RadEro model: A Physically-Based Model for Quantifying Soil Redistribution Rates Using 137Cs

Quantifying soil redistribution rates is crucial for addressing environmental challenges related to land degradation and sustainable resource management. To complement conventional methodologies, alternative techniques were developed to enhance soil erosion model calibration and testing. Fallout radionuclides (FRNs), particularly ¹³⁷Cs, have been widely recognized as reliable tracers for monitoring soil movement and assessing erosion and deposition rates. Existing conversion models using FRNs to estimate soil redistribution rates often struggle to adapt to diverse soil conditions or to incorporate physical processes. RadEro is a mass balance model implemented in R, based on the compartmental, vertically-resolved, physically-based mass balance framework developed by Soto and Navas (2004, 2008). The model calculates simulated inventories by considering ¹³⁷Cs mass specific activity in the fine fraction density, effective volume (Veff), annual ¹³⁷Cs fallout, radioactive decay, and dominant vertical diffusion processes, including the effects of tillage. This enables RadEro to estimate rates while integrating the effects of soil stoniness in both ploughed and unploughed soils with either sectioned or bulk profiles. Redistribution rates are estimated by assuming that reference sites represent the natural profile distribution and decay of ¹³⁷Cs inventory for the study area. Additionally, deposition is assumed to originate from a nearby site with similar ¹³⁷Cs activity to that of the measured soil point. An accurate user-defined configuration of the model is essential for estimating reliable results. The variables in the model optimization process define the limits and resolution of the simulation sampling domain. By specifying the ranges for the diffusion coefficient (𝑘) and redistribution rates (𝑒), the model iterates to align with the measured ¹³⁷Cs inventory of a stable reference profile. The optimal 𝑘 value is then applied to estimate the corresponding soil redistribution rate (𝑚) in eroded and depositional profiles. In cases of extreme erosion or deposition, simulations with wider initial ranges for 𝑒 may be necessary to capture the full spectrum of possibilities. Our contribution highlights the need to understand the limitations of input data and model results. RadEro allows users to adjust parameters to fit their needs but relies on expert knowledge to select appropriate reference values and sampling points. By carefully evaluating input data, RadEro delivers reliable results and highlights the importance of addressing uncertainties in radionuclide distribution for accurate conclusions.

 

RadEro: ¹³⁷Cs Conversion Model https://github.com/eead-csic-eesa/RadEro

CRAN: Package RadEro https://cran.r-project.org/web/packages/RadEro/index.html