Sharon Oosthoek | July 2, 2015Ancient carbon buried deep in the soil is leaching into rivers around the world as a result of human development — a finding with significant implications for climate change. Trent University professor and aquatic ecologist Maggie Xenopoulos was part of a team of Canadian and American researchers who recently uncovered the extent of the problem. They showed how disturbing soil for agriculture and urban development is releasing carbon buried for thousands of years. Carbon in soil comes from decayed plants and, in the case of ancient carbon, is sequestered deep in the earth where it is locked away from the atmosphere. But now this old carbon is leaching into rivers where aquatic bacteria can consume it. Just like people, bacteria don't use everything they eat. Whatever doesn’t fuel their growth or reproduction, the bacteria expel as waste. One of those waste products is carbon dioxide (CO2), which can then be emitted into the atmosphere where it may contribute to climate change. Xenopoulos's research brings to light an important but largely unconsidered contribution to human-caused greenhouse gas emissions: development in watersheds. "The effect (on CO2 emissions) is like driving a car, but nobody sees it that way," says Xenopoulos. "The global carbon budget isn't balanced. This could be one reason why, but more studies are needed." Confirming suspicions While many scientists suspected development in watersheds released ancient carbon into rivers, and from there into the atmosphere, no one had compiled a database to prove it. That is until Xenopoulos and her colleagues tallied up the age of dissolved organic carbon leaching into 135 rivers around the world, including about a dozen in Ontario. They used a technique called radiocarbon dating, which estimates the age of organic material based on how much carbon 14 it contains. Carbon 14 is a radioactive form of the element which decays at a known rate. Measuring how much is left in a river's dissolved organic carbon gives a fairly accurate estimate of its age. The researchers found the age of dissolved organic carbon in rivers increased with population density and development. Extrapolating their findings to rivers around the world, Xenopoulos and her team estimate that in watersheds with human disturbance old carbon could account for 3 to 9 per cent of the total dissolved organic carbon in rivers. "We are returning this old carbon into the modern carbon cycle, which should instead stay buried deep into the soils," says Xenopoulos. She proposes a simple solution: "Apply better management practices and keep wetlands and riparian areas healthy."