HR: 1340h
AN: H53C-1265    [Abstracts]
TI: Fingerprinting suspended sediment sources using fallout and in-situ radionuclides in forested watershed in Japan
AU: * Onda, Y
EM: onda@atm.geo.tsukuba.ac.jp
AF: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tenno-dai, Tsukuba, 305-8572 Japan
AU: Koga, S
EM: s0323508@ipe.tsukuba.ac.jp
AF: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tenno-dai, Tsukuba, 305-8572 Japan
AU: Fukuyama, T
EM: t_fuku@atm.geo.tsukuba.ac.jp
AF: Japan Science and Technology Agency, Kawaguchi Center Building, 4-1-8, Honcho, Kawaguchi, 332-0012 Japan
AU: Hiramatsu, S
EM: shira@ee.kochi-u.ac.jp
AF: Faculty of agriculture, Kochi University, Nankoku, Kochi, 783-8502 Japan
AB: In Japan, forest plantations have became unmanaged because of the lowering of the log price. In unmanaged Hinoki ({\itJapanese cypress, Chamaecyparis obtusa Sieb. et Zucc.}) plantations, understory vegetation decreases because of low light conditions, and forest surface become a bare land. The occurrence of Hortonean overlandflow and soil erosion has been reported. Fine surface materials removal from forest floor due to Hortonean overlandflow will affect the downstream environment and fish habitat. However, no studies have been conducted fingerprinting the suspended sediment from unmanaged forest plantations. To study the sources of suspended sediment in forested watershed in Shikoku Island, Japan, the concentration of Cs-137 and Pb-210ex, U and Th decay series radionuclides were analyzed. Soil sampling was conducted in hillslopes in various locations such as landslide scar, surface erosion area in unmanaged Hinoki plantation and forest road, and sampling of deposited sediment in the channel 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 gamma spectroscopy. We also sampled the suspended sediment by pumping up from the streams, and the time-integrated sediment sampler (Phillips et al, 2000) was also used to collect the various storm event samples. The study area is a 0.33 km$^{2}$ watershed, upstream of the Shimanto river basin, located about 700 km southwest of Tokyo. High concentrations of Cs-137 and Pb-210ex in suspended sediment were detected, which suggest that the suspended sediments are mostly derived from surface soil of the forests. The concentrations of Cs-137 and Pb-210ex vary between events to events, suggesting that the different sources among the storm events.
DE: 1815 Erosion and sedimentation
DE: 1821 Floods
DE: 1824 Geomorphology (1625)
DE: 1860 Runoff and streamflow
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting