Recovery of surface waters in the northeastern U.S. from decreases in atmospheric deposition of sulfur

C. T. Driscoll, G. E. Likens, M. R. Church

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


A simple mass flux model was developed to simulate the response of SO42- concentrations in surface waters to past and anticipated future changes in atmospheric deposition of SO42-. Values of bulk (or wet) SO42- deposition and dry deposition of S determined from measured air concentrations and a deposition velocity were insufficient to balance watershed SO42- export at the Hubbard Brook Experimental Forest, NH and for a regional survey of watersheds in the northeastern U.S. We propose two explanations for the unmeasured S source: I) a significant underestimation of dry S deposition, and/or 2) internal watershed S sources, such as weathering and/or mineralization of soil organic S. Model simulations based on these two mechanisms agreed closely with measured stream SO42- concentrations at Hubbard Brook. Close agreement between measured and model predicted results precluded identification of which of the two mechanisms controlled long-term trends in stream SO42-. Model simulations indicated that soil adsorption reactions significantly delayed the response of stream water to declines in SO42- inputs since 1970, but could not explain the discrepancy in watershed S budgets. Extrapolation of model predictions into the future demonstrates that uncertainty in the source of the S imbalance in watersheds has important implications for assessments of the recovery of surface water acid neutralizing capacity in response to anticipated future reductions in SO2 emissions.

Original languageEnglish (US)
Pages (from-to)319-329
Number of pages11
JournalWater, Air, and Soil Pollution
Issue number1-2
StatePublished - Jul 1998


  • Acid neutralizing capacity
  • Hubbard Brook Experimental Forest
  • Mass balance model
  • Reduced SO emission
  • Sulfur deposition
  • Surface water sulfate

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Ecological Modeling
  • Water Science and Technology
  • Pollution


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