| 英文摘要 |
This project completed first the works of sonar seismic scan before coring. Then two sites were chosen for getting cores in Sun-Moon Lake based on the seismic results, and 5 sediment cores which have a total recovered length over 825 cm have succeeded to be taken in accordance with the project’s objects. After, sediment descriptions, photos, non-destructive analysis of Multi-Sensor Core Logging, Color Reflectance Spectrum and X-ray Fluorescence scanning were carried out for each core. Besides, 55 samples were chosen for radioactive age dating according to the EPA's demand.
The obtained results including radioactive age dating pointed out that all the cores cover the age interval from present back to older than AD 1934 which the dam began to be constructed. Age dating results also indicate that the sediments from Sun Lake provide better age controlled data than that of the Moon Lake. The estimated sedimentation rate showed that the site Sun 2 was three times faster than that of the site Moon 1. The result reveals that the main sediment transportation path is from northeastern side of Sun Lake toward the Moon Lake. Physical property parameters, such as the -ray density, porosity, magnetic susceptibility etc., all show very different patterns before and after the dam construction. The trend reflects that the organic material content in the lake sediments dramatically decreased after the reservoir running. Results of X-ray Fluorescence scanning present that the variations in composition of heavy elements may be also due to sediment source changes. High Ni content before AD 1934 may represent the sediment source from the in-situ basin. Thus, the contents of Pb, Zn, Cr increased and the content of Ca started rising and fluctuating after the dam been constructed might conduct the sediment source from faraway after AD 1934. Increasing Pb, Zn, Cr and Ca may imply the pollutions derived from Zhuoshui River or surrounding area, which is worth to be paid attention on it in the future. Besides, extra high sedimentation rate found in our cores most recently may be due to the destructions of 1999 Chi-Chi earthquake and much heavy rainfall brought by several later typhoons passed through. Therefore, the rapid sediment accumulation in the reservoir may be another important issue to be paid attention on.
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