This award supports the study of carbon transport and transformation in river networks. Farmers apply crushed rock to enrich agricultural soils. Through a process known as enhanced weathering, the crushed rock also reacts with the atmosphere to remove carbon dioxide. However, some of the captured carbon may be lost as runoff into streams and rivers. This project will quantify that downstream carbon loss and improve carbon accounting associated with enhanced weathering. This work will also support geoscience and data science education. The project will develop a river carbon tracking model to quantify carbon transport and transformation in river networks following terrestrial enhanced weathering. The Mississippi-Atchafalaya River Basin serves as a natural laboratory for this study based on its history of agricultural liming. This project will integrate river hydrography, river and groundwater chemistry, watershed and climate data, lime application timeseries, machine learning, and reactive transport modeling. The relative effects of various carbon transformation mechanisms will be compared to understand the factors controlling rates of carbon loss. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.