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Recovery of Surface Waters in the Northeastern U.S. from Decreases in Atmospheric Deposition of Sulfur |
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| Authors: | Driscoll CT Likens GE Church MR |
| Institution: | 1. Department of Civil and Environmental Engineering, Syracuse University, Syracuse, NY, 13244, USA 2. Institute of Ecosystem Studies, Box AB, Millbrook, NY, 12545, USA 3. U.S. EPA, 200 SW 35th Street, Corvallis, OR, 97333, USA |
| Abstract: | A simple mass flux model was developed to simulate the response of SO4 2- concentrations in surface waters to past and anticipated future changes in atmospheric deposition of SO4 2-. Values of bulk (or wet) SO4 2- deposition and dry deposition of S determined from measured air concentrations and a deposition velocity were insufficient to balance watershed SO4 2- 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: 1) 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 SO4 2- 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 SO4 2-. Model simulations indicated that soil adsorption reactions significantly delayed the response of stream water to declines in SO4 2- 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. |
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