Natural and Cultural Histories of San'in Region

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The main objects of the research are sea-level changes and synthetic studies on geographical, cultural, and social environments of lagoons, especially in Lakes Nakaumi and Shinji. The detailed geographic developments were reconstructed on the basis of drilling, core sampling and echo-sounding surveys and sea-level changes since 10,000 y.B.P.were discussed. Many lowland archaeological sites around Lakes Nakaumi and Shinji were reexamined from the view point of the Holocene sea level changes. The activities of our ancestors have been newly recognized as multi-sided using of the lakes as fishery ground, fishery ports and transportation bases. The surrounding lowland areas had provided convenient conditions for human activities especially for rice cultivation. These had made possible the prosperity of Paleo-Izumo. The effects of sea-level rise due to global warming on coastal lagoon areas such as salinity increase, salt water intrusion into freshwater aquifers, were examined. The depositional environment during the Holocene climatic optimum have been established from geochemical study of the sediment cores of Lake Nakaumi. The results will offer basic information for projections of lagoonal environments in future glob warming.A long-term observation system for the study of Halocline behavior in coastal lagoons and estuaries has been developed. This system was successfully carried out in Lake Nakaumi and would contribute to control the movement of oxygen-free saline water in near future, The system was also successfully carried out at River Gonokawa in Shimane Prefecture, one of the most famous tidal rivers in Japan.The Lake Nakaumi Reclamation Project, which was started in 1963, and have been suspected, are discussed from the view point of environmental sciences, and a program for wise use and balanced ecosystem has been proposed.