| Project/Area Number |
63043032
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| Research Category |
Grant-in-Aid for Overseas Scientific Research
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| Allocation Type | Single-year Grants |
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| Section | Field Research |
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| Research Institution | Nagoya University |
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Principal Investigator |
SAIJO Yatsuka Professor Emeritus, Nagoya University, 名誉教授 (70022506)
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| Co-Investigator(Kenkyū-buntansha) |
FUKUHARA Haruo Associate Professor, Niigata University, 教育学部, 助教授 (50108007)
MITAMURA Osamu Associate Professor, Osaka Kyoiku University, 教育学部, 助教授 (50030458)
NAKAMOTO Nobutada Associate Professor, Shinshu University, 繊維学部, 助教授 (40109202)
SUNAGA Tetsuo Professor, Kagawa University, 教育学部, 教授 (00035883)
IKUSIMA Isao Professor, Chiba University, 理学部, 教授 (20009046)
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| Project Period (FY) |
1987 – 1988
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| Project Status |
Completed (Fiscal Year 1988)
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| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1988: ¥1,900,000 (Direct Cost: ¥1,900,000)
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| Keywords | tropical lake / nutrients / bottom sediment / aquatic macrophytes / plankton / emergence of chaoborid / fish community / 変水層 |
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| Research Abstract |
The study was carried out from June to July 1987 to clarify the limnological feature of the Rio Doce valley Lakes in dry season.
1. The greater part of the nitrogen source for phytoplankton was ammonia. The phytoplankton preferentially utilized ammonia and urea. the regenerated forms of nitrogenous nutrients played significant role as nitrogen source for phytoplankton in the euphotic layer in lakes.
2. The accumulation mechanism of large quantities of sedimentary organic matter in Lakes Dom Helvecio and Amarela were studied based on the fatty acids composition. In both the surface sediments, about 90 mg C/g dry sediment was derived from terrigenous sources, and the autochtonous contributions in Lakes Dom Helvecio and Amarela were about 50 and 110 mg C/g dry sediment respect-ively.
3. The biomass production of a semi-emergent plant Eichhornia azurea Kunth was determined. The mean rate of leaf emergence was 8.7 to 11.0 days. The mean value of the life span of leaves was estimated as 70 to 74 days. The life span of the steam was estimated as 2 years and 4 months.
4. Diurnal and diel emergence patterns of chaoborids were investigated in Lake Dom Helvecio. One of Chaoborus showed the highest catch up to 96 % of the overall, which emerged largely on the night of a new moon. Emergence of species occureed actively before sunrise. The synchronization of growth of this species under the luner cycle is stronglyh suggested.
5. More than 260 fish belonging to 16 species (11 families) were obtained during the survey period. Comparing with results in 1985, both species diversity and relative abundance of fish were decreased in all the lakes except Lake Amarela. The authors concluded that the drastic change observed in the fish community of Lake Carioca was caused by the predation effect of the Tucunare (Cichla ocellaris) introduced in 1985.
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