Soil acidification along a topographic gradient on Roundtop Mountain, Quebec, Canada

Abstract

We examined the effects that different acidic loadings have had on soil chemistry along a toposequence on Roundtop Mountain. Due to fog interception by the forest canopy, the amount of time in the clouds is a major factor determining the amount and chemistry of precipitation reaching the soil and hence, acid precipitation loading is directly related to elevation. Soils on a transect from 520 to 850 m show a pattern of chemistry that corresponds to the loading of acidic deposition. Soil solutions collected at two elevations show different levels of both SO₄ and Cl, two of the anions in fog water as well as differences in concentrations of H ion and Al. Surface horizons of soils located at 850 m have pH in water as low as 3.7; in mineral horizons base saturation is extremely low (<5%) and Al saturation exceeds 95% in many cases. In contrast, lower on the mountain slope (below 650 m), pH is slightly higher (about 4.1) and base saturation rises to over 50% for the same soil horizons. There is a clear relationship between soil acidification and position on the mountain.