1989 Fiscal Year Final Research Report Summary
Environmental Change on the Limestone Areas in the Nansei Islands
| Project/Area Number |
62580202
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
自然地理学
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| Research Institution | Komazawa University |
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Principal Investigator |
NAGANUMA Nobuo Professor, Dep. Geography, Komazawa University, 文学部, 教授 (30052517)
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| Co-Investigator(Kenkyū-buntansha) |
URUSHIBARA-YOSHINO Kazuk Associate Professor, Dep. Natural Sciences, Komazawa University, 文学部, 助教授 (00101329)
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| Project Period (FY) |
1987 – 1989
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| Keywords | Environmental change / Limestone area / Nansei Islands / Landreclamation / Sugar cane / Dry summer / Water resource / Ground water |
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| Research Abstract |
This project tried to clarify the environmental change of landreclamations in the areas of uplifted coral reefs in the Nansei Islands. The conditions after landreclamations in the northern areas of Okinawa, where the climate is rather wet, were compared with those in the southern areas of Okinawa, where rather dry summer occurs frequently.
i) Kikai Island was chosen as an example in the northern area of Okinawa. On this island, the effect of landreclamation on sugercane harvest is not clear, but landreclamation resulted in loosing soils and fertilizer. The farmer say that two time of fertilizer were given to the fields after landreclamation. Therefore, pollution of underground water also had begun gradually.
ii) In the southern part of Okinawa, Hateruma and Minamidaito were chosen as examples of poor-water-resourse-islands with dry summer. Ishigaki Island was chosen as an example of rich-water- resource with dry summer. On Ishigaki Island, the landreclamation with irrigation system is successful and, as a result, the productivity is becoming stable and high, even through drought occurs some time. However, one should pay attention more on loose of soils here also.
iii) On Hateruma Island, a striking effect of landreclamation on sugar cane yields is not detectable. Area of fields reclaimed is larger than the area of fields before the landreclamation. Almost of the reclaimed area does not have irrigation system, because of poor water resource. In near future, shortage of labor power will be seen in spite of expanding area of reclaimed fields.
iv) On Minamidaito island, people has pumped up too much water until salinization occur after the landreclamation introducing drop irrigation from the underground water. The harvesters introduced made harder soils of fields. The productivities of sugar cane in the serious drought years are poor.
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