Movement and transformation of(35)S-labelled sulphate in the soil of a heavily polluted site in the Northern Czech Republic.

Changes in chemistry and vertical distribution of(35)S were investigated in column experiments using intact topsoil and repacked mineral soil horizons 1 to 20 weeks after tracer application (901 kBq(35)S-SO4 (2-) per column 6.5 cm in diameter). Horizons O, A, AE and Bvs of an Orthic Podzol were incubated at 20°C and wetted twice a week with 11 mm of natural throughfall precipitation (38.5 mg S04 (2-) L(-1-), pH 3.3). The top 35 cm of the soil contained 1,290 kg S ha(-1), or 18 times more than is the annual atmospheric S input (71.4 kg S ha(-1) yr(-1)). Of this amount, 17.8 % was stored as inorganic sulphate S, 4.6 % as reduced inorganic S, and 77.6 % as organic S. In O + A and AE, free sulphate was the most abundant(35)S form, while in Bvs the 35S activity of free and adsorbed sulphate was similar. The proportion of adsorbed sulphate increased with depth, averaging 23, 30 and 47 % of total inorganic sulphate(35)S in O + A, AE and Bvs, respectively. Total specific activity of chemically transformed(35)S (i.e., of reduced inorganic S and organic S) constituted 3.4, 3.8 and 105 % of inorganic sulphate(35)S activity in O + A, AE and Bvs, respectively, in averaged weeks 2-4, and 7.5, 6.4 and 39.6 % in averaged weeks 11-13 in O+A, AE and Bvs, respectively. The turnover time of C-bonded(35)S was shorter than that of ester sulphate(35)S. An increase in FeS2- (35)S with time indicated anaerobic conditions suitable for bacterial sulphate reduction. After 13 weeks, 68 % of the tracer was found deeper than 8 cm below soil surface.