Sulphur forms in open and afforested areas of two scottish peatlands

Sulphur forms were determined at two peatland sites in Scotland, each having both open bog vegetation and afforested areas. Afforestation activity (including initial ploughing and, in one case, active drainage) had a significant effect on peat physical characteristics, depending on the depth sampled, but had less influence on S chemistry. There was no significant difference in mean total S concentration (mean of 0.24% over the upper 100 cm peat) between the two sites or between the afforested and open areas. Organic S was dominant with approximately 64% of the total S being C-bonded S and 27% ester sulphate S. Reduced inorganic forms (acid volatile S, elemental S and Cr-reducible S) accounted for approximately 8% of the total S. On average, only half of the Cr-reducible S could be accounted for by pyrite S as determined by analysis of the Fe; the remainder was considered to be an organic S fraction. The presence of both S-oxidizing thiobacilli and sulphate-reducing bacteria were indicative of an active oxidation/reduction cycle that resulted in the accumulation of S at or below the mean water table. The results are discussed in terms of S retention and alkalinity generation in peatlands.