TESTING DIFFERENT SUB-MODELS FOR THE PARTITION-COEFFICIENT AND THE RETENTION RATE FOR RADIOCESIUM IN LAKE ECOSYSTEM MODELING

The partition coefficient (K-d) and the retention rate (RR) are fundam ental components of dynamic, mass-balance models, not just for radionu clides in fresh waters but for most contaminants in most ecosystems. K -d may be regarded as an 'entry gate' and RR an 'exist gate'. Uncertai nties in K-d and RR cause uncertainties in model predictions. It also means that uncertainties in important rates for within-ecosystem proce sses, like sedimentation, diffusion, advection, biouptake and excretio n, cannot be adequately evaluated when great uncertainties exist for K -d and RR. Empirical data show that K-d may vary two orders of magnitu de with environmental factors, like pH. This is important since K-d re gulates the amount of substances in dissolved and particulate phases a nd hence also pelagic and benthic transports. The pelagic transport is directly linked to the outflow and retention of substances in the wat er mass, and thus also to concentrations and ecological effects. There are many approaches for sub-models for K-d and RR. Which provide the best predictive power? The aim of this work is to test different appro aches for K-d and RR, and to discuss benefits and drawbacks of these a lternatives within the framework of a lake model for radiocesium (the VAMP model). (C) 1997 Elsevier Science B.V.