Stemflow-induced spatial heterogeneity of radiocesium concentrations and stocks in the soil of a broadleaved deciduous forest.

The transport of radiocesium from the canopy and quantification of the spatial distribution of radiocesium in the soil of konara oak forests are important to better understand the variability of137 Cs stocks in the soil between proximal and distal stem areas as well as fine-scale variations around the tree trunk. Moreover, a better understanding of fine-scale spatial variabilities of137 Cs concentrations and stocks will provide insights for optimizing soil sampling strategies to provide a more robust estimation of contamination at the stand scale. This study aims to elucidate the transport of137 Cs by stemflow in a radioactively contaminated konara oak forest in Tsukuba, Japan by describing and quantifying the fine-scale spatial distribution of137 Cs in the soil and preferential flowpaths of stemflow on the tree stem by a dye tracing experiment.137 Cs concentrations and stocks were higher in the soils of the proximal stem area than distal stem area when they corresponded with the preferential flowpaths of stemflow. There was a significant relationship between canopy projection area of individual trees and average soil137 Cs concentrations and stocks, even though canopies of the trees overlapped. Our results demonstrate that the spatiality of137 Cs concentrations and stocks in the soil of the proximal stem area are governed (at least partially) by the preferential flowpaths of stemflow along the tree trunk. In addition, higher137 Cs concentrations and stocks in the near-trunk soils of trees with larger crown areas might be caused by an enhanced ability to capture dry deposition.