Soil acid-base chemistry of a high-elevation forest watershed in the great smoky mountains national park: Influence of acidic deposition

Meijun Cai, Amy M. Johnson, John S. Schwartz, Steve E. Moore, Matt A. Kulp

Research output: Contribution to journalArticle

14 Scopus citations


Understanding the acid-base chemistry of soil and the soil processes related to the release or retention of sulfate and nitrate is important in order to predict watershed recovery from long-term acid deposition. Soils were sampled from the Noland Divide Watershed (NDW), a small, high-elevation watershed in the Great Smoky Mountains National Park receiving high rates of acid deposition over several decades. Soil samples were measured for chemical properties related to acidification and used to conduct sulfate adsorption and nitrogen (N) incubation experiments. Shallow soil was higher in acidic and basic ions than deeper soils, and the mean effective cation exchange capacity was 8.07, 5.06, and 3.57 cmol ckg -1 in the A, Bw, and Cb horizons, respectively. In all three soil horizons, the base saturation was equal to or below 7% and the ratio of Ca/Al was below 0.01, indicating that the NDW is very sensitive to acid deposition. Based on results from sulfate adsorption isotherms, the NDW has not reached its maximum sulfate adsorption saturation and is likely able to retain further additions of sulfate. Desorption of sulfate from NDW soils is expected if sulfate concentrations in soil solution drop below 50 μeq L -1 but is highly dependent on soil pH and organic carbon content. Total soil organic N was 500 times greater than inorganic N in the A soil horizon, and net N mineralization and nitrification remained constant during a 28-day incubation indicating a large reservoir of N substrate for soil microbes. Nitrogen experiment results suggest that nitrate export from the watershed is largely controlled by biological processes rather than by nitrate deposition flux. Soil data collected in this study contributes to our understanding of biogeochemical processes affecting the response of acid-impacted ecosystems such as the NDW to future changes in atmospheric deposition.

Original languageEnglish (US)
Pages (from-to)289-303
Number of pages15
JournalWater, Air, and Soil Pollution
Issue number1
StatePublished - Jan 1 2012


  • Acidic deposition
  • Biogeochemical processes
  • Nitrification
  • Soil characteristics
  • Southern Appalachian
  • Sulfate adsorption

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