Water Ways & River Ecosystems

A drop of waterways from Antarctica to Europe to the Amazon flowed into Kent State University for study. A whopping 152 researchers from 40 countries contributed data on carbon cycling, making it the largest study, in terms of global coverage, to examine carbon cycling.

David Costello, a Kent State ecology assistant professor and aquatic ecologist, was a co-author of a Science Advances journal article on the three-year study’s findings and did much of the data analysis at his Kent State lab. He worked closely with Scott Tiegs, an associate biology professor at Oakland University in Michigan who led the study.

The researchers investigated how carbon moves through river systems and goes back into the atmosphere through decomposition. Understanding rivers is important, especially since rivers are a vital source of drinking water and the threat of climate change looms.

“How well a stream is decomposing organic matter can tell us how healthy the stream is,” says Devan Mathie, a Kent State student who worked in Costello’s lab.

To know more about how carbon cycles through river-based systems, researchers did a water sample test using a plant-based cotton, the same material painting canvases are made from. Researchers got the cotton mailed to them and put it into a river or stream and the surrounding land. They noted how quickly the carbon disappeared from the cotton pieces and mailed them back.

The study looked at how factors such as leaves influence the way carbon moves through different freshwater systems. Costello’s lab group, including Mathie, tested four rivers in Northeast Ohio, including Triple Springs at West Branch State Park and Breakneck Creek at the Kent State South slates property. The team took samples in different proximities to the river, and early data on Northeast Ohio can predict that leaves falling on land would stay on the soil 10 times longer than leaves falling in the river.

“The tricky thing about this is the way the carbon decomposes really depends on all the other things that come along in a package of leaves,” Costello says. “Things like the waxy cuticle on the outside of the leaf or the other chemicals the tree produces. All these things sort of influence how fast that carbon decomposes.”

Most previous studies on carbon cycling use varying methodologies, so findings couldn’t easily be compared on a global scale. But using the same cotton on such a big scale in this study means that samples could be compared. That standardized method allowed researchers to quantify decomposition rates in over 500 rivers on every continent, and they now have baseline data on how decomposition rates vary river to river.

The study found that climatic factors such as temperature and moisture influence the carbon cycling rates of river-based ecosystems. For example, the data indicates that colder temperatures slow carbon loss from streams in northern regions. With climate change, those streams are getting warmer, causing carbon to dissipate into the atmosphere much faster.

The study also looked at how human actions, such as introducing runoff water from landscaping into larger water ecosystems, are affecting the climate and carbon’s movement through ecosystems both globally and locally.

“If you dumped water on the ground or it rains at your house, where does that water eventually make it to?” Costello muses. “What we do as far as carbon emissions affects every river on the planet.”

Looking toward the future, Costello continues to use this study to further other research. Using the cotton samples from around the world, he’s now studying more closely how nutrients that are a large part of carbon decomposition move through the rivers. To do so the team clipped samples from the cotton test strips and placed them in an elemental analyzer to measure nitrogen and carbon levels.

“The question is: How are streams decomposing the cotton? Our part of the project was correlating that with the nutrients,” says Mathie. “Certain levels of nutrients can facilitate different processes or organisms in that ecosystem to decay the cotton quicker.”

Costello says the most impactful aspect of the study was the sheer number of researchers who got involved and how it provides a footprint for more studies to gather more data on our important rivers. One day this research could eventually help shape policies to improve stream health or approve streams for certain uses.

“We think this is a model for the way big-scale projects can be done in the future,” Costello says, “not just to understand how fast this cotton disappears, but also to think about the functioning of these rivers that humans rely on.”