The ratio of electricity consumption in sewage treatment to the total electricity consumption in Japan is increasing yearly. Thus, it is important to efficiently operate sewage treatment plants considering the quality of incoming sewage. However, no study has identified how the overall quality of sewage water in urban areas relationships to its sewershed characteristics. Therefore, in this study, we analyzed data from the Tokyo metropolitan area to understand the relationship between the spatiotemporal distribution of sewershed characteristics and sewage water quality. Results indicate that biochemical oxygen demand and total nitrogen concentration are correlated to daytime population density in each sewershed, which is affected by land use. In addition, sewage water quality showed seasonal relationships to utility expenditures and monthly air temperature, indicating the temporal relationship between these sewershed characteristics and sewage water quality. In conclusion, through this study, the spatiotemporal distribution of sewershed characteristics was clarified and the relationship was identified between sewershed characteristics and sewage water quality. Results imply that the sewage water quality in the Tokyo metropolitan area can possibly be modeled on the basis of daytime population density, land use, utility expenditures and monthly air temperature, which might be beneficial for the efficient long-term operation of sewage treatment plants.

In the aerobic layer in the upper part of meromictic Lake Abashiri, blue-green algae grow and Anabaena has easily been the dominant species in summer since the 1950s. However, in recent years, other blue-green algae such as Microcystis are coming prevalent. We carried out an investigation of water quality and phytoplankton community up to three times a month in order to clarify the reason for this change. Dissolved inorganic nitrogen (DIN) loading to the aerobic layer was greatly affected by the influx of river water, and dissolved inorganic phosphorus (DIP) loading to the aerobic layer was greatly affected by the supply from the anaerobic layer. It was found that DIN is easily depleted in the aerobic layer in summer, and the amount of Anabaena, which is capable of atmospheric nitrogen fixation, easily increases. However, it is considered that when the effect of river water becomes large, the amount of DIN loading increases and the amount of blue-green algae other than Anabaena easily increases. Recent changes in agricultural and other activities in the basin and an increase in river flow rate, which results in greater DIN load in the influent river water, are considered to be the main factors behind the changed in the dominant species of blue-green algae in Lake Abashiri.

Several small distributary rivers exist downstream of the Gosho Dam in the Shizukuishi River of the Kitakami River system. Although there are human-influenced areas surrounding these rivers, such as pastures, fields, residential areas, major national roads and highways, many rare aquatic organisms exist, including Margaritifera laevis. This rare aquatic organism is decreasing in number and increasingly threatened presumably because of the presence of various type of human activity. Therefore, we attempted to evaluate the effects of land use type on water quality on the basis of relationship between the land use classification of areas within the watershed and the results of water quality surveys conducted once a month for one year at several locations along a small river. The results of this study revealed that in addition to the effects of fertilizers from fields and pastures, drainage, and treated water from residential areas, along with the strong effects of antifreezing agents applied to roads during the winter were observed. Small streams are susceptible to inflow loads because of their low flow rate and limited dilution effects. If aquatic life conservation is regarded as important, then measures must be taken to address road drainage problems.