Variability of sulfate sorption in a sandy Gleyic Podzol under a pine stand

In acid forest soils sulfate can be stored by sorption processes. We studie d the vertical heterogeneity and the horizontal variability of sulfate sorp tion in a sandy forest soil under a pine stand. Disturbed soil samples were taken from the horizons of a Gleyic Podzol (vertical heterogeneity). From a 120-m transect, 25 soil samples were taken from depth increment 35-50 cm and 65-80 cm at 5-m intervals by means of a hand auger (horizontal variabil ity). in batch experiments, sulfate sorption isotherms were measured for al l profile and transect samples. The Freundlich equation is suitable to desc ribe the individual isotherms. The sulfate sorption isotherms show consider able differences in the horizons of the profile, systematic relations betwe en the isotherm parameters and soil properties are not obvious. In order to quantify the spatial variability of the sulfate sorption isotherms, a scal ing technique is used. The spatial distribution of scale factors for depth 35-50 cm along the transect reveals a periodicity of about 17 m length. The same recurrent pattern is also identified in the spatial distribution of t he cumulative sulfate deposition by canopy throughfall along the transect, and in the spatial distribution of contents of iron and aluminium oxides so luble in oxalic acid at depth level 35-50 cm. This does, however, not refer to organic carbon content and pH at this depth. From these results it is c oncluded that in this soil at depth 35-50 cm oxide contents are related to the amount of sulfate deposition by throughfall. In spatial ranges with hig h sulfate and thus acid deposition, oxide contents of the soil are decrease d by accelerated podzolization, and therefore, also the sulfate sorption of the soil is low in these ranges. The period length of this recurrent patte rn of about 17 m is probably only an apparent period length that results fr om aliasing, because a very probably real periodicity of 3-4 m length, rela ted to the canopy edge distribution of the pine trees along the transect, i s sampled at an interval of 5 m. In the subsoil (65-80 cm depth) such relat ions could not be detected.