Forms and hydrolytic behavior of sulphur in humic acid and residue fractions of four peats from the Fraser Lowland

Humic acid (HA) and alkali-insoluble residue fractions (Residue) were isolated from four types of peat from the Fraser River Delta area. The peat fractions were characterized with respect to sulphur forms and response to acid hydrolysis. Total S content of HA fractions ranged from 0.3 to 5.5% on an ash-free basis, with 69–83% in C-bonded S form. Nitrogen: sulphur ratios varied between 0.64 and 5.9. The highest S contents and lowest N:S ratios were associated with peats formed under the influence of brackish water. Similar patterns were observed for the Residue fractions. Only small proportions of S (7.9–17.3%) were recovered in soluble form from the peat fractions after acid hydrolysis, and hydrolysis was accompanied by S losses attributed to volatilization. On average 4% of the initial C-bonded S was recoverable in that form in the hydrolysates, whereas 46% of the initial organic sulphate appeared in the hydrolyzate in sulphate form. The low recovery of S in hydrolyzates indicated a correspondingly small contribution of S-amino acids to the C-bonded S fraction. The large proportions of sulphur and carbon resistant to hydrolysis indicated a rather high degree of chemical (and perhaps biological) stability. Key words: Sulphur forms, hydrolyzable-S, peat humic acid, gyttja, peat fractions