River chemistry constraints on the carbon capture potential of surficial enhanced rock weathering

Abstract

Technologies and approaches that remove and sequester carbon dioxide (CO2) from Earth's atmosphere are likely to play a significant role in mitigating anthropogenic climate disruption in the coming century. Enhanced rock weathering (ERW) on the land surface is one extensively discussed approach toward carbon dioxide removal (CDR), but the capacity of rivers to carry dissolved products derived from ERW without CO2 re‐release is largely unexplored, hindering a full understanding of the life cycle of ERW and its associated maximum CDR potential. Here, we use a conceptual model built upon river/stream carbonate chemistry to estimate the upper limits on the carbon transport potential (CTP) of rivers and groundwaters. Our model yields a riverine CTP ranging between 0.26–0.89 GtCO2 yr−1 for the United States and 7.1–21.3 GtCO2 yr−1 globally for accelerated silicate weathering, and between 0.090–0.37 GtCO2 yr−1 for the United States and 2.5–8.8 GtCO2 yr−1 globally for accelerated carbonate weathering. Although these limits will be challenging to achieve in practice, our results support the notion that the transport of dissolved constituents in surface waters is unlikely to be a primary bottleneck limiting the CDR potential of ERW. This supports the notion that accelerated mineral weathering should be considered as an additional component of greenhouse gas mitigation portfolios. However, future research on the kinetics of ERW reactions and river responses, along with consideration of possible added CO2 emissions by activities needed to accomplish ERW, are needed for a more realistic quantification of the net CDR via ERW in the land–soil–river system.

New estimates of the storage permanence and ocean co-benefits of enhanced rock weathering

“…Exploring this process with higher-resolution, fully coupled ocean biogeochemistry models will be an important avenue for future work. In addition, developing better constraints on the potential for carbon leakage during transport from deployment locations to the ocean is a critical topic for future research ( 44 , 45 ). Nevertheless, our results indicate that the overall loss of initially captured carbon from the ocean is a small fraction of the ERW life cycle and that it is potentially predictable to a relatively high degree of precision.…”

Techno-Economic and Life Cycle Assessment of Enhanced Rock Weathering: A Case Study from the Midwestern United States

“…Although estimates vary, rock weathering naturally removes roughly 0.1−1.0 billion metric tons of CO 2 annually, 2 and ERW could potentially more than double natural carbon sequestration through the application of industrially processed rocks that readily react with CO 2 �typically Ca-and Mg-rich silicates�to managed lands (croplands, rangelands, and managed forests). 3 Silicate rocks mined for ERW include mafic to ultramafic rocks, such as basalt and dunite, and other Ca-and Mg-rich silicate minerals, like wollastonite ore. 4 Less traditional materials can be used for ERW, such as waste silicate materials (e.g., fly ash from energy production), industrial wastes (e.g., red mud and slag), and other demolition wastes (e.g., cement kiln dust). 5−8 Previous literature has highlighted the potential benefits of utilizing waste materials for ERW, e.g., avoiding mining and grinding activities to reduce emissions and costs 9 and utilizing low-cost waste materials.…”

“…Enhanced rock weathering (ERW) is one CDR strategy that leverages the natural process of rock weathering to sequester CO 2 on human time scales. Although estimates vary, rock weathering naturally removes roughly 0.1–1.0 billion metric tons of CO 2 annually, and ERW could potentially more than double natural carbon sequestration through the application of industrially processed rocks that readily react with CO 2 typically Ca- and Mg-rich silicatesto managed lands (croplands, rangelands, and managed forests) …”

Considerations for hypothetical carbon dioxide removal via alkalinity addition in the Amazon River watershed

“…Finally, the carbonate-poor river waters may help 50 suppress secondary chemical precipitation of the added alkalinity, a risk that can reduce the efficiency of OAE (Bach et al, 2019;Hartmann et al, 2022). Overall, global deployment of alkalinity in rivers is seen as CDR technique with the potential to scale to the gigaton level (Zhang et al, 2022). Therefore, we examine the Amazon River-ocean continuum for its potential as a site of OAE.…”