Abstract
Surface water degradation in urban areas is a common problem in many countries, and degradation hampers ecosystem services provided by rivers, having negative impacts on aquatic organisms and human beings. Unpleasant odor arising from impaired rivers causes annoyance to people, and the study quantitatively analyzed unpleasantness of odor in Tokyo through the application of hedonic tones of odor. Unpleasantness remained or worsened while overall dissolved oxygen (DO) concentration increased downstream. The phenomenon is considered to be caused by multiple external factors, such as combined sewer outflow, hypoxia at Tokyo Bay, and effluent from water reclamation centers (WRC). Converting descriptive odor types into numeric values helped to see changes over time and enabled to depict the relation between DO concentration and the type of odor. In Tokyo, the ratio of effluent from WRC to stream flow increased over time, and it partially contributed to odor becoming more unpleasant. Malodor is no longer a major issue since the situation improved by developing an advanced treatment facility; however, human olfactory sense detects the existence of unpleasant odor in urban rivers. The study presented the complexity of analyzing odor problems in tidal urban areas because these are caused by external factors.
Highlights
Rivers have sustained our livelihood by providing freshwater for consumption, serving as a mode of transportation, and being a venue for ritual and cultural gatherings
This study aims to explore changes in odor characteristics along with water quality changes over time and to identify problems remained in urban areas
Odor and water quality upstream of the Kanda River had been stable at high dissolved oxygen (DO) concentration and moderate odor throughout the period while changes in odor and water quality in other sites were apparent
Summary
Rivers have sustained our livelihood by providing freshwater for consumption, serving as a mode of transportation, and being a venue for ritual and cultural gatherings. The growing population in one area changed the natural landscape into built-up areas to accommodate people and economic activities. Anthropogenic activities degraded water quality, changing water unsuitable for direct consumption. The development of other transportation routes as roads and railroads led to the decline of inland navigation, and technological development in water management changed flood and erosion control functions of natural rivers. Human well-being and sustainability have become more important in parallel with economic development, and studies in the past found that natural environment plays a role for maintaining human well-being in urban areas [3,4]. Improving water quality is necessary to restore ecosystem services in urban areas
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