Researchers, including plant scientist Johan Six of the University of California, Davis, say that while earlier studies have found erosion can bury carbon in the soil, acting as a carbon sink or storage, part of that sink is only temporary.
They estimated roughly half of the carbon buried in soil by erosion will be re-released into the atmosphere within about 500 years, and possibly faster due to climate change.
"It's all part of figuring out the global carbon cycle," Six said. "Where are the sources, and where are the sinks? Erosion is in some ways a sink, but, as we found out, it can also become a source."
The researchers used radiocarbon dating to calculate the amount of carbon emissions captured in soils and released to the atmosphere during the past 6,000 years along the Dijle River in Belgium.
They confirmed the gradual reintroduction of buried carbon to the atmosphere, much of it due to agriculture.
"Our results showed that half of the carbon initially present in the soil and vegetation was lost to the atmosphere as a result of agricultural conversion," said study co-author Gert Verstraeten at KU Leaven, Belgium.