Constraining carbon loss from rivers following terrestrial enhanced rock weathering

Enhanced rock weathering (EW) has garnered increasing interest as a promising technique for durable carbon dioxide removal, with a range of potential co-benefits including increased soil pH and nutrient release.However, the impacts of EW on river chemistry and the potential loss of initially captured CO2 during river transport remain poorly constrained.The current lack of tools for robustly predicting the effect of riverine degassing on the EW life cycle undermines the use of this practice as a carbon mitigation strategy.Here, we present results from a first-of-its-kind dynamic river network model designed to quantify the impact of EW on river carbonate chemistry in North American watersheds.We map key water quality parameters across the river network of North America using machine learning, and use a dynamic river network model to simulate changes in river carbonate chemistry and carbon degassing during EW.Our model predicts low carbon loss (<5%) from river networks and limited changes to carbonate mineral saturation states for many of the river pathways explored here.However, there are some instances in which carbon degassing is significantly higher (>15%) and it is possible to induce large changes in carbonate saturation states, indicating that riverine carbon storage and the impacts of EW on river chemistry must be evaluated in a deployment-specific context.Although there remains uncertainty in the impact of EW on stream/river chemistry, our approach represents a step forward in the development of tools for quantifying the impacts of carbon cycling in downstream catchments on the overall EW lifecycle. Significance StatementEnhanced rock weathering (EW) has emerged as a promising long-term carbon dioxide removal (CDR) method with potential soil and crop co-benefits.However, its impact on river chemistry and the potential loss of captured CO2 during river transport is unclear.We have developed a dynamic river network model to evaluate EW's effects on North American watersheds.Following EW application to a preliminary example set of locations, many rivers show low carbon loss and limited carbonate saturation state change.However, regional variation exists, emphasizing the need for deployment-specific evaluation and further development of process-based models of stream/river carbon cycling.This study provides a step forward in the development of tools for quantifying the impact of EW on river systems, supporting the potential for large-scale EW, and informing CDR strategy decisions and carbon markets.