An investigation was pursued on the eutrophication problem in Hakata Bay from June 1981 to April 1982. By the chemical analysis and the examination for Phytoplankton of the water samples collected from the surface and bottom of several stations, it was proved that eutrophication was remarkable in the eastern region of the bay.
The population density of phytoplankton revealed a range of 44 to 2, 200 cells/ml in the western region, while the density frequently exceeded a level of 20, 000 cells/ ml in the central and eastern regions. Several species of diatoms and flagellates were found in the red tides developed in the bay during the investigation period.
In addition, Algal Growth Potential (AGP) was determined in the water samples by the use of Skeletonema costatum and Olisthodiscus sp., and the ratio of AGP to COD value in Hakata Bay was caluculated. Thus, the range of 0.44 to 0.80 and 0.27 to 0.60 were obtained respectively by the former plankton and by the latter. In conclusion, the results obtained from the ratio suggested the fact that eutrophication more profoundly proceeds in Hakata Bay under the optimal condition of phytoplankton growth.

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Nitrogen and phosphorus concentrations, phytoplankton, primary production, total community respiration, and sediment were studied during 1977-1931 in Mikawa Pay, one of the representative bays which have been highly eutrophic for the last ten years in central Japan.
Oxygen and carbon balances were presented on the interrelations during stagnation period, June-August 1931 as follows : The range of gross production varied from 7.1 to 41.9 gO₂/m²/day with an average rate of 17.7 gO₂/m²/day (6.6 gC/m²/day), and less than one half of the total fixation was consumed by phytoplankton itself. Mean daily net production, therefore, was estimated to be about 9.4 gO₂/m²/day (3.5 gC/m²/day). Community respiration, being due to heterotrophic organisms, ranged from 3.2 to 20.9 gO₂/m²/day with an average rate of 3.6 gO₂/m²/day (3.2 gC/m²/day) in the euphotic zone, which contributed about 90 % of the nutrient sources required for the mean net production. Mean daily sedimentaion rates in terms of COD and organic carbon were 0.52 gO₂/m²/day and 0.54 gC/m²/day, respectively. The flux of sedimentation was only 5-6 % and about 15 % of the mean net production, in terms of oxygen and carbon, respectively. From these results, it was suggested that regeneration of nutrients by heterotrophic organisms is of the greatest importance in maintaining the primary production.
Nitrogen and phosphorus concentrations, requiring to increase COD by 1 mg/l, were equivalent to 0.166 and 0.026 mg/l, respectively. On the basis of the assessment, total nitrogen levels, regulating the environmental quality standard in a shallow bay, were also discussed.

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Water qualities of household sewage from many communities were analyzed, and pollution loads of detergents were investigatcd with different kinds of washing detergents.
Approximately half of the daily amounts of pollutants were discharged from 7 a.m. to 11 a.m. The maximum concentrations of anionic and nonionic surfactants were 41 mg/1 and 25 mg/1, respectively. During the period when only soap was used for washing, the BOD load was increased by 10 - 13 g/person/day, but loads of anionic surfactants and phosphorous were decreased by 1.2 - 2.0 g/person/day and 0.16 -0.39 g/person/day, respectively.

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The effects of covering nutrient-rich sea sediment with sand and silicic calcium (iron slag) upon the release of nutrients into the overlying seawater were investigated by using 6-month indoor cultures under illumination, which contained sea sediment from a young yellowtail plantation, covering material and seawater. In the control tank without covering, the overlying water turned dark reddish brown, due to the mass production of Cryptomonas sp. No color appeared in the tanks with either silicic calcium or sand covering until the addition of phosphate to the former and sulfide as well as phosphate to the latter (Exp. 1), The prevention of the growth of Cryptomonas by covering seems to be due to the inhibition of.PO_4-P and S^2-S release from the sediment bed. These elements are concentrated in the deepest part of the iron rich sand layer adjacent to the sediment bed and distributed throughout the iron poor silicic calcium layer (Exp. 2), suggesting that the elements released from the sediment pass through the silicic calcium layer more easily than through the sand layer.

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Phosphorus concentration in lake water (C) is described in the following equation, C = Lp × πr = Lp X Rp/Rw, where Lp is the concentration of phosphorus in inflow water and πr is the ratio of residence times of phosphorus and water (Rp/Rw). Characteristics of seasonal changes and variation of πr were studied in Takahamairi Bay, Lake Kasumigaura where is the typical example of shallow eutrophic lake in Japan. Phosphorus concentrations (P) in the most inner part of the bay where is strongly affected by the inflow of rivers was predicted from the following equation, P = 0.5 Lp. That concentration in the central part of the bay was predicted from the following equation, P = Lp x (0.18 + 0.025Temp.), where Temp. is water temperature (°C). Chlorophyll-a concentration in Takahamairi Bay was predicted from the estimated phosphorus concentration and from Lp and water temperature.

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The seasonal variations of concentrations and loadings of the polyoxyethylene nonionic surfactants (as iodbismuthate active substances : BIAS) and some of the water qualities were investigated in the Sakai river in Kanagawa prefecture, from 1980 to 1982. The daily variations were also investigated at Tsuruma-bashi, where was strongly polluted by mainly domestic wastes in the Sakai river, September 16-17, 1981 and Janualy 6-7, 1982. Results obtained were as follows :
(1) BIAS concentrations and loadings in the river water of the winter were the highest values of four seasons and BIAS concentrations of the winter were about twice higher than that of the summer.
(2) the daily variations of BIAS loadings were similar in variations to daily life-cycle.
(3) The ratio of sum of BIAS loadings of a day to sum of BIAS loadings from A.M. 10 to P.M. 2 was 100 : 39.
(4) Correlation coefficients were calculated between stream-flow and concentrations of BIAS, MBAS, BOD, TOC and T-P. These values showed high correlation between each parameters and each correlation coefficients was o.7 or more.
(5) The ratio of BIAS concentrations to total LAS (linear alkylbenzen sulfonate, C₁₀-C₁₄) on the daily variations were 1 : 2.3, and the coefficient BIAS concentration and total LAS was 0.77.

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The method of land disposal was subjected to a field test. An irrigation of wastewater was kept continued from January 1972 to June 1977 at a mean rate of 3001/ (m-trench-d). The soil permeating water was sampled by three soil-permeating-water sampling devices set at a depth of 120 cm and analyzed together with original wastewater. The average removal of nutrients in soil permeating water based on the original wastewater was registered as 95.0% biological oxygen demand (BOD), 50.6% total nitrogen (T-N), and 87.2% total phosphorus (T-P). Soil samples were collected from the wastewater permeating area at each 50-cm-mesh point in the range of 50 to 280 cm in depth and of 600 cm in width and analyzed together with soil samples collected from the control plot. The concentration of T-P in soil samples increased significantly in the region directly below trench 1 (T₁) in the range of 60 to 100 cm in depth as compared with that in the control plot. However, no remarkable increase in the concentration of T-N and total carbon (T-C) could be observed even in the soil samples collected from directly below T₁.

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