The enhanced mineralization of organic nitrogen by bacteriophagous protozoa has often been reported, hoever, the effects of the protozoa on nitrification are not well known. In this study, the effects of Testacealobosia Arcella vulgaris on nitrification were investigated by batch culture experiments. A. vulgaris could grow well with two kinds of nitrifying bacteria, Nitrosomonas europaea and Nitrobacter winogradskyi. These results indicate that the predation of nitrifying bacteria by A. vulgaris may affect the biomass of nitrifying bacteria and nitrification activity in the food chain. Experiments in semi-continuous culture of A. vulgaris and nitrifying bacteria indicated that nitrification efficiency and activity of nitrifying bacteria were increased in the presence of A. vulgaris. The same tendency was found in the mixed culture system of A. vulgaris and activated sludge whose protozoa and micrometazoa were killed by heating with water bath for 5min. at 45°C. Nitrification efficiency was improved by adding a large number of A. vulgaris because of the increase of the activity of nitrifying bacteria, though the number of nitrifying bacteria decreased.

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The Senkawa-josui irrigation canal is a small artificial watercourse of treated wastewater from a sewage plant. The simple structure of the channel (linear flowing, concrete banks and uniform riverbed) and the presence of a large number of carp seemed to prohibit distribution of diverse species. In order to improve the situation, the concrete bank (80 m long) was removed and two semi-stagnant sections which large carp could not enter were made in April 1996. Aquatic plants were also planted in the area. The aquatic fauna and flora were researched for three years after the channel improvement.
Many species were found soon after the improvement. Juvenile fish and tadpoles grew in the stagnant sections. Male dragonflies also created their territories in the stagnant sections and the females laid eggs in them. The number of species of benthic macroinvertebrates increased. Spotbill ducks and little egrets were also found in the improved area. Diverse relations between aquatic plants and insects were observed. Species diversity of aquatic organisms was successfully raised in the imprgved area, showing that changing simple channel structures to complicated ones can help increase the number of species in artificial watercourses and urban streams.

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Removal mechanisms of bacteria (Escherichia coli : E. coli, total coliform : T. coli, heterotrophic plate counts : HPC) in a contact purification process for river flow were examined with experimental apparatus which had activated carbon or string as packed medium. Bacteria was adsorbed to biofilm or sediment quite effectively (60-90%) within one hour treatment and the maximum removal rate of E. coli was 3.0 CFU · ml^-1 · min^-1 with string type medium. 99% of E. coli removed during for 2 month experiment were inactivated, but the concentration in the biofilm and sediment was so high that the sludge accumulated in the process must be handled carefully to avoid secondary contamination.

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The filtration rate and thermal effects on the rate were evaluated in various marine bivalves. 1) The filtration rates by a clam population (F, l · m^-2 · h^-1) estimated using the following equation were compared with Pseudocardium sachalinensis in Hamanaka Bay, Hokkaido and Ruditapes philippinarum in Banzu tidal flat, Tokyo Bay.
F=Σ^m_n=1f_n · R_T · R_S · P_n
where ; f_n, filtration rate of a clam with L_n mm (mean shell length of divided size class) examined under the experimental conditions ; R_T, correction coefficient for f_n at field temperature T (°C) ; R_S, correction coefficient for f_n at field salinity S (psu), P_n ; clam density (no. · m^-2) of 15 size classes in P. sachalinensis and 7 size classes in R. philippinarum ; m, number of size classes. Filtration rate and effects of body size, temperature and salinity on the filtration rate were examined using the clam collected from each study sites. Monthly changes of temperature, salinity and clam density were investigated in Hamanaka Bay, and were evaluated from analysis of available data in Tokyo Bay, 2) The individual filtration rate corrected for body size and temperature was compared between 4 bivalve species, P. sachalinensis, R. philippinarum, Mytilus galloprovincialis, and Perna viridis. 3) Thermal effects on the filtration rate were examined in 8 bivalve species, including Mactra chinensis, Meretrix lamarcki, M. lusoria, and Mytilus coruscus.
Following are major findings ;
1) The contribution of the 2 year-old population to the eatimated filtration rate was dominant in P. sachalinensis (65%) and R. philippinarum (58-78%). Following contributions were for the 3 (19%), 4 (8%), 1 (5%), and over 5 year-old (3%) in P. sachalinensis and over 3 (14-22%), and 1 year-old (8-20%) in R. philippinarum. In the case of P. sachalinensis, a irregular occurrence of dominant year class may be major factor affecting on the filtration.
2) The estimated filtration rates (l · indiv.^-1 · h^-1) of 30mm individual at 15°C were as follows : M. galloprovincialis (2.5), R. philippinarum (1.5), P. sachalinensis (1.3), and P. viridis (0.64).
3) The temperature considered to be optimum for filtration was 20°C for P. sachalinensis, M. lamarcki and M. lusoria, 25°C for M. chinensis, R. philippinarum and M. galloprovincialis, 27.5°C for M. coruscus, and 32.5°C for P. viridis.

