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, the K d variability 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 of in-situ apparent K 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 Sea K d(a) dataset was undertaken, focusing on the temporal trend of K d(a) and comparing the results to K d values derived elsewhere. For Sr and Pu, for which there were fewer data records available a more rudimentary analysis was carried out. The Cs K d(a) median values derived from 137Cs data in this study were estimated to be 2154 l kg−1 for seabed sediment and 10 000 l kg−1 for suspended sediment. The value derived for seabed sediment is in good agreement with the previously recommended ocean margin Cs K d value of 4000 l kg−1. The analysis demonstrated the important distinction in the Baltic Sea between K d values for seabed sediment and suspended sediments, which differed by an order of magnitude. The analysis also highlighted the dependence of K d values 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.