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This article in SSSAJ

  1. Vol. 52 No. 4, p. 1148-1154
    Received: June 15, 1987

    * Corresponding author(s):
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Potential for Buffering of Acidic Precipitation by Mineral Weathering in a Forested Entisol

  1. J. G. Bockheim ,
  2. J. E. Leide,
  3. C.S. Li and
  4. D. A. Wentz
  1. Dep. of Soil Science, 1525 Observatory Dr., Univ. of Wisconsin, Madison, Wi 53705
    Res. Ctr. for Eco-Environmental Sciences, Academia Sinica, Beijing, China
    Water Resources Div., U.S. Geological Survey, Madison, WI 53719



Bulk precipitation, soil-water, and groundwater chemistry were monitored at Round Lake, a small, forested catchment receiving acidic precipitation (pH 4.6) in northwestern Wisconsin. The groundwater basin retained H ion and released nonhydrolyzable cations (NHC = Ca, Mg, Na, K) and Si. The percentages of plagioclase feldspar, hornblende, olivine, and augite increased with depth in soils from the catchment; quartz, orthoclase feldspar, and weathered mica decreased with depth. Thermodynamic stability indices estimated from water-quality and mineralogic data, and from the WATEQF chemical speciation model indicate that the soil-water and groundwater are undersaturated with respect to hornblende, chlorite, olivine, augite, plagioclase, and orthoclase feldspars and that these minerals may be undergoing dissolution. Minimally disturbed soil cores were leached with dilute H2SO4 and distilled water (pH 3.0 to 5.7). When the pH of the extracting solution was ≥4.5, Ca was released in the greatest amounts, followed by Si, Mg, K, Na, and Al. This ranking is similar to that for cations in groundwater. Leaching with a pH 3.0 solution released Si in the greatest amounts from the C horizon, followed by the Bw2, Bw1, and A + B/E horizons. This trend parallels the depth distribution of weatherable minerals in the very fine sand fraction. Results from the laboratory leaching study confirm the chemical modeling studies, indicating that mineral weathering (hydrolysis) can contribute to buffering within the groundwater basin at Round Lake.

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