Sedimentation rate and sedimentary environment during the past 100 years in Lake Biwa, Shiga Prefecture, central Japan.

Abstract

Two core samples were taken from the northern basin of Lake Biwa in 2001 and 2014, and their sedimentation rates were determined using Pb-210 and Cs-137 methods. One of the sampling locations is off Imazu, near the deepest bottom of the lake and the other is off Takashima, shallower bottom like top of saddle. The average sedimentation rates were about 0.1 g/cm²/y (0.1–0.3 cm/y), which are within the range of conventional reports, although that of the former was a little higher than that of the latter. As for the core taken near the deepest bottom of the lake, much sediment with excess Pb-210 deposited before1960s, suggesting that they were supplied by flood and turbidity current. They are assumed to be caused by the seismic turbidites in 1981 and 1963 and the heavy rains and floods in1896, 1917, 1950s and 1960s. On the other hand, surface sediment of the core taken at off Takashima showed the variation of water content and Pb-210 concentration, which are ascribed to the disturbance and mixing by surface biota and/or human activities.