Paper No. 3
Presentation Time: 8:45 AM
UNDERSTANDING SULFATE DYNAMICS IN UNGLACIATED EASTERN U.S. CATCHMENTS
RICE, Karen C.1, DEVINEY, Frank A.
2, COSBY, Bernard J.
2 and LYNCH, Jason
3, (1)USGS and University of Virginia, USGS and University of Virginia, Department of Environmental Sciences, P.O. Box 400123, Charlottesville, VA 22904, (2)University of Virginia, Department of Environmental Sciences, P.O. Box 400123, Charlottesville, VA 22904, (3)U.S. Environmental Protection Agency, Clean Air Markets Division, 1200 Pennsylvania Ave. NW, Washington, DC, 20460, kcrice@usgs.gov
Several decades of acidic atmospheric deposition have affected the quality of eastern U.S. stream water. Sulfate, derived from acid rain, is the primary acidifying component deposited in surface waters. The Clean Air Act legislation and amendments have gone far in reducing sulfate deposition to Earth’s surface. Studies of trends in sulfate concentrations in surface waters in the northeast have shown declines in sulfate concentration accompanying the declines in sulfate deposition. Stream sulfate concentrations in the Mid-Atlantic and southeast, however, have shown no significant change. The common explanation for the lack of response in streams in the Mid-Atlantic and southeast is that sulfate deposited from the atmosphere is adsorbed onto clay minerals in soils and retained in the catchment. Long-term sulfate input/output budgets for catchments in the region are needed to test this hypothesis.
To conduct such a sulfate input/output budget analysis, we searched for sites with simultaneous monitoring of stream discharge and sulfate concentrations and for which estimates of dry and wet deposition are available. We compiled data from long-term studies of forested catchment streams in the eastern U.S. south of the line of glaciation, from northern Pennsylvania to northern Georgia along the spine of the Appalachian Mountains. We analyzed stream discharge and sulfate concentrations in 34 catchments, with records at some sites as long as 35 years. Estimates of wet deposition were derived from the National Atmospheric Deposition Program and extrapolated to each of the 34 sites. Dry deposition estimates were derived from U.S. EPA’s CMAQ model for each site. Although the biogeochemical budgets of several of the individual catchments have been analyzed extensively, this study presents the first regional analysis of the sulfate budgets for all 34 catchments. Our analysis demonstrates that over the period of record for this data set, atmospheric deposition has exceeded stream export in most cases, supporting the hypothesis that catchment soils in this region are strong retainers of sulfate.
