To clarify the relationship between the occurrence of aquatic macrophytes and the chemical nature of the water, the flora of aquatic macrophytes grown in 122 irrigation reservoirs in Tokai District was investigated along with some major elements (pH and concentrations of Ca, K and Mg) in the water of 65 randomly selected reservoirs. By dividing the irrigation reservoirs into three altitudinal locations (plain, lower hillside and higher hillside), it was revealed that 23 species of the aquatic macrophytes (exclusive of two omnipresent species, Phragmites communis and Zizania latifolia) inhabiting these reservoirs could be classified into six groups.
Since both pH and the concentrations of the three elements in the water gradually lowered with the higher altitude of reservoirs, it was supposed that the flora of each reservoir was considerably influenced by some elements of its water, and the latter must in turn have been affected by the geographical feature of the basin in which the reservoirs were located.

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A bacterium of the Chromatiaceae family was isolated from a dense layer of phototrophic bacteria at the mid-depth of Lake Kaiike. The bacterium could be purely cultured in the medium given by PFENNIG and LIPPERT (1966). When sulfide was amply present in the medium, a very elongated form of the bacterium, which contained sulfur globules inside the cell, predominated. With decreasing sulfide concentration, it changed to a sulfur-containing and finally to a motile sulfur-free rod-shaped bacterium measuring 1-2 μm in length to achieve the stationary phase of the culture. Some environmental factors, pH, light, temperature, NaCl, vitamin B₁₂ and sulfur compounds, on the bacterial growth were examined.

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In order to clarify the mechanism triggering the occurrence of a freshwater red tide of Uroglena americana that took place in Lake Biwa from May to June since 1977, a series of studies were undertaken in the northern basin of the lake.
In 1978, Dinobryon barvaricum, Uroglena americana, Closterium aciculare, Aphanothece clathrata, and Planktosphaeria gelatinosa occurred successively as dominant phytoplankton species from early May to late June. Mean concentrations of dissolved inorganic nitrogen (DIN), urea-N, phosphate-P, and silicate-Si at a representative station (St. 4) were 9.8, 1.2, 0.18, and 1.5 1μg at. 1^-1, respectively, and changes of these concentrations were not so large except for the increasing silicate-Si concentration on June 29. Concentrations of chlorophyll a were ca 2-40 mg m^-3, 50-340 mg m^-2 and these concentrations usually were high and variable near the surface, especially at the time of the occurrence of freshwater red tide. The results suggested that the effects of growth and accumulation of U. americana were large in the occurrence of freshwater red tide in the lake.

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A freshwater red tide of Uroglena americana usually occurred after the continuation of windless weather for several days and disappeared after stormy weather.
Three typical distribution patterns were obtained as the results of observation of the distribution of temperature and chlorophyll. In Type I, the vertical distribution of both chlorophyll and temperature were uniform from the water surface to the bottom. In Type II, the peak of chlorophyll concentration was found at the depth of 2-3 m. In Type III, the maximum concentration of chlorophyll in the vertical distribution was found at the surface of lake water where water temperature was remarkably high compared with that of the deeper water. A dense accumulation in the horizontal pattern of colonies of U. americana was found in the area where the temperature of surface water was relatively low, in the case of Type II. On the contrary, with Type III, the population maximum was found in the area where the water temperature was relatively high.

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In this study are reported for the first time the results of observations of the seawater intrusion into the coastal aquifer at the mouth of the Kiki River in Ehime Pref. This phenomenon was then analyzed with the aid of the hydrological model found by FUKUO, KAKINUMA, KISHI and IFUKU. Concentrations of chloric ions were observed since 1972 in groundwater pumped up from 50-60 wells in this plain. Very high concentrations of chloric ions were observed in the fan-shaped region near the coast during the period from 1972 to 1974. It turned out, however, from data in 1976 and thereafter that concentrations of chloric ions in the above region were decreased considerably, so the phenomenon of seawater intrusion into the coastal aquifer virtually disappeared in fact. In order to determine the reason for such a sudden change in this phenomenon, the above mentioned model was applied to the groundwater in this plain. The decrease in the total amount of groundwater pumped in this plain was found to be the main cause of the shrinkage of the saline region near the coast.

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Underwater irradiances were measured in Lake Biwa in terms of lux, quanta (400-700 nm) and total energy in the shortwave range (300-2500 nm). The attenuation of irradiance was most rapid in energy, least in illuminance and in-between in quanta. Similar results were obtained from computations using the spectral sensitivity of sensors in conjunction with the earlier reported measurements of underwater spectral irradiance obtained for Lake Biwa. Thus, the differential attenuation of irradiance among these three expressions is due to the differences in the spectral sensitivity among the sensors together with characteristics of Lake Biwa regarding the selective absorption of spectral irradiance. Computed results also indicated that the penetration of energy flux in the range of 400-700 nm was virtually equal to that of photon flux.
Analysis and discussion are extended to other lakes and marine environments reported in the literature. The significant deviations of underwater irradiance in lux from irradiance as photon flux density underscores the importance of using quanta or energy measurements in the photosynthetically active wavelength range in studies of primary production in aquatic habitats.

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The species composition and abundance of zooplankton of Lake Baikal were examined by vertical net collections in both pelagic (1, 300 m deep) and littoral (100 m deep) areas in September 1980. Thirteen species (two Copepoda, two Cladocera, eight Rotifera and one Protozoa) were identified, in which Episclaura baicalensis, Keratella quadrata and Vorticella sp. were dominant. Cladocerans were very scarce. Most of the zooplankters were distributed in the epilimnion (0-50 m deep), in which their biomass in the pelagic area was estimated to be 31.7 g (d.w.)·m^-2. Some 83% of the biomass was occupied by E. baicalensis alone. Other copepods (including nauplii), rotifers and protozoans accounted for 13.9, 2.4 and 0.60 of the biomass, respectively. A large number of rotifers (7.4×10⁶ animals·m^-2) and Vorticella sp. (9.1×10⁶) were also noted, despite the oligotrophic condition, suggesting the important role of minute suspended matter like bacteria as a food resource.

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Diurnal rhythm of Planktonic organisms in relation to various physico-chemical variables was monitored during dry, hot and rainy seasons in Jos Plateau (Nigeria) water reservoir. Diurnal fluctuations in water temperature, dissolved oxygen concentration, free carbon dioxide, total alkalinity and specific conductance were significant. pH was circum-neutral throughout with relatively narrow diel variations. Chloride content seemed conservative, exhibiting little fluctuation. This investigation describes the role of the diurnal cycle of various abiotic environmental factors in regulating the diurnal movement of plankters.

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