Modeling dynamics of Cs in forest surface environments; Application to a contaminated forest site near Fukushima and assessment of potential impacts of soil organic matter interactions

Ota, Masakazu  ; Nagai, Haruyasu  ; Koarashi, Jun   

A model for Cs transfer in forest was developed to assess behavior of Fukushima-derived Cs. The model simulation well reproduced observed 3 year migration of Cs in organic layer and mineral soil. Long-term predictions indicated that more than 90% of the deposited Cs remains in the top 5 cm soil till 30 years, suggesting that forest acts as a long-term reservoir of Cs with limited loss via groundwater pathway. Impacts of soil organic matter (SOM) on Cs dynamics were investigated by modifying parameters of Cs turnover. The results showed that SOM-induced reduction of Cs adsorption, slower fixation of Cs by clay and enhanced mobilization of the fixed Cs elevate soil-to-plant transfer of Cs by increasing fraction of dissolved Cs. A substantial proportion (27% 73%) of Cs in these soils was delivered to horizons deeper than 5 cm decades later. These results suggested that SOM significantly influences behavior of Cs over long-term.