studied. It was found that, as the proportion of organically‐complexed Fe and Al increases, the ability of the soil to adsorb SO 2‐ 4 decreases. The amount of adsorbed SO 2‐ 4 expressed on the basis of the amounts of oxalate‐soluble Fe and Al was generally smaller in areas with low S deposition (< 60 mmol m ‐2 a ‐1 ). The ratio between pyrophosphate‐soluble C and oxalate‐extractable Fe and Al was negatively correlated with pH in water. It was concluded that Fe and Al associated with organic matter cannot adsorb SO 2‐ 4 and that the degree of this association is pH dependent. These observations have important implications regarding the effects of anthropogenic acidification.