Quantifying CO2 Removal at Enhanced Weathering Sites: a Multiproxy Approach

Knapp, William J.; Stevenson, Emily I.; Renforth, Phil; Ascough, Philippa L.; Knight, Alasdair C.G.; Bridgestock, Luke; Bickle, Michael J.; Lin, Yongjie; Riley, Alex L.; Mayes, William M.; Tipper, Edward T.

Abstract

Enhanced weathering is a carbon dioxide (CO2) mitigation strategy that promises large scale atmospheric CO2 removal. The main challenge associated with enhanced weathering is monitoring, reporting, and verifying (MRV) the amount of carbon removed as a result of enhanced weathering reactions. Here, we study a CO2 mineralization site in Consett, Co. Durham, UK, where steel slags have been weathered in a landscaped deposit for over 40 years. We provide new radiocarbon, δ13C, 87Sr/86Sr, and major element data in waters, calcite precipitates, and soils to quantify the rate of carbon removal. We demonstrate that measuring the radiocarbon activity of CaCO3 deposited in waters draining the slag deposit provides a robust constraint on the carbon source being sequestered (80% from the atmosphere, 2σ = 8%) and use downstream alkalinity measurements to determine the proportion of carbon exported to the ocean. The main phases dissolving in the slag are hydroxide minerals (e.g., portlandite) with minor contributions (<3%) from silicate minerals. We propose a novel method for quantifying carbon removal rates at enhanced weathering sites, which is a function of the radiocarbon-apportioned sources of carbon being sequestered, and the proportion of carbon being exported from the catchment to the oceans.

Citation

Knapp, W. J., Stevenson, E. I., Renforth, P., Ascough, P. L., Knight, A. C., Bridgestock, L., …Tipper, E. T. (2023). Quantifying CO2 Removal at Enhanced Weathering Sites: a Multiproxy Approach. Environmental Science and Technology, 57(26), 9854-9864. https://doi.org/10.1021/acs.est.3c03757

• Journal Article Type: Article
• Acceptance Date: Jun 1, 2023
• Online Publication Date: Jun 21, 2023
• Publication Date: Jul 4, 2023
• Deposit Date: Jun 21, 2023
• Publicly Available Date: Jun 26, 2023
• Journal: Environmental science & technology
• Print ISSN: 0013-936X
• Electronic ISSN: 1520-5851
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 57
• Issue: 26
• Pages: 9854-9864
• DOI: https://doi.org/10.1021/acs.est.3c03757
• Keywords: Radiocarbon; Carbon dioxide removal; Mineralisation; Isotopic tracers; Monitoring
• Public URL: https://hull-repository.worktribe.com/output/4316055