Reconstruction of Post-Wildfire Soil Erosion Using Lake Archives (1975-2024): a French Mediterranean case study

Wildfires are among the main disturbances affecting Mediterranean ecosystems. These extreme events significantly impact erosion dynamics over long periods and can affect environmental systems by causing excessive sediment transfers downstream. Traditional methods for studying soil erosion in post-wildfire contexts generally focus on short temporal scales, such as months or a few years after wildfire events. 

However, this temporal framework does not allow to capture the dynamics, trajectory, and resilience of erosion processes over a longer time scale (e.g. 20 years). In this context, the study of sedimentary archives provides a powerful resource for reconstructing the resilience of ecosystems to such disturbances.

This study is based on the analysis of sediment cores collected in a small reservoir draining the Peguière headwater catchment (Var, 0.18 km², south-east France), which was completely affected by a historic wildfire in 2003. These sediment cores were dated using natural and artificial radionuclides (²¹⁰Pb_xs, ¹³⁷Cs), and their physical and chemical properties were characterized using a range of techniques, including high-resolution geochemical elemental analysis (XRF), tomography scanning, and the characterization of  organic matter properties.

Initial results show that this wildfire caused significant changes in geochemical properties of sediment. Certain elements, especially manganese, became more abundant during the post-fire period, which was also observed for radionuclides such as ¹³⁷Cs. The post-fire period was also characterized by a change in the properties of organic matter and an acceleration of sediment inputs into the reservoir.

These post-fire processes affect the reservoir water quality and highlight the consequences of fire damage on long-term soil stabilization, plant cover and regeneration.

These retrospective and multi-proxy approaches provide a comprehensive understanding of the resilience of post-fire erosion dynamics. Understanding these processes over extended timescales will improve landscape management and the implementation of environmental protection measures to fight against the detrimental effects of wildfire on the degradation of soil and water resources.