Estimating Be-7 association with soil particle size fractions for erosion and deposition modelling

Purpose

Estimates of beryllium-7 (⁷Be) enrichment in soil particle size fractions are important for correction in existing soil redistribution models. Little attention has been given to documenting methods of estimating ⁷Be enrichment and assessing differences in enrichment between soil types in the context of soil redistribution modelling. Here, we detail a method for estimating ⁷Be enrichment and correcting soil redistribution estimates.

Materials and methods

Beryllium from a solution of BeCl₂ was adsorbed to two soils with contrasting texture using a batch procedure. Soil fractions were separated by settling according to Stokes’ Law, and samples of bulk and settled fractions were digested and analysed for Be concentration and for specific surface area.

Results and discussion

Both soils demonstrated increasing enrichment of Be with increasing specific surface area. There was a marked difference in enrichment between the soil types with the coarse soil showing greater enrichment in the finer fractions. Calculated enrichment ratios for the coarse soil more than doubled between subfractions of the <63 μm class. Failure to account for the selective transport of fractions during soil redistribution studies could incur substantial errors in soil erosion estimates.

Conclusions

Stable Be provides a practical means of estimating ⁷Be enrichment in soil and subsequent corrections can be incorporated into the conversion model where it is proposed that corrections should be applied to the inventory deficit at each eroding point. The marked difference in enrichment between soil types in these experiments suggested that characterising enrichment and associated correction factors should be done on a site-specific basis. Implementation of the particle size correction procedures requires additional field and laboratory data to standard application of the established soil erosion conversion model.