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Research by Professor Barnes Looks at Carbon Mobilization in Rivers

Assistant Professor Rebecca Barnes, who teaches in CC's environmental program, recently was published in Nature Geoscience. Her article, "Increased Mobilization of Aged Carbon to Rivers by Human Disturbance," looks at how human activity in a watershed affects the release of carbon into the ecosystem. The article analyses radiocarbon measurements from dissolved organic carbon in 135 rivers, by far the largest data set ever collated for aquatic ecosystems.

Most dissolved organic carbon in rivers originates from young organic carbon from soils and vegetation, but aged carbon removed from the modern carbon cycle is also exported in many systems.

The article examines a global data set of radiocarbon ages of riverine dissolved organic carbon and spatial data on land cover, population and environmental variables. Barnes and the co-authors find that the age of dissolved organic carbon in rivers increases with population density and the proportion of human-dominated landscapes within a watershed, and decreases with annual precipitation.

The authors reason that disturbance reintroduces aged soil organic matter into the modern carbon cycle, although fossil carbon in fertilizer or petroleum products may also be a source of aged carbon in disturbed watersheds. The total export from the terrestrial environment to freshwater systems remains unknown; nevertheless, the results suggest that 3 to 9 percent of dissolved organic carbon in rivers is aged carbon mobilized by human disturbance.

In the accompanying News and Views article, Chris Evans, a professor at the Centre for Ecology and Hydrology in Wales, writes that the work of Barnes and her colleagues provides a better understanding of human influence on riverine carbon, and of the role of this carbon in the global carbon cycle.

"An important fraction of total terrestrial carbon loss occurs through the lateral transfer of carbon from the land into rivers, including the transfer of old carbon," writes Evans. "If this aged carbon is subsequently converted to CO2, it could comprise an additional, hidden source of greenhouse-gas emissions." In other words, as stated by Barnes and co-authors, it is "analogous to the burning of fossil fuels."

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