Application of two simple models to the transport of ¹³⁷Cs in an upland organic catchment

In situ measurements were made of the ¹³⁷Cs solids-aqueous distribution coefficient (K_d) in a saturated peat bog within the catchment of Devoke Water, Cumbria, UK. Measured values ranged between 1.9-13 × 10³ l/kg. The advection-diffusion equation was used to model ¹³⁷Cs activity-depth profiles in these soils. K_d values obtained from curve-fitted effective diffusion coefficients ranged between 1.4-8.5 × 10³ l/kg for Chernobyl fallout and 2.1-4.2 × 10³ l/kg for pre-Chernobyl fallout. Losses of activity from peat bogs to streams were also modelled using K_d as a fitting parameter, giving values of 0.75 - 1.8 × 10³ l/kg for both pre-Chernobyl and Chernobyl activity. These results show that the transport of ¹³⁷Cs is consistent with the low K_d's observed in these soils. It is suggested that it may be possible to develop a simple model for ¹³⁷Cs runoff in upland catchments on the basis of K_d estimates.