Composition, distribution and neutralization of 'acid rain' derived from Masaya volcano, Nicaragua.

Acid rain (pH 2.5-5.0) from the volcanic plume of Masaya Caldera, Nicaragua, is composed of HCl and H₂SO₄ in systematically varying proportions. The dominance of HCl in volcanic acid rain makes it distinctly different from anthropogenic acid rain. The pH of volcanic acid rain is largely controlled by its HCl concentration. Volcanic acids are locally damaging, killing vegetation with the conspicuous exception of the shrubs Malanthora and Lantana. These shrubs have the ability to rapidly and completely neutralize acid rain by releasing K⁺ at their leaf surfaces. The mechanism by which these plants sustain their acid neutralizing capacity is evidently by pumping acidity into the soil in exchange for K⁺ from soil exchange surfaces. In effect the Malanthora shrub layer is acting as a short-term acid sink for incident acid rain. However, the final acid sink in this system is the base exchange reservoir of the local soils. -Authors