35S-sulphate reduction and transformation in peat

The incorporation of 35S-labelled sulphate into reduced inorganic forms and into organic S has been studied in peat samples from two contrasting sites, a deep blanket peat and a shallow hill blanket peat. During anaerobic incubation, 35S was rapidly incorporated into AVS (acid volatile sulphide), elemental S and Cr-reducible S but these pools showed evidence of rapid recycling. In the longer term, 35S was found in the ester sulphate pool and in a residual S pool, taken to be principally C-bonded organic S. Incorporation was more rapid in the deep peat than in the hill peat, in peat from wet areas more than dry areas and in subsurface (10–20 cm) peat more than in surface (0–10 cm) peat. Incorporation in the hill peat under aerobic incubation into either reduced inorganic or organic forms was very limited. Mean sulphate reduction rates at the temperature of incubation (26°C) were estimated to be in the range 60–12,000 μg S kg−1 wet weight peat d−1 while mean turnover times of reduced S were 17 and 550 d for the deep and hill peats, respectively.