Temporal changes in radiocesium deposition in various forest stands following the Fukushima Dai-ichi Nuclear Power Plant accident

Abstract

In this study, we investigated the transfer of canopy-intercepted radiocesium to the forest floor following the Fukushima Dai-ichi Nuclear Power Plant accident. The ¹³⁷Cs content of throughfall, stemflow, and litterfall were monitored in two coniferous stands (plantations of Japanese cedar) and a deciduous mixed broad-leaved forest stand (oak with red pine) from July 2011 to December 2012. The forest floor of cedar stands had received higher levels of additional ¹³⁷Cs deposition compared with the mixed broad-leaved stand during the sampling period. The cumulative ¹³⁷Cs deposition during the study period was 119 kBq m^-2 for the mature cedar stand, 105 kBq m^-2 for the young cedar stand, and 41.5 kBq m^-2 for the broad-leaved stand. The deposition of ¹³⁷Cs to the forest floor occurred mainly in throughfall during the first rainy season, from July to September 2011 (<200 d after the initial fallout); thereafter, the transfer of ¹³⁷Cs from the canopy to forest floor occurred mainly through litterfall. A double exponential field-loss model, which was used to simulate the removal of ¹³⁷Cs from canopies, was the best fit for the temporal changes in the canopy ¹³⁷Cs inventory.

Keywords: Canopy interception; Cesium-137; Forest environment; Fukushima Dai-ichi Nuclear Power Plant accident; Transfer.