|Budget Amount *help
¥3,300,000 (Direct Cost : ¥3,300,000)
Fiscal Year 1999 : ¥900,000 (Direct Cost : ¥900,000)
Fiscal Year 1998 : ¥2,400,000 (Direct Cost : ¥2,400,000)
Urban estuarine sediments are rich in organic materials and provide an anaerobic environment where hydrogen sulfide, one of the substances responsible for malodor, is intensively produced through microbial and/or chemical reduction of sulfate ions from seawater and finally removed from water to the sediment in the form of iron sulfides. In this study, the chemical states of iron, and its vertical distribution, have been investigated by ^<57>Fe Mossbauer spectroscopy for the sediments collected from several urban rivers. Mossbauer spectra of the estuarine sediments consist of three doublets and one sextet, which are ascribable to paramagnetic high-spin Fe^<2+>, paramagnetic high-spin Fe^<3+>, pyrite (FeS_2) and magnetic high-spin Fe^<3+>, respectively. The relative amount of pyrite shows a maximum at the depth of 20-40 cm from the surface, whereas that of paramagnetmc Fe^<2+> changes complementarily to pyrite. This suggests that this component in the estuarine sediments converted to pyrite under reducing conditions. No significant seasonal variation was found in this trend. The stratified distribution of pyrite was also found in the sediment collected from Kitajukken-river and Tate-river, which are canal-rivers in Tokyo. On the other hand, pyrite was not always found in the Sagami-river sediments, but the same trend of pyrite distribution was found in the sediment collected near a sewage treatment plant. In order to clarify the contribution of sulfate-reducing bacteria to pyrite formation in the sediments, we determined the vertical distribution for number of living sulfate-reducing bacteria in the sediments by plating method. This distribution was found to be consistent with that of pyrite.