Fallout volume and litter type affect ¹³⁷Cs concentration difference in litter between forest and stream environments

It is important to understand the changes in the ¹³⁷Cs concentration in litter through leaching when considering that ¹³⁷Cs is transferred from basal food resources to animals in forested streams. We found that the difference of ¹³⁷Cs activity concentration in litter between forest and stream was associated with both litter type and ¹³⁷Cs fallout volume around Fukushima, Japan. The ¹³⁷Cs activity concentrations in the litter of evergreen conifers tended to be greater than those in the litter of broad-leaved deciduous trees because of the absence of deciduous leaves during the fallout period in March 2011. Moreover, ¹³⁷Cs activity concentrations in forest litter were greater with respect to the ¹³⁷Cs fallout volume. The ¹³⁷Cs activity concentrations in stream litter were much lower than those in forest litter when those in forest litter were higher. The ¹³⁷Cs leaching patterns indicated that the differences in ¹³⁷Cs activity concentration between forest and stream litter could change with changes in both fallout volume and litter type. Because litter is an important basal food resource in the food webs of both forests and streams, the ¹³⁷Cs concentration gradient reflects to possible ¹³⁷Cs transfer from lower to higher trophic animals. Our findings will improve our understanding of the spatial heterogeneity and variability of ¹³⁷Cs concentrations in animals resident to the contaminated landscape.