Erosion and deposition history derived by depth-stratigraphy of ~(137)Cs and soil organic carbon

摘要

There are a number of basic, fundamental problems with the use of ~(137)Cs as a marker for deriving soil erosion rates (see VandenBygaart et al., 1999a). However, this should not limit other potential uses of this anthropogenic radionuclide in the study of landscape soil processes. This study outlines a sampling methodology which allows for the assessment of the history of erosion and depositional processes within a landscape unit. We used the depth distribution of ~(137)Cs and soil organic carbonas 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 each had 5 soil profiles excavated at the summit, sideslope, shoulder slope, footslope and toeslope. The soils were sampled in 5 cm increments and ~(137)Cs and soil organic carbon was determined on the samples. The results show that soil redistribution within landscape units of agricultural fields has been substantial both before and after fallout of ~(137)Cs to the soil surface. Soils in depositional areas contained significant ~(137)Cs and soil organic carbon at depths beyond which the plow can attain at present. This implies that the soil organic carbon beneath the present plow layer is being sequestered. Thus tillage practices may be modified to place organic residues at depths below the plow layer.