Utilising soil centrifugation for accurate carbon dioxide removal estimates via enhanced rock weathering

Enhanced rock weathering (ERW) is emerging as a promising scalable carbon dioxide removal (CDR) strategy. However, the lack of methods for in situ quantification of rock weathering currently limits the ability to monitor, verify, and report CDR via ERW. Given the technical challenges of durable carbon sequestration in heterogeneous ecosystems where ERW is applicable, accurate and reliable validation of ERW is essential. Therefore, we propose a novel aqueous-phase extraction approach, the centrifugation pore water extraction sampling method, to obtain and analyse soil pore waters. Using a large-scale, replicated field trial of ERW combined with tree planting at an afforestation site in mid-Wales, we demonstrate that soil centrifugation provides a reliable method for extracting pore water necessary for accurate CDR estimations. This method was particularly effective during periods of low precipitation and associated low soil water content when conventional aqueous-phase methodologies fail to obtain sufficient pore water samples. Additionally, soil centrifugation provided estimates of potential CDR by analysing weathering products accumulating within soil micropores, an aspect not adequately addressed by conventional aqueous-phase methodologies.