Eutrophication-induced changes in Lake Nakaumi,southwest Japan |
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| Authors: | Kota Katsuki Yasushi Miyamoto Kazuyoshi Yamada Hiroyuki Takata Keiko Yamaguchi Daisuke Nakayama Hugo Coops Hidenobu Kunii Ritsuo Nomura Boo-Keun Khim |
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| Institution: | (1) BK21 Coastal Environmental System School, Division of Earth Environmental System, Pusan National University, Busan, 609-735, Korea;(2) Tottori Prefectural Institute of Public Health and Environmental Science, Tottori 682-0704, Japan;(3) Research Department, Institutional Research Center for Japanese Studies, Kyoto 610-1192, Japan;(4) Marine Research Institute, Pusan National University, Busan, 609-735, Korea;(5) Faculty of Life and Environmental Science, Shimane University, Shimane 690-8504, Japan;(6) Research Center for Coastal Lagoon Environment, Shimane University, Shimane 690-8504, Japan;(7) WL/Delft Hydraulics, P.O. Box 177, 2600 MH Delft, The Netherlands;(8) Department of Education, Shimane University, Shimane 690-8504, Japan |
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| Abstract: | Lake Nakaumi, southwest Japan, is an enclosed lagoon characterized by polyhaline and halocline conditions. Since the last
century, its ecological state has been altered by eutrophication. We used a paleolimnological approach and studied multiple
proxies, including chemical compounds, diatoms, foraminifera and molluscs, to infer the eutrophication history of the ecosystem.
Eutrophication in Lake Nakaumi was associated with several factors, including increased nutrient loading, input of herbicides,
and dike building since the 1920s. The ecological condition of this lake was divided into several stages that reflect the
eutrophication process after the 1940s. A catastrophic “regime shift” from a clear state with aquatic vegetation to a turbid
one with phytoplankton occurred in the early 1950s. Environmental degradation in the Honjo area, a part of Lake Nakaumi, was
attributed primarily to physical changes caused by the construction of an enclosing dike. Eutrophication occurred almost simultaneously
with the physical changes to the Honjo area in the 1970s. Until recently, no regime shift was observed in this area, though
the core-top sediments show possible symptoms of incipient change. |
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| Keywords: | Lagoon eutrophication Sediment core Ecological shift Diatoms Foraminifera Mollusks |
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