The use of the IAEA MARIS database in determining the variability of sediment distribution coefficients in the marine environment and potential implications for marine dispersion modelling

Abstract

A prototype tool has been developed for deriving sediment distribution coefficients,K_d, in the marine environment by harvesting simultaneous measurements of activity concentrations of radionuclides in seawater and sediments based on the International Atomic Energy Agency's Marine Radioactivity Information System (MARIS). As a case study, theK_dvariability in the Baltic Sea was investigated as this region has been extensively monitored by HELCOM since 1984 resulting in a comprehensive dataset with good spatial and temporal coverage and required ancillary parameters. The prototype tool was used to derive a dataset ofin-situapparentK_d(a)values derived from measurements of seawater and sediment in quasi-equilibrium conditions from the Baltic Sea over a period of approximately 35 years. For Cs, a comprehensive analysis of the Baltic SeaK_d(a)dataset was undertaken, focusing on the temporal trend ofK_d(a)and comparing the results toK_dvalues derived elsewhere. For Sr and Pu, for which there were fewer data records available a more rudimentary analysis was carried out. The CsK_d(a)median values derived from¹³⁷Cs data in this study were estimated to be 2154 l kg^-1for seabed sediment and 10 000 l kg^-1for suspended sediment. The value derived for seabed sediment is in good agreement with the previously recommended ocean margin CsK_dvalue of 4000 l kg^-1. The analysis demonstrated the important distinction in the Baltic Sea betweenK_dvalues for seabed sediment and suspended sediments, which differed by an order of magnitude. The analysis also highlighted the dependence ofK_dvalues on the variation in both the salinity of seawater and the type of seabed sediment. Such variability can significantly influence outcomes when modelling the behaviour of radionuclides in marine dispersion modelling.

Keywords: Baltic Sea; K d; MARIS; marine radioactivity; sediment distribution co-efficient.