SOIL ACIDIFICATION ALONG A-TOPOGRAPHIC GRADIENT ON ROUNDTOP MOUNTAIN, QUEBEC, CANADA

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.