Streams and rivers in the United States release a total of 97 teragrams of carbon to the atmosphere each year, according to a study published online this week in Nature Geoscience. Until now, a scarcity of direct measurements has led to uncertainty about the role of inland waters in the carbon cycle.

David Butman and colleagues used measurements of stream and river water chemistry in the United States, coupled with estimates of surface area, in order to estimate the amount of carbon degassed from these waterways. They found that the release of carbon dioxide is positively correlated with annual precipitation, which they attribute to rainwater-induced flushing of carbon dioxide from soils and the regulation of stream surface area.