READING THE RECORD OF HUMAN ACTIVITIES IN THE BOTTOM SEDIMENTS OF SMALL LAKES ASSOCIATED WITH THE LAKE BIWA

为了从湖底沉积物中读出人类活动的记录，我们选择了琵琶湖东岸的三个内湖，即Nishinoko，Syonakanoko-Polder和Sonenuma进行岩心采样。对4个岩芯进行了各种分析。主要发现如下：根据碳测年数据估计的奈科的平均沉积速率比预期慢得多，西野古和西那卡诺科的矿物沉积物的平均沉积速率为0.1至0.15毫米/年。泥炭松枚举沉积物沉积速度快得多，为1~1.5 mm/cm。磁化率在岩芯中定位火山灰，但没有发现尖锐的峰值，可追溯到15,000 yBP。西野子和松枚举沉积物中寻找水稻植物蛋白石来定位水稻种植的开始，但都没有成功。铜和锌从几百年前到现在都呈线性增长趋势，这可能反映了人类活动的影响。粘土矿物成分反映了长期的气候变化，表现出高岭石的增加，云母和蒙脱石的相应减少。对索恩伦塔沉积物的孢粉分析表明，琵琶湖东海岸地区的植被发生了两个主要变化。其一是大约公元前2600年左右开始种植水稻，造成了当地原始林的破坏。从原始森林植被向次生森林植被的第二次更广泛的过渡发生在距今1 200yBP左右，导致松树取代了常绿落叶乔木和柳杉的优势地位。

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.