CONTRASTING THE GEOCHEMISTRY OF ALUMINUM AMONG PEATLANDS LEAH BENDELL-YOUNG* Department of Biological Sciences, Simon Fraser University, Burnaby, B.C. V5A 1S6 and FRANCES R. PICK Department of Biology, University of Ottawa, Ottawa, Ontario, KIN 6N5 (Received 25 August, 1993; accepted in final form 27 December, 1993) Abstract. Aluminum concentrations were measured in surface waters, pore waters and surface peats of 15 wetlands in south-central Ontario. Wetlands were grouped floristically and chemically as mineral- poor, moderately-poor or mineral-rich fen. Mineral-poor fens were dominated by Sphagnum, were low in alkalinity (0.31 #eq L- i) and pH (4.5-6.3). Moderately-~oor fens had a mixture of vegetation (Sphagnum, sedges and grasses), mid-alkalinity (23-91 #eq L- ) and pH (5.8-6.4). Mineral-rich fens were dominated by sedges and grasses, had high alkalinity (104-181 #eq L -l) and circumneutral pH (6.2-6.3). Surface water A1 concentrations were less in mineral-poor versus moderately-poor and mineral-rich fens (F = 32.0; P < 0.05). Pore water A1 concentrations were lower in 4 of 5 mineral versus the mineral-rich fens (F = 92.15; P < 0.05). In all but two cases pore water A1 (all species < 0.2 #m) were greater within the fen peats versus the overlying surface waters suggesting that peats could act as a source of A1 to the overlying waters. In all wetlands, 70 and 30% of peat A1 was recovered by a hydroxylamine hydrochloride/acetic extract (primarily inroganic) and an ammonium hydroxide extract (primarily organic), respectively. Differences in "extractable" A1 recovered by the two reagents (i.e., inorganic + organic A1) among the 15 wetlands were independent of wetland type. Distribution coefficients, K9, were different among the 3 types of wetlands (F -- 25.0; P < 0.05) with the Sphagnum dominated mineral-poor fens containing higher values versus the sedge and grass dominated mineral-rich fens. Lower surface and pore water concentrations of A1 in mineral- poor versus mineral-rich fens may in part be a result of differences in the degree of minerotrophic influences between the two types of peatlands. As well. the greater binding capacity of Sphagnum peat as indicated by higher KD's in the mineral-poor fens, may have contributed to the observed lower pore water and surface water A1 concentrations in mineral-poor versus mineral-rich fens. It has been postulated that anthropogenic acidification of peatlands will accelerate the transformation of a mineral-rich fen to that of a mineral-poor fen and ultimately to bog. Changes in A1 geochemistry that may ensue as this transition occurs include decreases in pore and surface water A1 concentrations with concurrent increases in peat bound A1. 1. Introduction The total area of wetlands in Canada has been estimated at 150 million ha (Kivinen and Pakarinen 1981). These areas are vital for the survival of mammals, migratory and non-migratory birds, plus a variety of common and endangered plants. Further, on the Canadian Precambrian shield, many streams and lakes receive drainage from wetland areas. This runoff has the potential to affect the chemistry of the receiving * To whom all correspondence should be addressed. Water, Air, and Soil Pollution 81: 219-240, 1995. 9 1995 Kluwer Academic Publishers. Printed in the Netherlands.