For decades, researchers believed most rivers were net carbon emitters. That’s because leaves, wood, and other organic material wash into the water, decompose, and release carbon dioxide, a process especially common in shaded, forested landscapes. Most of the data scientists had come from those kinds of environments, particularly in the eastern United States. But the West’s desert and shrubland rivers have been far less studied.
Taylor Maavara, an aquatic biogeochemist and one of the study’s lead authors, wanted to change that. Her team gathered data from thousands of river monitoring sites across the continental U.S. and used machine learning to estimate whether each reach of river tends to release carbon or take it up.
Their results point to a stark geographic split: Western rivers — from Nevada to Arizona to parts of New Mexico — are much more likely to act as carbon sinks. Maavara says the region’s open landscapes play a key role. With less tree cover, more sunlight reaches the water, boosting photosynthesis. And with fewer leaves and organic material falling in, there’s less decomposition, a process that releases carbon dioxide back into the air.
The findings, she says, “shed some light on the value of these desert ecosystems, which we tend to think of having a bit less life. We show that there’s just as much life, they’re just doing different stuff.”
While the U.S. as a whole still emits more carbon from its rivers than it absorbs, this study suggests that the “carbon gap” may be smaller than once believed.And because arid and semi-arid regions make up a large part of the world’s land surface, Maavara says these findings could have global implications.
The researchers also warn that this carbon uptake benefit depends on water staying in those rivers: if drought intensifies or flow drops off, the balance could swing back, turning these ecosystems from carbon sinks to sources.
Maavara hopes this work will close one of the “big gaps” in our understanding of the global carbon cycle and inform better conservation and climate modeling going forward.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
