Distribution and Variability of ⁷Be in Soils Under Different Surface Cover Conditions and its Potential for Describing Soil Redistribution Processes

Abstract

Measurements of 7 Be in soils can be used to indicate movement of topsoil, and this study aims to contribute to this technique by examining 7 Be in soils under a range of conditions. The penetration and areal concentration of 7 Be have been measured in bare soil, grassland, and eucalypt forest and compared with total measured fallout. Inventories in the bare soil decreased progressively from 64 to 46% of total fallout over the sampling period, probably owing to a decrease in infiltration capacity. This may have an effect on the interpretation of 137 Cs inventories under similar conditions. For grassed soil, average inventories were 96–142% of total fallout; for eucalypt litter plus soil, inventories were 73–95%. Natural variability of areal concentration of the nuclide was calculated to be about 20% (relative standard deviation), irrespective of soil type and/or surface cover. However, soil disturbance following logging operations increased variability to about 50%, even after more than 7 half‐lives of 7 Be had elapsed. Penetration could be approximated by an exponential in bare soil and in eucalypt forest soil without litter, and average penetration half depths ( P h ) in these soils were calculated to be 0.7 and 3.4 mm, respectively. Beryllium 7 concentration was found to increase as particle size decreased. The nuclide was not found below 20 mm depth in any soil or surface cover condition, thus confirming its utility in qualitative models that infer erosion processes by its use as a tracer of surface soil.