Modelling the genesis of equatorial podzols: age and implications for carbon fluxes

Abstract

Abstract. Amazonian podzols store huge amounts of carbon and play a key role in transferring organic matter to the Amazon River. In order to better understand their C dynamics, we modelled the formation of representative Amazonian podzol profiles by constraining both total carbon and radiocarbon. We determined the relationships between total carbon and radiocarbon in organic C pools numerically by setting constant C and 14 C inputs over time. The model was an effective tool for determining the order of magnitude of the carbon fluxes and the time of genesis of the main carboncontaining horizons, i.e. the topsoil and deep Bh. We performed retrocalculations to take into account the bomb carbon in the young topsoil horizons (calculated apparent 14 C age from 62 to 109 years). We modelled four profiles representative of Amazonian podzols, two profiles with an old Bh (calculated apparent 14 C age 6.8 × 10 3 and 8.4 × 10 3 years) and two profiles with a very old Bh (calculated apparent 14 C age 23.2 × 10 3 and 25.1 × 10 3 years). The calculated fluxes from the topsoil to the perched water table indicate that the most waterlogged zones of the podzolized areas are the main source of dissolved organic matter found in the river network. It was necessary to consider two Bh carbon pools to accurately represent the carbon fluxes leaving the Bh as observed in previous studies. We found that the genesis time of the studied soils was necessarily longer than 15 × 10 3 and 130 × 10 3 years for the two younger and two older Bhs, respectively, and that the genesis time calculated considering the more likely settings runs to around 15 × 10 3 -25 × 10 3 and 150 × 10 3 -250 × 10 3 years, respectively.

Soil organic carbon mobility in equatorial podzols: soil column experiments

“…Although the interest in better quantifying the deep carbon pool and understanding its dynamics was underlined 10 years ago (Rumpel and Kögel-Knabner, 2011), these points remain of interest due to a low amount of existing data. In recent works, deep carbon dynamics were inferred from various types of studies using isotopic tracers such as 13 C or 14 C (Mathieu et al, 2015;Stahl et al, 2016;Doupoux et al, 2017;Balesdent et al, 2018;van der Voort et al, 2019), field measurements (Lucas et al, 2012;Wan et al, 2018;Gibson et al, 2019) and laboratory experiments using column (Guo and Chorover, 2003) or respiration experiments (Fontaine et al, 2007;Lucas et al, 2020). Despite this, little is known about the fluxes and characteristics of organic matter capable of migrating at depth.…”

Co-evolution of soils and landscapes in the Anthropocene from natural to intensively managed landscapes

“…Models with different degrees of complexity have been applied to increase the understanding of pedogenic change and interactions in a variety of soil types. For example, the genesis of equatorial Podzols has been modeled by Doupoux et al (2017) by tracking carbon pools and fluxes with a compartment model. Luvisol development is extensively studied using the models SoilGen and its successor SoilGen2 (Finke and Hutson, 2008;Finke, 2012;Finke et al, 2015;Keyvanshokouhi et al, 2016).…”