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Laboratory Investigation of Leachate Chemistry from Six Appalachian Forest Floor Types Subjected to Simulated Acid Rain¹

ABSTRACT

In order to determine the role of the forest floor in neutralization of strong acidity in acid rain, simulated acid rain at pH 4.0 was applied under laboratory conditions to forest floor samples from six Appalachian forest types. Effects of forest type, storm size, and repeated storm applications on leachate chemistry were investigated. Forest floor leachate from a hemlock forest [Tsuga canadensis (L.) Carr.] showed significantly lower pH (mean pH 3.9) than other leachate types due to high concentrations of organic acids. Cove hardwood forest found in an area with calcareous soil parent material produced forest floor leachate with a significantly higher pH (mean pH 6.5) than other forest types. Forest floor leachates from mixed oak (Quercus spp.), northern hardwood, red pine (Pinus resinosa Ait.), and white pine (P. strobus L.) forests were intermediate in pH (mean pH 4.1–4.4) due to the acidifying influence of organic acid leaching balanced against the neutralizing effect of H⁺ exchange for Ca²⁺ in the forest floor. Weak acidity concentrations obtained by Gran plots were well correlated with 400-nm wavelength transmittance and anion deficits in the leachates. Organic anions dominated leachates from hemlock and mixed oak forest types. Increasing storm sizes caused reduced ionic concentrations, especially of H⁺, Mg²⁺, and Ca²⁺, but three repeated storms produced no consistent significant reductions in loads or concentrations.

Key Words: weak acidity • Gran titrations • organic acids • 400-nm transmittance

¹ Research sponsored by the USDA Forest Service, Northeastern Forest Exp. Stn., under Coop. Res. Agreement no. 23-557.

² Professor of forest hydrology, Inst. for Res. on Land and Water Resour. and School of Forest Resour., Pennsylvania State Univ., University Park, PA 16802; former environmental pollution control graduate student, Pennsylvania State Univ.; project leader and hydrologist, Timber and Watershed Lab., USDA Forest Service, Parsons, WV 26287, respectively.

Received for publication March 2, 1984.