Chlorination of secondary effluents produce strong toxic substance such as monochloramine or oxidant on growth of aquatic organisms. Therefore, alternative disinfection methods to chlorination should be considered. However, the effect of effluents disinfected with the alternatives on seaweed has not been clarified. In this study, the toxicity of secondary effluents disinfected with chlorine (NaOCl), chlorine dioxide (ClO₂), ozone (O₃), and ultraviolet rays (UV) were investigated by bioassay using Porphyra yezoensis conchospores. Secondary effluents used in this study were disinfected with disinfectants or rays which inactivated coliform groups in secondary effluents of 99.9%. Lowest-observed-effect concentrations (LOECs) of secondary effluents disinfected with NaOCl, ClO₂, and O₃ for germination ratio of conchospores were 1.0, 10, and 100% of effluent concentration, respectively. The toxicity of effluents disinfected with NaOCl and ClO₂ were very strong. In contrast, the effluents disinfected with UV rays did not affect the germination of conchospores. The toxicity of effluents disinfected with NaOCl, ClO₂, and O₃ were considered to depend on initial total residual oxidant (TRO). Dechlorination with Na₂SO₃ of effluents disinfected with NaOCl or ClO₂ did not affect the germination of conchospores, even in 100% of effluent concentration.

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The purpose of this study was to evaluate the influence of pollutant from Coho Salmon cultivation on water quality through analyzing the data of weather and water quality for several years, and to estimate the adequate loading amount into the Shizugawa Bay locating at Miyagi Prefecture.
As a result, it was recognized that COD in the bay was improved from 0.94 mg·l^-1 to 0.57 mg·l^-1, the delta DO in the bay was improved from 0.86 mg·l^-1 to 0.55 mg·l^-1, maximum COD in the salmon area changed from 1.13 mg·l^-1 to 0.68 mg·l^-1 and δDO in the salmon area changed from 1.28 mg·l^-1 to 0.69 mg·l^-1, respectively, at the end of the cultivation time compared with the large cultivation period.
From the results of multiple regression analysis, it was showed that the factors affecting the COD in the salmon area were input loading, temperature and duration of sunshine, whereas the factors affecting δDO in the salmon area were input loading, temperature, duration of sunshine and rainfall, respectively. In particular, it was found that both items were great influenced by the salmon cultivation. In addition, through evaluating the prediction equation for the bottom DO in the salmon area, it was suggested that the annual cultivation amount should be restricted by 4,000 ton·y^-1 to prevent the bottom water from the deficient water.

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Effect of ceramics carrier contained calcium on nutrient adsorption and microorganism-affinity in the microbial purification were examined. The carrier confined clay 40% with oyster shell 60%, which was modified with main component of Ca(OH)₂ having 100-fold solublity relative to natural oyster, could remove above 95% of PO_4-P compared with the oyster shell contained 98% of CaCO₃. At the same time the growth rates (μ) of nitrite bacteria and nitrifing bacteria were examined. It was found that the alkalinity of the treated water (90mg·l^-1) using ceramics carrier with calcium was 4 times higher than that of the control, followed by the favorable growth (μ=1.31d^-1), having effective adsorption of PO_4-P and acceleration of nitrification due to the release of OH^- from the carrier. Moreover ammonium-nitrogen of about 70% was found to be removed by the replacement reaction of Ca²⁺ for NH₄⁺ with PO_4-P in the hydroxyapatite, even with the use of the lowered carrier with adsorption of PO_4-P. Nutrients of NH_4-N (107mg·carrier-g^-1) and PO_4-P (20.4mg·carrier-g^-1) were collected as an fertilizer. It was also possible to recover the adsorptive activity.

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Mesocosm experiments were conducted in the Seto Inland Sea every summer seasons from 1987 to 1989. Effects of controlled conditions on phytoplankton succession in the mesocosm were examined. One control factor was a vertical mixing method, which included a direct circulation by pumps (run 1) and a new designed circulation system (run 2 and run 3). In the system, vertical jet entrained the surrounding water, making soft mixing in the mesocosm. The other factor was an enrichment pattern. Nutrients were added at the surface layer in run 1 and run 2, and introduced under the mixing layer in run 3. Phytoplankton species succession was observed every year from diatom to dinoflagellate. Red tide due to Chattonella antiqua was observed only in 1989, when the new circulation system was used and the vertical nutrient profile was set as similar to those for red tides in the field. The most important factors to control environmental conditions in mesocosms were found to be the vertical mixing power, the mixing depth, nutrient ratios (N : P : Si), and vertical distribution of nutrients.

