River waters filtered through glass fiber filter paper were left at 20°C. Brownish particulate matter was formed after about 30 h. The variations of DIP, DOP, PP, s-Fe and Si concentrations in their waters were investigated. PP usually increased with time although the magnitudes of its increase were different from season to season. In hot season, DIP, DOP, s-Fe and Si concentrations decreased with time in one or two steps. On the other hand, Si scarcely decreased in cold season although the fluctuations of the factors other than Si were similar to those in hot season.
The above particulate matter was found to contain Fe, Mn, Zn, Si and P by measurement of fluorescence X-ray spectra. On the other hand, IR spectra of the particulate matter indicated that humic acid was adsorbed on the surface of particle in cold season, while it was scarcely found in hot season.
Above-mentioned water qualities of river waters in the basin of Kurose river were measured in hot and cold season. Multiple regression analysis for their data suggests that in the formation of PP the production of colloidal particulate matter of both Fe and Si is primary in hot season, and phosphate is adsorbed in the process of its formation. On the contrary, the adsorption of phosphate on the surface of particulate matter which is floating in river water might be essential in cold season.

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Movement of suspended solids in Takahamairi area of Lake Kasumigaura was studied. Numerical model was developed to simulate the fate of suspended solids in the study area during flooding period. The model consider settling, scouring and convective/advective transport of the solids. The following results were obtained.
(1) Although the concentration of suspended solids of the influent rivers during flood was high, contribution of those influent solids to the concentration of lake suspended solids in the study area was relatively small.
(2) Scouring of the bottom sediments was occurred mostly in the mouths of influent rivers. Those scoured solids were the major source of lake suspended solids.
(3) Suspended solids were transported from the mouths of influent rivers to the center of the lake during flood.
(4) Scouring of bottom sediments was induced by water current of influent rivers as well as by wind. As far as wind induced scouring is concerned, south wind brought the largest scouring of bottom sediments in Takahamairi area, while west wind brought the smallest.

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The significance of epilithic microorganisms (algae and Sphaerotilus natans) in estimating the degree of organic pollution in streams are examined on the basis of the results of investigations in Toyama Prefecture from 1979 to 1985. Relationships between carbon content of epilithic microorganisms and water quality indexes (BOD, TIN and PO₄-P) show that these indexes influence the quantity of epilithic microorganisms. Species of the epilithic microorganisms examined can be classified into five types (Types IV) on the basis of the ranges of concentrations of BOD, TIN and PO₄-P in the stations where they are found. Concentrations of BOD, TIN and PO₄-P in streams can be estimated from the types of the epilithic microorganisms. Fourteen cases of such estimation of water quality are shown. Observed concentrations of BOD, TIN and PO₄-P are almost all within the ranges of their estimated concentrations, except one case of BOD.
It's shown that the epilithic microorganisms have the following advantage and disadvantage as indicators of water quality. The BOD range of 1.0 mg·l^-1 and over can be effectively distinguished with the species of Types IV and V. On the contrary, the ranges of estimated concentrations of TIN and PO₄-P are rather wide, and the estimation of lower range of BOD concentration such as below 1.0 mg·l^-1 is impossible.

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Denitrification characteristics of the biological fluidized bed reactor (B.F.B.R.) were studied using sodium acetate as a carbon source. The reactor has been in operated for 1 year, because glass beads bed have been used instead of a distribution plate at the bottom of the fluidized bed. When the ratio of total organic carbon to nitrate nitrogen (TOC ratio) in the synthetic waste-water was less than 2.0, denitrification efficiency decreased.
The conversion of nitrate to nitrogen gas through nitrite was followed by the 1st order consecutive reaction (NO₃^-→ NO₂^-→ N₂). Denitrification reaction was found to be zero-order kinetics in excess of the nitrate nitrogen and organic carbon region and the rates measured were 12.4 in the closed vial bottle and 4.2mg-N·(g-SS) ^-1·h^-1 (28) in the continuous B.F.B.R., respectively.
Activation energy for the reaction was 70.3 kJ·mol^-1.
The biofilm attached to support particles was observed by a scanning electron microscope. and Ps. denitrificans was found to be the dominant organism. This organism was different from the one in the case methanol was used as a carbon source. The dominant organism may depend on the carbon source for the denitrification process.

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