Organic and inorganic pathways of CO2 removal during enhanced weathering

Climate change remains one of the most pressing global challenges, requiring rapid and sustained reductions in greenhouse gas emissions. However, even under ambitious mitigation scenarios, emission reductions alone are not sufficient to meet climate targets, making the deployment of CO2 removal technologies necessary. Among these, enhanced weathering has emerged as a particularly promising approach, given its potential co-benefits for soil health. Yet, current assessments of CO2 removal through enhanced weathering remain incomplete, as they predominantly focus on two inorganic pathways during which CO2 removal occurs — bicarbonate leaching and pedogenic carbonate precipitation — while largely neglecting organic processes. This narrow perspective limits our understanding of the overall carbon balance and may lead to misestimation of the CO2 removal potential of enhanced weathering. To address this research gap, in three experiments this thesis adopted a more holistic approach, investigating the full carbon cycle, considering both inorganic and organic pathways of CO2 removal and loss. Results of this thesis demonstrate that the current focus on inorganic pathways captures only a limited fraction of the processes governing carbon dynamics during enhanced weathering. Future research will therefore need to move beyond the narrow focus on inorganic processes and instead consider the coupled dynamics of mineral weathering and soil organic carbon cycling. Aside from its mechanistic insights, the assessments carried out for this thesis also underscore the substantial methodological challenges associated with quantifying CO2 removal. The scaling of enhanced weathering will require adapted experimental designs and sampling strategies alongside more sophisticated statistical approaches (e.g. Bayesian inference) to overcome low signal-to-noise ratios. The development of standardised carbon crediting frameworks tailored to noisy datasets will be critical not only for enhanced weathering but also for other soil-based CO2 removal technologies that face similar challenges.