Rivers help regulate Earth’s climate by carrying the chemical byproducts of rock breakdown, or weathering, from land to oceans. This process removes carbon dioxide (CO₂) from the atmosphere and plays a long-term role in keeping Earth’s temperature stable. Scientists often study the chemistry of river water to understand how fast and where weathering is happening, but the signals can be hard to interpret due to complex rock types and water flow paths.

This study uses lithium isotopes (variations of the element lithium) to trace weathering processes in the East River watershed, a mountainous area in Colorado. We collected river samples in July 2024 and analyzed both their lithium isotope composition and overall chemical makeup. We found a wide range of lithium concentrations and isotope values, which suggests that weathering varies greatly across the watershed. Interestingly, we did not find a clear relationship between lithium isotopes and other commonly used chemical indicators, pointing to more complex interactions than previously thought.

Our findings show that lithium isotopes can provide unique insight into how water and rock interact in mountain environments. This research helps improve our understanding of how landscapes influence chemical weathering and, ultimately, Earth’s climate system.