CAS-Climate: Enhanced mineral weathering in agricultural fields: Quantifying carbon leakage in the river system

University Of Washington, Seattle WA

Investigators

Abstract

Removing carbon dioxide (CO2) from the atmosphere benefits society. One promising approach to CO2 removal is enhanced mineral weathering (EMW). In EMW, specific rocks are crushed and spread on agricultural fields. The rocks then react with CO2 and water to generate a dissolved form of inorganic carbon called bicarbonate. Successful CO2 removal requires the generated bicarbonate to travel from agricultural fields through rivers into the ocean. However, during the journey through rivers, bicarbonate can get converted back to CO2 and re-enter the atmosphere. The amount of bicarbonate re-emitted to the atmosphere is unknown. This project will address this gap in our knowledge by quantifying how much bicarbonate gets converted to CO2 and released to the atmosphere. The measurements will be made in an agricultural river system in Illinois. Successful completion of this project will benefit society by ensuring that EMW removes more CO2 from the atmosphere than it contributes, and creating a community quantification standard for EMW that aligns with the forefront of scientific discovery. Additional benefits to society will result from the development of a university-level course that is publicly available through ‘Teach the Earth’, aiming to enhance public access to STEM education. The goal of this project is to quantify the fate of weathered carbon within an agricultural river system in Illinois where lime (CaCO3) is applied to manage soil pH. Lime dissolution is a form of EMW with currently unknown CO2 removal potential that is now practiced at large enough magnitude to be detectable at stream network scale. Previous efforts to estimate the amount of carbon lost in rivers have all been model based. These efforts have only focused on CO2 degassing and carbonate precipitation as the dominant loss processes. In this project, the research team will exploit the fact that lime carbon is radiocarbon dead to allow differentiation between modern carbon and lime carbon in the stream. In addition, the research team will measure how submerged plants and algae uptake bicarbonate and convert it back to CO2. Finally, the team will assess how seasonal changes in temperature and stream flow control the balance between sequestration and re-emission of EMW-produced bicarbonate. Together, these experimental measurements will be used to generate a comprehensive dataset that supports the development and validation of future models. Successful completion of this project will lead to new insights into how temporal variation in biological processes and other stream processes affects the amount of carbon sequestered by EMW. 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.