Significant interest and capital are currently being channeled into techniques for durable carbon dioxide removal (CDR) from Earth’s atmosphere. A particular class of these approaches — referred to as enhanced weathering (EW) — seeks to modify the surface alkalinity budget to store CO2 as dissolved inorganic carbon species. Here, we use SCEPTER — a reaction-transport code designed to simulate EW in managed lands — to evaluate the throughput and storage timescales of anthropogenic alkalinity in agricultural soils. Through a series of alkalinity flux simulations, we explore the main controls on cation storage and export from surface soils in key U.S. agricultural regions. We find that lag times between alkalinity modification and climate-relevant CDR can span anywhere from years to many decades locally but can aggregate to shorter timescales depending on deployment region. Background soil cation exchange capacity, agronomic target pH, and fluid infiltration all impact the timescales of CDR relative to the timing of alkalinity input. There is likely scope for optimization of weathering-driven alkalinity transport through variation in land management practice. However, shifting management practices to reduce lag times will likely decrease total CDR from weathering and lead to non-optimal nutrient use efficiencies and soil nitrous oxide (N2O) fluxes. Although CDR lag times will be more of an issue in some regions than others, these results have significant implications for the technoeconomics of EW and the integration of EW into voluntary carbon markets, as there may often be a large temporal disconnect between deployment of EW and climate-relevant CDR.
