Importance of root HTO uptake in controlling land-surface tritium dynamics after an-acute HT deposition; A Numerical experiment

Ota, Masakazu  ; Nagai, Haruyasu  ; Koarashi, Jun   

To investigate the role of belowground root HTO uptake in controlling tritium (T) dynamics in a land surface ecosystem, a sophisticated numerical model predicting tritium behavior in an atmosphere-vegetation-soil system was developed and numerical experiments were conducted using the model. The developed model covered physical HT transport in multi-layered atmosphere and soil as well as microbial HT oxidation to HTO in the soil, and was incorporated into a well-established dynamical HTO transfer-OBT formation model. The model performance was tested through a simulation of an existing HT-release experiment, and the model-predicted HT deposition to the surface soil agreed with the field data at a factor of 1.1. Numerical experiments with a hypothetical acute HT exposure to a grassland field demonstrated that preferential uptake of the deposited HTO in the upper soil layers increased HTO concentrations both in the atmosphere and in the plant leaves through an enhanced soil-leaf-atmosphere HTO stream. Consequently, leaf OBT assimilation calculated with a shallow rooting depth increased by nearly an order of magnitude larger than that calculated with a deep rooting depth.