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Nutrient and Phytoplankton Dynamics in Harima-Nada, Eastern Seto Inland Sea, Japan During a 35-Year Period from 1973 to 2007 |
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| Authors: | Tetsuya Nishikawa Yutaka Hori Satoshi Nagai Kazutaka Miyahara Yukinobu Nakamura Kazuhiro Harada Minoru Tanda Takehiko Manabe Kuninao Tada |
| Institution: | 1. Tajima Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Kasumi, Kami, Mikata, Hyogo, 669-6541, Japan 2. National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, Maruishi 2-17-5, Hatsukaichi, Hiroshima, 739-0452, Japan 3. Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Minami-Futami 22-2, Futami, Akashi, Hyogo, 674-0093, Japan 4. Inland Waters Branch, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Touji 1134, Asago, Hyogo, 679-3442, Japan 5. International Center for the Environmental Management of Enclosed Coastal Seas, Wakinohama-kaigandori, Chuo-ku, Kobe, 651-0073, Japan 6. Laboratory of Biological and Chemical Oceanography, Kagawa University, Miki, Kida, Kagawa, 761-0795, Japan |
| Abstract: | Long-term monitoring of water quality and phytoplankton was conducted at 19 sampling stations in Harima-Nada, eastern Seto Inland Sea, Japan for 35 years from 1973 to 2007. There were two significant long-term changes, an increase in winter water temperatures of 0.042°C year?1, and a decrease in dissolved inorganic nitrogen (DIN) from about 10 μM in the 1970s to ~5 μM in the late 1990s due to the reduction in nutrient inputs. DIN concentrations and total phytoplankton cell density were both higher during the 1970s to the early 1980s and then exhibited a significant decrease in the mid 1980s and remained relatively constant thereafter. Diatoms were the dominant phytoplankton group (>90%) over the 35-year period, and there was a dramatic shift from Skeletonema dominance (~70%) to Chaetoceros in the mid 1980s. This shift in diatom species may be attributed to differences in the life cycle of Skeletonema and Chaetoceros and the response to the decrease in DIN concentration. |
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