A new soil-based approach for empirical monitoring of enhanced rock weathering rates

Abstract

Enhanced Rock Weathering (ERW) is a promising scalable and cost-effective Carbon Dioxide Removal (CDR) strategy with significant environmental and agronomic co-benefits. However, a major barrier to the widescale implementation of ERW is a robust Monitoring, Reporting, and Verification (MRV) framework. To successfully quantify the amount of carbon dioxide removed by ERW at scale, MRV must be accurate, precise, and cost-effective. Here, we outline a new method based on mass balance where metal analysis on soil samples is used to accurately track the extent of in-situ alkaline mineral weathering. We show that signal-to-noise issues of in-situ soil analysis can be mitigated by using isotope-dilution mass spectrometry to reduce analytical error. We implement a proof of concept experiment demonstrating the method in controlled mesocosms. In our experiment, basalt feedstock is added to soil columns containing the cereal crop Sorghum bicolor at a rate equivalent to 50 t ha-1. Using our approach, we calculate an average initial CDR value of 2.24 +- 1.33 tCO2eq ha-1 from our experiments after 235 days, within error of an independent estimate calculated using conventional elemental budgeting of reaction products. Our result corresponds to an initial CDR efficiency of 24.4 +- 14.5 % for the feedstock used. Our method provides a robust time-integrated estimate of initial CDR, and offers a path to track and validate large-scale carbon removal through ERW