Long-term prediction of $$^{137}$$Cs in Lake Onuma on Mt. Akagi after the Fukushima accident using fractional diffusion model

The Fukushima Daiichi Nuclear Power Plant accident also contaminates lakes in Japan. Especially in closed lakes, there is a problem of prolonged low-level $$^{137}$$ 137 Cs contamination because the activity concentration of $$^{137}$$ 137 Cs declines sharply immediately after the accident, but then begins to decrease slowly. In this paper, we derived a long-term prediction formula based on the fractional diffusion model (FDM) for the temporal variation in $$^{137}$$ 137 Cs activity concentrations of the water in Lake Onuma on Mt. Akagi, one of the closed lakes, and of pond smelt (Hypomesus nipponensis), a typical fish species inhabiting in the lake. The formula reproduced well the measured $$^{137}$$ 137 Cs activity concentration of the lake water and pond smelt for 5.4 years after the accident. Next, we performed long-term prediction for 10,000 days using this formula and compared it with the prediction results of the two-component decay function model (TDM), which is the most common model. The results suggest that the FDM prediction will lead to a longer period of contamination with low-level $$^{137}$$ 137 Cs than the TDM prediction.

The use of non-invasive field techniques in the study of small topographically closed lakes: two case studies in Sicily (Italy)

Small endhoreic (topografically closed) lakes represent a little percentage of continental waters but, in arid or sub-arid regions, they develop special ecosystems potentially prone to ecological involution due to climatic changes. The mandatory use of light, non-invasive field techniques is often required, especially in protected areas. In the present work the use of non-invasive techniques like GPS−based bathymetric and photographic surveys have been applied to the study of two lakes, Specchio di Venere and Sfondato (Sicily, southern Italy), both natural reserves. The comparison between historical surveys and modern GPS−based bathymetries highlighted the difficulty of using the former for the reconstruction of climatic-induced variations due to the low number of measurements (spatial aliasing). In particular, at the intracaldera Lake Specchio di Venere, a high resolution survey gave new insights into a peculiar geo-ecosystem whose evolution is driven by both volcanic phenomena and biomineralization processes. On the contrary, the morphology of Lake Sfondato floor is much more simple and driven only by the superimposition of a detrital sedimentation on the initial collapse that generated the lake. The comparison betweem direct measurements and estimated changes of lake level, carried out between February 2008 and October 2009 variations, allowed us to test different hypotheses of hydrological balances, leading to opposite conclusions with respect to previous studies and remarking the fundamental importance of direct measurements in the validation of theoretical hydrological models.