Environmental Destruction of the Tokyo Bay Tidal Flat -Memories of Lost Waterfront and Blue Tide 2001

Environmental Destruction of the Tokyo Bay Tidal Flat -Memories of Lost Waterfront and Blue Tide 2001

Around 2001, Tokyo Bay had lost a large number of tidal flats due to continuous reclamation since the period of high economic growth, and the shrinkage of the ecosystem had become apparent. The Yatsu Tidal Flat at the back of the bay is one of the "few remaining tidal flats in Tokyo Bay," and materials related to the International Wetlands Convention point out that more than 90% of the tidal flats in Tokyo Bay as a whole have been lost. A recent summary of the situation states that "approximately 90% has been lost in the past 100 years," making the preservation and restoration of coastal areas an urgent issue.

The loss of tidal flats has fragmented the self-cleaning function of the bay and the habitat of diverse organisms, weakening its role as a fishing ground for the Edo period and a stopover for migratory birds. The modification of the inner bay shape was determined by large-scale reclamation in the 1960s and 1970s, and today Sanbanse remains only as a shallow sea and tidal flat surrounded by reclaimed land on three sides. Government documents document how reclamation and land subsidence during this period gradually reduced the shallow area and degraded the habitat.

A typical environmental impact is the blue tide. From summer to early fall, the low-oxygen to anoxic bottom water that forms in the shipping channels and excavation sites at the back of the bay rises due to strong winds and other factors, causing the sea surface to turn bluish-white and muddy. The release of hydrogen sulfide accumulated in the bottom sediment causes mass mortality of fish and shellfish, and damages coastal fisheries and the lives of local residents. The Tokyo Metropolitan Government's explanations and numerical modeling studies suggest that blue tides are caused by the upwelling of anoxic water and sulfides in the bottom layer, and that countermeasures include reducing the size of negative oxygen water masses and improving bottom sediment.

In fact, the Ministry of the Environment data shows that in the summer of 1994, a large-scale blue tide occurred off the coast of Funabashi, causing extensive damage to the fishing industry. These cases were symbolic of the link between the loss of tidal flats and shallow areas and the deterioration of the bottom layer environment.

In 2001, the Ministry of the Environment announced that it was going to withdraw its plan to reclaim 101 hectares of the Sanbanse, thus promoting a policy shift from land reclamation to rehabilitation. In the same year, the Sanban Se was selected as one of the "500 Important Wetlands" by the Ministry of the Environment, and a framework for conservation and restoration was sought through collaboration among the national government, local governments, and citizens. The grave reality of the loss of 90% of the tidal flats and the lessons learned from the frequent occurrence of blue tides underscore the need for scientific monitoring and adaptive management in the restoration of Tokyo Bay.