Coloration factor and coloration mechanism of the Yudamari crater lake on Mt. Aso and the Yugama crater lake on Mt. Shirane, which are typical hyper-acid crater lakes in Japan and that were observed to be cloudy emerald green in color, are discussed using data from color measurements, chemical analyses of lake waters and the grainsize distribution of suspended elemental sulfur. The grain-size distribution of elemental sulfur in the crater lakes, which is formed by the reaction of SO_2(ap) and H₂S_(ap) originating from the bottom fumaroles, was seen to agree with that of a synthetic colloidal sulfur solution when it turned bluish white. The existence of colloidal sulfur particles involved in Rayleigh scattering and Mie scattering was confirmed. Color measurements using a colorimeter showed that the coloration of the crater lakes is not only caused by the scattering of sunlight by colloidal sulfur particles, but also by the absorption of sunlight by dissolved ferrous ion.

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A faunal investigation of the Tokachi coastal land-locked lagoons in Hokkaido, northern Japan was carried out in November 1996 to detect changes in the benthic communities and lagoon environment compared with a study done in 1942, and to examine the relationship between the benthic community structure and lagoon environment. The macrobenthic fauna of these lagoons were composed of species typical of Japanese oligo- and mesohaline brackish-waters. Multivariate analysis revealed a significant positive correlation between the community structure and some particular environmental variables, i.e., salinity and sediment particle size, which are the most important proximate factors in the community organization of brackish-water benthic species. The macrobenthic communities and their structural characteristics in the lagoons showed no drastic changes since the 1942 study. However, the low density of the bivalve Corbicula japonica and the distributional changes in the dominant polychaete species in this study indicated the peculiar conditions of these land-locked lagoons that may cause population fluctuations and the occasional dispersal event among the lagoons. The description and recognition of the biodiversity of brackish-water fauna is indispensable to conserve the brackish-water environment, moreover, the knowledge of the characteristics of the habitat structure of brackish-water and of the genetic structure of brackish-water species in recent years calls for new insights in future research.

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Several strains of microorganisms that lyse Microcystis cells were isolated from eutrophic lakes. These microorganisms degraded microcystin produced by the Microcystis cells in a temperature-dependent manner; they showed a higher degradation activity at 30°C. There were no correlations between the activities of the microorganisms in lysing the Microcystis cells and for the degradation of microcystin. Among the microorganisms, myxobacteria showed a higher activity for degrading microcystin.

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We studied whether or not a bacterial community structure in an epilithon on riverbed stones changes with the size of the sampling area. The aveage number of colony forming units (CFU) did not differ greatly using different sizes of sampling areas, but the number of CFU obtained from a 0.1 × 0.1 cm² sampling size varied significantly. Bacterial community structure obtained from a 2 × 2 cm² sampling size and a 0.1 × 0.1 cm² sampling size were compared based on the types distinguished by Gram staining, cell form and colony pigments. As a result, when a 0.1 × 0.1 cm² sampling size was used, more types were detected than in a 2 × 2 cm² sampling size.

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Dissolved oxygen (DO) and temperature were measured every 30 minutes in the deep water of Lake Biwa using an oxygen data logger with a thermometer from 5 June 2000 to 3 August 2001. The oxygen sensor of the data logger was a galvanic cell type sensor, and the thermosensor was a thermistor. The DO decreased from 60% in June and reached its minimum value of 25% in October 2000. The maximum value of 80% was reached in January 2001 due to the overturn in winter. There was no anoxic condition during this period. The temperature increased from June to December 2000 by 0.25°C and then decreased by about 1.5°C in January 2001 due to the overturn in winter.

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