| Co-Investigator(Kenkyū-buntansha) |
IWAMA Kenji UNIV.OF SHIGA PREF., SCHOOL OF ENVIRON.SCI., RES.ASSOC., 環境科学部, 助手 (60269727)
TAKAHARA Hikaru KYOTO PREF.UNIV., FACULTY.OF AGRIC., ASSOC.PROF., 農学部, 助教授 (30216775)
KITAGAWA Yasuo FUKUI PREF.UNIV., FACULTY OF BIORESOURCES, PROF., 生物資源学部, 教授 (90254242)
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| Budget Amount *help |
¥3,200,000 (Direct Cost: ¥3,200,000)
Fiscal Year 2000: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1999: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 1998: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Research Abstract |
To read out the records of human activities from the lake bottom sediments, three naiko, or literally inner lakes, on the east coast of the Lake Biwa, i.e.Nishinoko, Syonakanoko-polder, and Sonenuma, were chosen for core sampling. Various analyses were carried out on the 4 cores. The major findings were as follows :
Mean sedimentation rates in naiko, as estimated from the carbon dating data, was much slower than expected, 0.1 to 0.15 mm/y for mineral sediments in Nishinoko and Syonakanoko. Peaty Sonenuma sediments deposited much faster, 1 to 1.5 mm/y.
Magnetic susceptibility was logged to locate volcanic ashes in the cores, but no sharp peaks were found for the sediments, dating back to 15,000 yBP.Plant opals of rice(Oryza sativa)were looked for to locate the beginning of rice cultivation without success both for Nishinoko and Sonenuma sediments.
Copper and zinc tended to show a linear increase from several hundreds of years ago up till the present, maybe reflecting the influence of human activities.
Clay mineral composition reflected a long-term climatic change, showing an increase in kaolinite and a corresponding decrease in mica and smectite.
Pollen analysis with the Sonenuma sediments revealed two major changes in the vegetation of the east coast region of the Lake Biwa. One was the initiation of rice cultivation sometime around 2,600 yBP, causing a local disruption of the primary forest. Second and more extensive transition from the primary to the secondary forest vegetation occurred sometime around 1,200 yBP, resulting in the dominance of Pinus that replaced for the evergreen deciduous trees and Cryptomeria.
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