¹³⁷Cs diffusion in the highly organic sediment of Hidden Lake, Fraser Island, Queensland

Abstract

The vertical distribution of ¹³⁷Cs (originating from nuclear fallout since 1954) in the highly organic sediment of Hidden Lake is found to be inconsistent with ¹⁴C and ²¹⁰Pb data. Mathematical models of bioturbation indicate that this mechanism cannot explain the discrepancy. Diffusive migration of ¹³⁷Cs is modelled using the experimentally determined value of ≈140 for the distribution coefficient, K_D, of ¹³⁷Cs in Hidden Lake sediment. It is concluded that ¹³⁷Cs is diffusing in the sediment at an effective rate of c. cm2 s^-1 due to the low value of K_D The diffusive mechanism is further modified by adsorption or absorption at or near the sediment-water interface.