MOVEMENT AND TRANSFORMATION OF S-35 LABELED SULFATE IN THE SOIL OF A HEAVILY POLLUTED SITE IN THE NORTHERN CZECH-REPUBLIC

Changes in chemistry and vertical distribution of S-35 were investigated in column experiments using intact topsoil and repacked mineral soil horizons 1 to 20 weeks after tracer application (901 kBq S-35-SO42- per column 6.5 cm in diameter). Horizons O, A, AE and Bvs of an Orthic Podzol were incubated at 20 degrees C and wetted twice a week with 1 1 mm of natural throughfall precipitation (38.5 mg SO42- 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 S-35 form, while in Bvs the S-35 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 S-35 in O+A, AE and Bvs, respectively. Total specific activity of chemically transformed S-35 (i.e., of reduced inorganic S and organic S) constituted 3.4, 3.8 and 105 % of inorganic sulphate S-35 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 S-35 was Shorter than that of ester sulphate S-35. A, increase in FeS2-S-35 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.