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This series of images of southwestern Japan shows how one change can have far-reaching consequences.

The Ariake Sea is an important fishery and resource for cultured nori (seaweed). The controversial Isahaya Bay Reclamation Project has been blamed for recent reduced harvests of fish and nori in the sea. A dike across Isahaya Bay, which was built to create more farmland, has reduced the tidal current mixing of the sea. These weaker tidal currents have led to abrupt changes in the marine environment.

The 7-kilometer sea wall (dike) was completed in April 1997, cutting off Isahaya Bay from the waters of the Ariake Sea. It separated thousands of hectares of tidal flats from the Ariake Sea and turned what was once Japan’s largest area of tidal lands into 1,500 hectares of farmland.

In the Landsat series of images, the Ariake Sea is the large body of water, and Isahaya Bay lies to its west. The dike can be seen as the straight line in the 2003 and later images, separating dark blue from light blue colored water. Black or very dark blue indicates deep water, and light blue represents shallow water. Forested areas are green, and urban areas are pink. Cropland is distinguished by its rectangular pattern: green shapes are fields with crops, and pink shapes are fields with no crops growing at the time of the image.

Imagery

Every picture has a story to tell
Feb. 8, 1979, Landsat 2 (path/row 121/37) — Ariake Sea, Japan
May 15, 1993, Landsat 5 (path/row 113/37) — Ariake Sea, Japan
May 3, 2003, Landsat 7 (path/row 113/37) — Ariake Sea, Japan
Aug. 29, 2011, Landsat 7 (path/row 113/37) — Ariake Sea, Japan
Sept. 27, 2013, Landsat 8 (path/row 113/37) — Ariake Sea, Japan
Mar. 25, 2021, Landsat 8 (path/row 113/37) — Ariake Sea, Japan

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References

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NOAA, 2013, A “red tide” is a common term used for a harmful algal bloom: NOAA National Ocean Service, available online at http://oceanservice.noaa.gov/facts/redtide.html. (Accessed February 1, 2013.)

UNEP, 2005, Coastal areas—Isahaya Bay, Japan, in One planet, many people—atlas of our changing environment: Nairobi, Kenya, United Nations Environment Programme (UNEP), p. 106–107.

Yuk, J., Choi, B.H., and Kim, K.O., 2010, Changes of tides in Isahaya Bay due to a barrier: KSCE Journal of Civil Engineering, v. 15, no. 3, p. 427–437.

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