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The bottom sediment in the Seto Inland Sea taken in the period 1981-1985 and 1991-1994 was investigated to evaluate the change of heavy metal concentrations of the elements, Cd, Pb, Cu, Zn, and Mn. The sea area which had higher concentrations of heavy metals in the 1980's showed a decrease in some area in the 1990's. The test of the difference on average values for Cd, Pb, Zn, and Mn indicated that it was significant at the 1% or 5% level in the entire Seto Inland Sea as well as for the concentration of Cu in the Sea of Hiuchi and Osaka Bay. These results suggest that the regulation of waste water and the decrease in pollutant loadings conducted since 1970's was related to the decline of the heavy metal concentrations in the bottom sediment of the entire Seto Inland Sea. In some sea areas, however, the concentrations of heavy metals in the bottom sediments were maintained at the same level, or became worse than in the 1980's. This shows that it is necessary to make more of an effort to rehabilitate the condition of the bottom sediment

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Assuming negligible production of pseudofaeces, the amount of food filtered by the clam is equal to the amount of food ingested. The ingestion rate estimated as nitrogen per 1 m² per h (F) was given in the following equation :
F=Σ⁷_n=1(F_n·R_T·R_s·P_n)·N
where ; F_n, filtration rate of a clam at L mm shell length at 15°C and 35 psu ; R_T, correction coefficient for F_n at T °C ; R_s, correction coefficient for F_n at S psu ; P_n, clam density of 7 size classes and N, concentration of suspended particulate nitrogen (PN). L was given for the mean shell length of each size class. Filtration rate and effects of body size, temperature and salinity on the filtration rate were examined using the clam collected from Banzu tidal flat. Monthly changes of temperature, salinity, concentration of PN and clam density for the tidal flat were evaluated by analysis of available data. PN was calculated from Chl-a concentration and reported PN : Chl-a ratio.
The estimated ingestion rate was maximum at 300 mg-N·m^-2·h^-1 in August, and minimum at 19 mg-N·m^-2·h^-1 in February. From analysis of the results, it is suggested that both temperature and PN concentration affect significantly the seasonal changes of the rate, however, salinity has no detectable effect on them in Banzu tidal flat.

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The Seto Inland Sea in Japan is well known world-widely as one of the famous enclosed coastal sea, which is surrounded on all sides by the three large islands of Honshu, Kyushu and Shikoku, and is the largest inland sea in Japan (area ; 22,000Km², total coastline ; 6,600Km, average depth ; 38m). In order to obtain the information about the environmental condition in the Seto Inland Sea, the quantity and distribution of macrobenthos, especially Annelida which is considered to indicate the sedimental condition, were investigated from the 425 sedimental samples as the Investigation for Environmental Management of the Seto Inland Sea (IEMS), which conducted from 1991 to 1996.
The results obtained can be concluded as follows:
1) The macrobenthos mainly observed in the Seto Inland Sea were Lumbrineris longiforia, Paraprionospio spp., Prionospio ehlersi and Theora fragilis, which were recognized as the indicator species of organic pollution.
2) 16species of Spionidae were observed, i.e. Paraprionospio sp., Prionospio ehlersi, P. cirrifrea, Spiophanes sp. and so on.
3) The species number and the individual number of Annelida were decreased with increase of muddy ratio, IL, COD, T-N, T-P and TOC.
4) The species number and the individual number of Annelida were decresed with increase of Cd, Cu, Ph, Zn and Mn.
5) Organic pollution was suggested especially in inner bay area because of dominations of some species of Annelida, Spionidae.

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Trend of eutrophication and magnitude of marine-derived organic matter contributing to organic pollution were investigated in the Osaka Bay, Seto Inland Sea, which is semi-closed coastal bay surrounded by highly developed industrial areas and has been subjected to the effect of human activities. Average standing stocks of total nitrogen and total phosphorus in the bay during the 1990's were estimated to be 11,930ton and 1,620ton, respectively. These values decreased by 22% and 13% of those during the 1980's, respectively. The eutrophic level during the 1990's was approximately same as that during the mid 1970's. Results from carbon stable isotope ratio (δ¹³C) indicate that more than 80% of particulate organic carbon standing stock came from marine-derived organic matter in the Osaka Bay. This value was at least over 30% high compared to that estimated by the relation between particulate organic carbon and pigment.

