Journalof Paleolimnology 12: 35-47, 1994. 35 @ 1994 Kluwer AcademicPublishers.Printedin Belgium. Rates of peat accumulation over the past 200 years in five Sphagnum- dominated peatlands in the United States * R. Kelman Wieder 1, Martin Novgtk2, William R. Schell 3 & Thomas Rhodes 4 1Department of Biology, Villanova University, Villanova, PA, 19085 USA 2Czech Geological Survey, Kldrov 3, 118 21 Prague 1, Czech Republic 3Department of Environmental and Occupational Health and Toxicology, University of Pittsburgh, Pittsburgh, PA 15238, USA 4Rutgers University-Camden, Pinelands Research Station, New Lisbon, N J, USA Received 14 September 1993;accepted 16 March 1994 Key words." carbon cycling, climate change, organic matter, peat, peatland, Sphagnum Abstract Using 21°Pb-dating of peat cores, corroborated by pollen and acid-insoluble ash approaches, rates of vertical height growth, dry mass accumulation, and organic matter accumulation were determined for five Sphagnum-dominated peatland sites (one in Minnesota, one in Pennsylvania, one on the Maryland/West Virginia border, two in West Virginia), spanning a mean annual temperature range of 4.5 °C and differing in total annual precipitation by a factor of almost 2. Site differences in rates of vertical height growth and dry mass accumulation were documented, but both within-core and between-site differences in bulk density and ash concentrations of peat confound efforts to relate vertical height growth and dry mass accumulation to net organic matter accumulation. Taking bulk densities and ash concentrations into account, rates of net organic matter accumulation over the past 150-200 years were strikingly similar at four of the five sites, an unexpected result given the general trend that with decreasing latitude, peat deposits become older, thinner, and more highly decomposed. More comprehensive studies are needed in which net organic matter accumulation is determined at several locations within a single peatland, at several peatlands within a particular geographic/climatic region, and at peatland sites in different geographic/climatic regions. If additional studies confirm that recent (past 200 years) net organic matter accumulation is relatively insensitive to broad-scale regional climatic differences, boreal and subarctic peatlands may continue to function as a net sink for atmospheric CO2 and a net source of atmospheric CH4 with no change in rates of net organic matter accumulation, even under predicted scenarios of global climate change. Introduction Boreal and subarctic peatlands cover an estimated 346 million ha of the earth's land surface; their estimated 455 Pg of stored carbon represents approximately one third of the global soil carbon pool (Gorham, 1991). Most of these peatlands are located in regions that were covered with ice during the most recent glacial peri- * This publicationis the thirdpaperin a series ofpapers presented at the session on 'Past Climatic Change and the Developmentof Peatlands' at the ASLOand SWS Meetings in Edmonton, Canada, May 30-June 3, 1993. Dr E Kuhryand Dr S. C. Zoltai are serving as Guest Editors. od, so the large quantity of carbon presently stored as peat is a testament to the role of peatland ecosys- tems as a long-term net sink for photosynthetically fixed atmospheric CO2. Peatlands appear to contin- ue to be a net sink for atmospheric CO2, with esti- mates of present-day net carbon storage ranging from 0.076-0.3 Pg yr -1 (Miller 1981; Armentano & Ver- hoeven 1985, Gorham 1991). Contrastingly, peatlands may represent a substantial source of atmospheric CH4, concentrations of which continue to increase at about 0.9% yr -~ (Houghton et al., 1990). Globally, natural wetlands release an estimated 115 Tg of CH4 to the atmosphere (range 100-200 Tg) and thus may con-