Through the investigation about environmental impacts of Mega-Float, it is revealed that the effect of sessile organisms adhering on the floating structure is significant. However there had been little information about activities of the sessile organisms on floating structures and their influences on water and bottom quality. Therefore, some experiments were carried out to investigate the uncertain processes caused by the sessile organisms. An instrument called “Bell-jar”, which is composed of an enclosed container and several sensors for measuring water quality in it, was developed to measure the activities of sessile organisms on artificial bases set in Tokyo Bay. Through the experiments using Bell-jar, the consumption rate of dissolved oxygen and Chlorophyll-a, and emission rate of nutrients by the sessile organisms were measured. By fitting the model to these results, the parameters for activities of sessile organisms such as respiration rate and filtering rate were determined. The experiments have been carried out under various conditions of water temperature and salinity and it is clarified that the activities of sessile organisms very much depend on the water temperature and salinity. The behavior of particulate organic matters excreted from the sessile organisms is also investigated by laboratory experiments. These results were used to improving the model of sessile organisms, which is incorporated into the numerical ecosystem model for environmental impact assessment of very large floating structures.

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