2006 Volume 115 Issue 1 Pages 26-40
Records of short-term environmental changes caused by urbanization and industrialization are expected to be preserved in lake sediments. Besides, a consistent, high-resolution baseline record is required to interpret extreme influences of human impact such as heavy metal pollution and eutrophication. In this study, the numerical dates of the core samples taken from Lake Teganuma are determined using the 210Pb and 137Cs dating method. Concentrations of heavy metals are obtained for centrifuged water samples with wet core samples, and for HCl and acetic ammonium extracts with oven-dried core samples, to clarify the existing state and the mobility of metals. Total carbon content, total nitrogen content, and C/N ratio are also obtained for ovendried core samples to analyze the influence of human impact on water deterioration of Lake Teganuma. According to the analytical results for total carbon, nitrogen, and C/N ratio, the eutrophication in Lake Teganuma started around 1946 and shifted further to a critical condition in the late 1960's. Zn and Cu pollution began around 1955, while serious Cr pollution occurred around 1963. These responsible factors for the water environmental changes in Lake Teganuma represent stresses of population increase and drainage closure due to reclamation.