Dōkai Bay (Japanese: 洞海湾, Hepburn: Dōkai Wan), located in Kitakyushu City, Japan, is a long, narrow inland waterway-like bay measuring five or six hundred meters wide and 13 kilometers long. In modern times, it faces heavy industrial areas and once suffered from severe pollution and water contamination, but after a long period of successful purification efforts, the water quality has improved and the ecosystem has recovered.
Physical Geography
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Dōkai Bay, located in the northern part of Kyushu island, streches from the sea (Hibiki Nada) on the east side of the island to the west into the land.[1][2] It is long and narrow, shaped like waterway, and measures five or six meters wide and 13 kilometers long.[1] The average depth is shallow, about 7 meters.[1]
The formation of Dōkai Bay is closely related to the Quaternary cooling.[2] During the last glacial period, rivers formed a valley here.[2]
There are rivers that flow into the bay, including Egawa River, but they are all small and they all flow into the bay at the innermost point of the bay.[1][3]
The flow pattern of water masses in Dōkai Bay is a typical estuarine circulation.[1] Throughout the year, the predominant current in the surface layer is toward the mouth of the bay, while the predominant current in the bottom layer is toward the interior of the bay.[1] The surface water in the inner bay does not mix vertically, but flows along the surface and flushes out of the bay within two or two and a half days.[1]
Flora and Fauna
editDōkai Bay was a tidal flat several thousand years ago, and was home to many shellfish and other creatures suited to the tidal flat environment.[2] By historic times the bay had become deeper and was known for its abundant shrimp.[3][4]
In modern times the bay became a coal shipping port.[4] The bay was lined with factories, and wastewater from these factories caused the bay to become severely polluted.[5] In the 1960s, the bay was so polluted that it was called the "Dead Sea," because no fish could live there.[5] After that, the government strengthened its anti-pollution measures, and Japan's industrial structure changed[1].[5] As a result, the bay has recovered to the point where it is home to more than 100 species of fish and shellfish as of the 2020s.[5]
References
edit- ^ a b c d e f g h 「洞海湾の河口循環流と赤潮形成」『沿岸海洋研究』第44巻, 第2号, 147−155, 2007. (Tada et al. "Estuarine Circulation and Red Tide Outbreaks in Dokai Bay, Japan" Bulletin on Coastal Oceanography. Vol.44, No.2, 147−155, 2007) DOI: 10.32142/engankaiyo.44.2_147
- ^ a b c d "Dokai Bay". Kitakyushu Museum of Natural History and Human History. Retrieved 2024-11-13.
- ^ a b "History of Dokai Bay". Kitakyusyu City. 2022-07-15. Retrieved 2024-11-13.
- ^ a b "洞海湾は魚がいない「死の海」だった". タカミヤ環境ミュージアム. 2020-12-10. Retrieved 2024-11-13.
- ^ a b c d "ばい煙の空、死の海から奇跡の復活". Kitakyusyu City. 2022-06-30. Retrieved 2024-11-13.