Abstract
Regulation of anthropogenic carbon dioxide (CO2) is an urgent issue—continuously increasing atmospheric CO2 from burning fossil fuels is leading to significant warming and acidification of the surface ocean. Timely and effective measures to curb CO2 increases are thus needed in order to mitigate the potential degradation of natural ecosystems, food security, and livelihood caused by anthropogenic release of CO2. Enhanced rock weathering (ERW) on croplands and hinterlands may be one of the most economically and ecologically effective ways to sequester CO2 from the atmosphere, given that these soil environments generally favor mineral dissolution and because amending soils with crushed rock can result in a number of co-benefits on plant growth and crop yield. However, quantitative evaluation of CO2 capture by ERW in terrestrial soil systems to date has been conducted with tools that are mechanistically very simplified and/or allow limited flexibility. With the goal of working towards a more mechanistically grounded understanding of the geoengineering potential of terrestrial ERW, we developed new 1D reactive transport model — SCEPTER. The model is designed to: (1) mechanistically simulate natural weathering, including dissolution/precipitation of minerals along with uplift/erosion of solid phases, advection plus diffusion of aqueous phases and diffusion of gas phases; (2) allow targeted addition of solid phases at the soil-atmosphere interface, including multiple forms of organic matter (OM) and crushed mineral/rock feedstocks; (3) implement a range of soil mixing regimes as catalyzed by soil surface fauna (e.g., bioturbation) or humans (e.g., various forms of tilling); and (4) enable calculation of solid mineral surface area based on controlled initial particle size distributions coupled to a shrinking core framework. Here we describe the model structure and intrinsic thermodynamic/kinetic data, provide a series of idealized simulations to demonstrate the basic behavior of the code, and evaluate the computational and mechanistic performance of the model against observational data. We also provide selected example applications to highlight model features particularly useful for future prediction of CO2 sequestration by ERW in soil systems.
Highlights
We present the results of a basalt application experiment in which particle size distribution (PSD) tracking has the most prominent effects on the surface area 550 calculation (Figs. 11 and 12) and compare these with the default surface area parameterization and the calculation based on the PSD for bulk soil
625 SCEPTER is a traceable, open-access code with the capability to comprehensively realize phenomena occurring within soil weathering systems, including abiotic/biotic weathering of minerals, mixing of soil particles, and addition of organic matter (OM)/minerals under natural or managed conditions
This specific feature may be of particular importance for calculating the cost performance of terrestrial enhanced rock weathering, as a significant component of both economic cost 630 and secondary CO2 emissions is the grinding and transport of rock feedstocks (e.g., Renforth, 2012)
Summary
Enhanced rock weathering (ERW) at Earth’s surface is one potential means of executing CDR on a gigaton scale (e.g., Köhler et al, 2010; Taylor et al, 2016; Beerling et al, 2020). This class of CDR strategies involves the 40 sequestration of atmospheric CO2 as dissolved inorganic carbon (DIC) through reaction with silicate or carbonate minerals. To help facilitate robust prediction of the CO2 capture efficiency, environmental impacts, and operational costs of ERW in terrestrial soil systems, we have developed a new 1D reactive-transport model — SCEPTER. We compare model results to soil depth profiles of pH and OM from gridded U.S soil data (Section 3.2)
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