In the hilly area, intensity of soil erosion mainly depends on topographical location, slope and slope type, i.e. convex and concave. Therefore,it is difficult to correctly estimate accumulated amount of soil loss and redeposition at each site and its special distribution pattern on the slopes.Recently 137Cs is attracting attention as an effective tracer of soil material movement. 137Cs is an artificial fallout radionuclide caused by nuclear experiments in atmosphere during 1960* s. 137Cs is evenly deposited on the soil surfaces and is strongly absorbed by soil solid particles. To grasp the relation between soil erosion and topographical parameters, we conducted 137Cs measurements for 26 sites of an undulating field in hilly area of central Hokkaido. About 60% of the survey sites showed the measured 137Cs concentration (MCs kBq*m-2 ) less than 2 , while its standard in Hokkaido (SCs) was 3.44kBq*m-2 . Extremely severe soil erosion was recognized on interfluve and convex creep slopes. At the upper margin of the field with steep convex slope, the minimum value of MCs (0.16kBqm-2) was observed and average soil loss per year was estimated at about 12% (3 cm in depth). On the contrary, the MCs values at some sites alluvial toeslopes apparently exceeded the SCs, indicating the redeposition of 137Cs enriched soil materials. The distribution patterns of MCs, Ap + Ab horizon thickness and total carbon content were comparable but showed somewhat different features. 137
Cs accumulation method proved to be more effective in estimating reliable values compared to the other methods utilizing Ap + Ab layer thickness and total carbon content. However, it is most important to obtain the local standard of 137Cs accumulation in the nearby undisturbed slopes.
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