APPLICATION OF A SEQUENTIAL EXTRACTION PROCEDURE TO THE DETERMINATION OF THE DISTRIBUTION OF SULPHUR FORMS IN SELECTED PEAT MATERIALS

Total S (St), soluble sulphate, pyritic S, elemental S, carbon-bonded S (C-S) and organic sulphate S were determined on four peat samples and three sedimentary gyttja samples, one of which (Ginc.) had been subjected to aerobic incubation. A sequential extraction procedure was used to assess the distribution of St and of organic S forms in a series of peat fractions. Total S varied from 0.42 to 3.67%, with values below 1% associated only with freshwater-derived peats. The S content of brackish peat and of gyttja was consistently high and in some cases, organic S exceeded 6% of the organic matter. With the exception of Ginc., organic S accounted for a very high proportion of St (mean 94%), with C-S the dominant organic S form. Ginc. showed a very different S form distribution from the unincubated gyttja samples, with organic S accounting for only 44.5% of St, and organic sulphate-S exceeding C-S. Ginc. also had a lower pH, suggesting acidification resulting from oxidation of the organic C-S fraction during incubation. The recovery of St in seven peat (or gyttja) fractions averaged 99%, and indicated that humic acid and residue ("humin") fractions together generally accounted for most of the organic S (73.3–90.4%), with the notable exception of Ginc., for which these fractions only accounted for 42–47% of organic S. The proportion of humic acid-S increased with increase in degree of peat decomposition. The fulvic acid fraction contained variable proportions of St and had relatively more oxidized S forms than humic acid or residue fractions. Some oxidation of C-S occurred during alkaline extraction. Minor amounts of organic S were extracted with water, chloroform and ethanol-benzene. Key words: Sulphur forms, peat sulphur, gyttja, peat fractions