Tracing the impact of enhanced basalt weathering with strontium isotopic composition in the solid and liquid phases of soil
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- In the face of climate emergency, the development of robust strategies for atmospheric carbon capture and storage has become essential. Enhanced rock weathering (ERW) – consisting of spreading rock powders on agricultural soils to accelerate mineral weathering and sequester CO2 in the form of bicarbonates – is attracting growing interest, but its geochemical verification remains a major challenge. This study evaluated strontium isotopic signature (87Sr/86Sr ratio) as a tracer of the weathering of a basanite from Clermont-Ferrand applied to a temperate agricultural soil in Vieusart, in Wallonia. Through a coupled monitoring of solid phases (exchangeable fraction) and liquid phases (soil pore water collected using Rhizons), the study reconstructs Sr transfers between the different compartments of the soilsolution system over the first eighteen months following application. The results show that classical physicochemical indicatos (pH, conductivity, CEC) are insufficient to detect the ERW signal in this neutral pH and highly base-saturated soil. In contrast, the 87Sr/86Sr ratio reveals a contrast between the basalt (0.7038) and the native soil (0.7284), sufficient to identify a growing contribution of basaltic Sr in the liquid phase over time, and a more subtle incorporation into exchangeable fraction. The coupled solid-liquid approach demonstrates its superiority over any single-phase method, as the soil solution responds more rapidly to weathering than the exchange complex. This work contributes to the geochemical foundations of MRV (monitoring, reporting and verification) protocols applied to ERW, and opens perspectives towards a dual isotopic approach (87Sr/86Sr + δ⁸⁸/⁸⁶Sr) and long-term multi-tracer monitoring.