Chemical and pedogenetic effects of simulated acid precipitation on two eastern Canadian forest soils. I. Nonmetals

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Abstract
An experiment involving the addition of simulated acid rain to two Canadian Shield orthic humo-ferric podzolic forest soils was carried out in the field and in the laboratory. Soils were subjected to treatments of pH 5.7, 3.5, and 2.0 water containing added nitric and sulphuric acids in a 1:2 molar ratio. Pore-water concentrations of H+, NH4+, NO3-, SO42-, and Cl- were monitored at depths of 15-60 cm for up to 2 years. Some of the laboratory columns were dismantled after 1 year and total soil N, S, soil pH, and S adsorption characteristics were measured. Half the columns were sterilized in an attempt to assess the relative importance of microbial processes. Considerable H+ buffering by the soils was indicated, with soil pH unchanged even under the most acidic treatment. Nitrate but not ammonium production was suppressed under highly acid treatment conditions in the laboratory, while in the field only small concentrations of both nitrogen species were detected in pore water. No change in total soil N was detected. Sulphur retention was assessed, with major amounts retained by the soil just below the Ae horizon where iron and aluminum oxides along with organic matter accumulate. Sterile column data indicates microbial processes are also of considerable importance in the immobilization of S inputs.