A seasonal change in the filtration rate of Corbicula japonica in shallow experimental pond constructed to study the effect of C. japonica on bio-geochemical cycles was measured using the laboratory, outdoor tank and in situ methods. Different formulas for determining the correlation between filtration rate and water temperature were obtained in each case. The total volume of water filtered by C. japonica in the pond was estimated using these formulas. High volumes were calculated using the in situ method; they were about 2.5 ∼ 3 times higher than those calculated using the laboratory method. The amount of suspended solid (SS) removed was estimated from these volumes of water filtered and compared with the observed amount, which was calculated from the differences of SS concentrations in inflow and outflow waters and inflow water volume. The amount estimated using the in situ method showed a linear relationship to the observed one (y=1.16x + 18.6, R²=0.84). It was concluded from these results that the filtration rate of C. japonica could be expressed as y=0.336e^0.0569T in relation to water temperature in the range from 10 to 30°C.

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From field observations in a stratified reservoir with an anaerobic hypolimnion, thin turbid layer was found between the oxidative and reductive layers. This phenomenon is considered to result from an oxidation-reduction reaction of iron and phosphorus in the hypolimnion. Thus, to investigate the behavior of iron and phosphorus and the adsorption of phosphorus to iron under such conditions, laboratory experiments were carried out. Ferrous iron released from anaerobic sediments is oxidized, forms iron hydroxide, and adsorbs phosphate. Therefore, as a certain quantity of phosphate released from anaerobic sediments is adsorbed by iron, phosphates are not completely utilized by phytoplankton in the surface euphotic layer.

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The effects of copper and zinc ions on intestinal parasites in freshwater fish Odontobutis obscura were investigated in the laboratory. The survival of the cestode Amurotaenia mogurndae, and the survival and reproduction of the trematode Asymphylodora macrostoma in CuSO₄ and ZnCl₂ solutions were tested for five days. The copper levels of the CuSO₄ solutions were at 0.00 (control), 0.02 and 0.05 mg·l^-1, and the zinc levels of ZnCl₂ solutions 0.01 (control), 2.83, 3.19 and 3.38 mg·l^-1. No significant differences were detected in the survivals of both parasites and the reproduction of Am. mogurndae between the control and the CuSO₄ and ZnCl₂ solutions. The concentrations of copper and zinc in water from O. obscura's original habitat and in its muscle tissue measured using ICP-AES showed that the metals did not accumulate in the muscle tissue during the experiment, and that zinc was actually excreted.

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The purpose of this study is to develop a new method for treating wastewater containing diamines using yeasts. We isolated yeasts that could assimilate ethylendiamine (EDA) and hexamethylendiamine (HMDA) from approximately fifty yeasts stocked in the National Research Institute of Brewing that are mainly wastewater treatment yeasts. Consequently, three yeasts, Hansenula fabianii J640, Hansenula anomala J224-1, and Candida utilis IFO0626 were revealed to be able to grow well in culture containing EDA or HMDA as sole nitrogen source. In these yeasts, C. utilis IFO0626 showed the best removable ability, that is, it removed greater than 98% of 1,000 ppm EDA dichloride and HMDA dichloride in 48 h. The assimilation of 1 g of these diamine dichlorides needed approximately 10 g of glucose as a carbon source; therefore the ratio of C:N was calculated as 100:5. These yeasts were shown to prefer ammonium sulfate and urea to EDA and HMDA as nitrogen sources. It was shown that EDA or HMDA could be more effective decomposed by increasing the initial number of yeast cells in the treatment medium.

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A subsurface flow-constructed wetland with a zeolite substratum (S.F.Z.) is characterized by a high removal rate of ammonium nitrogen due to its high ion-exchange capacity. However, after the saturation of ammonium ions (NH₄⁺) in the zeolite, the rate is markedly decreased. We investigated the effect of nighttime drainage operation for the recovery of the NH₄⁺ ion-exchange capacity of zeolite using a large-scale experimental S.F.Z plant. The experiment was carried out using two channels which had different influent water loads and frequencies of drainage operation. Channel 1 was drained every night and Channel 2 was drained three times per week in the nighttime (0:00∼6:00). The results showed that the amount of adsorbed NH₄⁺ in the zeolite was decreased by nitrification after the operation. NO₃^--N concentration was increased in the effluent of Channel 1, however, it was not increased in Channel 2. The increase in NO₃^--N by nitrification could be reduced by controlling the frequency of the drainage operation and the influent water load. High removal rates of NH₄⁺ and inorganic nitrogen were observed for 9 months after the start of drainage operation. Therefore, the S.F.Z. can be used long-term with a high performance in nitrogen removal through the introduction of a suitable drain operation.

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We calculated long-term estimates of the chemical oxygen demand (COD), and nitrogen and phosphorus loads of Ariake Bay using a simplified model with data from 1979 to 2003. After confirming small changes in land use and population around the bay during that term, we calculated the yearly changes of loads with some assumptions and the formula L=a×Q^b (L: load, Q: amount of river flow, a,b: parameter) applying the parameters provided from the Koku-cho-hi simulations, which were carried out in 2000 and 2001 by four ministries of Japan; The Ministry of Agriculture, Forestry and Fisheries, The Ministry of Economy, Trade and Industry, The Ministry of Land Infrastructure and Transport, The Ministry of the Environment. We confirmed that the loads calculated in our simple estimation showed good agreement with the observed data, by comparing of the calculated and observed water qualities of rivers. We found that the river discharges and loads ranged from 0.5∼1.5 fold the averages for these 24 years and the loads of COD in years with rich precipitation seemed to be higher than the average comparing with the cases of nitrogen and phosphorus loads.

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