Characteristic of COD in Rikimaru Reservoir in Fukuoka Prefecture was surveyed from April 1986 to February 1988, in oder to study applicability for trophic state index of TCOD and obtain the optimum sampling sites. The results were as follows :
(1) TCOD represented well the standing crop of algae at each sampling site. This tendency was recognized more clearly at St. 1 (damsite).
(2) DCOD results from the metabolic matter of algae was much higher than that of the previous reports.
(3) DCOD correlated with the standing crop of algae at St. 1 and St. 5 (sub-inlet of reservoir).
(4) CCOD calculated from the slope of the regression line between Chla and TCOD was seemed to contain DCOD results from the metabolic matter of algae.
(5) St. 1 was the optimum sampling site of reservoir dam up river.

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The purpose of this study is to clarify the sources structure of Organic Halogens Precursor (OXP) in a whole river basin. First, runoff characteristics of OXP on three non-point sources (precipitation, urbanized area, forest area) were surveyed and their mechanisms were grouped into two categories, one was the STORM model type (precipitation, urbanized area) and another was the direct proportionate type to cumulative flow (forest area). Organics from urbanized area was abundant in OXP. Second, the runoff load at the confluence of three branch rivers were divided into four components (direct runoff, indirect runoff, the Lake Biwa, point sources). Expressed in the product of flow by water quality coefficient, cumulative load of each component was calculated throughout a year. As results, the load of OXP at the confluence amounted to 1.91 × 10⁶kg and about 76% of that was attributed to both direct runoff and the Lake Biwa. Organics by direct runoff was abundant in OXP. Lastly, some factors related to sources control were mentioned as to direct runoff and point sources.

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Linear alkylbenzenesulfonates (LAS) were detected in a, 0-30cm-deep sediment column at the upperstream point in Lake Teganuma. The range of the LAS concentration in sediments was between 0.1 and 500 ppm (C₁₁C₁₄ LAS per dry solid), and its vertical profile demonstrated the seasonal variation. A mathematical model with a diffusion term and the biodegradation term was applied to simulate the seasonal variation of LAS in the sediment column and to calculate the diffusive flux rate of LAS across the sediment-water interface.
An averaged value 2.4×10^-5 cm²·s^-1 for the diffusion coefficient in the sediment column was obtained from the experiments using the sediment core samples in Lake Teganuma. The biodegradation rate constant of LAS in the sediments was obtained from both the experiments and the model analysis. The obtained rate constant between 0.001 and 0.01 d^-1 was less than the reported value of biodegradation rate constant of LAS in the water on anaerobic condition.
It was suspected that the model which described diffusive transport and biodegradation of LAS could have simulated the seasonal variation of LAS in near surface sediments. The calculated diffusive flux rate across the sediment-water interface was between -0.20 and 0.52 (C₁₁C₁₄ LAS) mg·m^-2·h^-1, and the annual net flux rate from water to sediment was 0.7 g·m^-2·y^-1.

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[in Japanese]

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