Clay‐mineral contribution to the weathering mechanisms in two contrasting watersheds

SUMMARY Two mountain watersheds in eastern USA showed sensitivity of their bedrock type to acidification from changes in atmospheric input: they were a Catoctin Mountain watershed on Precambrian metabasalt, and a Massanutten Mountain watershed developed on Silurian metaquartzites and shales. The role of clay minerals to neutralize potential increases in acid deposition was examined. Landscape position and drainage characteristics influence the clay mineral suites present at Catoctin, and an expandable clay component enables this watershed to adequately buffer the hydrochemical systems. A 14 A hydroxy-interlayer vermiculite provided a sink for A13+, and also a possible neutralizing effect in the second watershed which was highly sensitive to acid deposition.