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

Abstract

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.