Rare earth elements as tracers of pedogenetic processes

To discern and quantify the impact of successive processes on pedogenesis, an approach using rare earth elements (REE) as tracers of processes was developed. Considering that a given horizon results from the evolution of the underlying horizon under a given pedogenetic process, we proposed to normalize the REE contents of that horizon by the REE contents of the underlying horizon. Pedological features, representative of the considered pedogenetic process, can also be used. We applied it to a well-characterized solum, developed from limestones, that underwent two different phases of redox conditions. Results evidenced that the two stages of redox conditions acted differently on REE mobilization. The first stage induced the enrichment of Ce in Fe–Mn concretions, while the second stage induced an impoverishment in MREE following the dissolution of the Fe/Mn-(hydr)oxides cementing the finest soil fractions. This approach of normalization emphasizes the potential of REE as tracers of pedogenetic processes, even if some difficulties remain.