Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach

Quantification of vertical solid matter transfers in soils during pedogenesis by a multi-tracer approach

PURPOSE Vertical transfer of solid matter in soils (bioturbation and translocation) is responsible for changes in soil properties over time through the redistribution of most of the soil constituents with depth. Such transfers are, however, still poorly quantified.

MATERIALS AND METHODS In this study, we examine matter transfer in four eutric Luvisols through an isotopic approach based on 137Cs, 210Pb(xs), and meteoric 10Be. These isotopes differ with respect to chemical behavior, input histories, and half-lives, which allows us to explore a large time range. Their vertical distributions were modeled by a diffusionadvection equation with depth-dependent parameters. We estimated a set of advection and diffusion coefficients able to simulate all isotope depth distributions and validated the resulting model by comparing the depth distribution of organic carbon (including 13C and 14C isotopes) and of the 0–2-μm particles with the data.

RESULTS AND DISCUSSION We showed that (i) the model satisfactorily reproduces the organic carbon, 13C, and 14C depth distributions, indicating that organic carbon content and age can be explained by transport without invoking depth-dependent decay rates; (ii) translocation partly explains the 0–2-μm particle accumulation in the Bt horizon; and (iii) estimates of diffusion coefficients that quantify the soil mixing rate by bioturbation are significantly higher for the studied plots than those obtained by ecological studies.

Fig. 1 Temporal evolution over 15,000 years of the 0–2-μm fraction vertical distribution at Mons grassland based on the transfer coefficients determined by this modelling. Tillage is simulated from year 14,700 to year 14,939

CONCLUSIONS This study presents a model capable of satisfactorily reproducing the isotopic profiles of several tracers and simulating the distribution of organic carbon and the translocation of 0–2-μm particles.

Jagercikova Marianna, Cornu Sophie, Bourlès Didier, Evrard Olivier, Hatté Christine, Balesdent Jérôme

Reference : J. Soils Sediments (2016) doi:10.1007/s11368-016-1560-9.