ACIDIFICATION AND RECOVERY OF A SPODOSOL BS HORIZON FROM ACIDIC DEPOSITION

A laboratory study was conducted to examine acidification and recovery of a Spodosol Bs horizon from acidic deposition in the Bear Brook Watershed (BBW) in central Maine. A mechanical vacuum extractor was used to draw solutions through a soil column at three treatments containing 40, 100, or 160 μmol/L SO42−. Following 44 days of leaching, all treatments were decreased to the 40 μmol/L SO42− level to examine recovery from acidification. Acid additions were initially neutralized by release of basic cations and sulfate adsorption. Following attainment of steady-state conditions for basic cations and SO42− with respect to the soil adsorption complex, Al dissolution was the primary neutralization mechanism. Aqueous Al activities appeared to be regulated by equilibrium with an Al(OH)3 mineral phase. Following decreases in acid loadings, recovery was rapid resulting in retention of basic cations, reversible release of SO42−, and a marked reduction in the concentrations of soluble Al. © 1990, American Chemical Society. All rights reserved.