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The formation of water blooms with blue-green algae Microcystis spp. has been observed in Lake Koyamaike (Tottori Prefecture) every year, and the changes of the water quality for the worse is of concern. An algal growth potential assay using Microcystis aeruginosa isolated from the lake and water quality examination of the lake and four inflowing rivers were carried out in order to determine the mechanism of the heavy algal growth. Both examinations were continued every month from April 1995 until August 1998.
The substance limiting the algal growth was estimated to be chelate compounds. This proved true throughout the year except during the summer. The chelate compounds were found not only in the lake water but also inflowing river water in June. This was attributed to be basal fertilizer which contains molasses used in paddy fields. The algal growth under the elimination of the effects of nitrogen and phosphorus showed good correlation with the copper complexing capacity.

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The algal growth in the Tsukui Reservoir, one of the typical eutrophicated reservoir in Japan, was modeled numerically with considering the water flow dynamics in the reservoir. After evaluating the predictability of the model, we simulate the operation of the in situ algal filtration method. The results suggested that there are non-linear relationships between the filtration rate and algal growth, or material recovery. The optimum operation condition of the in situ algal filtration method which removes 50% of algae in the Tsukui Reservoir was calculated as 10⁶ · m³ · day^-1∼10⁷m³ · day^-1.

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The mechanisms of nutrient removal in sand-filled reed filter bed system (RFB system) are explained by filtration, sedimentation, plant uptake and microbial degradation occurring in soil-water interface and in the plant rhizosphere, which includes nitrification-denitrification process. There is, however, little information on it, especially information on denitrificaton rate in RFB system has not been obtained. The objective of this study is to measure denitrification rates using ¹⁵N tracer method and investigate seasonal changes of them throughout a year. The results of bench-scale RFB system using ¹⁵N tracer method showed that the denitrification rates of the RFB and the sand tank without reeds ranged from 0.0∼5.5 (average 2.28) and 0.0∼3.4 (average 1.48) g-N · m^-2 · d^-1, respectively. These values mean that about 60% in the RFB and about 80% in the sand tank for inflow nitrogen loading were removed by denitrification. A part of remaining nitrogen loss in nitrogen balance of the RFB tank might be caused by plant uptake. High denitrification rate in the RFB suggested that microbial activity in the reed rhizosphere played an important role in nitrogen removal efficiency during the stationary phase of reed's growth curve.

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The target of this study is to quantify the amount of nitrogen and phosphorus removed from enclosed eutrophic water through the food web participated by filter-feeding bivalves, aquatic birds, and macrophytes. In an estuarine lagoon, Lake Nakaumi, dredge of the sludge removed 13 tons nitrogen and 6.7 tons phosphorus per year. On the other hand, present amount of nitrogen and phosphorus removed through food web is estimated to be 9.1 tons and 2.9 tons, respectively. It is suggested that the potential amount of nitrogen and phosphorus removed through food web in L. Nakaumi is 35 tons and 8.6 tons, respectively.

