To maintain a safe drinking water supply, it is essential to understand the occurrence of pathogenic microorganisms in the catchment area of source water. In this study, the previously developed adsorption–elution method of using a negatively charged membrane was optimized in terms of the MgCl₂ concentration for adsorption, the H₂SO₄ volume for acid rinsing, and the NaOH immersion time for elution in order to determine the stable and efficient concentration conditions for viruses in surface water samples. The optimized method was applied to samples collected in Lake Biwa and the Yodogawa River Basin, and pepper mild mottle virus, rotavirus, and norovirus contaminations were investigated. The surface water contamination with feces of human or animal origin was evaluated by measuring Bacteroidales genetic markers specific to humans, pigs, and ruminants, and pharmaceuticals (carbamazepine, sulfamethoxazole, and sulfamonomethoxine) for humans and animals. As a result, the concentrations of viruses and Bacteroidales genetic markers in surface water were found to increase as the Yodogawa River flowed downstream from Lake Biwa. Our observations through the measurements of viruses, bacteria, and pharmaceuticals in surface water demonstrated that the Katsuragawa River was mainly contaminated with feces of human origin, while the Kizugawa River was contaminated with those of animal origin.

Dredged pits are a negative legacy of the Nakaumi Reclamation and Desalination Project, because the generation of hydrogen sulfide, which is the major cause of the destruction of the Nakaumi ecosystem. In the present study, hydrogen sulfide generation in a small pit (0.05 km²) of Hosoi district was significantly suppressed by the application of granulated coal ash (30,000 m³, 50 cm in thick) . However, the generation of hydrogen sulfide was again observed after 1.5 years later because of consecutive organic matter sedimentation. A numerical model examination revealed 10,000 m³ (17 cm thick) of granulated coal ash was sufficient to suppress the generation of hydrogen sulfide in the pit. It was concluded that repeating the application of the material in every few years until the pit is filled would be the best measure for preventing hydrogen sulfide generation due to the consecutive organic matter sedimentation.

To quantitatively evaluate the structure of biological communities using environmental DNA (eDNA) data, it is important to know the decay and shedding rates as well as the concentration of eDNA. However, this information is lacking for marine decapods. Thus, in this study, the decay and shedding rates of eDNA were investigated by performing rearing experiments using Portunus pelagicus (Linnaeus, 1758) . The decay rate of eDNA was calculated to be 0.0397 for nonacclimated individuals and 0.0515–0.0586 for acclimated individuals. The values for acclimated individuals were slightly lower than those of fish (0.0585–0.0919) reported in a previous study. The shedding rate after 48 h of rearing was not calculated for nonacclimated individuals, but it was calculated to be 1.97–7.75 pg hr^-1 ind^-1 for acclimated individuals. The shedding rate of fish, according to previous studies, is 10³–10⁷ pg hr^-1 ind^-1, thus the shedding rate of marine decapods was lower than that of fish. These results indicate that marine decapod eDNA is utilized for a quantitative evaluation. This would require an increase in sample volume, which is different from of fish.

In this study, we gathered the information on catchment area, elevation, land uses in the catchment area and within a 3 km buffer area, and five water quality parameters, including, i.e., pH (minimum) , biochemical oxygen demand, suspended solids, total phosphorus, and total nitrogen, for 2925 water quality monitoring (WQM) sites (environmental reference points) in rivers throughout Japan. The hierarchical cluster analysis was supplementarily performed using physicochemical characteristics to classify the WQM sites into the following four groups: Group 1 (986 sites) was characterized by the predominant forest land use in the catchment area and relatively good water quality. Groups 3 and 4 (345 and 310 sites, respectively) were characterized by predominantly paddy and dry fields, and urban land uses, respectively, and relatively poor water quality. Group 2 (1284 sites) had intermediate features between Group 1 and Groups 3 and 4. Thus, we developed the database of physicochemical characteristics for WQM sites in Japan to readily examine, for example, the features of WQM sites contaminated with a given chemical substance.

Dissolved oxygen in the bottom layer (Bottom DO) was newly added to the environmental water quality standards for protecting the living environment in 2016. Tokyo Bay is a highly closed water area, so red and blue tides occur every year, and Bottom DO is often lower than 2 mg L^-1 in summer. To consider the cause of the reduced Bottom DO, the vertical distribution of water quality characteristic, that is, temperature, salinity, chlorophyll-a, and DO, has been measured several times a month from 2003 to 2017 at fixed points in Tokyo Bay. During this time, the stratification of water temperature has been observed every summer. From autumn to winter, the stratification disappears. The decrease in salinity has been observed with the inflow of fresh water caused by rain fall. At St.A (the point of a dredged trench on the bottom) , as a result of the decrease in depth, the mass of hypoxic water has been decreasing. These data should be useful for studies of Tokyo Bay.