The distribution of heavy metals and organic matter in the bottom sediment of Lake Nakanoumi was observed. Sampling was carried out at sixty stations in a netwark form in Lake Nakanoumi. Sediment quality data of each sample were determined for fifty-five items (Heavy metals and Organic matter).
Many heavy metals (Co, Cr, Pb and Zn) concentration in the bottom sediments (0-3cm) were high at the stations, where domestic wastes are inflow.
And then, sediment quality data were analysed by the Principal Component Analysis (PCA) method. About 73% of total variance of the original data were contributed to the three components (Z₁, Z₂ and Z₃) by PCA method.

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Denitrification caused by attached biomass on a river bed was investigated using mass balance model which incorporated mass transfer on the surface, diffusion and bacterial growth in the biofilm. The biofilm was divided into two layers, aerobic and anaerobic, and denitrification took place in the anaerobic layer.
From the parameter sensitivity analysis, it became apparent that the diffusion rate and density of the bacteria in the biofilm were controlling factors for denitrification per unit area.
Even in the case when the DO concentration in the flow was 20g·m^-3, denitrification can occur in shallow and eutrophic rivers, and the attached biofilm to the river bed has the ability of the denitrification of about 2×10^-6g·m^-2, s^-1.

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Organic suspended solids which settle and concentrate at the bottom of lakes and streams exert an oxygen demand on the overflowing water.
This oxygen demand is examined for bottom sediments of Nihonbashi River in Tokyo. In laboratory studies, the following conclusions are presented ;
1. The oxygen uptake rate was obtained 0.20.4 g-O₂/m²· day in the stagnant conditions. But, under the slight mixing conditions, turbulence increases the oxygen demand to 0.81.2 g-O₂/m²·day.
2. On the experiments that a fresh supply of water was added to the reaction tank, the oxygen demand of surface of the sludge is obtained 7.011.0 g-O₂/g-dry sludge, and its values was constant during experiments.
3. The effect of water temperature on the oxygen demand was observed.
4. On the experiments that the bottom sediments was contacted with water by filtration, the oxygen uptake rate of 0.30.6 g-O₂/m²·day/cm and the BOD loading rate of 0.51.6 g-BOD/m²·day/cm were obtained.

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[in Japanese]

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