Recent sedimentation rates derived from 210Pb and 137Cs methods in Ise Bay, Japan

Ten sediment cores were collected from Ise Bay, Japan, and excess 210Pb and 137Cs were measured gamma-spectrometrically. Using the constant flux of lead-210 (CFL) model, the temporal and spatial variations of sedimentation rates in Ise Bay were determined. A generally increasing trend in sedimentation rate over the last century, especially since the mid-20th century, was found at all of the locations. The increase in sedimentation rate since the mid-20th century is consistent with the rapid economic growth and corresponding intensification of environmental alteration. The spatial distribution of sedimentation rates is timeindependent. The high sedimentation rates were found near the Kiso Rivers mouth, indicating the river input is a main source of sediment. The sedimentation rates in the eastern half of the bay are higher than those in the western half, reflecting the transport pathway of suspended matter. The mean sedimentation rates over the last 40 years derived from both 210Pb and 137Cs methods were roughly consistent. The inventories of excess 210Pb and 137Cs in sediment are accounted for by the direct atmospheric fluxes, except one core near the river mouth.