Freshwater streams and rivers actually release carbon dioxide, but the source of those emissions has been unclear to scientists for years. Now, researchers have shown that the greenhouse gas appears in streams by way of two difference sources—either as a direct pipeline for groundwater and carbon-rich soils, or from aquatic organisms releasing the gas through respiration and natural decay. David Butman, professor of environmental and forest sciences and civil and environmental engineering, is part of the team that recently found that CO2’s origins—land or life—depend largely on the size of the stream or river.