Microbially Accelerated Weathering for CDR: Reactive Transport Modeling to Quantify Rates and Sinks

Microbes alter biogeochemical cycles at spatial scales ranging from soil pores to the globe. For example, it’s increasingly recognized that microbes affect mineral weathering by influencing solubility and metal speciation. This presents an opportunity to leverage microbial processes to accelerate silicate weathering as a carbon dioxide removal (CDR) strategy. Microbially-accelerated weathering is similar to enhanced rock weathering but instead of adding crushed mineral feedstocks, microbes are added to the soil to increase weathering of native silicate minerals. Recent work has demonstrated that the addition of a particular Bacillus subtilis strain can enhance silicate dissolution in both laboratory and field environments (Timmermann et al., 2025, Global Change Biology). Here, we use the CrunchFlow reactive transport model to better understand how microbial acceleration of mineral dissolution may alter the soil weathering system, including quantifying changes in weathering rates, impacts on soil pH, and the predominant sinks of weathering products. The latter determines whether microbial-driven increases in weathering correspond with actual CDR. Our results suggest that in laboratory mesocosm experiments, microbes can accelerate the weathering of some silicate mineral by as much as 10x. We also explore the role of secondary carbonate precipitation as a key mechanism in microbially-accelerated weathering, and we consider the implications for CDR measurement, reporting, and verification.