2005 年 58 巻 3 号 p. 4-14
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.