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 (Kd) 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. Kd 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 Kd 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 Kdʹs 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 Kd estimates.