Erosion and deposition history derived by depth-stratigraphy of Cs-137 andsoil organic carbon

There are a number of uncertainties in the use of Cs-137 as a marker for de riving soil erosion rates. However, this should not limit other potential u ses of this anthropogenic radionuclide in the study of soil landscape proce sses. This study outlines a sampling methodology which aids in the assessme nt of the history of erosion and depositional processes within a landscape unit. The depth distribution of Cs-137 and soil organic carbon (SOC) was ut ilized as a means of determining the erosion and depositional history of a conventionally tilled agricultural field in southern Ontario, Canada. Three transects oriented along the slope of a large field had five soil profiles excavated at the summit, sideslope, shoulder slope, footslope and toeslope landscape positions. The soils were sampled in 5 cm increments, and Cs-137 and SOC were determined on the samples. The results show that soil redistr ibution within landscape units of agricultural fields has been substantial both before and after fallout of Cs-137 to the soil surface. Soils in depos itional areas contained significant Cs-137 and SOC at depths beyond which t he plow can attain at present. This implies that a significant amount of ca rbon is being sequestered beneath the present plow layer. and the character ization of this pool must be considered in deriving the dynamics of SOC in agroecosystems. (C) 2001 Published by Elsevier Science B.V.