Abstract
Soils reclaimed for 7-10 years were surveyed at Yasugi area of Lake Nakaumi to investigate the microbiological aspect of the forming process of acid sulfate soils. Contents of water-soluble (WS) Na^+ and Cl^- gradually increased with depth, indicating that remnant of sea water was being removed with percolating water due to rainfall. On the contrary, contents of WS Ca^<2+> and SO_4^<2+> widely fluctuated in the profile. This was probably caused by dissolution of shell with sulfuric acid formed by oxidation of pyrite. Soil pH was low in the upper oxidized layers in the profile while it remained about 7 in the lower reduced layers. The results demonstrated that oxidation was proceeding from the top to the bottom of the profile. It was found that the number of Thiobacillus ferrooxidans became large in parallel with lowering of soil pH. The number of T. thiooxidans reached a maximum at a shallower layer than that of T. ferrooxidans. This fact suggested that pyrite was oxidized at first by T. thiooxidans and then by T. ferrooxidans : Microbial succession from T. thiooxidans to T. ferrooxidans was going on during pyrite oxidation in the reclaimed soils.
