Behaviour of sulphur during diagenesis of a maritime ombrotrophic peat from Yell, Shetland Islands, UK

Surface water, pore water, vegetation and peat cores were sampled from a waterlogged ombrotrophic peat bog on the Shetland Isles, UK and analysed for different S forms and their isotopic composition, in an attempt to elucidate the biogeochemical processes affecting S during peat diagenesis. Surface waters show that inputs of S to the peat have a maritime-dominated isotopic composition close to +20 parts per thousand(CDT). Uptake of S by vegetation introduces a -10 parts per thousand. shift in delta S-34 from these input values. Below the vegetation layer and down to 18 cm depth, bacterial SO42- reduction is the major control on S species distribution and isotopic composition within the solid peat and pore waters. In this part of the peat, preferential reduction of (SO4)-S-32 in pore water during metabolism produces isotopically light sulphide, which is incorporated into the solid phase in both inorganic and organic forms, while pore water SO42- becomes enriched in 34S. From 18 to 28 cm, organic 4 S content falls relative to C and residual organic S becomes 34 S-enriched, indicative of mineralization of organic S, a process which releases isotopically light S to the pore waters. Still deeper in the core (28 to similar to 50 cm), bacterial reduction of pore-water SO42- S-34, now enriched in, results in addition of isotopically heavy S to the solid phase. Limited pore water data suggest that below 50 cm mineralization reactions again release S from the organic fraction of the peat. (c) 2005 Elsevier Ltd. All rights reserved.