INSIGHTS FROM RIVER CHEMISTRY INTO CARBON CAPTURE POTENTIAL THROUGH SURFICIAL ENHANCED ROCK WEATHERING

Capture and sequestration of carbon dioxide (CO₂) from Earth’s atmosphere is generally regarded as necessary to keep global temperature increases below those predicted to cause significant degradation of livelihoods, food security, and water supplies in the coming century. Carbon capture through surficial enhanced rock weathering (ERW) is one extensively discussed carbon mitigation strategy. Estimates of potential carbon capture through ERW have typically come from the evaluation of dissolution potentials in soils. Here we provide new insights into the potential for carbon dioxide removal (CDR) through enhanced basalt and carbonate mineral weathering considering the limits imposed by river water chemistry. Specifically, we consider the capacity of rivers to transport cations and alkalinity without inducing calcite precipitation, which leads to rerelease of CO₂ to the atmosphere. Using an iterative model coupling enhanced rock weathering to river/stream carbonate chemistry, we estimate regional (U.S.) and global carbon capture potentials for plausible threshold saturation states. Our model yields significant U.S. and global CDR potentials (at the gigaton scale) and provides new support for the notion that accelerated carbonate mineral weathering should be considered as a component of accelerated rock weathering portfolios and greenhouse gas mitigation strategies. Overall, our results suggest that there is significant untapped carbon capture potential in surficial weathering systems relative to existing estimates for enhanced rock weathering.