Discrepancies in Watershed S Budgets in Southeast Canada and Northeast U.S.: A Comparative Mass-Balance Approach

Myron Mitchell1, Cathy Eimers2, Gary Lovett3, Daniel Houle4, Scott Bailey5, Dean Jeffries6, Fred Beall7, Gene Likens3, Steve Norton8, Doug Burns9, Donna Schwede10, Don Buso11, Thomas A. Clair12, Jamie Shanley13, Kathleen Weathers3, Francois Courchesne14, Robert Vet15 and Louis Duchesne4

Atmospheric deposition of S has declined in eastern North America resulting in the partial recovery of watersheds from acidification. This partial recovery may be reduced by internal sources of S that can contribute sulfate to surface waters. To evaluate the role of various S sources we developed S budgets at 15 locations with well-studied forested watersheds in the Northeast U.S. and Southeast Canada. A major limitation in deriving accurate S budgets is obtaining an unbiased estimate of dry S deposition. We developed an empirical model using dry deposition values from the U.S. CASTNET and the Canadian CAPMoN networks. Our analyses included latitude, longitude, and the sulfur dioxide emissions for predicting SO2 concentrations in the atmosphere (r2=0.88). There was a strong relationship between estimated sulfur dioxide concentrations and estimates of total dry S deposition for both the CASTNET (r2 =0.90 and CAPMoN (r2 =0.93) networks. These estimates of SO2 concentrations and total dry S deposition were also compared to the regional CMAQ and AURAMS model for 2002. For each watershed dry deposition estimates were combined with measured wet deposition estimates. There were substantial differences in S budgets both within and among sites. Our results suggest that there is strong evidence of a substantial internal source of S in many of these watersheds. In a few cases this internal source includes the weathering of S minerals while in other cases this contribution appears to be derived from the mineralization of organic S in the soil. As atmospheric S deposition continues to decline the relative importance of these internal S sources as contributors to sulfate to drainage waters increases. Evaluating the contribution of these internal S sources is critical for making long-term predictions of the recovery of surface waters from acidification.

1SUNY-ESF, Syracuse, NY, Email:, Phone: 315-470-6765;
2Trent U., Peterborough, ON, Canada;
3Cary-IES, Millbrook, NY; 4Ministère Res. naturelles et de la Faune, QC, Canada;
5USDA Forest Service, Campton, NH;
6Environment Canada, Burlington, ON, Canada;
7Canadian Forest Service, Sault Ste. Marie, ON, Canada;
8U. Maine, Orono, ME;
9USGS, Troy, NY;
10USEPA, Research Triangle Park, NC;
11Cary-IES, Campton, NH;
12Environment Canada,Sackville, NB, Canada;
13USGS, Montpelier, VT;
14U. Montréal, Montréal, QC, Canada;
15Environment Canada, Toronto, ON, Canada