Source limitation of carbon gas emissions in high-elevation mountain streams and lakes

Inland waters are an important component of the global carbon cycle through transport, storage, and direct emissions of CO₂ and CH₄ to the atmosphere. Despite predictions of high physical gas exchange rates due to turbulent flows and ubiquitous supersaturation of CO₂—and perhaps also CH₄—patterns of gas emissions are essentially undocumented for high mountain ecosystems. Much like other headwater networks around the globe, we found that high-elevation streams in Rocky Mountain National Park, USA, were supersaturated with CO₂ during the growing season and were net sources to the atmosphere. CO₂concentrations in lakes, on the other hand, tended to be less than atmospheric equilibrium during the open water season. CO₂ and CH₄ emissions from the aquatic conduit were relatively small compared to many parts of the globe. Irrespective of the physical template for high gas exchange (high k), we found evidence of CO₂ source limitation to mountain streams during the growing season, which limits overall CO₂emissions. Our results suggest a reduced importance of aquatic ecosystems for carbon cycling in high-elevation landscapes having limited soil development and high CO₂ consumption via mineral weathering.