HR: 0830h
AN: H51E-1126    [PDF]
TI: Fingerprinting the sources of fluvial sediment using fallout and in-situ radionuclides in forested watershed in Japan
AU: * Kato, H
EM: hiros980@zae.att.ne.jp
AF: Institute of Geoscience, University of Tsukuba, Tsukuba 305-8571, Japan, Tsukuba, 305-8571 Japan
AU: Onda, Y
EM: onda@atm.geo.tsukuba.ac.jp
AF: Institute of Geoscience, University of Tsukuba, Tsukuba 305-8571, Japan, Tsukuba, 305-8571 Japan
AU: Hiramatsu, S
EM: shira@fs.kochi-u.ac.jp
AF: Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, Japan, Nankoku, 783-8502 Japan
AU: Seki, R
EM: seki@chem.tsukuba.ac.jp
AF: Institute of Chemical Science, University of Tsukuba, Tsukuba 305-8571, Japan, Tsukuba, 305-8571 Japan
AB: To study the fluvial sediment sources in forested watershed in Shikoku island, Japan, the concentration of Cs-137 and Pb-210ex, U and Th decay series radaionuclides were analyzed. The soil sampling was conducted in hillslopes in various locations such as landslide scar, surface erosion in unmanaged Hinoki (Chamaecyparis obtusa) plantation, and detailed sampling in the channel deposit was also conducted in several tributaries. The activities of Cs-137, Pb-210ex, Bi-214 and Tl-208 of soils and fluvial sediments were determined by gammaspectroscopy. We also analyzed landuse of the watershed and forest logging area and landslide area were measured by air photo interpretation. The study area is Shimanto river basin, located 700 km southwest of Tokyo. The 2270 km2 area watershed ranges in elevation from 0 m to 1485 m above sea level. Low concentration of Cs-137 and Pb-210ex in fine sediments and surface soil at landslide scar suggest that fluvial sediments are derived from surface soil of the landslide scars or from channel walls. The concentrations of Cs-137 and Pb-210ex of fluvial sediment are found to be decrease as the landslide area increases. The data of U and Th decay series radionuclides, Bi-214 and Tl-208, indicate that the sources of fluvial sediment are adjacent to the sampling sites. The results suggest that landslide scar and adjacent to the channel are dominant sources of fluvial sediment in this watershed.
DE: 1040 Isotopic composition/chemistry
DE: 1815 Erosion and sedimentation
SC: Hydrology [H]
MN: 2003 Fall Meeting