Using Self-Integrating Accumulators (SIAs) to Monitor Enhanced Rock Weathering (ERW) in German Agricultural Fields

The commercial scaling potential of enhanced rock weathering (ERW) as a carbon dioxide removal (CDR) strategy remains limited due to the need for reliable and cost-effective monitoring, reporting, and verification (MRV). Soil- and porewater-based MRV approaches present several challenges: soil-based mass balance methods require extensive measurements to account for loss pathways, increasing uncertainty, while water sampling relies on frequent and expensive analyses that require significant operational effort. To overcome these limitations, we evaluated the field performance of self-integrating accumulators (SIAs) – ion exchange resin-based passive samplers – as an ERW MRV tool that has the potential to increase accuracy while reducing analysis and operating costs.

For this field study SIAs were installed in summer 2024 across three agricultural fields in southern Germany and captured time-integrated fluxes of major cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and anions (NO₃⁻) over one year. In total, 216 SIAs were deployed below topsoil (20 cm on grassland and 30 cm on cropland). Each field was divided into untreated control and basanite-amended plots. SIAs were deployed in sets of 12 replicates per treatment and field for two installation methods and were paired with suction lysimeters. Annual SIA-derived ion fluxes were compared against soil and porewater datasets to assess consistency and performance.

This study represents the first field-scale evaluation of SIAs as an MRV approach for ERW. On well-drained cultivated land, SIA-derived ion fluxes corresponded closely with porewater-based measurements, demonstrating their potential as scalable, time-integrative, and cost-effective tools for quantifying both cation and anion fluxes. In contrast, SIAs installed in soils that remained waterlogged for extended periods consistently overestimated fluxes. The measurement principle of the SIAs assumes vertical drainage flux, but lateral flow is possible in waterlogged soils. Under continually saturated conditions, the resins’ high adsorption efficiency (>90%) could also induce concentration gradients that enhance ion transport toward the device.

These findings highlight the importance of careful site selection for ERW and the need to assess which MRV method is most appropriate for each project location. Nevertheless, broader adoption of SIA-based MRV could significantly accelerate ERW deployment by reducing logistical and analytical requirements, lowering operational costs, and increasing the likelihood of full credit issuance without losses due to insufficient aqueous-phase sampling. Additionally, SIAs have negligible impact on farming operations, making them well-suited for large-scale agricultural deployment.