The determination of estuarine sedimentation rates by [formula omitted] and other artificial radionuclide profiles

Abstract

The profiles of 137Cs, 134Cs, 106Ru, 144Ce, 95Zr Nb and the 134Cs 137Cs ratio in a sediment core and their discharge patterns from the Windscale Nuclear Plant have been used to determine the net sedimentation rate on an estuarine inter-tidal bank. The use of multi-radionuclide and 134Cs 137Cs ratio profiles suggest that previous single radionuclide profiles which have been used for sedimentation rate determinations may be subject to errors. Apparent diffusion coefficients ( Duursma & Bosch, 1970; Hetherington & Jefferies, 1974) have been used in a modification of Lerman's (1971) model to correct the input pattern of the radionuclides for post-depositional migration. A comparison of the corrected profiles, with the observed profiles suggests that the vertical distribution of radionuclides is not significantly altered after deposition, and closely relates to the discharge pattern. The multi-radionuclide discharge patterns and sediment profiles indicate that the net sedimentation rate is in the range 50–80 mm year −1, while the 134Cs 137Cs ratio data give a more reliable estimate of 67 mm year −1.