Cesium-134 as a tracer to study particle transport processes within a small catchment with a buffer zone

The purpose of the study is to use soil particles labeled with the radioactive tracer cesium-134 (134Cs) as a method for studying soil erosion and sedimentation pattern within a small catchment with buffer zones. Cesium is adsorbed to soil particles, and by measuring changes in the 134Cs activity on the soil surface, erosion, sedimentation, and pathways for particles can be traced. A harrowed area was surface-contaminated with 134CsCl, while the buffer zone was left uncontaminated. A grid net in the tilled plot and buffer zone was established for in situ measurements of the 134Cs activity after major runoff events from October 1993 to May 1996. In addition, 134Cs activity and suspended solids in runoff were followed during the events. At the end of the experiment, the vertical distribution of 134Cs in soil profiles and uptake of 134Cs in vegetation within the buffer zone were determined. At the end of the experiment, about 54% of the applied tracer remained at the soil surface. Surface soil erosion occurred relatively uniformly across the hillslope due to sheet flow. Most of the tracer was transported vertically into the soil profile, probably during the first heavy rainfall 3 wk after application when the soil was newly tilled. Sedimentation occurred in the upper part of the buffer zone. The correlation between suspended particles in runoff and 134Cs activity was good (R2=0.76). The study also demonstrates the benefit of utilizing 134Cs2+ tracer for investigating transport pathways for contaminated partic1les within a hillslope system without disturbing the surface soil system.