Aluminum Leaching by Mineral Acids in Forest Soils: I. Nitric‐Sulfuric Acid Differences

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Abstract
In laboratory studies simulating snowmelt leaching of forest soils, HNO3 leached more Al than did H2SO4 from soil columns containing a forest floor‐spodic horizon sequence (FF/Bs) representative of high elevation forest soils and watersheds thought to be sensitive to acidification by acid precipitation. Increasing the HNO3 concentration 100‐fold (pH 5 to 3) increased total Al concentration in leachates from 0.70 to 0.85 mM, while increasing H2SO4 concentration had no effect. Addition of pH 3 H2SO4 to the FF/Bs columns raised leachate pH relative to pH 3 HNO3 and control treatments, and resulted in the lowest Al concentrations of all treatments in the first three of four sequential leachings. In albic (E) and ochric (A) mineral soil horizons below a forest floor, there were no differences between the acids and no effects of changing acid concentration. Concentrations of Al leached by the acids did not differ from those in control treatments. The differences in effects of HNO3 and H2SO4 on soluble Al and pH in the Bs horizon and the lack of effect of either acid in the E and A horizons imply that the type of mineral horizon below the forest floor and the kind of acid leaching through these horizons are pertinent to predicting lake acidification in diverse forested watersheds. The results also have implications for pollution control strategies focusing solely on SO2 emissions and designed to mitigate lake acidification.