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

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. Assuming much of this SO4^2- 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 SO4^2- from atmospheric deposition, which reduced SO4^2- mediated cation leaching to some extent. In contrast, subsoils from the yellow poplar stand showed a current net output of SO4^2- (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 site 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⁺.

Duke Scholars

Author Daniel D. Richter Earth and Climate Sciences