Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.3,2005

Estimating soil erosion rates using Cs‐137 in Eastern Mongolia

Tomoyuki NISHIKAWA Yuichi ONDA Yukiya TANAKA Hiroaki KATO Maki TSUJIMURA Riki SEKI
Gombo DAVAA Dambaravjaa DYUNBAATAR Maki ASANO

Abstract

Desertification becomes significant problems in the grazing land in semi‐arid Mongolia. The purpose of this study is to evaluate the present soil erosion processes using Cs‐137. We investigated two small watersheds (BGN: underlain by granite, vegetation cover in rainy season is 70%, KBU: underlain by sedimentary rocks, vegetation cover in rainy season is 30%). In the undisturbed soils, most of the Cs‐137 is concentrated uppermost layer and the depth distribution exhibits an exponential decline with depth. Using Cs‐137, we estimated the depth, rates and processes of soil redistribution by comparing the reference value at the reference site. The soil erosion rate for the past 40 years using Profile‐Distribution Model was estimated as net erosion rate in BGN watershed of 0.3 t/ha/y, and the sediment delivery ratio of 12%. In contrast, in KBU watershed, the net erosion rate is estimated as 3.8 t/ha/y, which is about 13 times as large as BGN watershed, and sediment delivery ratio is estimated as 78%. The significant differences for many phenomena in connection with soil erosion were found between watersheds with different vegetation cover.

Key words:Cs‐137, profile‐distribution model, empirical model, semi‐arid area, sheet erosion

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