HR: 1340h
AN: H53C-1387    [Abstracts]
TI: Determining soil erosion rate and sediment residence time on hillslopes using radionuclides in semiarid grassland of Mongolia
AU: * Kato, H
EM: hiroakis980@ybb.ne.jp
AF: Department of Integrative Environmental Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Laboratory of Advanced Research A501, 1-1-1 Tennodai, Tsukuba, 3058572, Japan
AU: Onda, Y
EM: onda@geoenv.tsukuba.ac.jp
AF: Department of Integrative Environmental Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Laboratory of Advanced Research A501, 1-1-1 Tennodai, Tsukuba, 3058572, Japan
AU: Mizugaki, S
EM: gakimizu@geoenv.tsukuba.ac.jp
AF: JST Research Fellow, Department of Integrative Environmental Sciences, Graduate School of Life and Environmental Sciences, University of Tsukuba, Laboratory of Advanced Research A, 1-1-1 Tennodai, Tsukuba, 3058572, Japan
AU: Tanaka, Y
EM: ytanaka@khu.ac.kr
AF: Department of Geography, Kyung Hee University, 1 Hoegi-dong, Dongdaemun-gu, Seoul, 130701, Korea, Republic of
AB: Radionuclide technique has been attracted increasing attention as an alternative method for soil erosion studies. Recently, the potential use of ²¹⁰Pb which is a naturally occurring radionuclide has been explored as an alternative for ¹³⁷Cs. This study estimated long-term soil erosion rate by using ¹³⁷Cs and ²¹⁰Pb_ex in semiarid grassland of Mongolia; where overgrazing has been considered to be the cause of intensive soil erosion and land degradation. A couple of the experimental watershed (<10 ha) was established in areas of different grazing conditions. In order to determine the spatial distribution of radionuclides, more than thirty soil cores were collected within the watersheds. The activity of radionuclides was measured using HP N-type Gamma ray detector in the laboratory of University of Tsukuba. The gain/reduction rate of radionuclides to the reference inventory was converted to soil erosion rate by using the Diffusion and Migration model (He and Walling, 1993). Based on ¹³⁷Cs inventories, an intensive erosion was detected in the overgrazed watershed; whereas soil erosion was negligible at the watershed where there was currently no overgrazing. In contrast, ²¹⁰Pb_ex inventories exhibited that the soil erosion rate was very much smaller than that based on ¹³⁷Cs inventories; especially at the no overgrazed site. In addition to this, along a transect on erosion slopes, the ¹³⁷Cs inventory tended to decreased downward, while the ²¹⁰Pb_ex/¹³⁷Cs inventory ratio and the activity of surface soil (< 20 mm) of ²¹⁰Pb_ex increased. The downslope increase of ²¹⁰Pb_ex activity may be attributed to the direct deposition of atmospheric ²¹⁰Pb_ex onto soil surface. Therefore, given the direct deposition rate of ²¹⁰Pb_ex, the sediment transport on hillslopes should be determined from the increasing rate of ²¹⁰Pb_ex in the surface soil. A simple budget calculation of ²¹⁰Pb_ex activity of surface soil roughly estimated the residence time of sediment on hillslopes. The results of this study suggest that, under the environments where the sediment transport is very slow, ²¹⁰Pb_ex is seen to be inappropriate for the estimation of soil erosion rate because the conversion models for the estimation of soil erosion rate assumes eroded sediment to be readily removed from hillslope; instead, the use of ²¹⁰Pb_ex should be proposed to quantifying the residence time of sediment on hillslopes.
DE: 1800 HYDROLOGY
DE: 1815 Erosion
DE: 1826 Geomorphology: hillslope (1625)
DE: 1862 Sediment transport (4558)
SC: Hydrology [H]
MN: 2007 Fall Meeting