Quantifying CO2 removal at enhanced weathering sites: a multiproxy approach

Knapp, W. J. et al. (2023) Quantifying CO2 removal at enhanced weathering sites: a multiproxy approach. Environmental Science and Technology, 57(26), pp. 9854-9864. (doi: 10.1021/acs.est.3c03757) (PMID:37340979)

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.

• Item Type: Articles
• Additional Information: W.J.K. acknowledges funding from NERC studentship NE/S007164/1. The radiocarbon analyses were supported by the National Environmental Isotope Facility (NEIF) under grant NE/S011587/1 (allocation number 2442.1021). Digital Terrain Model (DTM) data displayed in Figure 1 were kindly provided by the Ordnance Survey under the following license: Crown copyright and database rights 2023 Ordnance Survey (100025252), where 2023 is the current year. E.T.T. acknowledges funding from NERC grants NE/T007214/1, NE/P011659/1, and NE/M001865/1. P.R. and W.M.M. acknowledge funding from UKRI greenhouse gas removal research programme (NE/P019943/1), and P.R. acknowledges funding from the Industrial Decarbonisation Research and Innovation Centre (EP/V027050/1).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Ascough, Dr Philippa
• Authors: Knapp, W. J., Stevenson, E. I., Renforth, P., Ascough, P. L., Knight, A. S.G., Bridgestock, L., Bickle, M. J., Lin, Y., Riley, A. L., Mayes, W. M., and Tipper, E. T.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Environmental Science and Technology
• Publisher: American Chemical Society
• ISSN: 0013-936X
• ISSN (Online): 1520-5851
• Published Online: 21 June 2023
• Copyright Holders: Copyright © 2023 The Authors
• First Published: First published in Environmental Science and Technology 57(26):9854-9864
• Publisher Policy: Reproduced under a Creative Commons license