RIASSUNTO
ABSTRACT:
Various water purification technologies have been developed to mitigate the significant environmental impacts on ocean caused by the rapid economic developments in coastal areas. This paper estimates the performances of these technologies in Tokyo Bay through numerical experiments and inclusive impact assessments. The assessment results using Triple I (III: Inclusive Impact Index) suggest that efforts in seaside are more effective that those in landside; and the bioengineering technologies can get larger effects than the engineering ones, from the viewpoint of sustainability. A new method of calculating III is also proposed to estimate the ecological risk, which is the bottleneck of figuring out the indicator.
INTRODUCTION
The Tokyo Bay is a bay in the southern Kantō region of Japan (Fig. 1). It is surrounded by the Boso Peninsula to the east and the Miura Peninsula to the west, and links to the Pacific Ocean through the Uraga During the period of rapid economic growth, large scale reclamation has been carried out along with the high level development of the coastal area. As a result, serious environmental problems occurred in the Tokyo Bay. Since 1970s, 40 to 60 red tide events and 2 to 7 blue tide events have been observed annually (Ministry of Environment, 2005). For the purpose of preventing the further pollution of the water environment, the Water Pollution Controlling Law (WPCL) was enacted in 1970 to control the pollutant density in the sewage treatment. After that, the limitations of the Total Maximum Daily Loading (TMDL) of chemical oxygen demand (COD) (in 1978), nitrogen and phosphorus (in 1993) were included into the WPCL. However, the cleaner inflow to the ocean which means lower external environmental load did not significantly improve the environment in the enclosed sea areas such as the Tokyo Bay (Ministry of Environment, 2005).