ANALYZING THE REFLECTANCE SPECTRA OF SOILS AMENDED WITH FINELY GROUND CARBONATE AND SILICATE MINERALS FOR ENHANCED ROCK WEATHERING

Among the ex-situ carbon capture and sequestration (CCS) techniques that have been developed to mitigate the damages of anthropogenic climate change, Enhanced Rock Weathering (ERW) is recently gaining traction. It is the spreading of finely ground silicate rock in agricultural settings to increase soil alkalinity and form secondary (pedogenic) carbonate minerals that trap CO₂. While ERW has been shown to be an effective method of drawing down CO₂, one challenge with the rapid uptake of ERW is the difficulty of quantifying and verifying CO₂ drawdown over large areas. Current sampling and measurement practices utilize laborious and/or expensive techniques, such as QXRD, calcimetry, and alkalinity or CO₂ flux monitoring. Given the heterogeneity of soils, and the difficulties of accessing croplands year-round, these techniques can only reliably and economically provide snapshot quantifications of CO₂ capture. One potential solution to this measurement problem is the incorporation of remotely sensed data to monitor the progress of ERW. Here we assess the accuracy and precision of handheld remote sensing instruments (optical and shortwave) in quantifying the dissolution of silicate minerals and the production of carbonate minerals, and subsequently correlate these measurements with the rate of carbon drawdown in ERW trials. To do this, we collected spectral measurements of various ground silicate rocks: kimberlite, wollastonite, serpentinite, basalt, and metabasalt. We then took baseline spectral measurements of agricultural soil amended with these rocks (and with ground calcite as a reference) and correlated the spectral data with traditional mineralogical and geochemical results, thus providing a spectral baseline for the initial state of our ERW trials. Over the course of ERW trials, we are looking for the spectral differences, and tracking these differences over time, between soils amended with silicate and carbonate rocks. Scans have so far been done on Petri dishes containing soil and feedstock minerals at concentrations of 0.1, 0.5, 1.0, and 5.0 kg/m², encompassing the range of typical ERW treatments. These initial scans and calibration will act as guidelines for the development of further remote sensing techniques for monitoring and verifying the ERW process at commercial farms and ERW pilot projects.