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The effect of water loading on water purification ability of a bivalve, Corbicula japonica, was studied using outdoor experimental tanks. Seven tanks were set up at the lakeside of Lake Jinzai, and the lake water was pumped up and continuously flowed into each tank. Water load and bivalve density were fixed for 2, 4, 6 (m³ · m^-2 · d^-1) and 1500, 3000 (ind. · m^-2). Removal rate of SS and Chl-a by C. japonica increased with the increase of water loading. On the other hand, the removal rate at high bivalve density (3000ind. · m^-2) was lower removal rate at natural density in Lake Shinji (1500ind. · m^-2). From the above results, it was concluded that high water loading and density control are necessary for effective water purification by C. japonica.

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In order to elucidate the factors controlling the coverage and species of floating-leaved plants and the influence of the plants on the water quality, we heve investigated land use in the watershed, water quality and plant coverage in 20 irrigation ponds in the Kamo Hight, Hiroshima Prefecture. Both water depth and surface area were the dominant factors controlling the area of coverage of the plants. In addition, nutrient concentration in the water significantly affects the species. The percentage coverage potentially influences not only the seasonal changes in chlorophyll a concentration, UV absorbance : DOC ratio and chlorophyll a : COD ratio, but also the ratio of chlorophyll a to limiting nutrient. This percentage coverage may also affect the nutrient concentration in the water, particularly nitrogen, possibly through its uptake from the water.

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Four polyphenols, gallic acid (GA), ellagic acid (EA), pyrogallic acid (PA), and (+)-catechin (CAT), released from Myriophyllum spicatum, are anti-algal allelochemicals. In this paper, we investigated the inhibitory effects of each of these polyphenols on blue-green algae (Microcystis aeruginosa and Phormidium tenue), green algae (Selenastrum capricornutum and Scenedesmus quadricauda), and diatoms (Nitzschia palea and Achnanthes minutissima). We also determined the collective actions of the 4 polyphenols on the inhibition of algal growth.
Among the 6 algae, M. aeruginosa was the only one whose growth was significantly inhibited by each of the 4 polyphenols, while PA, GA, and EA each caused some degree of growth inhibition in P. tenue and the 2 green algae. Because none of the 4 polyphenols showed any inhibitory effect on growth of N. palea and growth of A. minutissima was not inhibited by PA, GA or CAT, diatoms appear to have strong resistance to such polyphenols. The algal assays we used to investigate the collective effects of polyphenols showed that (i) blue-green algae, M. aeruginosa and P. tenue were most sensitive to the synergistic actions of PA, GA and CAT, and (ii) the synergistic actions toward the 2 green algae and the 2 diatoms were concentration-dependent. These results indicate the possible feasibility of selectively controlling growth of blue-green algae through use of these polyphenols and/or the allelopathic effects of M. spicatum. Measurement of the autoxidation rates of the 4 polyphenols suggests that (i) their inhibitory effects on the growth of M. aeruginosa could be caused by products of their autoxidation, such as radicals, and (ii) the synergistic action of PA, GA and CAT might be due to acceleration of their autoxidation resulting in increasing production of such autoxidation products.

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Two bacterial strains, N-21 and N-22, which were isolated from natural oil-producing wells at Kurokawa, Niigata Prefecture, Japan, were identified as Pseudomonas cepacia by using the phylogenetic analysis based on the 16SrDNA sequences. Both strains were gram negative rods capable of decomposing naphthalene. The degradation rates were 2.24 × 10^-5 M/h in both strains. The main metabolite was cis-1,2-dihydro-1,2-naphthalenediol. Salicylaldehyde, salicylic acid, gentistic acid and catechol were also identified. These metabolites were less mutagenic than naphthalene itself in the Ames test using the S. typhimurium TA100 strain. The mutagenicity of naphthalene also decreased by the two bacterial strains.

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