As the first step in the calculation of an appropriate quantity of oyster, we conducted growth tests of oyster and environmental observations in Oginohama Bay, and formulated a growth model of oyster by improving parts of a model for Hiroshima prefecture, western Japan. For the main improvements, we devised a calculation formula of the oxygen consumption rate OCR = 0.0012×t^2.16×W_d^0.75 (t; temperature, W_d; dry weight) , and filtration rate, FR = 0.26e ^(0.1584×t) ×W_d in low temperature. Although other set conditions were basically the same as those used in the Hiroshima model, this modified growth model of oyster is applicable for the Tohoku area where the water temperature from winter to spring is below 10 degrees. Although the oyster grows rapidly from early summer in the time trend of the growth model, the oyster weight temporarily decreases owing to egg deposition. After egg deposition, the oyster grows again. The filtration rate of oyster increases rapidly with oyster growth and increasing temperature after early summer. The largest bloom of phytoplankton, which is the main diet of oyster, occurs from January to April. Therefore, we inferred that the oyster diet diminishes after early summer.

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Dissolved organic matter (DOM) contained in the Tone River as an example of resource for drinking water was analyzed by fluorescence intensity (FI) and fractionation with ozonation. The fractionation into hydrophobic acid and hydrophilic matter was conducted. And the FIs of the fractionated samples were measured as quantitative analysis of the contained DOM. As a result, any FIs in the samples had no relationship with the assimilable organic carbon (AOC) . However, the decrease of FIs of the hydrophilic fractionated samples by ozonation (CT = approx. 0.5 mg min L^-1) had highly correlation with AOC. The wavelength used for measuring these FIs were 250 nm/435 nm and 335 nm/435 nm as excitation/emission which were correspondent with the existence of a fulvic acid or humic acid-like substance. Especially those correlation were observed in case of AOC determined by the Pseudomonas fluorescens P17 strain and not by the Aquaspirillum sp. NOX strain. It was suspected that the correlation between AOC and the decrease of FI by ozonation was based on the correspondence of biodegradable organic matter for P17 strain with ozone reactive matter.

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Cyanobacterial blooms, consisting mainly of Microcystis spp., occur during summer in Lake Kasumigaura, Japan. Some previous studies have suggested that these blooms are enhanced by the recruitment of overwintering cells from the lake sediment. However, the volume and distribution of Microcystis in the sediment of Lake Kasumigaura are unknown. The purpose of this research was to clarify the volume, distribution, and seasonal variation of Microcystis in Lake Kasumigaura using real-time polymerase chain reaction (PCR) . The results showed that cell densities differed among stations and seasons. Moreover, it was suggested that cell recruitment occurred in early June in Tsuchiura Bay. Additionally, the lake bottom sediment is an unsuitable environment for the accumulation of Microcystis cells because the cells decomposed immediately and/or were transported by disconcertion at the surface of the sediment in Lake Kasumigaura.

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