The geochemical behavior of natural radionuclides in coastal waters: A modeling study for the Huelva estuary

Abstract A numerical model to study the behavior and distribution of natural radionuclides in sediments of an estuary (Odiel and Tinto rivers, SW Spain) affected by acid mine drainage and industrial activities has been developed. The model solves water circulation due to tides and river stream flows. The dispersion model includes uptake/release reactions of radionuclides between the dissolved phase and bed sediments in a dynamic way, using kinetic transfer coefficients. Seasonal pH and chlorinity distributions are simulated, and a formulation has been developed to consider these seasonal variations on kinetic coefficients. Calculated concentrations of 226 Ra and 238 U in sediments have been compared with measurements from four seasonal sampling campaigns. Numerical experiments have been carried out to study the relative significance of the different radionuclides sources into the estuary as well as the effect of the two components of water circulation (tides are river flows) on radionuclide dispersion patterns.