ECN publication
Modelling fluxes and bioavailability of radiocaesium and radiostrontium in freshwaters: final report ECOPRAQ project
Published by: Publication date:
ECN 1-12-1999
ECN report number: Document type:
ECN-C--99-104 ECN publication
Number of pages: Full text:
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ECOPRAQ (ECOlogical PROcesses in AQuatic systems) refers, together withthe full title of the project, to the process- or mechanistically-based approach to modelling the fluxes and the availability of radionuclides to the biosphere in the aquatic environment. The global objectives of the project are the development of mechanistic and general applicable whole-ecosystem models. Because of their mechanistic basis, these models enable the advancement of a sound theoretical basis for chemical and hydrological countermeasures. The models can also be applied to test the effectiveness of existing countermeasures. The project focuses on radiocaesium and radiostrontium, with emphasis on the former radionuclide, and is subdivided into the following six 'work packages': (1) Development of mechanistic submodels for the solid/liquid partitioning and (bio)availability of particle-bound radiocaesium and radiostrontium (WP2); (2) Development of mechanistic submodels for the accumulation and elimination of radiocaesium and radiostrontium by aquatic biota (WP3); (3) Development and assessment of chemical and/or hydrological countermeasures (WP4); (4) Development of mechanistically-based whole-ecosystem models (WP5); (5) Model validation of sediment-water exchange and bioavailability of radionuclides in a large-scale controlled laboratory setup and in situ (WP6); and (6) Model validation of radionuclide scavenging by suspended particles and uptake by aquatic plants (WP7) The development of mechanistic submodels for the basic aquatic processes such as partitioning of the radionuclides with inorganic (suspended and sediment) particles, accumulation and elimination by biota, transport processes in lakes/rivers and their catchments, and the incorporation of these basic processes/models in whole-ecosystem models, is organised in the first 4 work packages. Useable versions of these (sub)models are available and presented and discussed in Chapter 3 of this report. lt is clearly shown that these models can predict transport, solid/liquid partitioning, and biological uptake and biological elimination of radiocaesium much more accurately and over a range of very different aquatic environments, compared to the (more empirical) models that were available at the start of the project. This is the case both at the submodel ecosystem level and at the whole-ecosystem level. The key parameters that affect these basic transport and availability processes have been identified and the (sub)models are tested for systems that span the range over which these parameters may be encountered in different aquatic environments. Contrary to many earlier projects/studies, all laboratory experiments, large-scale tests, and field measurements have been designed to identify the role of the major environmental variables on basic model-parameters such as the solid/liquid distribution coefficient (KD), the Concentration Factor (CF), and the rates of radionuclide 'fixation'/ remobilization by sediments and uptake/elimination by aquatic plants and fauna. All experimental and field data have been collected and interpreted in the framework of the above (sub)models. lt is shown that these monitoring data have been used for a successful model validation and parametrisation. 13 refs.

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