2004 Fiscal Year Final Research Report Summary
Human impact on fluvial environment during the reclamation period in Tokachi Plain, Hokkaido, JAPAN.
| Project/Area Number |
14580099
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
自然地理学
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| Research Institution | Joetsu University of Education |
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Principal Investigator |
YAMAGATA Kotaro Joetsu University of Education, Associate Professor, 学校教育学部, 助教授 (80239855)
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| Co-Investigator(Kenkyū-buntansha) |
HIRAKAWA Kazuomi Hokkaido University, Graduate School of Environmental Science, Professor, 大学院・地球環境科学研究科, 教授 (40126652)
KURASHIGE Yoshimasa The University of Shiga Prefecture, School of Environmental Science, Associate Professor, 環境科学部, 助教授 (20241383)
HASEGAWA Hiroshi The University of Shiga Prefecture, School of Environmental Science, Professor, 環境科学部, 教授 (00090457)
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| Project Period (FY) |
2002 – 2004
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| Keywords | Tokachi plasin / Human impact / wetland deposits / lake deposit / suspended deposit / environmental radionuclide / reed / gene |
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| Research Abstract |
Hokkaido is a region where the main factor of production changed drastically from hunting and gathering society of Ainu to farming society of Wajin on the boundary of Meiji Restoration. Therefore, the region is an extremely important region for examining the influence of human impact to natural environment. It can be thought that the deposit of the flood plain and lakes and marshes in the downstream recorded past environmental changes occurred in the drainage area, such as large-scale deforestation and reclamation. The aim of this research is to clarify the situation of the artificial environmental destruction and its influence to the fluvial environment during the development period in Tokachi Plain.
By means of detailed analysis of the floodplain and lake deposits and observation of soil profiles in the drainage basins, it was confirmed that the coarsening of the deposits and increasing of depositional speed occurred in response to the human activity in the most of river basins of sou
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thern Tokachi Plain. By the chronological investigation using 137Cs and tephra, it was confirmed that rapid sand deposition occurred in response to the postwar abrupt farmland expansion in the Toberi river basin. And we also found the evidence of frequent forest fires during early Meiji era. The main source of the coarse materials was identified as a tributary (Toberi Horonai River) by grain-size sediment-tracer technique and mineralological investigation. Furthermore, such active sediment supply from the river induced the transportation of reed rhizomes from the upper course to the wetland to form new population. The lake sediment core was taken from the lagoon (Yudou-Pond) and analyzed. As a result, it was clarified that the coarsening of the deposit began in around 1920, and depositional speed had accelerated further in 1960's. By the observation of soil profiles in the Yudou river basin, it was suggested that the reclamation of pastures is the most important cause of the soil erosions. Less
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