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

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 GtCO(2) yr(-1) for the United States and 7.1-21.3 GtCO(2) yr(-1) globally for accelerated silicate weathering, and between 0.090-0.37 GtCO(2) yr(-1) for the United States and 2.5-8.8 GtCO(2) 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.