How Mountain Streams Breathe Out Carbon Dioxide

U.S. Geological Survey researchers are studying streams in Rocky Mountain National Park to learn how they take part in the global carbon cycle. In the mountains, part of that cycle is the exchange of carbon dioxide gas between streams and the air.

Why it matters

Mountain streams were long thought to give off little CO2, a greenhouse gas. But a 2019 study by Horgby and others suggested that the turbulence of steep mountain streams can drive high exchange rates, adding more to the world's CO2 release than expected. Measuring when and how much CO2 streams like these release lets researchers pin down their global contribution and their possible influence on warming.

The Loch Vale outlet in Rocky Mountain National Park. NPS photo.

What they found

• Storms: rain flushes carbon from soils into streams, driving up CO2 levels and gas exchange over short periods.
• Seasons: CO2 in the streams tracks the build-up and melting of snow. In winter the snowpack acts as a lid, limiting exchange with the air and raising CO2 in the water. At peak snowmelt, exchange rises sharply as runoff flushes CO2 from the soil into streams.
• Years: stream CO2 levels and releases rose with the year's total precipitation.

Climate models predict changes in the type and pattern of precipitation as temperatures rise. Because precipitation shapes how much CO2 streams release, those changes could set off feedbacks, positive or negative, among water, land and air in the carbon cycle.

The research is published as "Spatiotemporal Dynamics of CO2 Gas Exchange From Headwater Mountain Streams". Data are online for Loch Vale weather and the Andrews Creek stream gage.

The scientist

David Clow, a USGS research hydrologist in Denver with a 1992 PhD in geochemistry from the University of Wyoming, points out that intensively instrumented places like Loch Vale let researchers dig deep into how natural systems work and respond to disturbances such as air pollution and climate change.

Sources

• National Park Service, Rocky Mountain National Park, "Spatiotemporal Dynamics of CO2 Gas Exchange From Headwater Mountain Streams." https://www.nps.gov/articles/gas-exchange-of-mountain-streams.htm
• A portrait of the scientist is not reproduced here.