To clarify the mechanism of water quality change in the estuary of the Asahi River and Kojima Bay, Okayama Prefecture, we analyzed the concentrations of Cl ion, SS and COD (Mn) and discussed the relationship between the surface concentrations and vertically averaged ones.
The conclusions may be summarized as follows :
1. Judging from the distribution of Cl ion concentrations, the Asahi River estuary is of a partly mixed type within the range of freshwater inflow from 0 to 50 m³ /s.
2. If we compare the daily or half daily time average of surface and vertically averaged concentrations, the curves of their longitudinal distrbution are very similar. However, we do not always find a correlation between surface and vertical concentrations at the same spot at the same time.
3. As for the standard deviations and the coefficients of variation, those of surface concentrations are greater than those of the vertically averaged.
4. As mentioned above, the surface water quality of the Asahi River estuay varies more than the vertically averaged qualities. So to obtain the longitodinal distribution of water quality level from surface water quality, samples for analysis must be taken sufficient times a tidal cycle.

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Laboratory experiments were carried out to simulate the degradation of organic materials in rivers. Glucose was fed to a complete mixed reactor continuously where an attached biofilm was developed. Soluble COD of the effluent was almost constant (10-15 mg/l) under various COD loadings up to 12.3 g/m²·d, and did not decrease when the hydraulic retention time was extended. Gel chromatography of the substrate and the effluent revealed that organic compounds whose molecular weight were as low as that of glucose remained in the effluent.·The attached biomass was 2-15 g/m² irrespective of the glucose loading. These values were equivalent to 44-326 mg/l-reactor volume, which were much larger than the suspended biomass. The number of heterotrophic bacteria in the attached biofilm increased with the increase of glucose loading, and was about 100-1000 times that in the effluent. Oxygen consumption by the attached biofilm was estimated from oxygen balance around the reactor, and it was 0.65 g/g-soluble COD removed, which suggests that the growth yield of the biofilm was 0.35. The endogenous respiration required 98 mg-oxygen/ g-attached biofilm · day.

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98 organic compounds were selected to investigate their trihalomethane formation characteristics. The selected organic compounds were chlorinated at 20°C in phosphate buffer solution (pH 7), and chloroform concentrations were measured after 24 hours. The results of this research are as follows :
(1) Aliphatic 1, 3-diketones, acetyl compounds and citric acid form chloroform.
(2) Aromatic 1, 3-diketones, acetophenones, phenols, anilines, methoxybenzenes and pyrrole compounds also form chloroform. The amount of chloroform formed from phenols is strongly affected by the type of isomers, that is meta-isomar forms higher amount of chloroform than ortho- and para-isomer. But this effect is not observed in the chlorination of acetophenones and anilines.
(3) The chloroform yields from 1, 3-diketones, 1, 3-dihydroxybenzens, aminoacetophenone, hydroxyacetophenone and aminophenol are high. The chloroform yields from aromatic compounds are higher than those from aliphatic compounds.
(4) It is suggested that chloroform yields from 1, 3- diketones and acetyl compounds are affected by enolization of these compounds.
(5) 1-hydroxyethyl compounds is difficult to form chloroform.
(6) Chlorine is consumed by oxidation or chlorination of organic compounds than by chloroform formation reaction.

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With use of the two-way classification model in variance analysis, spatial and temporal variabilities of water quality in a lake are separated additively. For that purpose, the so-called extended logarithmic transformation is applied to measured data. The values of parameters in the transformation equation and the model are determined by the maximum likelihood procedure. They can be obtained in no analytical way, but through an iterative computational procedure. By the aid of statistical hypothesis test, grouping of measurement points for water quality is carried out, through the parameters expressing the spatial variability. The method is developed first for a single item and it is then extended to a method for multi-items. The technique is applied to analyzing a set of time-series data measured over several years in Lake Biwa.

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A follow-up study was carried out on secular changes from 1974 to 1977 of mercury concentrations in bottom sediments of the Suimon River and other rivers polluted by the effluent from a chemical plant which had been manufacturing acetaldehyde with mercurial catalyst. The results obtained were summarized as follows.
1) Mercury concentrations in sediments from each sampling station were found to have fairly changed in the period.
2) There was no possibility of additional pollution by other industrial sources.
3) There was very little possibility of release of mercury from bottom sediments.
4) The changes of mercury concentrations in sediments appeared to relate closely to the state of rainfalls, especially outbreak of torrential downpours in the catchment area.
5) Torrential downpours were observed to exert a considerable influence on the change of particle size distribution of sediments.
6) Mercury concentrations in sediments correlated significantly to the contents of fine particle fraction of sediments.

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Two species of algae, namely Microcystis aeruginosa which is a dominant species in eutrophic lakes and Nitzschia palea which mainly appears in urban rivers were cultivated in our laboratory. The relationship between the organic substances produced during the growing process and the concentration of trihalomethane produced by their chlorination was investigated. Furthermore, by gel chromatography, the organics were fractionated to elucidate the property of the component and the variation of trihalomethane formation potential during the growing process.
It is concluded that, in the case of Microcystis aeruginosa, total organic carbon is increased by the increase of degraded products during the death phase and those products form a high amount of trihalomethane by chlorination. Besides. some organics, whose trihalomethane formation potential is high, are excreted during the exponential phase.
The result of gel chromatography shows that the composition of soluble organics in the culture medium changes depending on the growth phase of algae.
And it is concluded that the formation of trihalomethane depends on the amount of organic which molecular weight is larger than 2, 000 and also possesses UV absorbance at 260 nm.

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