ACIDIC ATMOSPHERIC DEPOSITION AND CANOPY INTERACTIONS OF ADJACENT DECIDUOUS AND CONIFEROUS FORESTS IN THE GEORGIA PIEDMONT

The effects of acidic atmospheric deposition on leaching of base catio ns from the canopy and the origin of the major ions in throughfall and stemflow were evaluated in a 2-year study of adjacent deciduous and c oniferous forests at Panola Mountain Research Watershed in the Georgia Piedmont. In each forest, the NO3- and SO42- in throughfall and stemf low were derived primarily from atmospheric deposition, whereas the ba se cations Ca2+, Mg2+, and K+ were derived primarily from canopy leach ing. Acidic atmospheric deposition was partially neutralized in each f orest. Exchange of H+ with base cations appeared to be the major mecha nism for the neutralization of atmospheric acidity by the deciduous ca nopy. Major neutralization mechanisms could not be differentiated in t he coniferous canopy. Base-cation leaching accounted for 86% of the ba se cations in throughfall and stemflow in the deciduous forest and 69% in the coniferous forest. Exchange with H+ accounted for about 30% of base cations in throughfall in the deciduous forest, whereas it could not be clearly estimated in coniferous throughfall. The current level of acidic atmospheric deposition is hypothesized to have caused an in creased leaching of base cations of the deciduous canopy, but methods were insufficient to determine its effect on the coniferous canopy.