A study of the change in uranium load of streamwater during downstream -mainly about the biofilm on the riverbed-
Abstract
We conducted the researches on the migration of uranium at Kaminosawa River in northeastern Japan. We measured flow rate, temperature, pH, conductivity, dissolved oxygen, oxidation-reduction potential, and concentration of chemicals of streamwater at 3.5-km segment of Kaminosawa River. Uranium load, which is calculated by multiplying uranium concentration and flow rate together, was adopted as the index of uranium mass. In August 2004, uranium load drastically decreased from 10.9 mg min-1 to 6.3 mg min-1 through 400-m section from the upper end of the research segment, and we found fluffy sediments (biofilms) there. We picked up these biofilms, and measured uranium concentration in them. In consequence these biofilms had 130 ppm of uranium per gram, whereas uranium concentration in streamwater was 2 ppb per mL. But in August 2005, we could not find any fluffy-type biofilms and decreasing segment in uranium load could not be seen. Some properties in Kaminosawa showed us some specific characteristics occurred in 2004. At first, flow rate at the point where we found biofilms in 2004 was much lower than that in 2005, but there were little difference in uranium load between in 2004 and in 2005. So in 2004, uranium concentration of streamwater was much higher than in 2005, and biofilms could adsorb more uranium. Secondly, the value of oxidation-reduction potential in 2004 was lower than that in 2005. Thirdly, the record of rainfall at the nearest meteorological observatory told us that there was a torrential downpour in July and afterward it had not rained for several weeks in 2004, whereas it rained hard every week in 2005. From these results described above, we supposed that the biofilms adsorbed uranium in the streamwater in 2004 were formed through the following process: (i) trees, branches, and leaves brought down by the torrential downpour in July stimulated on the dam for landslip and degraded anaerobically, which supplied anaerobic atmosphere and organic compound with streamwater, (ii) microbes formed the fluffy-type biofilms and grew up without flown down because flow rate was very low.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.H23B1515S
- Keywords:
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- 1806 Chemistry of fresh water;
- 1850 Overland flow;
- 1854 Precipitation (3354);
- 1860 Streamflow;
- 1871 Surface water quality