Using environmental tracers to understand soil organic carbon and soil erosion on a steep slope hillslope in south-east Australia

Context: It is well recognised that soil organic carbon (SOC) can be transported and deposited along the same pathways as those of soil erosion and deposition. Aims: To examine the viability of environmental tracers 137Cs and unsupported 210Pb (210Pbex) as tools to inform soil erosion and deposition patterns as well as that of the distribution of SOC. Methods: Multiple soil cores were collected along two transects of similar length and aspect in a steep-slope soil mantled environment in south-east Australia. Key results: Average SOC concentration was high for both transects (~6% and 4%). SOC decreased moving downslope suggesting loss of SOC by erosion. There were strong and significant positive relationships of SOC with 137Cs and 210Pbex (both r > 0.77, P < 0.0001). At this site, SOC concentration appears related to erosion and deposition patterns. Conclusion: The hillslope distribution of 137Cs and 210Pbex were very similar, indicating that both tracers were viable in this environment (r = 0.9, P < 0.0001). The different origins and half-lives of 137Cs and 210Pbex also demonstrate that the patterns of erosion and deposition are consistent at decadal time scales. Implications: The use of 210Pbex provides an alternative method for understanding erosion and deposition patterns as well as that of SOC, given that the viability of 137Cs (half-life of 30.1 years) is now questionable due to no new replenishment.