3 DECADES OF OBSERVED SOIL ACIDIFICATION IN THE CALHOUN EXPERIMENTAL FOREST - HAS ACID-RAIN MADE A DIFFERENCE

Three decades of repeated soil sampling from eight permanent plots at the Calhoun Experimental Forest in South Carolina allowed us to estima te the rate of soil acidification, the chemical changes in the soil ex change complex, and the natural and anthropogenic sources of acidity c ontributing to these processes. During the first 34 yr of loblolly pin e (Pinus taeda L,) forest growth, soil pH, (pH in 0.01 M CaCl2) decrea sed by 1 unit in the upper 0- to 15-cm of soils and by 0.4 and 0.3 uni ts in the 15- to 35- and 35- to 60-cm layers, respectively. Throughout the 0- to 60-cm horizon, base ration depletion averaged 1.57 kmol(c) ha(-1) yr(-1) and effective and total acidity increased by 1.26 and 3. 28 kmol(c) ha(-1) yr(-1), respectively. A forest H+ budget estimated f or these decades indicated that 38% of soil acidification was due to a cid deposition, while 62% of soil acidification was attributed to the internal functioning of the ecosystem. Soil samples archived during th e three-decade experiment also document decreases in soil-adsorbed SO4 2-, presumably in response to decreasing atmospheric inputs in recent years.