Effects of Forest Floor Leachate on Sulfate Retention in a Spodosol Soil
1988
Gobran, George R. | Nilsson, S Ingvar
Because of the involvement of several different mechanisms, sulfate retention in forest soils is a rather complicated process. We have investigated the effect of the dissolved substances from the forest floor of a Haplorthod soil (A0 horizon) on SO²⁻₄ mobility in the upper mineral soil (A1/A2 horizon). Sulfate retention (SO²⁻₄ retained in a solid phase) was estimated using two different solutions—distilled water solution (DWS) and forest floor leachate (FFL). Different concentrations of SO²⁻₄ (0.00–2000 mg S L⁻¹) were added to both extractants as Na₂SO₄-³⁵S. The results show that sulfate retention by the mineral soil (A1/A2) increased linearly with increasing SO²⁻₄ concentration in the DWS containing up to 500 mg S L⁻¹, whereas retention was zero when the soil was equilibrated with the FFL containing <250 mg S L⁻¹. However, retention started to increase linearly when the FFL contained more than 250 mg S L⁻¹. These data indicate that in the range of SO²⁻₄ found under field conditions, SO²⁻₄ retention was completely inhibited by the leachate solutions. These data also suggest that the organic ligands in the FFL were competing with SO²⁻₄ on the exchangeable positive charge sites. Moreover, they may have an inhibitory effect on the growth of some SO₄-Al mineral compounds, mainly jurbanite and/or basaluminite.
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