Radionuclide distribution in tidal flat sediments of the Westerschelde estuary

EDF, Laboratoire National d'Hydraulique et Environnement, 6 quai Watier, 78401 Chatou cedex, France

Abstract

Depth profiles of the particle-reactive radionuclides ²¹⁰Pb, ¹³⁷Cs and ⁷Be were established in sediments of a tidal flat in the Westerschelde. Cores were collected at different seasons at selected sites with contrasting characteristics. Accumulation rates estimated from ¹³⁷Cs profiles are consistent between the five sites with values comprised between 1.1 at the marginal sites and 2.5 cm y^-1 for the central part. Although the very low level of excess ²¹⁰Pb limits the precision of this method, profiles of ²¹⁰Pb_xs with depth allow calculating a range of sedimentation rates equivalent to those derived from ¹³⁷Cs data. At the muddy site, the vertical distribution of radionuclides revealed the existence of an important accumulation layer of fine particles at a depth of around 10 cm at the muddy site, may be in relation with biological and physical processes. The vertical distribution of ⁷Be in the top 6 cm exhibits wide variability on seasonal scale, with the highest inventories and bioturbation rates observed in summer. This trend is clearly related to the seasonal variation of silt content of surface sediments.