The relationship of soil organic carbon to 210Pbex and 137Cs during surface soil erosion in a hillslope forested environment

The relationships of erosion-induced displaced soil organic carbon (SOC) to discharged Pb-210(ex) and Cs-137 in a hillslope forested area were investigated using runoff plots in three different forest types. A significant correlation was found between the displaced SOC and the radionuclides in each examined forest type. Compared with Cs-137, however, the discharge of Pb-210(ex) is more closely correlated with the displaced SOC and shows a far lower RMSE value by approximately a factor of two. This finding suggests that Pb-210(ex) and SOC are more likely than Cs-37 and SOC to move together in the course of soil erosion processes. Moreover, because Cs-137 was introduced in the 1960s by thermonuclear bomb tests and is being depleted, its availability in the environment could be limited in the foreseeable future. Pb-210(ex), in contrast, is continuously replenished from its ubiquitous natural source (Rn-222) in a manner similar to the replenishment of SOC from sources consisting of organic material (e.g., litter). In the light of this basic understanding, our findings provide practical evidence of the potential of Pb-210(ex) application for assessing and documenting the water-induced distribution of SOC on forested hillslopes. (C) 2012 Elsevier B.V. All rights reserved.