Effects of sulfuric acid rain on two model hardwood forests: throughfall, litter leachate, and soil solution

Abstract

Simulated sulfuric acid rain (pH 3.0, 3.5, 4.5, and 5.6) was applied to model forests containing either sugar maple (Acer saccharum) or red alder (Alnus rubra). Water samples were collected above and below the canopy, below the litter, and from 20 cm and 1 m below the surface of the soil. While throughfall chemistry was not very different from rain chemistry, the litter leachate (the actual input to the soil) had consistently higher concentrations of calcium and magnesium, and higher pH than the acid rain. For the first 6 months, sulfate absorption by the soil prevented any apparent differences in sulfate, calcium, or magnesium concentrations in the 20-cm soil solution among plots receiving acid or control rain treatments. Sulfate concentrations on plots receiving the most acid rain (pH 3.0) then became increasingly higher than on the other plots until after 3 years, they were approximately equal to sulfate concentrations in the rain. Twenty-cm soil solutions corresponding to the pH 3.5 and 4.0 treatments responded similarly starting respectively 1 year and 2 years after initiation of exposure to acid rain. Increased calcium and magnesium concentrations and lowered pH in 20-cm soil solution occurred simultaneously with increased sulfate concentrations. No acid rainmore » related effects were evident in the 1-m soil solution even after 3.5 years exposure to pH 3.0 sulfuric acid rain. Cation responses to increased anion concentrations followed those predicted by a computer-simulation model. However, sulfate concentrations in 20-cm soil solutions increased considerably faster than predicted by a Langmuir formulation of sulfate absorption.« less