SOIL RESPONSE TO ACID DEPOSITION, WIND RIVER MOUNTAINS, WYOMING .1. SOIL PROPERTIES

In the western USA, alpine and subalpine ecosystems with shallow soils and large areas of rock outcrop may be particularly sensitive to damaging effects from acid precipitation, especially downwind of pollutant sources. This study was conducted to characterize the capacity of subalpine soils in the Wind River Mountains of Wyoming to neutralize acid deposition through cation exchange and SO4 adsorption, and to relate buffer capacity and SO4-adsorption isotherms to other soil properties. Although B and C horizons of one Dystric Cryochrept pedon have low exchange capacity ( < 6 cmol(c) kg-1) and low base saturation ( < 0.1), soils in general appear to have sufficient base-exchange capacity to neutralize anticipated acid-deposition rates. All other horizons sampled have base saturations in excess of 0.2. Most soils will adsorb SO4, although adsorption maxima are estimated at < 1.5 mmol kg-1. High organic-matter content of A horizons in Humic Cryaquepts interferes with SO4 adsorption. Buffer capacities above pH 4 average 4.00 cmol kg-1 pH-1; below pH 4, soils are more strongly buffered, averaging 18.7 cmol kg-1 pH-1. Base exchange is probably the dominant process controlling buffering above pH 4, and dissolution of Al (OH)3 controls buffering in the pH range 2.8 to 4.