Abstract
Recently, lakes and reservoirs have been still entrophicated with the discharge of agricultural and domestic waste water inflow. Even in drinking water treatment plant that has kept good water quality source condition, musty-odor problem has been frequently occurred. Musty-odor compounds are mainly 2－methyl－iso－borneol (2－MIB) and geosmin, produced by some filamentous cyanobacteria and actinomycetes in aquatics. In 2002 and 2004, the Ibaraki, Lake Kouzogawa experienced musty-odor occurrence with high concentration of 2－MIB, associating with the growth of Phormidium sp. This research is aimed to clarify the correlation between the occurrence of musty-odor compounds and the dynamics of their causative microorganisms. It was revealed that the lake was mesotrophic and phosphorus restriction, and thermocline was unformed through the years; however dissolved oxygen was decreased nearly on the sediment surface in the lake in summer. In the summer of 2006, 5ng/l of geosmin, and in the autumn, over 10 ng/l of geosmin was detected. And from 2007 to 2008, the low concentration of geosmin was frequently observed. Then, the proliferated period of cyanobacteria which was suspected to produce musty-odor compounds didn’t coincide with the occurrence period of the musty-odor compounds. Therefore, it was indicated that cyanobacteria were not responsible for the occurrence of musty-odor compounds. Although actinomycetes always existed high density in the lake sediment relative to water column, its colony number changed by the depth and the season. Furthermore, there were many geosmin producing actinomycetes in the isolated colonies; consequently it was suggested that geosmin in water column of the lake was attributed to actinomycetes in the sediment from 2006 to 2008.
