Ecotrophic modelling of cesium-137 dispersion and bioaccumulation in the Gulf of Lion following hypothetical nuclear accident scenarios

The Fukushima nuclear accident highlighted the complexity of the processes involved in the dispersion of cesium-137 within the ecosystem during the post-accident phase. In particular, it underscored the role of benthic invertebrates and the need for an accurate representation of these organisms in any modelling effort. In this study, we present improvements to GOLEM (Gulf Of Lion Ecopath model), a complete Ecopath, Ecosim, Ecospace and Ecotracer model based on the Gulf of Lion ecosystem. This region of both economic and ecological importance is under the influence of the Rhône River, one of the most nuclearized rivers in the world. GOLEM features a highly detailed trophic network (66 living groups) and the Ecotracer (contaminant tracking) module has been parametrized for cesium-137. GOLEM was used to simulate 4 accidental release scenarios, under varying meteorological conditions (summer and winter) and release duration: a short one (6 days), corresponding to a release in liquid phase and a long one (47 days), corresponding to an atmospheric release followed by deposition. The simulations reveal, among other findings, a delay in cesium-137 concentration peak in higher trophic level groups, two groups (rays and microzooplankton) of particular interest in terms of uptake/depuration, and a higher concentration of cesium-137 in benthic groups compared to pelagic groups during a certain period after the release. Overall, the results demonstrate that GOLEM behaves consistently and proves useful for modelling contaminant dispersion, although there remains room for further improvement.