A multiple approach to the determination of radon fluxes from sediments

Determination of sedimentary fluxes of Rn-222 via diffusion was required as an input for a mass balance model of radon in a freshwater lake. We obtained these fluxes by: (1) direct measurement in the laboratory using a simulated sediment bed and water column; (2) a "sediment equilibration" technique; and (3) porewater modeling. The first method, analogous to an in situ benthic chamber approach, uses direct observation of the increasing Rn-222 activity in water overlying a sediment bed packed in plastic columns. This allows one to directly measure the fluxes and determine the effective wet bulk sediment diffusion coefficient (D-s). Radon flux estimates using these three techniques agreed to within approximately 10-15%.