Purpose
The 137Cs tracing technique has strong potential to monitor and evaluate soil loss in complex karst geomorphology regions. However, 137Cs might move downward with soil fine particles under adequate rainfall conditions. This is critical because it directly affects accuracy of using the 137Cs conversion model to evaluate soil erosion. Thus, the objectives of this study were to explore whether 137Cs actually moved downward and to evaluate the movement distance and the factors influencing the movement.
Materials and methods
Magnetic powder (Fe3O4) and rare earth oxides (CeO2 and La2O3) were used as the substitute tracers under different conditions of a simulated leaching experiment, which possess similar properties as 137Cs and have no radiotoxicity problems in humans and the environment.
Results and discussion
The results showed that tracers moved downward 6 cm when water was added to simulate 1–10-year rainfall conditions and 8 cm when water was added to simulate 15–20-year rainfall conditions. The movement distance of tracers increased slowly with increasing water input, and the concentration of the tracers that moved related indirectly to the leaching area. Tracer movement at the edge of the simulated profile was affected by tracer type and concentration since there was no transition layer between soil and plastic column. However, in the case of sufficient rainfall, the movement difference among tracers can be ignored. Previous studies and our field observations in karst watersheds showed that ignoring the vertical movement of tracer can cause the overestimation of soil loss amount by 5.83–95.23%.
Conclusions
This study proved that 137Cs could move vertically in the karst area of Southwest China, and the soil loss will be overestimated if the vertical movement distance of the tracer is ignored.
He, J., Zhang, K., Cao, Z. et al. Tracer vertical movement and its affecting factors in karst soil profiles in simulated leaching context. J Soils Sediments (2021). https://doi.org/10.1007/s11368-021-03063-1