Impact of Preferential Flow on Radionuclide Distribution in Soil

Abstract

Migration of radionuclides in soils and their transfer to edible plants are usually estimated using volume-averaged bulk concentrations. However, radionuclides might not be homogeneously distributed in soils due to heterogeneous water flow and solute transport. One important cause of heterogeneous transport is preferential flow. The aim of this study was to investigate the spatial distribution of radionuclides in the soil in relation to preferential flow paths and to assess the possible consequences for their transfer from soil to plants. We identified the preferential flow paths in a forest soil by staining them with a blue dye, and we compared radionuclide activity in samples from the stained preferential flow paths with those from the unstained soil matrix. The activities of the atmospherically deposited radionuclides 137 Cs, 210 Pb, 239,240 Pu, 238 Pu, and 241 Am were enriched in the preferential flow paths by a factor of up to 3.5. Despite their different depositional histories, the distribution of the radionuclides between preferential flow paths and matrix was similar. Our findings indicate increased transport of radionuclides through the preferential flow paths, representing a possible risk of groundwater contamination. Furthermore, enrichment of radionuclides in the preferential flow paths might influence the uptake by plants. The heterogeneous radionuclide distribution in the soil and the more intense rooting in the preferential flow paths can be incorporated into soil-to-plant transfer models. Taking the correlated radionuclide and root distribution between the two flow regions into account provides a more physical and biological basis for the calculation of plant activities with transfer models than using the homogeneously mixed bulk soil activities as input parameters.

Effects of fine root length density and root biomass on soil preferential flow in forest ecosystems

“…Those results collected from fine root length density imply that plant roots content are higher in preferential pathways than in soil matrix, supporting studies like Bundt et al (2000Bundt et al ( , 2001, and the results are also in agreement with Bonger et al (2010) and Bengough (2012), because plant fine roots usually form root channels called pref- 10 ties (e.g., soil bulk density, porosity, organic carbon, citation exchange capacity and so on). For example, the topsoil tend to have higher recharge rate that brings the soil moisture close to saturation compared with the subsoil (Vogt et al, 1996;Schmid & Kazda, 2002).…”

Characteristics of preferential flow paths and their effects on soil properties

“…This indicates a possible link between soil organic matter and soil environment (Nardi et al 2002). Higher organic matter may be due to the higher number of decaying roots in the flow paths than in the soil matrix (Bundt et al 2000).…”

Lower variability of radionuclide activities in upland dairy products compared to soils and vegetation: Implication for environmental survey

“…Thus, recent models to predict soil-to-plant transfer of radionuclides more and more incorporate soil chemical and physical properties, root zone radionuclide availability and soil/soil-solution interactions (Ehlken and Kirchner, 2002). Moreover, Bundt et al (2000) showed a heterogeneous distribution of 137 Cs and plutonium in the root zone of a forest soil due to the presence of preferential flow paths. Due to the more intense rooting along the preferential flow paths this phenomenon must be incorporated into soil-to-plant transfer models (Bundt et al, 2000).…”