Soil Calcimetry Dynamics to Monitor Weathering Flux: Method Calibration in Wollastonite-Amended Croplands - Preprint

[Geoengineering News]

https://www.preprints.org/frontend/manuscript/79abbb2ebd200ae9449811ba009cc941/download_pub

Authors: Francisco SM Araujo, Rafael M Santos

26 September 2025

Abstract 

Enhanced Rock Weathering (ERW) is a promising carbon dioxide removal (CDR) strategy that accelerates mineral dissolution, sequestering atmospheric CO2 while improving soil health. This study builds on prior applications of soil calcimetry by investigating its ability to resolve short-term carbonate fluxes and rainfall-modulated weathering dynamics in wollastonite-amended croplands. Conducted over a single growing season (May–October 2024) in temperate row-crop fields near Port Colborne, Ontario—characterized by lacustrine clay soils and variable rainfall—the study tests whether calcimetry can differentiate between dissolution and precipitation phases and serve as a proxy for total weathering flux within the sentinel layer. Monthly measurements of soil pH (Milli-Q and CaCl2 extractions) and calcium carbonate equivalent (CCE) were collected from 10 plots. Results show significant alkalinization (p< 0.001) in both pH measures, whereas CCE exhibited high spatial and temporal variability with no consistent seasonal trend. The calcimetry-derived weathering proxy, log (Σ ΔCCE/Δt), correlated positively with pH (r= 0.652), capturing net carbonate accumulation, while the kinetic dissolution rate model correlated strongly and negatively with pH (r≈− 1), reflecting acid-promoted dissolution. This divergence confirms that the two metrics capture complementary stages of the weathering–precipitation system. Rainfall exerted a strong short-term influence on carbonate formation, with cumulative precipitation over the preceding 7–10 days showing a saturating positive effect, while dissolution fluxes were unaffected by rainfall. These findings expand calcimetry’s potential for ERW MRV, providing a direct, scalable, and dynamic measure of CO2 sequestration in suitable climates and soils.

Source: Preprints.org