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The purpose of this study is to investigate the deposit and decomposition characteristics of microalgae using the gravel bed contact-purification method. The following results were obtained : The deposit ratio of Tetraselmis tetrathele is higher than that of Nitzchia closterium due to the shape and size of their cells. The deposit characteristic is expressed by the Iwasaki's filtration equation, and the filter coefficient is a function of real velocity and specific surface area of gravel bed. The decomposition rate constant of deposited microalgae is ranged from 0.10 to 0.14 hr^-1 winch is 20-30 times as high as that under suspended condition. The decomposition rate has a proportional relation to the specific surface area in case enough amount of microalgae deposit in gravel bed. Under a few assumptions, both the deposit and decomposition rates are defined by gravel diameter. Therefore, it is possible to design the optimum gravel diameter for the effective and sustainable removal of microalgae using this system.

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As water pollution and red tide due to aquatic eutrophication in the Seto Inland Sea became a social issue at the beginning in the 1970's, various countermeasures were carried out by peculiar laws for environmental improvement in the Seto Inland Sea. We investigated how water pollutant loads in the basin and the water qualities in the sea changed by the countermeasures. The changes of pollutant loads from effluent, census data associated with the loads and water qualities in the Seto Inland Sea were examined from public statistical tables and official data of national Environment Agency. Though the population in the basin increased remarkably after 1970, it has no influence for the change of pollutant loads, because the sewerage treatment systems also increased simultaneously. There are also little changes in industrial products and farm animal numbers. Nevertheless, the COD loads decreased by 63.2% after 1968, and the reduction of nutrient loads during 1979 and 1994 were 5.3 and 30.3%, in T-N and T-P, respectively, because of pollutant load restriction by the laws.
The water quality in the Seto Inland Sea has not shown a clear improvement at all, in spite of these load reductions. It got well a little in COD concentration, but worse in transparency on the whole. On the other hand, T-N and T-P concentrations increased during 1985 and 1989, then decreased a little.
In the relations among pollution elements in the sea, there was a significant relationship between COD and Chl.a concentrations, which means organic pollution is strongly affected by algal growth by aquatic eutrophication in the Seto Inland Sea. The comparison of the primary productivity with effluent loads in COD demonstrated that the former was about 20 times larger than the latter.

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Geometrical properties of particle deposit on the medium surface are studied in bench-scale channels (horizontal flow). A basic mathematical model describing particle deposition is presented on the spherical coordinates, which can give the ratio of the attached surface area (R_A) and the angle of repose (ø_r) with the data of the ratio of the projected area (A_A/A₀).
The statistical analysis of measurements along the length and depth of the channel shows that R_A(50%) of 22mm spherical media is approximately constant at 15-16% of the cumulative probability regardless of the sampling location or their sediment mass in the filter bed. This result means that suspended particles tend to be deposited within 45-48 degree of ø_r on the spherical medium surface. R_A(50%) of 91mm Rock media is about 26.1% and 1.6-1.7 times as high as that of 22mm media. In the model calculations, the dimensionless thickness of deposits (RQ/TQ) is estimated to be 9-17% for 40-50% of the sediment porosity, and the actual volume is estimated to he about 60% of the theoretically maximum (circular cone) value since the upper media themselves block a part of the void space for the lower media where particles would be deposited. A model for prediction of the deposit mass is introduced with the following assumptions: (1) the averaged deposit volume of the rock medium equals that of the equivalent spherical medium and (2) RQ/TQ is constant regardless of the medium diameter. This model gives a good approximation with the experimental results. The model also predicts the decrease in porosity of the bed as filtration proceeds, and estimates 4% of the pore volume in the reactor at the most. Therefore, in the rock bed channel it would be expected that the deposit mass on media surface is not a main body of removed particles, but the particles would settle down to the lower layer, finally forming sediments in the bottom.

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In order to estimate the physical and chemical state of sediments in the Seto Inland Sea, the horizontal distributions of grain size component, organic matter and nutrients in the sediments were investigated. The investigation was carried out 2 times in 1980s (1981-1985) and 1990s (1991-1994) throughout all over the Seto Inland Sea to estimate whether pollution of the sediment improved during past 10 years. The results obtained in 13 sea areas were different in each sea area. It is generalized roughly that the environment of sediment becomes worse in the sea area where the basin has been carried out some development during past 10 years. On the other hand, it hardly changes in the sea area that the basin was developed before the first survey. Although the cut of pollutant loads from the watershed has been performed legally for the last 18 years, the improvement of the sediment environment in this area could hardly be recognized from the results of these survey.

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