The mitigating effect of decreasing anthropogenic SO4 deposition on acidifi
ed soils and waters can be delayed by the release of previously stored soil
SO4. We investigated SO4 pools and desorption in the weathered substrata (
0.5-10 m depth) of a forested catchment on granite to quantify the importan
ce of these layers to SO4 dynamics. Solid-phase materials from 10 boreholes
to a maximum depth of 10 m were analyzed for water- and phosphate-extracta
ble SO4, SO4 desorption, cation-exchange capacity (CEC), pH, and dithionite
- and oxalate-extractable Fe (Fe-d and Fe-o) and Al (Al-d and Al-0). Seven
of the investigated boreholes were used to monitor water table depth and to
obtain samples for measurement of solution SO4 concentrations. The storage
of phosphate-extractable SO4 in the weathered substrata was estimated at 9
0 kmol ha(-1), of which approximate to 50 kmol ha(-1) were water soluble, S
ulfate pools and their desorption behavior were highly variable, which coul
d partly be explained by the variation of pH and extractable Fe and Al cont
ents of the samples, Sulfate concentrations in groundwater were dependent o
n the depth of groundwater table and corresponded with the depth gradients
of solid-phase SO4. The SO4 pools of the substrata were apparently regulati
ng solution concentrations. Thus, groundwater acidification in such aquifer
s will not be easily reversed by decreasing SO4 deposition because of the r
elease of previously stored SO4.