137Cs loss via soil erosion from a mountainous headwater catchment in central Japan

Eroded sediment and coarse organic material were sampled for a year at the outlet of the study catchment in central Japan to investigate characteristics of Cs-137 loss and to quantify erosional Cs-137 loss in a forested headwater catchment. Results showed that loss of both eroded sediment and Cs-137 varied markedly according to the magnitude of rainfall events. About 90% of the total sediment delivery and the total Cs-137 loss was associated with only two storm rainfall events. The significant contribution of high-magnitude-low-frequency storm events to Cs-137 loss from the catchment was emphasized. To quantify the contribution of erosional Cs-137 loss to Cs-137 cycling, the current mean Cs-137 inventory of the study catchment was estimated from direct measurements of Cs-137 in soil cores collected from 27 points. The input of Cs-137 through litterfall to the soil was estimated from monitoring the annual litterfall of the study catchment. The present Cs-137 fallout input was estimated from published Cs-137 fallout data. Consequently, the loss of Cs-137 associated with eroded sediment was estimated to represent 0.013% of the Cs-137 inventory of the study catchment, which is comparable to the input through litterfall. The equivalent value for Cs-137 runoff with coarse organic material was estimated as 0.0003%. Therefore, the effect of Cs-137 loss in association with coarse organic material on estimates of erosion rate obtained by measuring Cs-137 inventories in soil core samples was inferred to be negligible in Japanese cypress plantations. Results confirm the applicability of Cs-137 measurements to estimate erosion rates in other relatively stable forested areas. (c) 2005 Elsevier B.V All rights reserved.