Sediment export in marly badland catchments modulated by frost-cracking intensity, Draix–Bléone Critical Zone Observatory, SE France

Abstract

Abstract. At the interface between the lithosphere and the atmosphere, the critical zone records the complex interactions between erosion, climate, geologic substrate, and life and can be directly monitored. Long data records (30 consecutive years for sediment yields) collected in the sparsely vegetated, steep, and small marly badland catchments of the Draix–Bléone Critical Zone Observatory (CZO), SE France, allow analyzing potential climatic controls on regolith dynamics and sediment export. Although widely accepted as a first-order control, rainfall variability does not fully explain the observed interannual variability in sediment export. Previous studies in this area have suggested that frost-weathering processes could drive regolith production and potentially modulate the observed pattern of sediment export. Here, we define sediment export anomalies as the residuals from a predictive model with annual rainfall intensity above a threshold as the control. We then use continuous soil temperature data recorded at different locations over multiple years to highlight the role of different frost-weathering processes (i.e., ice segregation versus volumetric expansion) in regolith production. Several proxies for different frost-weathering processes have been calculated from these data and compared to the sediment export anomalies, with careful consideration of field data quality. Our results suggest that frost-cracking intensity (linked to ice segregation) can explain about half (47 %–64 %) of the sediment export anomalies. In contrast, the number of freeze–thaw cycles (linked to volumetric expansion) has only a minor impact on catchment sediment response. The time spent below 0 ∘C also correlates well with the sediment export anomalies and requires fewer field data to be calculated than the frost-cracking intensity. Thus, frost-weathering processes modulate sediment export by controlling regolith production in these catchments and should be taken into account when building predictive models of sediment export from these badlands under a changing climate.

Seasonal dynamics of marly badlands illustrated by field records of hillslope regolith properties, Draix–Bléone Critical Zone Observatory, South‐East France

“…The mountainous climate and easily erodible lithology induce a strong seasonal pattern in regolith formation and sediment export. During winter, regolith is formed mainly due to frost-cracking processes (Ariagno et al, 2022), leading to a heterogeneous surface and desiccation features, as also observed in similar Spanish badlands (Nadal-Romero & Regüés, 2010;Regüés et al, 1995). Spring flash floods induce a peak in sediment export (Ariagno et al, 2022;Mathys, 2006).…”

“…The higher values of D50 and resistance at the end (Feb20) compared to the beginning (Nov19) of the winter season is interpreted as a lack of weathering of the regolith. As frost‐cracking has been inferred to be the main physical weathering process in this catchment (Ariagno et al, 2022), we computed the frost‐cracking intensity indicator (FCI) for both winters, following the approach of Ariagno et al (2022). Between the campaigns of November 2019 and February 2020, we found an FCI of about −11°C min/cm on south‐facing slopes, whereas for the same period during winter 2020–2021 and 2021–2022 the FCI is about −411°C min/cm and −866°C min/cm, respectively.…”

“…In the denuded marly badlands of Draix-Bléone, where 8 mm/yr of erosion is recorded and a supply-limited regime occurs during part of the year (Ariagno et al, 2022;Bechet et al, 2016), estimating the regolith thickness is determinant to predicting sediment export.…”

“…Modelling the seasonal cyclicity of the regolith state we demonstrate here requires developing landscape models with sub-annually varying erosion/ weathering processes and, therefore, sub-annual time steps. The identification of a weathering proxy and its quantification (Ariagno et al, 2022) allows calibrating the parameters of the soil-production function (Heimsath et al, 1997)…”

“…During winter, regolith is formed mainly due to frost-cracking processes (Ariagno et al, 2022), leading to a heterogeneous surface and desiccation features, as also observed in similar Spanish badlands (Nadal-Romero & Regüés, 2010;Regüés et al, 1995). Spring flash floods induce a peak in sediment export (Ariagno et al, 2022;Mathys, 2006). Because of the ample availability of sediment and the high network connectivity (Jantzi et al, 2017), the Draix-Bléone catchments record some of the highest observed specific sediment yields worldwide, with an annual value around 14,000 t/km 2 /y for the Laval catchment (0.86 km 2 ) and sediment concentrations that can reach 800 g/L (Draix-Bléone Observatory, 2015;Le Bouteiller et al, 2021).…”