Nitrogen pollution could trigger global carbon shift from soil

Colorado University Professor Alan Townsend says that roughly 300 times more carbon is stored in soils than is being pumped into the atmosphere as CO2, with 20 times more carbon released annually from soil than from industry. Soil emits carbon through the decomposition of organic matter, a process finely balanced by plant growth. “Increasing nitrogen falling on ecosystems could change that balance,” says Townsend.

In a study co-authored with European scientists, published in the latest issue of Nature, Townsend shows that tundra soils are unexpectedly sensitive to added nitrogen, suggesting the increased nitrogen from fertilizers and fuel burning could affect CO2 sinks in land.

“The nitrogen deposited on land might act like fertilizer and cause plants to grow more, at least for a while, which would suck up some carbon from the atmosphere,” says Townsend. “But it also could cause soils to lose some of their carbon, which would add even more CO2 to the atmosphere.”

With such a large reserve of carbon in the soil, even a small change could have a big effect on the atmosphere, argue the scientists. “If these sinks slow down or turn off in the near future, we could see much larger increases in atmospheric CO2,” says Townsend.

Nitrogen levels are on the rise in the Western World, with a 10% increase measured in US rivers. Townsend suggests that because fertiliser is often applied to crops in excess, farmers could make small changes in how much fertilizer they use, leading to an overall decrease in nitrogen released into the environment.