SULFATE ADSORPTION AND SULFUR FRACTIONS IN A HIGHLY WEATHERED SOIL UNDER A MIXED DECIDUOUS FOREST

A laboratory study was undertaken to test the hypothesis that sulfur is accumulating by sulfate adsorption in a mixed deciduous forest soil. Sesquioxide-rich subsurface soils had a large reservoir of phosphate-soluble, adsorb sulfate-S (2700 kilograms per hectare), but would not permanently adsorb more. Surface soils had no detectable adsorbed sulfate, but a substantial reserve of water-soluble sulfate-S(110 kilograms per hectare). Surface soils were also capable of adsorbing more sulfate into forms not extactable with water of phosphate solution. The high proportion of water-soluble sulfate appears to play an important role in determining sulfate concentrations in headwater streams. During peak storm flow periods, sulfate concentrations in headwater streams increase, and it is hypothesized that this is due to leaching from surface horizons in the variable source areas of the watershed. It is hypothesized further that the water-soluble sulfate pool in surface horizons is active in sulfur-cycling processes, whereas water-insoluble sulfate in subsurface horizons constitutes an inactive, long-term sulfur reserve. © 1979 The Williams & Wilkins Co.