How inland waters "breathe" carbon – and what that means for global systems

For a long time, scientists who evaluated the global carbon cycle have considered rivers and streams related to pipelines, channeling carbon and other solutes from the land to the sea. Today, however, Scientists know that these inland waters also "breathe" carbon and other gases into the atmosphere.

In fact, the crucial role of this "escape" of greenhouse gases from rivers and streams was incorporated for the first time in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. the changing climate of the United Nations in 2014.

However, much remains to be said about the amount of gas actually released by these water systems and the chemical and ecological dynamics that affect their transport.

A new Yale study reveals important information on the factors that influence greenhouse gas emissions from these inland waters, including a key relationship between storms, ecology, and topography to moderate these releases.

In a headwater analysis in central Connecticut, scientists found that concentrations of three greenhouse gases – carbon dioxide, nitrous oxide, and methane – were increasing in wetland watercourses during rainstorms, but decreased or remained constant in wooded watercourses. However, they also found that these gases were less likely to be released from wetland watercourses than those from forest areas.

Write in the Journal of Geophysical Research: Biogeosciences, they conclude that these variations are likely due to the fact that wooded streams tend to be steeper, which creates greater turbulence which, in turn, promotes gas releases. At the same time, in wetlands, these inputs were more likely to flow downstream of their source, said Kelly Aho, a PhD candidate at the Yale School of Forestry and Environmental Studies and lead author of the 'study.

"When you think of what a wetland looks like, it makes sense: the wetlands are really flat, which is why water and organic matter can accumulate there," Aho said. . "As a result, during a rainstorm, these wetlands and their soils are a source of greenhouse gases."

"But," she added, "gas concentrations are only half of the equation."

The release of gas from rivers and streams also depends on the rate of transfer of gas or the rate of passage of gases across the air-water boundary. A lack of turbulence tends to produce a lower gas transfer rate and lower speeds. Thus, while greenhouse gas concentrations in wetland watercourses will increase suddenly during a rainstorm, these gases are more likely to remain trapped in watercourses. water more flat and less turbulent until they meet more steep terrain further downstream.

It is essential to understand these dynamics, Aho said, to develop more accurate projections of the carbon cycle and climate models, particularly as extreme weather events are expected to increase over the next few decades.

"If a researcher studies carbon sequestration from a local point of view, he could simply monitor the vertical entrances and exits of a land," she said. "But if this area includes a wetland creek, for example, the gases may escape from the plot that they are monitoring; carbon could be released into the atmosphere outside of their point." So you could totally miss it so it's important to think about this idea of ​​lateral transport.

"That's why streams and rivers are so interesting," she added. "They are moving solutes across the landscape, so we have to consider that."

The paper was co-authored by Peter Raymond, Professor of Ecology Ecosystems at F & ES.