The Acid-Base Balance of Peatlands: a short-term perspective N. R. Urban Environmental Engineering Program, University of Minnesota 122 CME Bldg, 500 Pillsbury Drive, Minneapolis, Mn 55455 USA S. E. Bayley Dept. of Botany, University of Manitoba, Winnipeg, Manitoba R3T 2N2 Canada ABSTRACT. Acidity budgets for an artificially acidified and an unacidified peatland in mid-continental North America are dominated by the production and export of organic acids. A fraction (about 50%) of these acids are neutralized by alkalinity from atmospheric deposition and upland run-off. The acid applied to the experimentally acidified site is neutralized by uptake of nitrate and sulfate. Short-term measurements show that nitrate is taken up rapidly in surface layers of moss while sulfate penetrates more deeply into the peat. Sulfate retention within the two sites ranges from 56 to 70% on an annual basis. Stripping of basic cations is shown to result from acid application to base-rich peat. These results suggest that short-term effects of acid deposition on peatlands will be slight, but long-term site acidification is possible. I. Introduction There are many important chemical links between peatlands and other systems. Globally peatlands are significant reservoirs of carbon (Clymo, 1986), and they may be important sources and sinks for N and S gases (Hemond, 1983; Urban, 1983). Wetlands greatly modify the composition of precipitation and upland or stream run-off flowing through them. They may consume alkalinity (Bayley and Schindler, 1986), remove trace metals (Eger et al., 1981), sequester nutrients (van der Valk et al., 1978), and neutralize acid mine drainage (Wieder and Lang, 1982). Perhaps most importantly, peatlands export large amounts of organic acids (Hemond, 1980; Urban et al., 1986) which have a profound impact on the acid-base balance of receiving waters (Gorham, 1957; Glover and Webb, 1979; Henriksen and Seip, 1980; Webb, 1982; Wright, 1983; Kerekes, 1984). Hemond (1980) presented the first acidity budget for a bog and found that production of organic acids, primarily humic and fulvic , acids arising from the decomposition of vegetation (McKnight et al. 1985), Water, Air, and Soil Pollution 30 (1986) 791-800. © 1986 by D. Reidel Publishing Company.