The effects of atmospheric deposition on potassium, calcium, and magnesium cycling in two deciduous forests

Abstract

Sulfate was the dominant anion in throughfall and soil solutions from a chestnut oak (Quercus pinus L.) and a yellow poplar (Liriodendron tulipifera L.) forest in eastern Tennessee [USA]. Assuming much of this SO42- was of anthropogenic origin, cation-leaching rates from foliage and in soils of these forests would have to have been accelerated by acid deposition by two- to three-fold. This accelerated leaching could, in turn, cause changes in the rates of K+, Ca2+, or Mg2+ cycling according to any of a number of possible scenarios explored in this paper. Subsoils beneath the chestnut oak stand adsorbed SO42- from atmospheric deposition, which reduced SO42--mediated cation leaching to some extent. In contrast, subsoils from the yellow poplar stand showed a current net output of SO42- (perhaps desorbing sulfate adsorbed during previous periods of higher input) and much higher rates of cation leaching. The yellow poplar site showed net annual exports of Ca2+, Mg2+, K+, and Na+, but the chestnut oak showed a net accumulation of Ca2+ and lower net annual exports of Mg2+ and K+ than the yellow poplar site. both sites had inexplicably large net exports of Na+.