『Abstract
This review aims at considering the use of REEs to trace pedogenetic
processes, in order to quantify the respective contribution of
the successive processes on pedogenesis.
We first consider the origins and contents of REEs in soils,
to assess their natural occurrence, and tackle the common data
treatment used to interpret their concentrations. We review subsequently
the impact of the different pedogenetic processes on the fate
of REEs in soils: from their release into a soil solution by primary
mineral (heavy minerals, phosphates, silicates and carbonates)
dissolution during weathering, to their fixation on- or into main
REE-bearing secondary minerals (clay minerals, Fe-Mn-oxides and
carbonates), then their mobilization by plant recycling and organic
matter, and finally the impact of argilluviation and redox processes
on their fractionation. We conclude that REEs, much more than
other trace elements, can interestingly trace the considered processes
that are encountered in a large diversity of non-polluted soils
arising from diverse parent materials. Weathering generally fractionates
REEs and accounts for a significant part of the variation in the
initial REE stock of the soils. Plant recycling induces a weak
mobilization of REEs and their accumulation in topsoil. Argilluviation
can be traced using the MREE-enrichment and the Eu-anomaly of
the clay minerals. Redox processes can be traced by the Ce-anomaly
caused by the precipitation of cerium on Mn-oxides. To use REEs
as tracers of pedogenetic processes, we recommend to: (i) precisely
characterize the REE-bearing minerals, (ii) adapt the choice of
reference(s) for normalization and (iii) perform mass balance
calculations.
Keywords: Lanthanides; Lessivage; Pedological carbonates; Redox
processes; Weathering』
Contents
1. Introduction
2. Contents and origins of REEs in soils
3. Normalization and anomalies
4. Impact of weathering on REE mobilization
4.1. REEs in primary minerals
4.1.1. Minerals with high REE concentrations
4.1.2. REE-bearing minerals abundant in soils and parent materials
4.2. Impact of the properties of the different REEs in the solution
on their distribution within weathering profiles
4.3. Impact of the degree of weathering on the REE distribution
into weathering profiles
5. Secondary mineral formation and REE immobilization
5.1. Clay mineral formation
5.2. Fe-Mn-oxide formation
5.3. Formation of pedogenetic carbonates
6. Impact of biological recycling and organic matter on REE mobilization
6.1. Biological recycling of REEs and REE mobilization
6.2. Complexation and mobilization of REEs by organic matter
7. Remobilization of secondary mineral by pedogenetic processes
and REE mobilization
7.1. Argilluviation
7.2. Hydromorphy and soil degradation
8. Conclusions
Acknowledgments
References