Limnol. Oceanogr., 39(5), 1994, 1172-l 185 0 1994, by the American Society of Limnology and Oceanography, Inc. Sulfur during early diagenesis in Sphagnum peat: Insights from 634S ratio profiles in 2 l”Pb-dated peat cores Martin Novcik Geological Survey, Klarov 3, 118 2 1 Prague 1, Czech Republic R. Kelman Wieder’ Department of Biology, Villanova University, Villanova, Pennsylvania 19085 William R. &hell Center for Environmental and Occupational Health and Toxicology, University of Pittsburgh, Pittsburgh, Pennsylvania 15238 Abstract 210Pb chronologies and depth profiles of stable S isotope ratios (834S) and concentrations of organic and inorganic S fractions were determined in peat cores from nine sites in the U.S. and the Czech Republic. Results indicate that depth profiles in S concentrations, S accumulation, and 634Sratios in peat deposits are affected not only by historical patterns in atmospheric S deposition but also by ongoing depth- dependent changes in S reduction-oxidation and S immobilization-mineralization processes within a peat deposit. These processes impart a certain degree of mobility to S in peat, bringing into question the validity of reconstructing historical records of S accumulation using dated peat profiles. Over long-term diagenesis, isotopically light S may be continually released from deep peat. This release may result in redistribution of S and S isotopes in peat and suggests that short-term patterns in S accumulation may not persist over much longer time scales. Sphagnum-dominated wetlands often ex- hibit a net retention of atmospherically de- posited S (cf. Bayley et al. 1986; Urban et al. 1989; Spratt and Morgan 1990). Sulfur reten- tion apparently is not the result of a fraction of the incoming S atoms becoming immobi- lized within the peat, with the remaining frac- tion passing through the peatland unaltered. Rather, the biogeochemical cycling of S in peat is quite dynamic. The quantity of S that cycles internally through oxidation and reduction re- actions in peat may far exceed S inputs (Urban et al. 1989; Spratt and Morgan 1990; Wieder et al. 1990). Subsurface peaks in total S, or- ganic S, and FeS,-S concentrations, typically I Corresponding author. Acknowledgments This work was supported by grants from the U.S. En- vironmental Protection Agency (R-812379) and the Na- tional Science Foundation (BSR 90-20583). WC thank FrantiSek Vesclovskjl and Bedfich Moldan for facilitating the collection of peat cores in the Czech Republic and Dale Nichols and Sandy Verry for assistance in collecting the cores from the bog in watershed S-2 of the Marcel1 Experimental Forest. We also appreciate the ongoing cooperation of the staff of the Monongahela Na- tional Forest in granting permission to work at Big Run Bog. located near the top of the permanently satu- rated peat (Urban et al. 1989; Novak and Wieder 1992), have been interpreted as re- sulting from bacterial sulfate reduction and the formation of both organic C bonded S (formed relatively slowly, but relatively stable once formed) and reduced inorganic S (e.g. FeS-S and FeS,-S; formed relatively rapidly, but rel- atively labile once formed). Thus, localized ac- cumulation of the reduced S end products of sulfate reduction has been implicated as the key process contributing to the generally re- ported retention of S in Sphagnum peatland ecosystems. However, little is known about the long-term fate of S in peatlands as peat accu- mulation proceeds. Previously (Novak and Wieder 1992), we reported changes in the concentrations of or- ganic and inorganic S fractions as a function of depth in peat cores collected from nine sites. In this paper, we apply 210Pb dating and stable sulfur isotope (634S) analyses to these same peat cores in an effort to better understand both the short-term cycling of S in near-surface peat and the longer term cycling of S during diagenesis. Study sites The nine sites, seven in the U.S. and two in the Czech Republic, have a predominantly 1172